An rRNA-based analysis for evaluating the effect of heat stress on the rumen microbial composition of Holstein heifers

Gastrointestinal Microorganisms and Blood Metabolites in Holstein Calves with Different Heat Stress Responses in the Same Hot Environment

This study investigated differences in gastrointestinal microbiota and blood metabolomes in calves with different heat stress (HS) responses in the same hot environment. Ten high (H) and ten low (L) HS response preweaning Holstein calves were selected based on their heat stress level (respiratory rate and rectal temperature), jugular vein blood samples and ruminal and fecal samples were collected. Notable variations were observed in the serum levels of heat shock protein 70 (HSP-70) and IL-2 between the two calf groups (p < 0.05). In group H, rumen and fecal microbiota synergism was disrupted. In the H group, the host metabolome exhibited enrichment in pyruvate metabolism and the tricarboxylic acid cycle (p < 0.05). Key factors bridging the relationship between gastrointestinal microbiota and serum metabolites included the rumen bacterial genus g__Ruminococcus, serum HSP-70, malic acid, and fumaric acid. These hubs served as potential indicators for distinguishing the response to heat stress in calves (p < 0.05). In conclusion, this study identified the relationship between gastrointestinal microbiota characteristics and different HS responses of the host, thus providing evidence and new directions for future studies aimed at understanding HS in individual calves (gut microbiota-host interactions).

Heat stress has divergent effects on the milk microbiota of Holstein and Brown Swiss cows

Heat stress (HS) is one of the pivotal causes of economic losses in dairy industries and affects welfare and performance, but its effect on milk microbiota remains elusive. It is also unclear if and how different breeds may cope with HS in sustaining productive performance. The objectives of this study were to compare (1) the performance of 2 dairy breeds, namely Holstein and Brown Swiss, subjected to HS and (2) the different effects of HS on the milk microbiota of the 2 breeds in thermal comfort conditions and HS. The study was carried out on 36 dairy cows, 18 per breed. The HS was induced by switching off the cooling system during a natural heat wave for 4 d. In addition to the temperature-humidity index, animal stress was confirmed by measuring respiratory frequency and rectal temperature twice daily at 0400 h and 1500 h. The HS affected the 2 breeds differently. The rectal temperature increased with HS in both breeds. Milk yield recording and sampling were performed during the morning milking of d 1 (at 0400 h) and afternoon milking of d 4 (at 1700 h). Productive parameters were also different: milk yield, FCM, ECM, protein and casein content, and renneting parameters were decreased in Holstein cows but remained unaffected in Brown Swiss cows. The HS also modified the milk microbiota of the 2 breeds differently. During HS, the Brown Swiss cows had milk microbiota that was richer (α diversity) than that of the Holstein cows. Comparing the time points before and during HS within breeds showed that Brown Swiss cow milk microbiota was less affected by HS than Holstein cow milk microbiota. Under the same thermal comfort condition, milk microbiota did not discriminate between Brown Swiss and Holstein. Consistently with α and β diversity, the number of operational taxonomic units (OTU) at the genus level that changed their abundance during HS was higher in Holstein (74 OTU) than in Brown Swiss (only 20 OTU). The most significant changes in abundance affected Acinetobacter, Chryseobacterium, Cutibacterium, Enterococcus, Lactococcus, Prevotella-9, Serratia, and Streptococcus. In conclusion, the present report confirms and extends previous studies by demonstrating that Brown Swiss cows regulate their body temperature better than the Holstein breed. The relative thermal tolerance to HS compared with Holstein cows is also confirmed by changes in milk uncultured microbiota, which were more evident in Holstein cows than in Brown Swiss cows.

Impacts of Protein and Energy Levels on Rumen Fermentation and Microbial Activity Under Different Incubation Temperatures

This study aimed to explore the effects of different incubation temperatures on ruminal fermentation and rumen microorganisms and determine the appropriate protein and energy levels to enhance microbial protein synthesis using an in vitro system. Rumen inoculum was collected from two fistulated Holstein heifers (trial 1: BW: 652.3 kg ± 25.2; trial 2: BW: 683.3 kg ± 30.2) and assessed using a closed-batch culture system. The experimental model employed a 2 × 5 factorial arrangement using incubation temperatures set to 39 and 41 °C, with protein levels set to 12.0, 13.5, 15.0, 16.5, and 18.0% of DM in trial 1 or with energy levels set to 2.4, 2.5, 2.6, 2.7, and 2.8 Mcal/kg of DM in trial 2. The data were analyzed using the MIXED procedure. The results showed increased (p < 0.05) NH3-N concentrations and total volatile fatty acids (TVFAs) with higher incubation temperatures, while the liquid-associated bacterial (LAB) amounts decreased (p < 0.05) in trials 1 and 2. The interaction between the energy level and incubation temperature affected (p < 0.05) the LAB protein levels in trial 2. Higher protein levels led to increased (p < 0.05) NH3-N and acetate concentrations, but it decreased (p < 0.05) the propionate percentage. Conversely, higher energy levels decreased (p < 0.05) the amount of acetate and increased the propionate concentration, altering the acetate-to-propionate ratio. However, no interaction involving TVFA and LAB was observed between the incubation temperature and the protein or energy levels. Changes in the NH3-N, TVFAs, and LAB protein amounts were observed under different incubation temperatures and energy levels. In conclusion, these findings provide insight into the metabolic adaptation under different ruminal temperatures and the impacts of dietary adjustments on rumen fermentation and microbial activity. However, there are limitations to replicating the complex physiological responses that occur within the whole body solely through in vitro experiments.

An Automated Sprinkler Cooling System Effectively Alleviates Heat Stress in Dairy Cows

(1) Background: Heat stress detrimentally restricted economic growth in dairy production. In particular, the cooling mechanism of the spraying system effectively reduced both environmental and shell temperatures. This study was designed to investigate the underlying modulatory mechanism of an automatic cooling system in alleviating heat-stressed dairy cows. (2) Methods: A total of 1208 multiparous dairy cows was randomly allocated into six barns, three of which were equipped with automatic sprinklers (SPs), while the other three were considered the controls (CONs). Each barn was considered a replicate. (3) Results: Body temperatures and milk somatic cell counts significantly decreased, while DMI, milk yield, and milk fat content significantly increased under SP treatment. Rumen fermentability was enhanced, embodied by the increased levels of total VFA, acetate, propionate, and butyrate after SP treatment. The rumen microbiota results showed the relative abundances of fiber-degrading bacteria, including the Fibrobacters, Saccharofermentans, Lachnospira, Pseudobutyrivibrio, Selenomonas, and Succinivibrio, which significantly increased after receiving the SP treatment. (4) Conclusions: This study demonstrated that SP effectively alleviated heat stress and improved production performances and milk quality through modulating the rumen microbiota composition and fermentation function of dairy cows.

Differences in Lactation Performance, Rumen Microbiome, and Metabolome between Montbéliarde × Holstein and Holstein Cows under Heat Stress

Heat stress negatively affects lactation performance and rumen microbiota of dairy cows, with different breeds showing varying levels of heat tolerance. This study aimed to compare the lactation performance of Montbéliarde × Holstein (MH, n = 13) and Holstein (H, n = 13) cows under heat stress, and 16S rRNA sequencing and liquid chromatography-mass spectrometry (LC-MS) were used to determine the rumen microbiome and metabolome in experimental cows. The results indicated that during heat stress, milk yield (p = 0.101), milk fat yield, milk protein yield, milk protein, and milk lactose (p < 0.05) in Montbéliarde × Holstein cows were higher than those in Holstein cows, whereas milk yield variation and somatic cell counts (p < 0.05) were lower than those in Holstein cows. The sequencing results indicated that the rumen of Montbéliarde × Holstein cows was significantly enriched with beneficial bacteria, such as Rikenellaceae, Allobaculum, and YRC22 (p < 0.05). In addition, correlations were observed between specific ruminal bacteria and lactation performance. Ruminal metabolites related to antioxidant and anti-inflammatory properties were significantly higher (p < 0.05) in Montbéliarde × Holstein cows than in Holstein cows. Overall, Montbéliarde × Holstein cows showed higher production efficiency under heat stress, which may be related to the different rumen mechanisms of crossbred and Holstein cows in adapting to heat stress.

Long-term growth, feed efficiency, enteric methane emission, and blood metabolite responses to in utero hyperthermia in Holstein heifers

Dairy producers are experiencing production and animal welfare pressures from the increasing frequency and severity of heat stress events due to global climate change. Offspring performance during the preweaning and lactating periods is compromised when exposed to heat stress during late gestation (in utero). However, knowledge of the lingering effects of in utero heat stress on yearling dairy heifers is limited. Herein, we investigated the long-term effects of in utero heat stress on heifer growth, feed efficiency, and enteric methane emissions in postpubertal heifers. During the last 56 d of gestation, 38 pregnant cows carrying heifer calves were exposed to either heat stress (IUHT; n = 17) or artificial cooling (IUCL; n = 21). At 18 ± 1 mo of age, the resulting IUCL and IUHT heifers were enrolled in the present 63-d study. Heifers were blocked by weight and randomly assigned to 3 pens with Calan gates. Body weights were recorded on 3 consecutive days at the start and end of the trial and used to calculate ADG. Body condition score, hip width, body length, and chest girth were measured at the start and end of the study. All heifers were fed a TMR comprised of 46.6% oatlage, 44.6% grass/alfalfa haylage, 7.7% male-sterile corn silage, 0.3% urea, and 0.8% mineral/vitamin supplement (on a DM basis). The TMR and refusal samples were obtained daily, composited weekly, and dried to calculate DMI. During the study, each pen had access to a GreenFeed unit for 8 ± 1d to measure CH4 and CO2 gas fluxes. During the last 3 d of measuring CH4 and CO2 fluxes, fecal samples were collected, composited by animal, dried, and analyzed to calculate NDF, OM, and DM digestibility. On the last day of fecal sampling, blood samples were also collected via coccygeal venipuncture, and GC time-of-flight MS analysis was performed. Residual feed intake (RFI; predicted DMI - observed DMI), and feed conversion efficiency (FCE; DMI/ADG) were calculated to estimate feed efficiency. No differences were found in initial or final BW, hip width, chest girth, or BCS; however, IUCL heifers were longer in body length compared with IUHT heifers. Dry matter intake, ADG, RFI, and FCE were similar between IUHT and IUCL heifers. In utero heat-stressed and IUCL heifers produced similar amounts of CH4 and CO2, and no differences were found in the number of GreenFeed visits or latency to approach the GreenFeed. The concentrations of 6 blood metabolites involved in lipogenic pathways were different between in utero treatments. In conclusion, in utero heat stress does not seem to have long-term effects on feed efficiency or methane emissions during the postpubertal growing phase; however, IUCL heifers maintained a body-length advantage over their IUHT counterparts and differed in concentrations of several candidate metabolites that encourage further exploration of their potential function in key organs, such as the liver and mammary gland.

A Review of the Rumen Microbiota and the Different Molecular Techniques Used to Identify Microorganisms Found in the Rumen Fluid of Ruminants

Variations in environments, including climate, diet, and agricultural practices, significantly impact the composition and microbial activity. A profound understanding of these adaptations allows for the improvement of nutrition and ruminant production. Therefore, this review aims to compile data from the literature on the rumen microbiota and molecular techniques for identifying the different types of microorganisms from the rumen fluid of ruminants. Analyzing the literature on rumen microbiology in different ruminants is complex due to microbial interactions, influenced by the environment and nutrition of these animals. In addition, it is worth noting that the genera of protozoa and fungi most evident in the studies used in this review on the microbiology of rumen fluid were Entodinium spp. and Aspergillus spp., respectively, and Fibrobacter spp. for bacteria. About the techniques used, it can be seen that DNA extraction, amplification, and sequencing were the most cited in the studies evaluated. Therefore, this review describes what is present in the literature and provides an overview of the main microbial agents in the rumen and the molecular techniques used.

Understanding the Diversity and Roles of the Ruminal Microbiome

The importance of ruminal microbiota in ruminants is emphasized, not only as a special symbiotic relationship with ruminants but also as an interactive and dynamic ecosystem established by the metabolites of various rumen microorganisms. Rumen microbial community is essential for life maintenance and production as they help decompose and utilize fiber that is difficult to digest, supplying about 70% of the energy needed by the host and 60-85% of the amino acids that reach the small intestine. Bacteria are the most abundant in the rumen, but protozoa, which are relatively large, account for 40-50% of the total microorganisms. However, the composition of these ruminal microbiota is not conserved or constant throughout life and is greatly influenced by the host. It is known that the initial colonization of calves immediately after birth is mainly influenced by the mother, and later changes depending on various factors such as diet, age, gender and breed. The initial rumen microbial community contains aerobic and facultative anaerobic bacteria due to the presence of oxygen, but as age increases, a hypoxic environment is created inside the rumen, and anaerobic bacteria become dominant in the rumen microbial community. As calves grow, taxonomic diversity increases, especially as they begin to consume solid food. Understanding the factors affecting the rumen microbial community and their effects and changes can lead to the early development and stabilization of the microbial community through the control of rumen microorganisms, and is expected to ultimately help improve host productivity and efficiency.

Comparison of ruminal microbiota, IL-1β gene variation, and tick incidence between Holstein × Gyr and Holstein heifers in grazing system

Introduction

The variation in bacterial communities among breeds has been previously reported and may be one of the reasons why Holstein × Gyr dairy heifers have better development in grazing systems in tropical conditions. This study aimed to explore the ruminal microbiota composition, the IL-1β gene variation, tick incidence, and blood parameters of Holstein × Gyr (½ Holstein × ½ Gyr) and Holstein heifers grazing intensely managed Guinea grass (Panicum maximum Jacq. cv. Mombaça).

Methods

Sixteen heifers were divided into two groups consisting of 8 Holstein × Gyr and 8 Holstein heifers. The experimental period was comprised of 3 periods of 21 days. Ruminal samples were taken via the stomach tube technique. The sequencing of the V4 hypervariable region of the 16S rRNA gene was performed using the Illumina MiSeq platform. Counting and collection of ticks were conducted each 21 days. Blood and skeletal muscle tissue biopsies were performed at the end of the experiment.

Results

Firmicutes were the most abundant phyla present in both breed rumen samples and Bacteroidota showed differences in relative abundance between breed groups, with greater values for Holstein heifers (p < 0.05 with FDR correction). The 10 most abundant unique OTUs identified in each breed included several OTUs of the genus Prevotella. Holstein heifers had a greater tick count and weight (9.8 ticks/animal and 1.6 g/animal, respectively) than Holstein × Gyr (2.56 ticks/animal and 0.4 g/animal, respectively). We found nucleotide substitutions in the IL-1β gene that might be related to adaptation and resistance phenotypes to tick infestation in Holstein × Gyr heifers. Blood concentrations of urea, albumin, insulin-like growth factor 1, triiodothyronine, and thyroxine were greater in Holstein × Gyr than in Holstein heifers.

Conclusion

Adaptations in Holstein × Gyr heifers such as ruminal microbiota, tick resistance, nucleotide substitutions in IL-1β gene, and hormone concentration suggest a better energy metabolism and thermoregulation resulting in better performance in tropical grazing systems.

Recent Advances in Enteric Methane Mitigation and the Long Road to Sustainable Ruminant Production

Mitigation of methane emission, a potent greenhouse gas, is a worldwide priority to limit global warming. A substantial part of anthropogenic methane is emitted by the livestock sector, as methane is a normal product of ruminant digestion. We present the latest developments and challenges ahead of the main efficient mitigation strategies of enteric methane production in ruminants. Numerous mitigation strategies have been developed in the last decades, from dietary manipulation and breeding to targeting of methanogens, the microbes that produce methane. The most recent advances focus on specific inhibition of key enzymes involved in methanogenesis. But these inhibitors, although efficient, are not affordable and not adapted to the extensive farming systems prevalent in low- and middle-income countries. Effective global mitigation of methane emissions from livestock should be based not only on scientific progress but also on the feasibility and accessibility of mitigation strategies.

Effects of Chromium Propionate and Calcium Propionate on Lactation Performance and Rumen Microbiota in Postpartum Heat-Stressed Holstein Dairy Cows

Chromium propionate (Cr-Pro) and calcium propionate (Ca-Pro) are widely applied in dairy production, especially in the alleviation of heat stress (HS). HS can reduce the abundance of rumen microbiota and the lactation performance of dairy cows. The present work mainly focused on evaluating the effects of Cr-Pro and Ca-Pro on the performance, ruminal bacterial community, and stress of postpartum HS dairy cows as well as identifying the differences in their mechanisms. Fifteen multiparous postpartum Holstein cows with equivalent weights (694 ± 28 kg) and milk yields (41.2 ± 1.21 kg/day) were randomly divided into three groups: control (CON), Cr-Pro (CRPR), and Ca-Pro (CAPR). The control cows received the basal total mixed ration (TMR) diet, while the CRPR group received TMR with 3.13 g/day of Cr-Pro, and the CAPR group received TMR with 200 g/day of Ca-Pro. The rumen microbial 16S rRNA was sequenced using the Illumina NovaSeq platform along with the measurement of ruminal volatile fatty acids (VFAs) and milking performance. Cr-Pro and Ca-Pro improved lactation performance, increased the rumen VFA concentration, and altered the rumen microbiota of the HS dairy cows. Cr-Pro significantly improved the milk yield (p < 0.01). The richness and diversity of the microbial species significantly increased after feeding on Ca-Pro (p < 0.05). Gene function prediction revealed increased metabolic pathways and biological-synthesis-related function in the groups supplemented with Cr-Pro and Ca-Pro. Our results indicate that the application of Cr-Pro or Ca-Pro can provide relief for heat stress in dairy cows through different mechanisms, and a combination of both is recommended for optimal results in production.

Heat Stress Effects on Physiological and Blood Parameters, and Behavior in Early Fattening Stage of Beef Steers

This study was conducted to investigate the effect of heat stress (HS) on physiological, blood, and behavioral parameters, according to the temperature-humidity index (THI), in beef steers. Twelve Korean native beef steers (342.7 ± 13.81 days old, body weight (BW) of 333.0 ± 18.53 kg) were used in this experiment. Beef steers were randomly distributed into three homogenized groups (four beef steers each) for 14 days, namely, threshold (THI = 64-71), mild-moderate (THI = 72-79), and severe (THI = 80-87). Feed and water intake were recorded daily. Physiological parameters, including heart rate and rectal temperature, and behavioral patterns (standing and lying down) were measured weekly. Blood was sampled every week to analyze hormones, heat shock protein (HSP) levels, metabolites, and hematological parameters. All data were analyzed using repeated-measures analysis. Beef steers exposed to severe THI had significantly increased (p < 0.001) water intake, heart rate, and rectal temperature compared to the threshold and mild-moderate THI beef steers. Additionally, increased blood cortisol (p < 0.001), HSP70 (p < 0.001), blood urea nitrogen (BUN) (p = 0.014), and time spent standing (p < 0.001) were observed in beef steers after exposure to severe THI compared to beef steers in the threshold and mild-moderate THI groups. However, dry matter intake, blood glucose, and non-esterified fatty acids were not different among the THI groups. In conclusion, heart rate, rectal temperature, blood cortisol, HSP70, BUN, and time spent standing were closely associated with severe HS conditions in beef steers. These phenomena indicated that beef steers exposed to HS modulated their behavior and blood parameters, as well as their physiological response, to maintain homeostasis.

Animal board invited review: The contribution of adipose stores to milk fat: implications on optimal nutritional strategies to increase milk fat synthesis in dairy cows

A wide range of nutritional and non-nutritional factors influence milk fat synthesis and explain the large variation observed in dairy herds. The capacity of the animal to synthesize milk fat will largely depend on the availability of substrates for lipid synthesis, some of which originate directly from the diet, ruminal fermentation or from adipose tissue stores. The mobilization of non-esterified fatty acids from adipose tissues is important to support the energy demands of milk synthesis and will therefore have an impact on the composition of milk lipids, especially during the early lactation period. Such mobilization is tightly controlled by insulin and catecholamines, and in turn, can be affected indirectly by factors that influence these signals, namely diet composition, lactation stage, genetics, endotoxemia, and inflammation. Environmental factors, such as heat stress, also impact adipose tissue mobilization and milk fat synthesis, mainly through endotoxemia and an immune response-related increase in concentrations of plasma insulin. Indeed, as proposed in the present review, the central role of insulin in the control of lipolysis is key to improving our understanding of how nutritional and non-nutritional factors impact milk fat synthesis. This is particularly the case during early lactation, as well as in situations where mammary lipid synthesis is more dependent on adipose-derived fatty acids.

Gastro-Intestinal Microbiota in Equines and Its Role in Health and Disease: The Black Box Opens

Horses are large non-ruminant herbivores and rely on microbial fermentation for energy, with more than half of their maintenance energy requirement coming from microbial fermentation occurring in their enlarged caecum and colon. To achieve that, the gastro-intestinal tract (GIT) of horses harbors a broad range of various microorganisms, differing in each GIT segment, which are essential for efficient utilization of feed, especially to use nutrients that are not or little degraded by endogenous enzymes. In addition, like in other animal species, the GIT microbiota is in permanent interplay with the host's cells and is involved in a lot of functions among which inflammation, immune homeostasis, and energy metabolism. As for other animals and humans, the horse gut microbiome is sensitive to diet, especially consumption of starch, fiber, and fat. Age, breeds, stress during competitions, transportation, and exercise may also impact the microbiome. Because of its size and its complexity, the equine GIT microbiota is prone to perturbations caused by external or internal stressors that may result in digestive diseases like gastric ulcer, diarrhea, colic, or colitis, and that are thought to be linked with systemic diseases like laminitis, equine metabolic syndrome or obesity. Thus, in this review we aim at understanding the common core microbiome -in terms of structure and function- in each segment of the GIT, as well as identifying potential microbial biomarkers of health or disease which are crucial to anticipate putative perturbations, optimize global practices and develop adapted nutritional strategies and personalized nutrition.

Alleviation effects of niacin supplementation on beef cattle subjected to heat stress: A metagenomic insight

The objective of this study was to investigate the alleviation effects of niacin supplementation on beef cattle subjected to heat stress and to provide a theoretical basis for exploring the alleviation methods of heat stress environmental factors on the rumen of beef cattle. In the experiment, 36 Jinjiang bull cattle with a body weight of about 400 ± 20.0 kg were randomly divided into three treatments, each treatment contains four replicates, with three cattle in each replicate. Treatments included thermoneutral treatment (TN; temperature: 24–25°C, humidity: 45–55%), heat stress treatment, exposure to environmental temperature (HS; average THI: 82.74), and heat stress supplemented with niacin treatment (HN; high temperature + 800 mg/kg NA). Measured indicators were body temperature, respiratory rate, production performances, rumen fermentations, and microbial diversity. Results showed that adding niacin reduced the body temperature and respiratory rate (P &lt; 0.05) but had no significant effect on the production performances compared with heat-stressed beef cattle. HS treatment significantly increased body temperature and respiratory rate (P &lt; 0.01), while decreasing the content of acetic acid, butyric acid, and total volatile fatty acids (P &lt; 0.05) compared with the TN treatment. Supplement of niacin did not affect ruminal fermentation parameters (P &gt; 0.05) but had a decreased tendency on A/P (P &lt; 0.1). Microbial diversity results showed that, at the phylum level, the relative abundance of Desulfobacterota in the HS treatment was increased compared with TN and HN treatment (P &lt; 0.05). At the genus level, the relative abundance of Succiniclasticum and Family_XIII_AD3011 group in the HN treatment significantly proliferated compared with the HS treatment (P &lt; 0.05). In conclusion, niacin supplementation may alleviate heat stress by proliferating those bacteria belonging to the phylum Succiniclasticum, which may further contribute to the digestion of cellulose and the improvement of the metabolic function of Jinjiang cattle under heat-stress conditions.

Relationship between thermal environment, thermoregulatory responses and energy metabolism in goats: A comprehensive review

Knowledge on heat stress of animals is key to developing management strategies to mitigate its effects on livestock production. Efficiency and profitability of production systems will certainly be challenged by the forecasted global temperature increase of 1.5 °C between 2030 and 2050. Goats are a resilient animal model, much less affected by climatic variations than average livestock. However, this statement is only true to a certain threshold, which, if exceeded, may affect energy metabolism of goats thus affecting respiratory frequency, heart pulse, evaporative thermolysis and rectal temperature, also altering on hormonal profile of animals, leading to behavioural changes such as altering feed and water intake and sheltering in the quest for homeothermic status. Dairy goat breeds, such as Saanen, are more sensitive to heat stress. Adaptations in nutritional and environmental management, as well as selecting better adapted breeds are strategic practices targeting the mitigation of effects of thermal stress of goats in farming systems. However, studies on effects of ambient temperature on energy and basal metabolisms of goats are scarce. This review aims to elucidate energetic and basal metabolism responses of goats under heat stress targeting the development of management strategies to mitigate heat stress in the farming systems and the conservation of genetic resources, adaptability, phenotypic plasticity, and basal heat production in different breeds.

Effects of capsicum oleoresin supplementation on rumen fermentation and microbial abundance under different temperature and dietary conditions in vitro

This study aimed to determine the effect of capsicum oleoresin (CAP) on rumen fermentation and microbial abundance under different temperature and dietary conditions in vitro. The experimental design was arranged in a 2 × 2 × 3 factorial format together with two temperatures (normal: 39°C; hyperthermal: 42°C), two forage/concentrate ratios (30:70; 70:30), and two CAP concentrations in the incubation fluid at 20 and 200 mg/L with a control group. Regarding the fermentation characteristics, high temperature reduced short-chain fatty acids (SCFA) production except for molar percentages of butyrate while increasing acetate-to-propionate ratio and ammonia concentration. The diets increased total SCFA, propionate, and ammonia concentrations while decreasing acetate percentage and acetate-to-propionate ratio. CAP reduced acetate percentage and acetate-to-propionate ratio. Under hyperthermal condition, CAP could reduce acetate percentage and increase acetate-to-propionate ratio, lessening the negative effect of high heat on SCFA. Hyperthermal condition and diet altered the relative abundance of microbial abundance in cellulose-degrading bacteria. CAP showed little effect on the microbial abundance which only increased Butyrivibrio fibrisolvens. Thus, CAP could improve rumen fermentation under different conditions, with plasticity in response to the ramp of different temperature and dietary conditions, although hardly affecting rumen microbial abundance.

The Low Dose of Saccharomyces cerevisiae Is Beneficial for Rumen Fermentation (Both In Vivo and In Vitro) and the Growth Performance of Heat-Stressed Goats

This study aimed to investigate the effects of Saccharomyces cerevisiae on rumen fermentation and the growth performance of heat-stressed goats. The fermentation experiment was conducted using Saccharomyces cerevisiae added at 0‰ (HS1), 0.30‰ (SC1), 0.60‰ (SC2), and 1.20‰ (SC3) of the dry matter (DM) weight of the basal diet. The results showed that supplementing with 0.60‰ (SC2) could increase the pH, acetic acid to propionic acid ratio, the concentrations of ammonia nitrogen, total volatile fatty acids, acetic acid, propionic acid, butyric acid, and the degradability of DM, neutral detergent fiber, and acid detergent fiber in rumen fluids of heat-stressed goats. In the feeding experiment, twelve heat-stressed goats were assigned to a 4 × 4 Latin square experimental design, and the Saccharomyces cerevisiae supplement levels are similar to the fermentation experiment above. Similar effects on rumen fermentation and digestibility parameters were obtained with a supplement with 0.60‰ of Saccharomyces cerevisiae (SC2A) compared to the fermentation trial. Moreover, in the SC2A group, the DM intake and average daily gain also increased significantly compared with other groups. These results suggested that a low dose of Saccharomyces cerevisiae can still effectively improve the rumen fermentation and growth performance of heat-stressed goats.

Prophylactic Feeding of Clostridium butyricum and Saccharomyces cerevisiae Were Advantageous in Resisting the Adverse Effects of Heat Stress on Rumen Fermentation and Growth Performance in Goats

This study aimed to investigate the effect of the prophylactic feeding of Clostridium butyricum (CB), Saccharomyces cerevisiae (SC), and their mixture before the onset of heat stress on the rumen fermentation and growth performance of goats, and subsequently, on heat stress status. Forty-eight male Macheng Black × Boer crossed goats (22.25 ± 4.26 kg) were divided into four groups—the control group (fed the basal diet), and the CB (0.05% CB added to the basal diet), SC (0.60% SC added to the basal diet), and Mix (0.05% CB and 0.60% SC added to the basal diet) groups—and fed for fourteen days. Then, these goats were kept in a heat stress environment (with a temperature−humidity index of 87.04) for fourteen days. Then, the parameters of rumen fermentation and growth performance were measured. The results showed that the pH values, the activities of cellulolytic enzymes (avicelase, CMCaes, cellobiase, and xylanase), and the concentrations of ammonia-N, total volatile fatty acid, acetic acid, propionic acid, and butyric acid were significantly increased (p < 0.05) in the rumens of the CB, SC, and Mix groups compared to those of the control group. Moreover, the average daily gain and the digestibility of dry matter, neutral detergent fiber, and acid detergent fiber were significantly increased (p < 0.05) in the CB, SC, and Mix groups compared to those of the control group. These results suggest that these two probiotics and their mixture effectively alleviate the adverse effects of heat stress on rumen fermentation and growth performance via prophylactic feeding.

Saccharomyces cerevisiae and Clostridium butyricum Could Improve B-Vitamin Production in the Rumen and Growth Performance of Heat-Stressed Goats

Heat stress can adversely affect the rumen environment and the growth performance of goats. The present study aimed to investigate the effects of Saccharomyces cerevisiae (SC), Clostridium butyricum (CB), and their mixture on B-vitamin production in the rumen and the growth performance of heat-stressed goats. Firstly, twelve Macheng × Boer crossed goats (24.21 ± 2.05 kg, control) were modeled to become heat-stressed goats (HS1). Then, the B-vitamin concentrations in the rumen and the parameters of growth performance were measured in goats. The results showed that heat stress could cause significantly decreased vitamin B1, B2, B6, B12, and niacin concentrations (p < 0.05). It also could cause a significantly reduced dry matter (DM) intake (DMI) and average daily gain (ADG) (p < 0.05). However, the digestibilities of DM, neutral detergent fiber (NDF), and acid detergent fiber (ADF) were significantly increased (p < 0.05) in HS1 compared to controls. Then, these twelve heat-stressed goats were divided equally into four groups: control group (HS2, no probiotic supplemented), SC group (0.30% SC supplemented to the basal diet), CB group (0.05% CB supplemented to the basal diet), and mix group (0.30% SC and 0.05% CB supplemented to the basal diet). They were used in a 4 × 4 Latin square experimental design. The results showed that the concentrations of vitamins B1, B2, and niacin in the rumen and the DMI, ADG, and the digestibility of DM, NDF, and ADF were significantly increased (p < 0.05) with SC, CB, and their mixture supplementation (p < 0.05). These results suggest that dietary supplementation with SC and CB could improve B-vitamin production in the rumen and the growth performance of heat-stressed goats.

Diet Shift May Trigger LuxS/AI-2 Quorum Sensing in Rumen Bacteria

Recent studies have revealed that LuxS/AI-2 quorum sensing (QS) is the most universal cell-to-cell communication in rumen bacteria; however, it remains unknown how they respond to nutritional stress from a diet shift. This study aimed to explore whether a diet shift could trigger rumen bacterial LuxS/AI-2 QS and its influences on rumen fermentation characteristics and bacterial community diversity and composition. A total of fifteen Hu sheep were selected to undergo a pre-shift diet (Pre, concentrate to forage ratio 75:25) for one month and then abruptly switch to a post-shift diet (Post, concentrate to forage ratio 49:51). Results showed that the serum cortisol and immunoglobulin G concentrations were higher in Post than in Pre (p < 0.05). The microbial density, AI-2 concentration, biofilm formation, and the gene expression of ftsH were higher in Post when compared with Pre (p < 0.05), whilst the gene expression of luxS tended to be lower in Post (p = 0.054). The molar concentration of valerate and fermentation efficiency decreased after the diet shift, while the acetate to propionate ratio and the molar proportion of butyrate were higher in Post compared to Pre (p < 0.05). Moreover, the diet shift increased the richness of ruminal bacteria and the relative abundances of Roseburia, Prevotellaceae UCG-001, and Lachnospira, and decreased the relative abundances of Prevotella, Megasphaera, and Dialister (p < 0.05). A difference in trends was also observed in an analysis of similarity (R = 0.1208 and p = 0.064). This study suggests that a diet shift could trigger rumen bacterial LuxS/AI-2 QS by altering microbial density, AI-2 concentration, biofilm formation, and related gene expression, as well as affect the rumen fermentation pattern and bacterial community diversity and composition. This study may provide insight into a potential strategy for relieving nutritional stress via regulating bacterial communication.

Heat stress impacts the multi-domain ruminal microbiota and some of the functional features independent of its effect on feed intake in lactating dairy cows

Background

Heat stress (HS) affects the ruminal microbiota and decreases the lactation performance of dairy cows. Because HS decreases feed intake, the results of previous studies were confounded by the effect of HS on feed intake. This study examined the direct effect of HS on the ruminal microbiota using lactating Holstein cows that were pair-fed and housed in environmental chambers in a 2 × 2 crossover design. The cows were pair-fed the same amount of identical total mixed ration to eliminate the effect of feed or feed intake. The composition and structure of the microbiota of prokaryotes, fungi, and protozoa were analyzed using metataxonomics and compared between two thermal conditions: pair-fed thermoneutrality (PFTN, thermal humidity index: 65.5) and HS (87.2 for daytime and 81.8 for nighttime).

Results

The HS conditions altered the structure of the prokaryotic microbiota and the protozoal microbiota, but not the fungal microbiota. Heat stress significantly increased the relative abundance of Bacteroidetes (primarily Gram-negative bacteria) while decreasing that of Firmicutes (primarily Gram-positive bacteria) and the Firmicutes-to-Bacteroidetes ratio. Some genera were exclusively found in the heat-stressed cows and thermal control cows. Some co-occurrence and mutual exclusion between some genera were also found exclusively for each thermal condition. Heat stress did not significantly affect the overall functional features predicted using the 16S rRNA gene sequences and ITS1 sequences, but some enzyme-coding genes altered their relative abundance in response to HS.

Conclusions

Overall, HS affected the prokaryotes, fungi, and protozoa of the ruminal microbiota in lactating Holstein cows to a different extent, but the effect on the structure of ruminal microbiota and functional profiles was limited when not confounded by the effect on feed intake. However, some genera and co-occurrence were exclusively found in the rumen of heat-stressed cows. These effects should be attributed to the direct effect of heat stress on the host metabolism, physiology, and behavior. Some of the “heat-stress resistant” microbes may be useful as potential probiotics for cows under heat stress.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00717-z.

Effects of Replacing Alfalfa Hay With Native Grass Hay in Pelleted Total Mixed Ration on Physicochemical Parameters, Fatty Acid Profile, and Rumen Microbiota in Lamb

This study aimed to investigate the effects of replacing alfalfa with native grass on growth performance, meat quality, and rumen microbiota of lambs. Forty-five 6-month-old Ujimqin lambs with live body weight (BW) of 29.50 ± 0.26 kg were used for the experiment, and the lambs were assigned to three diet treatments (three pens per treatment and five lambs per pen) with 30 square meters per pen in semi-open housing based on similar BW. The lambs have received 30% alfalfa (HA, high alfalfa percentage group), 20% alfalfa (MA, moderate alfalfa percentage group), and 10% alfalfa (LA, low alfalfa percentage group) diets, respectively (dry matter basis). The diet treatments had a significant (P < 0.05) influence on the dry matter intake of lambs and the dry matter intake increased with the increasing percentages of native grass hay, while the significantly (P < 0.05) lower final BW and average daily gain were observed in the MA and LA groups compared with that in the HA group. The diet had a significant (P < 0.05) difference in meat pH value, water loss rate, cooked meat rate, moisture, and intramuscular fat, while no significant (P > 0.05) difference was found in protein. As native grass hay percentages increased in the diet, the contents of palmitic (C16:0) and palmitoleic (C16:1 cis-9) in the HA and MA groups were significantly (P < 0.05) lower than that in the LA groups, and compared with the HA group, the contents of elaidic (C18:1 trans-9), oleic (C18:1 cis-9), and linoleic (C18:2 cis-9–cis-12) were significantly (P < 0.05) increased in the MA and LA groups. The content of α-linolenic (C18:3n3) was significantly (P < 0.05) higher in the LA group than that in the HA and MA groups. The principal coordinate analysis profile displayed that the composition of the bacterial community of these groups was distinctly separated from each other. No significant (P > 0.05) difference was observed in the dominant rumen bacteria at the phyla and genus levels. In conclusion, the meat quality and fatty acid profile analysis revealed that replacing alfalfa hay with native grass hay is more beneficial for Mongolian lambs, and the meat from LA diet treatment is better than the others. In addition, correlation analysis of the association of rumen microbiome with growth performance, meat quality, and fatty acid profile provides us with a comprehensive understanding of the composition and function of rumen microbiota. These findings could provide knowledge of how the diet affects the animal performance, meat quality of lambs, and microbiota of the rumen, laying a theoretical basis for replacing alfalfa with native grass.

Heat Stress: Effects on Rumen Microbes and Host Physiology, and Strategies to Alleviate the Negative Impacts on Lactating Dairy Cows

Heat stress (HS) in dairy cows causes considerable losses in the dairy industry worldwide due to reduced animal performance, increased cases of metabolic disorders, altered rumen microbiome, and other health problems. Cows subjected to HS showed decreased ruminal pH and acetate concentration and an increased concentration of ruminal lactate. Heat-stressed cows have an increased abundance of lactate-producing bacteria such as Streptococcus and unclassified Enterobacteriaceae, and soluble carbohydrate utilizers such as Ruminobacter, Treponema, and unclassified Bacteroidaceae. Cellulolytic bacteria, especially Fibrobacteres, increase during HS due to a high heat resistance. Actinobacteria and Acetobacter, both acetate-producing bacteria, decreased under HS conditions. Rumen fermentation functions, blood parameters, and metabolites are also affected by the physiological responses of the animal during HS. Isoleucine, methionine, myo-inositol, lactate, tryptophan, tyrosine, 1,5-anhydro-D-sorbitol, 3-phenylpropionic acid, urea, and valine decreased under these conditions. These responses affect feed consumption and production efficiency in milk yield, growth rate, and reproduction. At the cellular level, activation of heat shock transcription factor (HSF) (located throughout the nucleus and the cytoplasm) and increased expression of heat shock proteins (HSPs) are the usual responses to cope with homeostasis. HSP70 is the most abundant HSP family responsible for the environmental stress response, while HSF1 is essential for increasing cell temperature. The expression of bovine lymphocyte antigen and histocompatibility complex class II (DRB3) is downregulated during HS, while HSP90 beta I and HSP70 1A are upregulated. HS increases the expression of the cytosolic arginine sensor for mTORC1 subunits 1 and 2, phosphorylation of mammalian target of rapamycin and decreases the phosphorylation of Janus kinase-2 (a signal transducer and activator of transcription factor-5). These changes in physiology, metabolism, and microbiomes in heat-stressed dairy cows require urgent alleviation strategies. Establishing control measures to combat HS can be facilitated by elucidating mechanisms, including proper HS assessment, access to cooling facilities, special feeding and care, efficient water systems, and supplementation with vitamins, minerals, plant extracts, and probiotics. Understanding the relationship between HS and the rumen microbiome could contribute to the development of manipulation strategies to alleviate the influence of HS. This review comprehensively elaborates on the impact of HS in dairy cows and introduces different alleviation strategies to minimize HS.

Effects of rumen-protected creatine pyruvate on blood biochemical parameters and rumen fluid characteristics in transported beef cattle

Background

The fasting and stress associated with road transportation contributes to a lack of energy and a decline in the immune system of beef cattle. Therefore, it is essential for beef cattle to enhance energy reserves before transportation. Creatine pyruvate (CrPyr) is a new multifunctional nutrient that can provide both pyruvate and creatine, which are two intermediate products of energy metabolism. To investigate the effects of transport and rumen-protected (RP)-CrPyr on the blood biochemical parameters and rumen fluid characteristics of beef cattle, twenty male Simmental crossbred cattle (659 ± 16 kg) aged 18 months were randomly allocated to four groups (n = 5) using a 2 × 2 factorial arrangement with two RP-CrPyr supplemental levels (0 or 140 g/d) and two transport treatments (5 min or 12 h): T_CrPyr140, T_CrPyr0, NT_CrPyr140, and NT_CrPyr0. After feeding for 30 days, three cattle per treatment were slaughtered.

Results

Compared with nontransport, transport decreased the total antioxidant capacity, catalase activity, contents of IgA, interferon γ, interleukin-1β (IL-1β), and IL-6 in serum, and the amounts of total volatile fatty acids (TVFA), acetate, and butyrate in rumen (P < 0.05); increased the serum lipopolysaccharide (LPS) level, contents of rumen LPS and ammonia nitrogen (P < 0.05). RP-CrPyr supplementation decreased the levels of cortisol and LPS in serum and the butyrate concentration in the rumen of beef cattle compared with those in the unsupplemented groups (P < 0.05). RP-CrPyr and transport interaction had a significant effect on the contents of serum tumour necrosis factor-α, IL-6, LPS, ruminal pH, acetate content, and acetate/propionate (P < 0.05). In terms of ruminal bacterial composition, group T_CrPyr0 increased the Prevotella genus abundance compared with group NT_CrPyr0 (P < 0.05), while group T_CrPyr140 increased Firmicutes phylum abundance and decreased Bacteroidetes phylum and genus Prevotella abundance compared with group T_CrPyr0 (P < 0.05). Moreover, Bacteroidetes was positively correlated with serum LPS.

Conclusions

These results indicated that dietary supplementation with RP-CrPyr might be beneficial to alleviate transport stress by decreasing serum cortisol and LPS levels and promoting the restoration of the rumen natural flora.

Clostridium butyricum Improves Rumen Fermentation and Growth Performance of Heat-Stressed Goats In Vitro and In Vivo

This study aimed to evaluate the effects of Clostridium butyricum on rumen fermentation and the growth performance of heat-stressed goats. The in vitro fermentation was carried out using Clostridium butyricum supplement at 0% (CG), 0.025% (CB1), 0.05% (CB2), 0.10% (CB3), and 0.20% (CB4) of the dry matter (DM) weight of basal diet. Results showed that ruminal pH and the concentrations of ammonia nitrogen, total volatile fatty acids, acetic acid, propionic acid, as well as the acetic acid to propionic acid ratio were significantly increased (p < 0.05) in CB2 and CB3 compared with the CG group. Additionally, significant increases (p < 0.05) in the degradability of DM, neutral detergent fiber, and acid detergent fiber were observed in CB2 and CB3 compared with the CG group. For the in vivo study, 12 heat-stressed goats were divided equally into three groups: the control (HS1) was fed the basal diet, and groups HS2 and HS3 were fed with 0.05% and 0.10% Clostridium butyricum added to the basal diet, respectively. The experiment was designed as a 3 × 3 Latin square. Similar effects on rumen fermentation and digestibility parameters were obtained with 0.05% of Clostridium butyricum supplement compared to the in vitro study. Moreover, the dry matter intake and average daily gain were significantly increased (p < 0.05) in HS2 compared with other groups. These results indicated that an effective dose of Clostridium butyricum supplement (0.05%) could improve the rumen fermentation and growth performance of heat-stressed goats.

Ruminal and Fecal Bacteriome of Dairy Calves Fed Different Levels and Sources of NDF

A starter concentrate containing different levels and sources of NDF can modify the gastrointestinal bacteriome. This study evaluated 18 Holstein calves housed in un-bedded suspended individual cages, fed one of three treatments: 22NDF: a conventional starter containing 22% NDF (n = 7); 31NDF: a starter with 31% NDF, replacing part of the corn by soybean hull (n = 6); and 22Hay: diet 22NDF plus coast-cross hay ad libitum (n = 5). All animals received 4 L of milk replacer daily, weaned at 8th week of age, and housed in wood shelters until week 10. To evaluate the bacteriome, the bacterial community of ruminal fluid and fecal samples was determined by sequencing V3 and V4 region amplicons of the 16S rRNA gene. Bacterial diversity in rumen was not affected by diet or age. The phyla Firmicutes and Bacteroidota, and Prevotella' genus were the most abundant in ruminal fluid and fecal samples. In feces, the α-diversity indices were higher for 22Hay. All indices were significantly affected by age. We believe that the ruminal bacteriome was affected by basal diet components, but not affected by NDF levels or sources. The supply of hay was effective in modifying the fecal bacteriome of dairy calves due to hind gut fermentation.

Dietary Supplementation With Creatine Pyruvate Alters Rumen Microbiota Protein Function in Heat-Stressed Beef Cattle

Creatine pyruvate (CrPyr) is a new multifunctional nutrient that can provide both pyruvate and creatine. It has been shown to relieve the heat stress of beef cattle by improving antioxidant activity and rumen microbial protein synthesis, but the mechanism of CrPyr influencing rumen fermentation remains unclear. This study aimed to combine 16S rDNA sequencing and metaproteomics technologies to investigate the microbial composition and function in rumen fluid samples taken from heat-stressed beef cattle treated with or without 60 g/day CrPyr. 16S rDNA sequencing revealed that there were no significant differences in the α-diversity indices between the two groups. By analyzing the level profiles of 700 distinct proteins, we found that the CrPyr administration increased the expression of enzymes involved in specific metabolic pathways including (i) fatty acid β-oxidation; (ii) interconversion from pyruvate to phosphoenolpyruvate, oxaloacetate, acetyl-CoA, and malate; (iii) glycolysis/gluconeogenesis and citrate cycle metabolism; and (iv) biosynthesis of amino acids. These results indicated that the increased generation of adenosine triphosphate during fatty acid β-oxidation or citrate cycle and the up-regulation synthesis of microbial protein in rumen of beef cattle treated with CrPyr may help decrease oxidative stress, regulate energy metabolism, and further improve the rumen fermentation characteristic under heat stress.

Dietary Supplementation with Saccharomyces cerevisiae, Clostridium butyricum and Their Combination Ameliorate Rumen Fermentation and Growth Performance of Heat-Stressed Goats

Simple Summary

Heat stress commonly happens to goats raised in the Jianghuai region of China during the summer and inevitably contributes to a loss of animal production. Dietary supplementation with probiotics is one of the practical approaches to improve animal production. By dietary supplementation with Saccharomyces cerevisiae, Clostridium butyricum, and their combination to the heat-stressed goats, the present study showed these probiotics effectively alleviate heat stress by improving the rumen fermentation function and growth performance. Therefore, this study provides a reference for the application of these two probiotics in ruminant production during heat stress.

Abstract

This study aimed to evaluate the effects of Saccharomyces cerevisiae, and their combination on rumen fermentation and growth performance of heat-stressed goats. Twelve heat-stressed goats (20.21 ± 2.30 kg) were divided equally into four groups: control group (CG, fed the basal diet, Saccharomyces cerevisiae supplemented group (SC, 0.60% Saccharomyces cerevisiae added to the basal diet), Clostridium butyricum supplemented group (CB, 0.05% Clostridium butyricum added to the basal diet), and their combination supplemented group (COM 0.60% Saccharomyces cerevisiae and 0.05% Clostridium butyricum added to the basal diet) and were assigned to a 4 × 3 incomplete Latin square design. The rumen fluid and feces were collected for fermentation parameters and feed digestibility analysis, and animal growth performance was also assessed during all the experiment periods. The results showed that rumen pH, rumen cellulolytic enzymes (avicelase, CMCaes, cellobiase, and xylanase) activities, and the concentrations of rumen total volatile fatty acid (TVFA), acetic acid, and propionic acid were significantly increased with Saccharomyces cerevisiae, Clostridium butyricum, and their combination supplementation (p < 0.05). Besides, the dry matter intake (DMI), average daily gain (ADG), and the digestibility of dry matter (DM), neutral detergent fiber (NDF), and acidic detergent fiber (ADF) were significantly increased (p < 0.05) with supplemented these probiotics. However, the ammonia nitrogen (NH₃-N) concentration only significantly increased in CB and A/P ratio (acetic acid to propionic acid ratio) only significantly increased in SC and CB. These results indicated that the supplementation with these probiotics could ameliorate rumen fermentation and growth performance of heat-stressed goats.

The Liquid Diet Composition Affects the Fecal Bacterial Community in Pre-weaning Dairy Calves

Feeding a liquid diet to the newborn calf has considerable implications for developing the intestinal microbiota, as its composition can shift the population to a highly adapted microbiota. The present work evaluated 15 Holstein calves individually housed and fed one of the three liquid diets: I – whole milk (n = 5), II – milk replacer (22.9% CP; 16.2% fat; diluted to 14% solids; n = 5) and III – acidified whole milk to pH 4.5 with formic acid (n = 5). All animals received 6 L of liquid diet, divided into two meals, being weaned at week 8 of life. Calves also had free access to water and starter concentrate. After weaning, all calves were grouped on pasture, fed with starter concentrate, and hay ad libitum. The fecal samples were collected at birth (0) and at weeks 1, 2, 4, 8, and 10 of life. The bacterial community was assessed the through sequencing of the V3-V4 region of the 16S rRNA gene on the Illumina MiSeq platform and analyzed using the DADA2 pipeline. Diversity indices were not affected by the liquid diets, but by age (P &lt; 0.001) with weeks 1 and 2 presenting lower diversity, evenness, and richness values. The bacterial community structure was affected by diet, age, and the interaction of these factors (P &lt; 0.01). Twenty-eight bacterial phyla were identified in the fecal samples, and the most predominant phyla were Firmicutes (42.35%), Bacteroidota (39.37%), and Proteobacteria (9.36%). The most prevalent genera were Bacteroides (10.71%), Lactobacillus (8.11%), Alloprevotella (6.20%). Over the weeks, different genera were predominant, with some showing significant differences among treatments. The different liquid diets altered the fecal bacterial community during the pre-weaning period. However, differences in the initial colonization due to different liquid diets are alleviated after weaning, when animals share a common environment and solid diet composition.

Heat stress on microbiota composition, barrier integrity, and nutrient transport in gut, production performance, and its amelioration in farm animals

Livestock species experience several stresses, particularly weaning, transportation, overproduction, crowding, temperature, and diseases in their life. Heat stress (HS) is one of the most stressors, which is encountered in livestock production systems throughout the world, especially in the tropical regions and is likely to be intensified due to global rise in environmental temperature. The gut has emerged as one of the major target organs affected by HS. The alpha- and beta-diversity of gut microbiota composition are altered due to heat exposure to animals with greater colonization of pathogenic microbiota groups. HS also induces several changes in the gut including damages of microstructures of the mucosal epithelia, increased oxidative insults, reduced immunity, and increased permeability of the gut to toxins and pathogens. Vulnerability of the intestinal barrier integrity leads to invasion of pathogenic microbes and translocation of antigens to the blood circulations, which ultimately may cause systematic inflammations and immune responses. Moreover, digestion of nutrients in the guts may be impaired due to reduced enzymatic activity in the digesta, reduced surface areas for absorption and injury to the mucosal structure and altered expressions of the nutrient transport proteins and genes. The systematic hormonal changes due to HS along with alterations in immune and inflammatory responses often cause reduced feed intake and production performance in livestock and poultry. The altered microbiome likely orchestrates to the hosts for various relevant biological phenomena occurring in the body, but the exact mechanisms how functional communications occur between the microbiota and HS responses are yet to be elucidated. This review aims to discuss the effects of HS on microbiota composition, mucosal structure, oxidant-antioxidant balance mechanism, immunity, and barrier integrity in the gut, and production performance of farm animals along with the dietary ameliorations of HS. Also, this review attempts to explain the mechanisms how these biological responses are affected by HS.

The Comparative Analysis of the Ruminal Bacterial Population in Reindeer (Rangifer tarandus L.) from the Russian Arctic Zone: Regional and Seasonal Effects

Simple Summary

The reindeer (Rangifer tarandus) is a unique ruminant that lives in arctic areas characterized by severe living conditions. Low temperatures and a scarce diet containing a high proportion of hard-to-digest components have contributed to the development of several adaptations that allow reindeer to have a successful existence in the Far North region. These adaptations include the microbiome of the rumen—a digestive organ in ruminants that is responsible for crude fiber digestion through the enzymatic activity of microorganisms. In this study, research was conducted on the ruminal microbiome of reindeer of the Nenets breed living in various climatic zones of the Russian Arctic (in the Yamalo-Nenetski Autonomous District and Nenetski Autonomous District. The impacts of the habitat, season of the year, sex, and age factors on the rumen microbiome were investigated. As a result, it was found that significant differences in the reindeer ruminal microbiome composition are associated with the region of habitat and change of seasons that the reindeer are exposed to. The distinctions mainly come down to different ratios of bacteria involved in the metabolism of volatile fatty acids and cellulose decomposition in the rumen, which is apparently a reflection of the different plant components in the diet in different regions and seasons.

Abstract

The reindeer (Rangifer tarandus L.) is a unique animal inhabitant of arctic regions. Low ambient temperatures and scant diets (primarily, lichens) have resulted in different evolutional adaptations, including the composition of the ruminal microbiota. In the study presented here, the effects of seasonal and regional aspects of the composition of the ruminal microbiota in reindeer (Nenets breed, 38 animals) were studied (wooded tundra from the Yamalo-Nenetski Autonomous District (YNAD) vs. from the Nenetski Autonomous District (NAD)). The ruminal content of calves (n = 12) and adult animals (n = 26, 15 males and 11 females) was sampled in the summer (n = 16) and winter seasons (n = 22). The composition of the ruminal microbial population was determined by the V3–V4 16S rRNA gene region sequencing. It was found that the population was dominated by Bacteroidetes and Firmicutes phyla, followed by Spirochaetes and Verrucomicrobia. An analysis of the community using non-metric multidimensional scaling and Bray–Curtis similarity metrics provided evidence that the most influential factors affecting the composition of ruminal microbiota are the region (p = 0.001) and season (p = 0.001); heat map analysis revealed several communities that are strongly affected by these two factors. In the summer season, the following communities were significantly larger compared to in the winter season: Coriobactriaceae, Erysipelothrihaceae, and Mycoplasmataceae. The following communities were significantly larger in the winter season compared to in summer: Paraprevotellaceae, Butyrivibrio spp., Succiniclasticum spp., Coprococcus spp., Ruminococcus spp., and Pseudobutyrivibrio spp. In NAD (tundra), the following communities were significantly larger in comparison to YNAD (wooded tundra): Verrucomicrobia (Verruco-5), Anaerolinaceae, PeHg47 Planctomycetes, cellulolytic Lachnospiraceae, and Succiniclasticum spp. The following bacterial groups were significantly larger in YNAD in comparison to NAD: cellulolytic Ruminococaceae, Dehalobacteriaceae, Veillionelaceae, and Oscilospira spp. The significant differences in the ruminal microbial population were primarily related to the ingredients of diets, affected by region and season. The summer-related increases in the communities of certain pathogens (Mycoplasmataceae, Fusobacterium spp., Porphyromonas endodentalis) were found. Regional differences were primarily related to the ratio of the species involved in ruminal cellulose degradation and ruminal fatty acids metabolism; these differences reflect the regional dissimilarities in botanical diet ingredients.

Heat stress influence the microbiota and organic acids concentration in beef cattle rumen

The objective of this study was to evaluate the effect of heat stress on meta-taxonomic and metabolic profiles of prokaryotes in beef cattle rumen. Six pure-breed Nellore heifers with ruminal cannulas were used in the study. Six treatments were tested in a 6 × 6 Latin Square with six periods of 21days. The treatments were evaluated in a 2 × 2 + 2 factorial arrangement, consisting of 4 combinations: two temperatures conditions (thermoneutral, TN: 24 °C; and heat stress, HS: 34 °C) and two dietary energy concentration [low-energy (37% non-fibrous carbohydrates - NFC, 12 Mcal of metabolizable energy per kg of dry matter) or high-energy concentration (50.5% NFC, 18.49 Mcal of metabolizable energy per kg of dry matter)] plus two additional treatments with animals maintained in TN conditions but with your intake restricted (TN-RI) to the same of the heifers in HS with the two dietary energy concentration. The meta-genome was sequenced by MiSeq Sequencing System platform, and the DNA sequences were analysed using Geneious 10.2.3 software. The metabolic profile was evaluated by liquid and gas chromatography. Animals under HS presented lower (P = 0.04) prokaryote richness than animals under TN conditions. The genera Flavonifractor (1.4%), Treponema (0.6%) and Ruminococcus (0.9%) showed the lowest (P < 0.04) and Carnobacterium (7.7%) the highest (P = 0.02) relative abundance when the animals were submitted to HS, in relation to animals in TN. A total of 49 different metabolites were identified in the ruminal samples. The concentration of isobutyric acid (4.32 mM) was highest in bovine rumen under HS conditions. Heat stress influenced the microbiota and concentration of some organic acids in beef cattle rumen. There was a reduction in the richness of rumen in cattle under heat stress, but the diversity of prokaryotes was not affected.

Impact of selected environmental factors on microbiome of the digestive tract of ruminants

Ruminants are an important part of world animal production. The main factors affecting their production rates are age, diet, physiological condition and welfare. Disorders related to low level of welfare can significantly affect the microbiological composition of the digestive system, which is essential to maintain high production rates. The microbiology of the ruminant gastrointestinal tract may be significantly affected by inappropriate keeping system (especially in juveniles), psychological stress (e.g. transport), or heat stress. This results in an increased risk of metabolic diseases, reduced fertility and systemic diseases. Therefore, the paper focuses on selected disorders i.e., aforementioned inappropriate maintenance system, psychological stress, heat stress and their effects on the microbiome of the digestive system.

Increasing the Sustainability of Maize Grain Production by Using Arbuscular Mycorrhizal Fungi Does Not Affect the Rumen of Dairy Cattle (Bos taurus) and Buffalo (Bubalus bubalis)

New approaches are needed to improve the sustainability of feed production and utilization by ruminants. Promising approaches include increased use of buffaloes for more sustainable milk production, and arbuscular mycorrhizal fungi (AMF) to reduce crop production input needs. However, studies assessing the effect of crops grown in the presence of AMF on rumen microbial utilization are limited. Based on current knowledge, we hypothesized that maize grain grown on AMF-inoculated soil affected ruminal fermentation and microbiota, and that this effect differed between buffalo and cattle. A dietary cross-over study (four weeks per diet) was conducted using rumen-cannulated cattle (n = 5) and buffalo (n = 6) to assess the effect of maize grain (3.9% (w/v) of diet) grown on soil with or without AMF (15 kg/ha) on ruminal fermentation and microbiota. Production of maize on AMF-treated soil did not affect any of the assessed ruminal fermentation parameters, microbial concentrations, or prokaryotic community composition (using prokaryotic 16S rRNA gene sequence analysis). In contrast, host type had numerous effects. Protozoal counts, lactate, total VFA and isobutyrate, were significantly higher in buffaloes compared to cattle. Conversely, butyrate was significantly lower in buffaloes than in cattle. Host type explained 9.3% of the total variation in prokaryotic community composition, and relative abundance of nine amplicon sequence variants significantly differed between host types. These findings indicate that AMF treatment of maize crops has no detrimental impact on the value of the resulting maize grains as a ruminant feed, and provides additional insight into rumen-based differences between cattle and buffalo.

Tibetan Sheep Adapt to Plant Phenology in Alpine Meadows by Changing Rumen Microbial Community Structure and Function

The rumen microbiota is strongly associated with host health, nutrient absorption, and adaptability. However, the composition, functioning and adaptability of rumen microbiota in Tibetan sheep (TS) across different phenological periods are unclear. In this study we used sequencing of the V4-V5 region of 16S rRNA, qPCR technology and metagenomics to investigate the adaption of rumen microbiota to forage in different stages of phenology. In a grassy period, due to the high nutritional quality of the forage, TS can produce high concentrations of NH₃-N and short fatty acids by increasing the content of key bacteria in the rumen, such as Bacteroidetes, Prevotella, Succiniclasticum, Treponema, Butyrivibrio fibrisolvens, Fibrobacter succinogenes, Prevotella ruminicola, Ruminococcus albus, and Ruminococcus flavefaciens to aid in growth. In the withering period, there was a positive correlation between microorganisms which indicated the closely cooperation between microorganisms, and metagenomic analysis showed that the high genes (GHs and CBMs) and subtribe (GH8, GH12, GH45, GH6, GH9, GH5, GH10, GH3, GH52, GH11, GH57, CBM1, CBM4, CBM6, CBM16, CBM37, CBM13, CBM35, CBM42, CBM32, and CBM62) that encode cellulolytic enzymes were significantly increased when the host faced low quantity and quality of forage. Genes involved in metabolic pathways, fatty acid biosynthesis and biosynthesis of antibiotics were significantly enriched, which indicated that rumen microbiota could improve plant biomass deconstruction and energy maintenance in the face of nutritional deficiencies. In the regreen period, both the composition and function of rumen microbiota had obvious disadvantages, therefore, to improve the competitiveness of microorganisms, we suggest TS should be supplemented with high-protein feed. This study is of great significance for exploring the high altitude adaptability of TS.

Modulation of rumen fermentation and microbial community through increasing dietary cation-anion difference in Chinese Holstein dairy cows under heat stress conditions

AIMS

The effect of increasing dietary cation-anion difference (DCAD) on rumen fermentation and ruminal microbial community in dairy cows under heat stress (HS) conditions were evaluated.

METHODS AND RESULTS

This study was performed as a two-period cross-over design during the summer season, with eight lactating dairy cows randomly distributed to either a control DCAD diet (CON: 33·5 mEq/100 g DM) or high DCAD diet (HDCAD: 50·8 mEq/100 g DM). Throughout the present study, the temperature and humidity index (THI; 80·2 ± 4·29) was generally elevated above the threshold (THI = 72) that is reported to cause HS in lactating dairy cows. Rumen liquid samples were collected on 15 and 21 d during each 21 d-period. The absolute concentration of ruminal total volatile fatty acid (TVFA) in HDCAD treatment was significantly (P < 0·05) higher than those in the control, whilst the ruminal pH, NH₃ -N, and VFA molar percentages were unaffected through increasing DCAD. Furthermore, the copy numbers of the cellulolytic bacteria Ruminococcus albus and Ruminococcus flavefaciens in rumen fluid significantly (P < 0·05) rose along with the increment of DCAD. Although the Alpha diversity indexes and the bacterial microbiota structure were unaffected, increasing DCAD significantly (P < 0·05) enriched the phylum Fibrobacteres and genus Fibrobacter in the microflora of rumen fluid, whilst the genera Flexilinea and Dubosiella were the most differentially abundant taxa in the control.

CONCLUSIONS

Increasing DCAD under HS conditions resulted in a greater concentration of total VFA without affecting rumen bacteria diversity or structure, although the enrichment of some cellulolytic/hemicellulolytic bacteria was observed.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study provides information on the modulation of rumen fermentation and microbial community through the increment of DCAD in Holstein dairy cows under HS conditions.

Heat stress on calves and heifers: a review

The current review is designed with aims to highlight the impact of heat stress (HS) on calves and heifers and to suggest methods for HS alleviation. HS occurs in animals when heat gain from environment and metabolism surpasses heat loss by radiation, convection, evaporation and conduction. Although calves and heifers are comparatively heat resistant due to less production of metabolic heat and more heat dissipation efficiency, they still suffer from HS to some degree. Dry matter intake and growth performance of calves and heifers are reduced during HS because of redistributing energy to heat regulation through a series of physiological and metabolic responses, such as elevated blood insulin and protein catabolism. Enhanced respiration rate and panting during HS accelerate the loss of CO2, resulting in altered blood acid-base chemistry and respiratory alkalosis. HS-induced alteration in rumen motility and microbiota affects the feed digestibility and rumen fermentation. Decreased luteinizing hormone, estradiol and gonadotrophins due to HS disturb the normal estrus cyclicity, depress follicular development, hence the drop in conception rate. Prenatal HS not only suppresses the embryonic development by the impaired placenta, which results in hypoxia and malnutrition, but also retards the growth, immunity and future milk production of newborn calves. Based on the above challenges, we attempted to describe the possible impacts of HS on growth, health, digestibility and reproduction of calves and heifers. Likewise, we also proposed three primary strategies for ameliorating HS consequences. Genetic development and reproductive measures, such as gene selection and embryo transfers, are more likely long-term approaches to enhance heat tolerance. While physical modification of the environment, such as shades and sprinkle systems, is the most common and easily implemented measure to alleviate HS. Additionally, nutritional management is another key approach which could help calves and heifers maintain homeostasis and prevent nutrient deficiencies because of HS.

Ruminal volatile fatty acid absorption is affected by elevated ambient temperature

The objective of this study was to investigate the effect of short-term elevated ambient temperature on ruminal volatile fatty acid (VFA) dynamics and rumen epithelium gene expression associated with the transport and metabolism of VFA. Eight ruminally cannulated Holstein heifers (200 kg) were used in a factorial, repeated measures experiment with two treatments and two periods. During the first period, animals were provided with feed ad libitum and housed at 20 °C. During the second period, one group (HS) was housed at 30 °C and fed ad libitum. The other group (PF) was housed at 20 °C and pair-fed to match the intake of the HS group. During each period, animals were kept on treatment for 10 day, with sample collection on the final day. In the second period, indicators of heat stress were significantly different between PF and HS animals (P < 0.05). There was a thermal environment effect on butyrate production (P < 0.01) that was not associated with feed intake (P = 0.43). Butyrate absorption decreased in HS animals (P < 0.05) but increased in PF animals (P < 0.05) from period 1 to period 2. There was a feed intake effect on BHD1 expression (P = 0.04) and a tendency for a thermal environment effect (P = 0.08), with expression increasing in both cases. Expression of MCT4 was affected by feed intake (P = 0.003) as were all NHE genes (NHE1, NHE2, and NHE3; P < 0.05). These results indicate that with low feed intake and heat stress, there are shifts in rumen VFA dynamics and in the capacity of the rumen epithelium to absorb and transport VFA.

Regulating appetite in broilers for improving body and muscle development - A review

Appetite is the desire for feed and water and the voluntary intake of feed and is an important regulator of livestock productivity and animal health. Economic traits such as growth rate and muscle development (meat deposition) in broilers are directly correlated to appetite. Factors that may influence appetite include environmental factors, such as stress and temperature variation, and animal‐specific factors, such as learning period, eating capacity and preferences. Feed preferences have been reported to be determined in early life, and this period is important in broilers due to their fast growth and relatively short growth trajectories. This may be of importance when contemplating the use of more circular and sustainable feeds and the optimization of appetite for these feeds. The objective of this review was to review the biological mechanisms underlying appetite using data from human, animal and bird models and to consider the option for modulating appetite particularly as it relates to broiler chickens.

The impact of short-term acute heat stress on the rumen microbiome of Hanwoo steers

Heat stress negatively affects cattle productivity by reducing feed intake. In the present study, we assessed if the rumen microbiome composition of Hanwoo steers was altered by exposure to heat stress. Rumen samples were collected from four Hanwoo steers that were individually housed in climate-controlled chambers with 60% humidity and environmental temperatures of: 1) 15°C (0-day group), 2) 35°C for 3 days (3-day group), and 3) 35°C for 6 days (6-day group). The total community DNA of samples was extracted, and 997,843 bacterial and 1,508,770 archaeal sequences were analyzed using next-generation sequencing. Assessment of the relative abundances revealed 15 major phyla of which Bacteroidetes was found to be the most dominant. After 3 days of heat stress exposure there were no significant changes in the rumen microbiome composition, except for a decrease in the Planctomycetes. However, after 6 days of heat stress exposure, we found that the relative abundance of fibrolytic Ruminococcaceae had decreased while that of lactate-producing Lactobacillaceae and amylolytic Prevotella and Ruminobacter had increased. The normal rumen microbiome of Hanwoo cattle was shown to be disrupted after 6 days of heat stress, which led to the decrease in fibrolytic bacteria that are sensitive to low pH and the increase in both lactate-producing and amylolytic bacteria. We have demonstrated that the microbiome composition of the rumen is affected by acute heat stress. Our findings may contribute to the development of different feeding strategies to restore heat stress-induced disruption of the rumen microbiome.

Betaine addition as a potent ruminal fermentation modulator under hyperthermal and hyperosmotic conditions in vitro

BACKGROUND

Climatic and dietary shifts predispose ruminal microbes to hyperthermal and hyperosmotic stress, leading to poor fermentation and subsequently adverse effects on ruminant productivity. Betaine may function as substrate, osmolyte, antioxidant, and methyl donor for microbes. However, its effect depends on the extent of microbial catabolism. This study revealed the ruminal disappearance kinetics of betaine and its dose effect on ruminal fermentation during thermal and osmotic stress using a rumen simulation technique.

RESULTS

Three different betaine doses were used: 0, 50, and 286 mg L-1 ; each was assigned to two incubation temperatures (39.5 and 42 °C) and two osmotic conditions (295 and 420 mOsmol kg-1 ). Betaine disappeared rapidly within the first 6 h of incubation; however, the rate was lower during hyperosmotic stress (P < 0.05), the stress condition that also suppressed the overall fermentation and degradation of organic nutrients and decreased the bacterial diversity (P < 0.001). During hyperosmotic stress, betaine shifted the fermentation pathway to more propionate (P < 0.05). Betaine counteracted the negative effect of hyperthermal stress on total short-chain fatty acid concentration (P < 0.05) without affecting the composition. Both stress conditions shifted the bacterial composition, but the effect of betaine was minimal.

CONCLUSION

Despite its rapid ruminal disappearance, betaine modulated microbial fermentation in different ways depending on stress conditions, indicating the plasticity of the betaine effect in response to various kinds of physicochemical stress. Although betaine did not affect the abundance of ruminal microbiota, the enhanced fermentation suggests an improved microbial metabolic activity under stress conditions. © 2020 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Effect of different seasons (spring vs summer) on the microbiota diversity in the feces of dairy cows

We aimed to study how seasonal heat stress (i.e., spring vs. summer) influenced microbiota diversity in the dairy cows' feces using Illumina MiSeq sequencing. Sixteen dairy cows were experiencing spring thermoneutral conditions (daily mean temperature = 18.8 ± 3.40 °; daily mean THI = 64.29 ± 4.94) and 16 under summer heat stress (daily mean temperature = 27.63 ± 5.34 °; daily mean THI = 82.56 ± 1.74). Fecal samples were collected per cow three times daily from day 18 to day 22 during each experimental period. Results revealed that the microbiota diversity in the feces was significantly lower (P < 0.05) under summer heat stress. At both the phylum and genera levels, significant differences were observed on microbiota composition in cow's feces between spring and summer. The most dominant phylum was Firmicutes, contributing 69.45% and 87.14% of the fecal microbiota in spring and summer, respectively, followed by Bacteroidetes, contributing 25.27% and 4.45%, respectively. Compared with the dairy cows in the spring season, the relative abundance of unclassified Peptostreptococcaceae, Turicibacter, and Clostridium_sensu_stricto_1 (P < 0.05) were greatly increased (P < 0.05), while the significant decrease in the proportion of Ruminococcaceae_UCG-005 and Rikenellaceae_RC9_gut_group as well as Bacteroides were observed in hot summer. Prediction of microbiota gene function in feces based on PICRUSt method found that different microbiota between spring and summer were mainly concentrated on the function related to membrane transport, infectious diseases, immune system diseases, and lipid metabolism. This study demonstrates that diversity and composition of fecal microbiota in dairy cows varies under different THI condition, and the relationship between fecal microbiota and cows' health needs further research.

Microbiota in viral infection and disease in humans and farm animals

The influence of the microbiota on viral infection susceptibility and disease outcome is undisputable although varies among viruses. The purpose of understanding the interactions between microbiota, virus, and host is to identify practical, effective, and safe approaches that target microbiota for the prevention and treatment of viral diseases in humans and animals, as currently there are few effective and reliable antiviral therapies available. The initial step for achieving this goal is to gather clinical evidences, focusing on the viral pathogens-from human and animal studies-that have already been shown to interact with microbiota. The subsequent step is to identify mechanisms, through experimental evidences, to support the development of translational applications that target microbiota. In this chapter, we review evidences of virus infections altering microbiota and of microbiota enhancing or suppressing infectivity, altering host susceptibility to certain viral diseases, and influencing vaccine immunogenicity in humans and farm animals.

Effect of chronic and acute heat challenges on fecal microbiota composition, production, and thermoregulation traits in growing pigs1,2

The present study aimed at investigating the impact of heat challenges on gut microbiota composition in growing pigs and its relationship with pigs’ performance and thermoregulation responses. From a total of 10 F1 sire families, 558 and 564 backcross Large White × Créole pigs were raised and phenotyped from 11 to 23 wk of age in temperate (TEMP) and in tropical (TROP) climates, respectively. In TEMP, all pigs were subjected to an acute heat challenge (3 wk at 29 °C) from 23 to 26 wk of age. Feces samples were collected at 23 wk of age both in TEMP and TROP climate (TEMP23 and TROP23 samples, respectively) and at 26 wk of age in TEMP climate (TEMP26 samples) for 16S rRNA analyses of fecal microbiota composition. The fecal microbiota composition significantly differed between the 3 environments. Using a generalized linear model on microbiota composition, 182 operational taxonomic units (OTU) and 2 pathways were differentially abundant between TEMP23 and TEMP26, and 1,296 OTU and 20 pathways between TEMP23 and TROP23. Using fecal samples collected at 23 wk of age, pigs raised under the 2 climates were discriminated with 36 OTU using a sparse partial least square discriminant analysis that had a mean classification error-rate of 1.7%. In contrast, pigs in TEMP before the acute heat challenge could be discriminated from the pigs in TEMP after the heat challenge with 32 OTU and 9.3% error rate. The microbiota can be used as biomarker of heat stress exposition. Microbiota composition revealed that pigs were separated into 2 enterotypes. The enterotypes were represented in both climates. Whatever the climate, animals belonging to the Turicibacter–Sarcina–Clostridium sensu stricto dominated enterotype were 3.3 kg heavier (P < 0.05) at 11 wk of age than those belonging to the Lactobacillus-dominated enterotype. This latter enterotype was related to a 0.3 °C lower skin temperature (P < 0.05) at 23 wk of age. Following the acute heat challenge in TEMP, this enterotype had a less-stable rectal temperature (0.34 vs. 0.25 °C variation between weeks 23 and 24, P < 0.05) without affecting growth performance (P > 0.05). Instability of the enterotypes was observed in 34% of the pigs, switching from an enterotype to another between 23 and 26 wk of age after heat stress. Despite a lower microbial diversity, the Turicibacter–Sarcina–Clostridium sensu stricto dominated enterotype was better adapted to heat stress conditions with lower thermoregulation variations.

Effect of Heat Stress on Bacterial Composition and Metabolism in the Rumen of Lactating Dairy Cows

Simple Summary

Heat stress negatively impacts the health and milk production of dairy cows, and ruminal microbes play an important role in the animal’s milk production. Understanding the link between heat stress and the ruminal microbiome could help to develop strategies to relieve the influence of heat stress by manipulating the ruminal microbial composition. We found that heat-stressed cows had decreased ruminal pH and acetate concentration, whereas the ruminal lactate concentration increased. Heat-stressed cows also had a significantly higher relative abundance of lactate producing bacteria (e.g., Streptococcus and unclassified Enterobacteriaceae), Ruminobacter, Treponema, and unclassified Bacteroidaceae, all of which utilize soluble carbohydrate as an energy source. The relative abundance of the acetate-producing bacterium Acetobacter decreased with heat stress treatment. Therefore, heat stress is associated with changes in ruminal bacterial composition and metabolites, with more lactate and less acetate-producing species in the population, which potentially negatively affects milk production.

Abstract

Heat stress negatively impacts the health and milk production of dairy cows, and ruminal microbial populations play an important role in dairy cattle’s milk production. Currently there are no available studies that investigate heat stress-associated changes in the rumen microbiome of lactating dairy cattle. Improved understanding of the link between heat stress and the ruminal microbiome may be beneficial in developing strategies for relieving the influence of heat stress on ruminants by manipulating ruminal microbial composition. In this study, we investigated the ruminal bacterial composition and metabolites in heat stressed and non-heat stressed dairy cows. Eighteen lactating dairy cows were divided into two treatment groups, one with heat stress and one without heat stress. Dry matter intake was measured and rumen fluid from all cows in both groups was collected. The bacterial 16S rRNA genes in the ruminal fluid were sequenced, and the rumen pH and the lactate and acetate of the bacterial metabolites were quantified. Heat stress was associated with significantly decreased dry matter intake and milk production. Rumen pH and rumen acetate concentrations were significantly decreased in the heat stressed group, while ruminal lactate concentration increased. The influence of heat stress on the microbial bacterial community structure was minor. However, heat stress was associated with an increase in lactate producing bacteria (e.g., Streptococcus and unclassified Enterobacteriaceae), and with an increase in Ruminobacter, Treponema, and unclassified Bacteroidaceae, all of which utilize soluble carbohydrates as an energy source. The relative abundance of acetate-producing bacterium Acetobacter decreased during heat stress. We concluded that heat stress is associated with changes in ruminal bacterial composition and metabolites, with more lactate and less acetate-producing species in the population, which potentially negatively affects milk production.