Effect of heat stress on ingestive, digestive, ruminal and physiological parameters of Nellore cattle feeding low- or high-energy diets

Genome-wide association study for feed efficiency indicator traits in Nellore cattle considering genotype-by-environment interactions

Introduction

Feed efficiency is a key factor in animal production sustainability, directly affecting production costs, environmental efficiency, and farmer profitability. The inclusion of feeding efficiency traits in cattle breeding programs has occurred later than other species due to longer life cycles and the high costs associated with measuring feed intake. However, genomic selection has facilitated the inclusion of difficult-to-measure traits in selection schemes. Thus, understanding the genetic basis of feed efficiency, particularly under varying environmental conditions, is essential.

Methods

This study aimed to identify genomic regions associated with dry matter intake (DMI) and residual feed intake (RFI) in Nellore cattle by performing a genome-wide association study (GWAS) based on single-step genomic reaction norm models that account for genotype-by-environment interactions (G×E). Phenotypic data from 23,170 young bulls and heifers were collected across 301 feed efficiency trials. Genomic windows explaining more than 1% of the total direct additive genetic variance were identified for both the intercept and slope components of the reaction norm for each trait.

Results

For RFI, ten and eleven genomic windows explained more than 1% of the genetic variance for the intercept and slope, respectively. For DMI, 12 windows were identified for the intercept and 17 for the slope. Within these regions, Multiple protein-coding genes were annotated (RFI: 66 for intercept and 47 for slope; DMI: 107 for intercept and 109 for slope), which are involved in key biological processes such as insulin, leptin, glucose, protein, and lipid metabolism; energy balance; heat stress response; feeding behavior; digestion; and nutrient absorption.

Discussion

The results highlight the functional diversity of genes involved in feed efficiency and their dynamic response to environmental variation. While certain genes remained central across environments, others were specifically important under more challenging conditions, emphasizing the role of G×E in regulating these traits. Furthermore, the magnitude and direction of SNP effects varied across environmental gradients, reinforcing the relevance of G×E. Consequently, genomic estimated breeding values for DMI and RFI also differed between environmental extremes. These findings underscore the adaptability of genetic networks to environmental changes and are essential for refining strategies to improve feed efficiency in Nellore cattle.

Identification of single nucleotide polymorphisms (SNPs) associated with heat stress and milk production traits in Chinese holstein cows

BACKGROUND

Heat stress (HS) poses a significant challenge to the dairy industry, affecting both the health and productivity of dairy cows. Identifying candidate genes and single nucleotide polymorphisms (SNPs) associated with HS is critical to improving heat tolerance of dairy cows. In our previous work, the eukaryotic translation initiation factor 4E (EIF4E), heat shock protein family A member 4 (HSPA4), and inositol 1,4,5-trisphosphate receptor type 2 (ITPR2) genes were found to play critical roles in the HS response of dairy cows.

RESULTS

In this study, we further validated the gene expression patterns and genetic effects of the three candidate genes on HS response and milk production in Chinese Holstein cows. A total of 21 SNPs were identified by sequencing the exon and 2000 bp flanking region of the EIF4E (4 SNPs), HSPA4 (8 SNPs), and ITPR2 (9 SNPs) in pooled DNA samples from 70 Holstein bulls. Among these, two SNPs (g.44653172A > G and g.44660065C > T) were located in the coding exon and the 3' untranslated region of the HSPA4 gene, respectively. Association analyses were conducted between identified SNPs and three HS traits and six milk production traits in a population of 1,160 Chinese Holstein cows. The SNP-based association analysis identified significant associations between ten SNPs and HS traits (P < 0.05), as well as eight SNPs and milk production traits (P < 0.05). In the HSPA4 gene, five SNPs (g.44618036G > A, g.44624256 A > C, g.44624428T > C, g.44653172 A > G, and g.44660065 C > T) were significantly associated with rectal temperature (RT; P < 0.05). Notably, no SNPs were associated with milk production traits. Haplotype blocks containing g.44,653,172 A > G and g.44,660,065 C > T also showed significant associations with RT (P < 0.05). Further analysis suggests that g.44,660,065 C > T affects the stability of the mRNA secondary structure, microRNA and transcription factor binding, thereby potentially influencing the gene expression of HSPA4.

CONCLUSION

In conclusion, we demonstrated that these three genes had significant genetic effects on HS and milk production traits. And g.44,660,065 C > T in the HSPA4 gene could be used as functional molecular markers for the genetic selection of dairy cows for improving heat tolerance without compromising their high milk performance.

Salivary heat shock protein 70 as a potential non-invasive biomarker of environmental thermal stress in dairy cattle

The present study aims to explore the potential biomarker application of salivary heat shock 70 kDa protein in detecting thermal stress in dairy animals noninvasively. The study spans for 45 days during the mid-summer season (April-May), involving twelve multiparous non-pregnant adult Jersey crossbred cows by randomly allocating them into groups (six animals in each group). The control animals were maintained in the shed, whereas the thermal stress group animals were exposed to environment heat between 10:00 h to 16.00 h and they were feed and watered ad libitum. During the experimental period, the hematobiochemical, physiological, behavioural, nutritional and production responses were recorded and the whole blood and saliva were collected fortnightly. Results revealed significant increase in WBC, AST, ALP, blood urea nitrogen, triglycerides, cholesterol, HDL, blood and salivary cortisol, respiratory rate, rectal temperature, skin temperature of neck, lumbar and forelimb regions, standing time, salivary and blood HSP70 mRNA expression and their protein concentrations in heat stressed animals. In addition, RBC, haemoglobin, MCV, PCV, platelet, platelet-large cell ratio (PLCR), lying time, feed intake, milk yield and rumination time were significantly decreased in thermally stress animals. Furthermore, ROC curve analysis revealed the biomarker potential of these significantly altered parameters with 100% sensitivity and specificity for predicting environmental heat stress in dairy cows with AUC and Youden's - index of 1.00 except platelet. Moreover, salivary HSP70 demonstrated significant correlation with these biomarkers. Noteworthily, salivary HSP70 also exhibited strong association with blood HSP70 and salivary cortisol. Furthermore, salivary HSP70 revealed 100% sensitivity and specificity in discriminating the dairy cattle succumbed to heat stress from healthy. In conclusion, the present study provides a newer insight into the multifaceted roles of HSP70 and identified salivary heat shock 70 kDa protein as a potential, reliable and more sensitive non-invasive biomarker for identifying environmental heat stress in dairy cattle.

Effects of Production System With or Without Growth-Promoting Technologies on Growth and Blood Expression of (Cyto)Chemokines and Heat Shock and Tight Junction Proteins in Bos taurus and indicus Breeds During Summer Season

Heat stress (HS) induced by global warming is a real welfare, productivity, and economic burden of cattle production. However, some cattle breeds have superior physiological adaptive traits to others, yet the underlying molecular mechanisms are not fully defined. The present study aimed, therefore, to determine the expression profile of stress-related molecular signatures in the blood of thermosensitive Angus (Bos taurus) and thermotolerant Brahman (Bos indicus) cattle breeds managed without (CON) or with growth-promoting technology (TRT) during the summer (April-October, 2023) season in Colorado, US. Body weight (BW) was significantly increased from April to October, and the amplitude was greater for the Angus compared to the Brahman breed. The TRT system slightly increased BW, mainly in the Angus breed. Molecular analyses showed that all tested genes were expressed in beef cattle blood. When comparing production systems, the expression of HSP1A1 was significantly upregulated, and HSP90 was downregulated in CON compared to TRT cattle. The expression of IL6, CCL20, and OCLN was induced by the CON system only in the Angus and not in the Brahman breed. At the breed level, Angus cattle exhibited greater expression of IL10, CCL20, and CLDN1 compared to their Brahman counterparts. There was a significant period by production system as well as period by breed interactions. The expression of HSP1A1 increased in both breeds during October. The expression of IL10, CXCL14, CXCR2, and CLDN1 was affected by the production systems in a period-dependent manner. However, the expression of IL6, CXCL14, CCL5, and CXCR2 was upregulated in Angus cattle in a period-sensitive manner. In summary, HSPs, (chemo)cytokines, and tight junction proteins are expressed in the whole blood of beef cattle, and their expression is regulated in a breed-, period-, and/or production system-dependent manner. This could open new vistas for future research to identify molecular signatures for non-invasive stress monitoring and/or marker-assisted genetic selection for robustness and resilience to HS.

Heat stress affects milk yield, milk quality, and gene expression profiles in mammary cells of Girolando cows

Heat stress during lactation affects the physiological responses, hormonal release, health, and productivity of dairy cows. However, the adverse effects of heat stress on milk synthesis, immune response, and cellular apoptosis in mammary cells remains unknown in Bos indicus cows. This study aimed to understand the relationship between milk yield, milk quality, and the expression of genes related to milk synthesis, cell apoptosis, and immune response in mammary cells of Girolando cows. A total of 24 Girolando cows (3/4 Holstein and 1/4 Gir) were subjected to control (CT; with a temperature-humidity index ranging from 60 to 74, n = 12) or heat stress treatments (HS; with a temperature-humidity index ranging from 60 to 85, n = 12), from 111 to 120 d of lactation. Heat stress significantly increased the expression of heat shock proteins (HSPD1 and HSPD90AA1), insulin receptors (INSR), and prolactin receptor (PRLRsf) genes, and decreased the expression of glucocorticoid receptor (NR3C1) gene in mammary cells of the HS cows when compared with the CT cows. The HS cows exhibited significantly higher vaginal temperatures and cortisol release compared with the CT cows. Moreover, the HS cows had significantly lower DMI and milk yield than CT cows. Although, HS cows showed higher percentage of lymphocytes in milk when compared with that from CT cows. We found no effect of heat stress on other leukocyte counts, somatic cell counts, bacterial counts in milk, or milk composition. Finally, this study demonstrated that Girolando cows are susceptible to heat stress, which decreases milk yield and affects the expression of genes linked to milk synthesis in the mammary cells.

Insights on early response to acute heat shock of bovine mammary epithelial cells through a multimethod approach

Heat stress is a significant challenge in dairy cattle herds, affecting milk production and quality, and generating important changes at the cellular level. Most in vitro research on heat shock (HS) effects on dairy cow mammary cells was focused on medium-long-term effects. In recent years, Fourier transform-infrared (FT-IR) micro-spectroscopy has been increasingly used to study the effects of several external stresses on different cell lines, down to the level of single cellular components, such as DNA/RNA, lipids, and proteins. In this study, the possible changes at the biochemical and molecular level induced by acute (30 min-2 h) HS in bovine mammary epithelial (BME-UV1) cells were investigated. The cells were exposed to different temperatures, thermoneutral (TN, 37 °C) and HS (42 °C), and FT-IR spectra were acquired to analyse the effects of HS on biochemical characteristics of BME-UV1 cellular components (proteins, lipids, and DNA/RNA). Moreover, cell viability assay, reactive oxygen species production, and mRNA expression of heat shock proteins (HSPA1A, HSP90AA1, GRP78, GRP94) and antioxidant genes (SOD1, SOD2) by RT-qPCR were also analysed. The FT-IR results showed a change already at 30 min of HS exposure, in the content of long-chain fatty acids, which probably acted as a response to a modification of membrane fluidity in HS cells compared with TN cells. After 2 h of HS exposure, modification of DNA/RNA activity and accumulation of aggregated proteins was highlighted in HS cells. The gene expression analyses showed the overexpression of HSPA1A and HSP90AA1 starting from 30 min up to 2 h in HS cells compared with TN cells. At 2 h of HS exposure, also the overexpression of GRP94 was observed in HS cells. Acute HS did not affect cell viability, reactive oxygen species level, and SOD1 and SOD2 gene expression of BME-UV1 cells. According to the results obtained, cells initiate early defence mechanisms in case of acute HS and probably this efficient response capacity may be decisive for tolerance to heat stress of dairy cattle.

Impact of Heat Stress on the Balance between Oxidative Markers and the Antioxidant Defence System in the Plasma of Mid-Lactating Modicana Dairy Cows

Animal health is affected during heat stress as a result of impaired immune responses, increased production of reactive oxygen species, and/or a deficiency of antioxidants. This leads to an imbalance between oxidants and antioxidants and results in oxidative stress. Heat stress is usually measured in dairy cattle via the temperature-humidity index (THI). In the present study, we aimed at assessing the influence of incremental THI on the balance between oxidative markers and the antioxidant defence system in the plasma of Modicana cows. Twenty-four multiparous, mid-lactating dairy cows were divided into two groups on the basis of different levels of mean THI reached in the period of the previous week up until the day of blood and milk sampling (April THI1:55, May THI2:68, June THI3:71, July THI4:80). The blood samples were collected to measure reactive oxygen metabolites (ROM) and antioxidant defense markers (ferric reducing ability of plasma (FRAP), paraoxonase (PON), advanced oxidation protein products (AOPP), plasma thiol groups (SHp), as well as lipid-soluble antioxidant pro-vitamin (β-carotene) and vitamins (tocopherol and retinol). Milk characteristics, haematological values, and plasma biochemical metabolites were also evaluated. Results showed a significant increase in ROM (p < 0.05) and a significant decrease in PON (p < 0.05), AOPP (p < 0.05), and β-carotene (p < 0.001). Incremental THI significantly decreased levels of milk fat content, red and white blood cells, plasma glucose, and non-esterified fatty acids, while significantly increasing monocytes and the concentrations of β-hydroxybutyrate and creatinine, but not fructosamine. The results of the study show that heat stress significantly affects reactive oxygen species production and antioxidant parameters. Carotenoid supplementation should be considered to alleviate the impact of these effects.

Changes in Parameters Registered by Innovative Technologies in Cows with Subclinical Acidosis

The hypothesis of this study was that there were changes in biomarkers registered by innovative technologies in cows with subclinical acidosis. The aim of this study was to identify changes in the in-line milk fat-to-protein ratio and cow feeding behaviors such as reticulorumen pH, reticulorumen temperature, cow activity, and water intake with subclinical acidosis. From a total of 98 cows, 59 cows were selected to meet the following criteria (2 or more lactations, with 31 days in milk (DIM)). The selected animals were separated into two groups based on general clinical examination and reticulorumen pH: the subclinical acidosis group (SCA, n = 23) and the healthy group (HC, n = 36). During the diagnosis of subclinical acidosis and following the clinical examination of the healthy group using the BROLIS HerdLine system, the daily averages of milk yield (kg/day), milk fat (%), milk protein (%), and the milk fat-to-protein ratio were recorded. Simultaneously, by using Smaxtec technology, reticulorumen parameters and cow activity, including pH, temperature (°C), rumination time (minutes/day), and water intake (hours/day), were registered. Changes in parameters measured using innovative technologies were able to identify cows with subclinical acidosis. Cows with subclinical acidosis had a lower reticulorumen pH by 18.8% (p < 0.0001), a decreased milk yield by 10.49% (p < 0.001), a lower milk fat-to-protein ratio by 11.88% (p < 0.01), and a decreased rumination time by 6.59% (p < 0.01). However, the activity of these cows was higher by 57.19% (p < 0.001) compared to healthy cows. From a practical point of view, we suggest that veterinarians and farmers track parameters such as reticulorumen pH, milk yield, milk fat-to-protein ratio, rumination time, and activity for the identification of subclinical acidosis.

Influences of a Supplemental Blend of Essential Oils Plus 25-Hydroxy-Vit-D3 and Zilpaterol Hydrochloride (β2 Agonist) on Growth Performance and Carcass Measures of Feedlot Lambs Finished under Conditions of High Ambient Temperature

Forty-eight Pelibuey × Katahdin male intact lambs (25.12 ± 3.79 kg LW) were used in a 70-d growing-finishing trial. Dietary treatments consisted of total mixed corn-based diet supplemented with: (1) no feed additives (Control); (2) 150 mg of essential oils blend plus 0.10 mg of 25-hydroxy-Vit-D3/kg diet offered throughout the 70-d experimental period (EOD3); (3) Control diet fed during the first 35 days and zilpaterol hydrochloride (ZH) supplementation at 6 mg/kg diet offered during the final 35 days of the experiment (32 days with ZH with a withdrawal 3-d before harvest), and (4) basal diet supplemented with EOD3 during first 35 days finishing, and EOD3 in combination with ZH (EOD3 + ZH) during the subsequent 32-days with ZH withdrawal 3 days before harvest. The temperature-humidity index during the experiment averaged 80.4 ± 3.2. There were no treatment interactions (p > 0.20) on growth performance and carcass measures. Supplemental EOD3 did not affect (p = 0.43) dry matter intake (DMI), but increased (p < 0.01) carcass adjusted average daily gain (ADG, 9.2%), gain efficiency (GF, 6.7%), and observed vs. expected dietary net energy for maintenance (NEm, 4.8%) and for gain (NEg, 6.4%). Supplemental ZH did not affect dry matter intake (DMI, p = 0.50) but increased (p < 0.01) carcass adjusted ADG (14.5%), GF (13%) and observed vs. expected dietary NEm (9%) and NEg (11.7%). Compared to control lambs, the combination of both additives increased ADG (24.9%), GF (21.2%), and observed vs. expected dietary NEm and NEg (14.2% and 18.9%, respectively). There were no treatment interactions on carcass characteristics, visceral organ mass, or on gene expression of IGF1, IGF2 and mTOR in longissimus muscle (LM). Supplemental EOD3 increased hot carcass weight (HCW; 4.0%, p < 0.01) but did not affect other carcass measures. Supplemental EOD3 decreased (3%, p = 0.03) intestine mass weight (g intestine/kg empty body weight). Supplemental ZH increased HCW (6%, p < 0.01), dressing percentage (1.7%, p = 0.04), and LM area (9.7%, p < 0.01), and decreased kidney-pelvic-fat percentage (16.2%, p < 0.01), fat thickness (14.7%, p = 0.03), and visceral fat. Compared to controls, the combination of EOD3 with ZH increased HCW (10.2%). It is concluded that growth performance responses to supplemental EOD3 and ZH are additive. Both supplements can be fed in combination without detrimental effects on expected benefits when fed separately. In addition, ZH supplementation improves carcass traits.

The Impacts of Heat Stress on Rumination, Drinking, and Locomotory Behavior, as Registered by Innovative Technologies, and Acid-Base Balance in Fresh Multiparous Dairy Cows

This study hypothesizes that heat stress adversely affects dairy cows, resulting in reduced rumination, altering eating and drinking behaviors, changes in their locomotory patterns, and significant variations in their acid-base balance. The aim of this study was to investigate the impacts of heat stress on rumination, drinking, and locomotory behavior, as registered by innovative technologies, and acid-base balance in fresh multiparous dairy cows. This study was conducted during the summer, from 15 June to 8 July 2023, on a Lithuanian commercial dairy farm. We assessed 350 German Holstein cows that produced an average of 11,400 kg of milk annually throughout their second and subsequent lactation periods. We used the temperature-humidity index (THI) to divide the cows under investigation into three periods: I. high HS-THI >78 (period: 15-23 June 2023); II. medium HS-THI 72-78 (period: 24-30 June 2023); and III. low HS-THI <72 (period: 1-8 July 2023). The appropriate RumiWatch sensor (RWS) parameters were assessed between 15 June 2023 and 8 July 2023. Cows were acclimatized to the rumination, drinking, and locomotory behavior parameters during the adaptation period (1-30 June 2023). The registration process started on 15 June 2023 and terminated on 8 July 2023 and was performed every hour during the 24 h day. The acid-base balance was recorded from 15 June 2023 until 8 July 2023, once per week. The cows' activity increased by 11.75% in the high HS period compared to the low HS period (p < 0.01); high mean differences were detected for rumination, which was 17.67% higher in the high HS period and 13.80% higher in the medium HS period compared to the low HS period (p < 0.01); and the change in activity was 12.82% higher in the low HS compared to the medium HS period (p < 0.01). Cows under high HS had higher blood urea nitrogen (BUN) levels compared with cows under medium HS (p < 0.01). The observed alterations in the rumination, drinking, and locomotory behaviors, in addition to the acid-base balance, highlight the multifaceted impacts of varying heat stress on the physiological and behavioral responses of dairy cows. This suggests that the utilization of advanced technologies may assist dairy farmers in effectively monitoring and controlling heat stress in cows. Additionally, regularly assessing blood urea nitrogen levels can enable farmers to modify their feeding practices, thus promoting optimal cow well-being and productivity.

Relationship between Dairy Cow Health and Intensity of Greenhouse Gas Emissions

The dairy industry is facing criticism for its role in exacerbating global GHG emissions, as climate change becomes an increasingly pressing issue. These emissions mostly originate from methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2). An optimal strategy involves the creation of an economical monitoring device to evaluate methane emissions from dairy animals. Livestock production systems encounter difficulties because of escalating food demand and environmental concerns. Enhancing animal productivity via nutrition, feeding management, reproduction, or genetics can result in a decrease in CH4 emissions per unit of meat or milk. This CH4 unit approach allows for a more accurate comparison of emissions across different animal production systems, considering variations in productivity. Expressing methane emissions per unit allows for easier comparison between different sources of emissions. Expressing emissions per unit (e.g., per cow) highlights the relative impact of these sources on the environment. By quantifying emissions on a per unit basis, it becomes easier to identify high-emission sources and target mitigation efforts accordingly. Many environmental policies and regulations focus on reducing emissions per unit of activity or output. By focusing on emissions per unit, policymakers and producers can work together to implement practices that lower emissions without sacrificing productivity. Expressing methane emissions in this way aligns with policy goals aimed at curbing overall greenhouse gas emissions. While it is true that total emissions affect the atmosphere globally, breaking down emissions per unit helps to understand the specific contributions of different activities and sectors to overall greenhouse gas emissions. Tackling cattle health issues can increase productivity, reduce GHG emissions, and improve animal welfare. Addressing livestock health issues can also provide favourable impacts on human health by reducing the prevalence of infectious illnesses in livestock, thereby mitigating the likelihood of zoonotic infections transmitting to humans. The progress in animal health offers the potential for a future in which the likelihood of animal diseases is reduced because of improved immunity, more effective preventative techniques, earlier identification, and innovative treatments. The primary objective of veterinary medicine is to eradicate clinical infectious diseases in small groups of animals. However, as the animal population grows, the emphasis shifts towards proactive treatment to tackle subclinical diseases and enhance production. Proactive treatment encompasses the consistent monitoring and implementation of preventive measures, such as vaccination and adherence to appropriate nutrition. Through the implementation of these measures, the livestock industry may enhance both animal well-being and mitigate the release of methane and nitrous oxide, thereby fostering environmental sustainability. In addition, advocating for sustainable farming methods and providing farmers with education on the significance of mitigating GHG emissions can bolster the industry's endeavours to tackle climate change and infectious illnesses. This will result in a more robust and environmentally sustainable agriculture industry. This review seeks to conduct a thorough examination of the correlation between the health condition of cattle, the composition of milk produced, and the emissions of methane gas. It aims to identify areas where research is lacking and to provide guidance for future scientific investigations, policy making, and industry practices. The goal is to address the difficulties associated with methane emissions in the cattle industry. The primary global health challenge is to identify the causative relationship between climate change and infectious illnesses. Reducing CH4 and N2O emissions from digestive fermentation and animal manure can be achieved by improving animal well-being and limiting disease and mortality.

Effects of extruded flaxseed and Salmate® inclusion in the diet on milk yield and composition, ruminal fermentation and degradation, and kinetic flow of digesta and fluid in lactating dairy cows in the subtropics

Background and Aim

Dietary supplements play pivotal roles in promoting productive and reproductive performance in ruminant animals. The aims of the present study were to evaluate the effects of extruded flaxseed and Salmate® (Ballard Group, Inc, OH, USA) inclusion in diets on milk yield and composition, ruminal degradation and fermentation, and flow of fluids and digesta in lactating cattle.

Materials and Methods

Six rumen-fistulated Holstein lactating cows were distributed to a 6 × 6 design of Latin square (L.S.). The groups were assorted into a control group fed a basal control diet and two treated groups fed diets containing extruded flaxseed (7.0%) or Salmate® (25 g/head/day). The basal control, extruded flaxseed, and Salmate® diets were formulated as isonitrogenous and isoenergetic. Each L.S. period of the group comprised 21 days, including 10 days for adaptation to the diet and 11 days for data sampling and recording.

Results

Feed intake did not differ among the control, extruded flaxseed, and Salmate® groups. Milk yield (kg) and protein and fat composition (%) were improved on feeding the extruded flaxseed diet compared with the Salmate® and control diets. Extruded flaxseed or Salmate® diet had no effect on the values of ruminal pH, ammonia, and volatile fatty acids except isobutyrate, which decreased in the Salmate® group. Degradable efficiency and ruminal digestibility were significantly decreased with the inclusion of extruded flaxseed and/or Salmate® in the diets. The extruded flaxseed and Salmate® groups had a greater digesta passage rate than the control group. The extruded flaxseed and control groups had a greater liquid passage rate than the Salmate® group.

Conclusion

The inclusion of extruded flaxseed in the diet improved (p < 0.05) milk yield, milk composition, and milk Omega-6: Omega-3 ratio with no changes in ruminal fermentation, notable negative effects on degradable efficiency and ruminal digestibility.

Review of the Heat Stress-Induced Responses in Dairy Cattle

In the dairy cattle sector, the evaluation of the effects induced by heat stress is still one of the most impactful and investigated aspects as it is strongly connected to both sustainability of the production and animal welfare. On the other hand, more recently, the possibility of collecting a large dataset made available by the increasing technology diffusion is paving the way for the application of advanced numerical techniques based on machine learning or big data approaches. In this scenario, driven by rapid change, there could be the risk of dispersing the relevant information represented by the physiological animal component, which should maintain the central role in the development of numerical models and tools. In light of this, the present literature review aims to consolidate and synthesize existing research on the physiological consequences of heat stress in dairy cattle. The present review provides, in a single document, an overview, as complete as possible, of the heat stress-induced responses in dairy cattle with the intent of filling the existing research gap for extracting the veterinary knowledge present in the literature and make it available for future applications also in different research fields.

Assessment of Ruminating, Eating, and Locomotion Behavior during Heat Stress in Dairy Cattle by Using Advanced Technological Monitoring

Heat stress (HS) significantly impacts dairy farming, prompting interest in precision dairy farming (PDF) for gauging its effects on cow health. This study assessed the influence of the Temperature-Humidity Index (THI) on rumination, eating, and locomotor activity. Various parameters, like rumination time, drinking gulps, chews per minute, and others were analyzed. The hypothesis was that precision dairy farming technology could help detect HS. Nine healthy Lithuanian Black-and-White cows were randomly selected for the trial. RumiWatch noseband sensors recorded behaviors, while SmaXtec climate sensors monitored THI. The data collection spanned from 14 June to 30 June. Cows in the THI class ≥ 72 exhibited reduced drinking time (51.16% decrease, p < 0.01), fewer chews per minute (12.9% decrease, p < 0.01), and higher activity levels (16.99% increase, p < 0.01). THI showed an inverse correlation with drinking time (r = -0.191, p < 0.05) and chews per bolus (r = -0.172, p < 0.01). Innovative technologies like RumiWatch are effective in detecting HS effects on behaviors. Future studies should explore the impact of HS on RWS biomarkers, considering factors such as lactation stage, number, yield, and pregnancy.

Impact of heat stress on dairy cattle and selection strategies for thermotolerance: a review

Climate change is a problem that causes many environmental issues that impact the productivity of livestock species. One of the major issues associated with climate change is an increase of the frequency of hot days and heat waves, which increases the risk of heat stress for livestock species. Dairy cattle have been identified as being susceptible to heat stress due to their high metabolic heat load. Studies have shown heat stress impacts several biological processes that can result in large economic consequences. When heat stress occurs, dairy cattle employ several physiological and cellular mechanisms in order to dissipate heat and protect cells from damage. These mechanisms require an increase and diversion in energy toward protection and away from other biological processes. Therefore, in turn heat stress in dairy cattle can lead numerous issues including reductions in milk production and reproduction as well as increased risk for disease and mortality. This indicates a need to select dairy cattle that would be thermotolerant. Various selection strategies to confer thermotolerance have been discussed in the literature, including selecting for reduced milk production, crossbreeding with thermotolerant breeds, selecting based on physiological traits and most recently selecting for enhanced immune response. This review discusses the various issues associated with heat stress in dairy cattle and the pros and cons to the various selection strategies that have been proposed to select for thermotolerance in dairy cattle.

Heat ameliorative measures in Murrah buffalo (Bubalus bubalis) heifers during summer: effect on microclimate, thermal comfort, and behavior

Water buffalo (Bubalus bubalis) is the mainstay of milk production in Asian countries including India. However, the hot climate of the country remains the biggest bottleneck to exploit the potential of this species. Therefore, a study was conducted to assess the effect of heat ameliorative measures on microclimate, thermal comfort, and behavior of Murrah buffalo heifers during summer. Buffalo heifers (n = 24) between the age of 15 and 20 months with a mean body weight of 363.75 ± 11.27 kg were randomly grouped into four treatments based on their age and body weight. The heifers kept in the shed without any cooling served as CON (control), while the animals of group CJ were tied with a cooling jacket. The buffalo heifers of the CJF group were subjected to the cooling jacket with forced air ventilation, whereas the intermittent (10 min at 2-h intervals) sprinkling followed by forced air ventilation was practiced in group SF between 900 and 1800 h throughout the experiment. The microclimatic variables were low in the sheds of groups CJ, CJF, and SF than the CON. The physiological responses such as rectal temperature, skin temperature, respiration rate, and pulse rate were reduced in groups CJ, CJF, and SF than the CON at 1400 h. The serum cortisol was less in the CJF and SF than those of CON group. The animals of the CJ, CJF, and SF groups spent more time for feeding and rumination with less frequent longer bouts. The extended periods of lying followed by shorter standing and idling were observed in groups CJ, CJF, and SF when compared with the CON. It may be therefore concluded that cooling jacket and intermittent sprinkling in combination with forced air ventilation might be helpful in improving the micro-environment, thermal comfort, and behavior of buffalo heifers particularly under tropical climates during summer.

Heat stress promotes adaptive physiological responses and alters mrna expression of ruminal epithelium markers in Bos taurus indicus cattle fed low- or high-energy diets

This research aimed to evaluate the impact of temperature and energy status on the thermal indices, physiological parameters, and ruminal papilla mRNA expression levels of Zebu beef heifers (Bos taurus indicus). In this trial, we used six ruminal-cannulated Nellore females. The experimental design was a 6 × 6 Latin square, with six treatments and six periods. The research used a 2 × 2 + 2 factorial scheme. The arrangement comprised: two thermal conditions [thermoneutrality (TN; 21.6 °C) or heat stress (HS, 34 °C)]; two dietary energy levels (low or high-energy); and two additional treatments, with heifers exposed to the TN, but pair-fed with females exposed to HS (PFTN). For our purposes, body temperature, heart and respiratory rates were measured and the relative mRNA expression was quantified using the PCR-RT technique. Compared to TN or PFTN, the HS increased the body temperature measurements in the morning and evening (p ≤ 0.04). Heart rate was 22% greater for heifers under HS than for TN (p < 0.01) and 13% higher for those under HS than PFTN (p = 0.03) in the morning. Respiratory rates increased with HS exposure compared to TN or PFTN (p < 0.01). Heifers submitted to HS and fed low-energy diets had and tended to have lower caspase 3 (CASP3, p <i=></i> 0.001) and sodium-glucose cotransporter type 1 (SGLT1; p = 0.17) mRNA expressions, respectively. Heat-stressed heifers fed low-energy diets also increased the putative anion transporter (PAT1; p ≤ 0.01) mRNA expressions by 60%. Heifers under HS-fed high-energy diets had greater kallikrein-related peptidase (KLK) 9 expressions (p = 0.02), while KLK10 (p = 0.11) tended to be up-regulated in heifers in TN-fed a low-energy diets. In conclusion, heat stress down-regulated the mRNA expression of rumen markers related to short-chain fatty acids transport and pH modulation.

Lysolecithin-derived feed additive improves feedlot performance, carcass characteristics, and muscle fatty acid profile of Bos indicus-influenced cattle fed in a tropical environment

Lysolecithin might increase ruminal and intestinal emulsification, leading to increased digestibility, but there is minimum information about which is the most appropriate phase to start supplementation and its impacts on feedlot performance and muscle fatty acid profile. Two experiments were conducted to evaluate the effects of phase-feeding of Lysoforte™ eXtend (LYSO). In the first experiment, 1,760 predominantly Bos indicus bullocks (initial body weight of 400 ± 0.561 kg) were allocated in a complete randomized block design. LYSO was supplemented at 1 g/1% of ether extract from the diet. Treatments were no LYSO supplementation (NON); LYSO starting during the growing period and continuing during the finishing period; LYSO starting during the finishing period (FIN); and LYSO during adaptation, growing, and finishing periods (ALL). In the second experiment, the same treatments were evaluated with 96 bullocks (64 Nellore and 32½ Nellore × ½ Angus) in a 4 × 2 factorial arrangement (treatments × genotype). For both studies, intake and average daily gain were accessed; carcass characteristics were evaluated in the first experiment, while digestibility of nutrients and profile of muscle fatty acids were measured in the second experiment. In the first experiment, LYSO increased final body weight (P &lt; 0.022) and average daily gain (GRO and FIN; P &lt; 0.05). In the second study, a treatment × breed × feeding phase interaction was observed with Nellore having a greater average daily gain (P &lt; 0.05) than crossbreds in every feeding phase that LYSO was introduced to the diet. A treatment × feeding phase interaction was observed for digestibility, such that LYSO increased total dry matter (P = 0.004), crude protein (P = 0.043), and NDF (P = 0.001) digestibility during the finishing period. A treatment × breed × day classification was observed (P &lt; 0.05). During the finishing phase, crossbreds treated with LYSO had greater DMI (P &lt; 0.05) on very hot days than NON. Also, animals treated with LYSO presented a greater C18:3 n3 concentration (P = 0.047) in the longissimus. Overall, feeding LYSO during GRO and FIN enhanced feedlot performance and should lead to higher intakes during very hot days of the finishing feeding period.

Relationship between Reticulorumen Parameters Measured in Real Time and Methane Emission and Heat Stress Risk in Dairy Cows

The objective of this study was to investigate a connection between CH4 emissions and reticulorumen pH and temperature. During the experiment, we registered the following parameters: reticulorumen pH (pH), reticulorumen temperature (RR temp.), reticulorumen temperature without drinking cycles, ambient temperature, ambient relative humidity, cow activity, heat index, temperature−humidity index (THI), and methane emissions (CH4). The experimental animals were divided into two groups based on the reticulorumen pH: 1. pH < 6.22 and 2. pH 6.22−6.42. We found that cows assigned to the second pH class had higher (46.18%) average values for methane emissions (p < 0.01). For the other indicators, higher average values were detected in cows of the first pH class, RR temperature (2.80%), relative humidity (20.96%), temperature−humidity index (2.47%) (p < 0.01), and temperature (3.93%) (p < 0.05), which were higher compared to cows of the second pH class. Reticulorumen pH was highly negatively correlated with THI and temperature (r = −0.667 to 0.717, p < 0.001) and somewhat negatively with heat index, relative humidity, and RR temperature (r = −0.536, p < 0.001; r = −0.471 to 0.456, p < 0.01). Cows with a higher risk of heat stress had a higher risk of lower reticulorumen pH.

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.