Thermoregulatory ability of beef heifers following intake of endophyte-infected tall fescue during controlled heat challenge

Heat stress adaptation in cows - Physiological responses and underlying molecular mechanisms

Heat stress is a key abiotic stressor for dairy production in the tropics which is further compounded by the ongoing climate change. Heat stress not only adversely impacts the production and welfare of dairy cows but severely impacts the economics of dairying due to production losses and increased cost of rearing. Over the years, selection has ensured development of high producing breeds, however, the thermotolerance ability of animals has been largely overlooked. In the past decade, the ill effects of climate change have made it pertinent to rethink the selection strategies to opt for climate resilient breeds, to ensure optimum production and reproduction. This has led to renewed interest in evaluation of the impacts of heat stress on cows and the underlying mechanisms that results in their acclimatization and adaptation to varied thermal ambience. The understanding of heat stress and associated responses at various level of animal is crucial to device amelioration strategies to secure optimum production and welfare of cows. With this review, an effort has been made to provide an overview on temperature humidity index as an important indicator of heat stress, general effect of heat stress in dairy cows, and impact of heat stress and subsequent response at physiological, haematological, molecular and genetic level of dairy cows.

Non-Invasive Techniques Reveal Heifer Response to Fescue Endophyte Type in Grazing Studies

Cattle grazing tall fescue (Schedonorus arundinaceous) infected with wild-type endophytes (WE) leads to a syndrome commonly known as fescue toxicosis. Replacing WE tall fescue with a novel endophyte-infected (NE) tall fescue can mitigate this problem but adoption of this technology has been limited. This study measured and determined the physiological and behavioral responses of heifers that grazed either WE or NE tall fescue, utilizing relatively non-invasive techniques including hair cortisol, thermography (for extremity temperatures), small loggers for intravaginal temperature, and remote observation of in-field behavior. Heifers that grazed WE had greater (p < 0.0001) hair cortisol levels, lower extremity temperatures (p ≤ 0.0075), and 0.3-0.9 °C greater (p ≤ 0.02) intravaginal temperatures (particularly during the daytime) than heifers that grazed NE. From 1200 h-1700 h each day, heifers on WE pastures spent 1.5 more (p = 0.0003) hours standing up and 0.9 fewer (p = 0.0402) hours lying down than heifers on NE pastures. Differences (p = 0.0160) in ADG were small (0.1 kg d^-1) and were only observed in the first year of these 8-week studies. However, even in the mild environment of the study site, grazing NE tall fescue provided clear welfare benefits as evidenced by heifer behavioral changes, temperature differentials, and hair cortisol levels. This study underscores the potential utility of non-invasive techniques, such as thermographic imaging and hair cortisol analysis, for evaluating animal responses to stress in extensive grazing systems.

Behavioral and Physiological Alterations in Angus Steers Grazing Endophyte-Infected Toxic Fescue during Late Fall

Fescue toxicosis is caused by grazing ergot alkaloid-producing endophyte (Epichloë coenophiala)-infected tall fescue (E+). Summer grazing of E+ leads to decreased productivity, associated impaired thermoregulation, and altered behavior. The goal of this study was to determine the role of E+ grazing-climate interaction on animal behavior and thermoregulation during late fall. Eighteen Angus steers were placed on nontoxic (NT), toxic (E+) and endophyte-free (E-) fescue pastures for 28 days. Physiological parameters, such as rectal temperature (RT), respiration rate (RR), ear and ankle surface temperature (ET, AT), and body weights, were measured. Skin surface temperature (SST) and animal activity were recorded continuously with temperature and behavioral activity sensors, respectively. Environmental conditions were collected using paddocks-placed data loggers. Across the trial, steers on E+ gained about 60% less weight than the other two groups. E+ steers also had higher RT than E- and NT, and lower SST than NT post-pasture placement. Importantly, animals grazing E+ spent more time lying, less time standing, and took more steps. These data suggest that late fall E+ grazing impairs core and surface temperature regulation and increases non-productive lying time, which may be partly responsible for the observed decreased weight gains.

Endophyte Infected Tall Fescue: Plant Symbiosis to Animal Toxicosis

Endophyte-infected fescue is a major cool season forage used for livestock production in the United States and through other areas of the world. A unique aspect of this forage resource is the symbiotic relationship with an endophytic fungus (Epichloë coenophiala) that has detrimental impact on herbivores due to toxic ergot alkaloids. Research over the past 50 years has unveiled details regarding this symbiotic relationship. This review focuses on the origin of tall fescue in the United States and the consequences of its wide-spread utilization as a livestock forage, along with the discovery and toxicodynamics of ergot alkaloids produced by E. coenophiala. The majority of past ergot alkaloid research has focused on observing phenotypic changes that occur in livestock affected by ergot alkaloids, but recent investigation of the metabolome, transcriptome, and proteome have shown that fescue toxicity-related illnesses are much more complex than previous research suggests.

Identification of Breed Differences in Known and New Fescue Toxicosis Associated Phenotypes in Charolais-and Hereford-Sired Crossbred Beef Cows

Simple Summary

The consumption of toxic fescue has caused significant losses in the U.S. beef industry. Widely accepted symptoms of toxic fescue exposure include the retention of a thick hair coat, tissue necrosis in the extremities, and reduced nutrient absorption. However, there is variability in the severity of these symptoms, both across and within breeds. The objective of this study was to characterize the effect of fescue toxicosis across Hereford- and Charolais-sired cows for known and new fescue stress-associated phenotypes. Results indicated that Hereford cows had a lessened ability to shed their winter coat and regulate body temperature along with lower serum mineral concentrations compared to Charolais cows when exposed to toxic fescue. Differences between and within sire breed in hair shedding were also observed, providing further evidence of genetic variation. This study provides evidence of variability in the fescue toxicosis that is potentially useful for genetic selection to reduce fescue stress and characterizes effects on pregnant cows which may impact calves in utero.

Abstract

Beef cattle phenotypes are affected by the consumption of toxic fescue. Toxic fescue’s impact is dependent on heat stress and breed composition, with genetic variability for robustness to toxin exposure believed to exist within and across breeds. The study objective was to characterize the effect of fescue toxicosis across breeds for known and novel heat and fescue stress-associated phenotypes. One-hundred crossbred fall-calving Charolais- and Hereford-sired cows of parities 1–3 were allocated to graze either toxic fescue (n = 50), non-toxic fescue (n = 25), or a rotation between toxic and non-toxic fescue (n = 25) for 156 days. Phenotypes impacted by breed (genetics) included hair coat score (p < 0.0001), hair reduction/shedding rate (p < 0.05), rectal temperature (RT) (p < 0.0001), vaginal temperature (p < 0.05), serum phosphorus concentration (p < 0.02) and respiration rate (RR) (p < 0.003). Cows on toxic fescue experienced reduced hair shedding efficacy (p < 0.0001), higher vaginal temperatures (p < 0.0001), increased systolic blood pressure (p < 0.04), increased RR (p < 0.0001) and reduced average daily gain (p < 0.0001), compared to cows grazing non-toxic fescue. Calves born from cows with higher RT during the last third of gestation had higher RT at weaning (p < 0.02), indicating potential physiological effects of in utero heat stress. The study indicates that beef cows exhibit variable responses to toxic fescue within and across breeds which may impact future calf phenotypes.

Complete Blood Count Analysis on Beef Cattle Exposed to Fescue Toxicity and Rumen-Protected Niacin Supplementation

Simple Summary

Fescue toxicity results from cattle consuming fungal (Ergot spp.) endophyte-infected tall fescue. Ergot alkaloids like ergovaline produce vasoconstriction in cattle. Our objectives were to analyze changes in complete blood count and performance due to ergot alkaloid detoxification in growing beef cattle and the effect of selecting dams tolerant or susceptible to fescue toxicity based on their tolerance index, measured through a genetic test currently available for beef producers. Furthermore, rumen-protected niacin supplementation is proposed as a potential alleviator for vasoconstriction produced by fescue toxicity. Therefore, we assessed the effects of consuming endophyte-infected tall fescue seeds in addition to rumen-protected niacin supplementation in offspring performance and hematological parameters. Signs for anemia were noticed in susceptible heifer offspring that did not receive rumen-protected niacin, whereas inflammation or infection was detected in tolerant steers that received niacin in their diet. Typical symptoms of heat stress and intoxication with ergot alkaloids were noticed in offspring. Our results suggest that susceptible heifer offspring might have a more active detox metabolism when under fescue toxicity. Findings from this study could be utilized as a new tool to help beef cattle producers to dampen the adverse effects of fescue toxicity.

Abstract

Offspring born to dams genetically tested for resistance to fescue toxicity were separated in groups based on their dams’ resistance level (tolerant vs. susceptible). Rumen-protected niacin (RPN) is proposed as a potential alleviator for vasoconstriction produced by fescue toxicity. Complete blood count (CBC) analysis was utilized for detection of significant responses to treatments applied. Our objectives were as follows: (a) to analyze changes in CBC due to fescue toxicity, maternal resistance level, and RPN in growing offspring; and (b) to assess the effects of maternal resistance level when consuming endophyte-infected tall fescue seeds in addition to RPN in offspring performance. Body weight, average daily gain, or health status were not improved by RPN or the genetic test to detect fescue toxicity resistance. Typical signs of alkaloids intoxication and heat stress were noticed in offspring. Particularly, rectal temperature was greater for susceptible control heifers. Results showed that susceptible control offspring presented signs of anemia denoted by low mean corpuscular hemoglobin (MCH) and mean corpuscular volume (MCV). High levels of white blood cells (WBC) and basophils in combination to low neutrophils to lymphocytes ratio were the signs of infection or inflammation detected in the CBC analysis, especially in tolerant niacin steers. Furthermore, offspring of control heifers had a greater percentage of reticulocytes and RDW, denoting signs of anemia.

Rumen and Serum Metabolomes in Response to Endophyte-Infected Tall Fescue Seed and Isoflavone Supplementation in Beef Steers

Fescue toxicosis impacts beef cattle production via reductions in weight gain and muscle development. Isoflavone supplementation has displayed potential for mitigating these effects. The objective of the current study was to evaluate isoflavone supplementation with fescue seed consumption on rumen and serum metabolomes. Angus steers (n = 36) were allocated randomly in a 2 × 2 factorial arrangement of treatments including endophyte-infected (E+) or endophyte-free (E−) tall fescue seed, with (P+) or without (P−) isoflavones. Steers were provided a basal diet with fescue seed for 21 days, while isoflavones were orally administered daily. Following the trial, blood and rumen fluid were collected for metabolite analysis. Metabolites were extracted and then analyzed by UPLC-MS. The MAVEN program was implemented to identify metabolites for MetaboAnalyst 4.0 and SAS 9.4 statistical analysis. Seven differentially abundant metabolites were identified in serum by isoflavone treatment, and eleven metabolites in the rumen due to seed type (p < 0.05). Pathways affected by treatments were related to amino acid and nucleic acid metabolism in both rumen fluid and serum (p < 0.05). Therefore, metabolism was altered by fescue seed in the rumen; however, isoflavones altered metabolism systemically to potentially mitigate detrimental effects of seed and improve animal performance.

Physiological response, function of sweat glands, and hair follicle cycling in cattle in response to fescue toxicosis and hair genotype

Fescue toxicosis is a syndrome that results when cattle consume toxic endophyte-infected tall fescue. The objective of this study was to compare the response in physiological variables, sweat gland function, hair follicle cycling, and gene expression to feeding a total mixed ration that included tall fescue haylage and tall fescue seed containing a toxic endophyte (EI) or tall fescue haylage containing a nontoxic novel endophyte (EN) in beef heifers (Angus × Senepol heifers, n = 31) with 2 different hair genotypes. Numbers in each subgroup were as follows: novel endophyte, heterozygous slick (EN-S; n = 8), novel endophyte, homozygous hairy (wild type, EN-W; n = 7), endophyte-infected, heterozygous slick (EI-S; n = 10), and endophyte-infected, homozygous hairy (wild type, EI-W; n = 6). Physiological measurements were taken weekly for 7 wk. Data were analyzed using the MIXED procedure of SAS including dietary fescue treatment (EN vs. EI) and hair genotype (S vs. W) as main effects, day as a repeated measure, and temperature-humidity index (THI) as a covariate. Skin biopsies were taken before treatment initiation and on day 37 of treatment. Average surface temperature (ST) increased as the THI increased (P < 0.0001). Average ST was greater (P < 0.01) for animals fed EI than for animals fed the EN fescue diet, and greater (P < 0.01) for animals with the W genotype compared with animals with the S genotype. The difference between heifers with the S and W genotype was greater at greater THI (genotype × day interaction, P < 0.01). Transepidermal water loss (TEWL) was greater (P < 0.05) for animals with the S genotype compared with the W genotype and greater (P < 0.05) for heifers with the S genotype than for heifers with the W genotype when fed EI (36.7, 38.5, 30.0, and 38.7 g/m2 per hour for EN-W, EN-S, EI-W, and EI-S, respectively). The fraction of follicles in telogen in plucked hair samples for heifers fed EI was greater for animals with the S genotype than the W genotype (fraction in telogen: 0.456, 0.565, 0.297, 0.702 for EN-W, EN-S, EI-W, and EI-S, respectively; diet × genotype interaction, P < 0.05). Fraction of follicles in anagen was the opposite. EI fescue resulted in increased ST, changes in hair follicle cycling that support greater hair growth, and decreased TEWL for heifers with the W genotype compared with S genotype, suggesting greater heat stress in response to EI.

Invited review: Physiological and behavioral effects of heat stress in dairy cows

Animal welfare can be negatively affected when dairy cattle experience heat stress. Managing heat stress has become more of a challenge than ever before, due to the increasing number of production animals with increased milk yield, and therefore greater metabolic activity. Environmental temperatures have increased by 1.0°C since the 1800s and are expected to continue to increase by another 1.5°C between 2030 and 2052. Heat stress affects production, reproduction, nutrition, health, and welfare. Means exist to monitor and evaluate heat stress in dairy cattle, as well as different ways to abate heat, all with varying levels of effectiveness. This paper is a summary and compilation of information on dairy cattle heat stress over the years.

Toxic tall fescue grazing increases susceptibility of the Angus steer fecal microbiota and plasma/urine metabolome to environmental effects

Impaired thermoregulation and lowered average daily gains (ADG) result when livestock graze toxic endophyte (Epichloë coenophialum)-infected tall fescue (E+) and are hallmark signs of fescue toxicosis (FT), a disease exacerbated by increased temperature and humidity (+temperature-humidity index; +THI). We previously reported FT is associated with metabolic and microbiota perturbations under thermoneutral conditions; here, we assessed the influence of E+ grazing and +THI on the microbiota:metabolome interactions. Using high-resolution metabolomics and 16S rRNA gene sequencing, plasma/urine metabolomes and the fecal microbiota of Angus steers grazing non-toxic or E+ tall fescue were evaluated in the context of +THI. E+ grazing affected the fecal microbiota profile; +THI conditions modulated the microbiota only in E+ steers. E+ also perturbed many metabolic pathways, namely amino acid and inflammation-related metabolism; +THI affected these pathways only in E+ steers. Integrative analyses revealed the E+ microbiota correlated and co-varied with the metabolomes in a THI-dependent manner. Operational taxonomic units in the families Peptococcaceae, Clostridiaceae, and Ruminococcaceae correlated with production parameters (e.g., ADG) and with multiple plasma/urine metabolic features, providing putative FT biomarkers and/or targets for the development of FT therapeutics. Overall, this study suggests that E+ grazing increases Angus steer susceptibility to +THI, and offers possible targets for FT interventions.

Effects of endophyte-infected tall fescue seed and protein supplementation on stocker steers: I. Growth performance and hemodynamic responses

Fescue toxicosis is a multifaceted syndrome common in cattle grazing endophyte-infected tall fescue and is detrimental to growth and performance. Recent research has shown that supplementing protein has the potential to enhance growth performance in weaned steers. Therefore, the objective of this study was to evaluate the effect of supplemental CP on physiological parameters in stocker steers experiencing fescue toxicosis. Thirty-six weaned Angus steers (6 mo of age) stratified by weight (196.1 ± 3.6 kg) were assigned to a 2 × 2 factorial arrangement for 56 d: endophyte-free (EF) seed and 14% CP (EF-14; n = 9), EF seed and 18% CP (EF-18; n = 9), endophyte-infected (EI) seed and 14% CP (EI-14; n = 9), and EI seed and 18% CP (EI-18; n = 9). Steer growth and hemodynamic responses were collected weekly during ergot alkaloid exposure. On day 14 of the trial, iButton temperature data loggers were subcutaneously inserted in the lateral neck region to record hourly body temperature for 42 d. Data were analyzed using PROC MIXED of SAS with repeated measures. No differences were observed in DMI, BW, ADG, F:G, or BCS during the treatment period (P > 0.05). Hair shedding scores, rectal temperatures, surface temperatures, and respiration rates were greater in EI steers compared to EF steers regardless of supplemental CP (P < 0.05). However, subcutaneous body temperature was greater in EI-14 steers (37.94 °C) compared to other steer groups (37.60, 37.68, 37.72 ± 0.04 °C for EF-14, EF-18, and EI-18, respectively; P < 0.05). Prolactin concentrations tended to be greater in EF steers when compared to EI steers (P = 0.07). Heart rate and hematocrit were reduced for EI-18 steers compared to other steer groups (P < 0.05). Caudal artery diameter was reduced in EI-18 steers compared to EI-14 steers (2.60 vs. 2.75 ± 0.05 mm, respectively; P < 0.05) and caudal vein diameter was reduced in EI-18 steers (3.20 mm) compared to all other steer groups (3.36, 3.39, 3.50 mm for EF-14, EF-18, and EI-14, respectively; P < 0.05). However, there was no difference observed in systolic or diastolic blood pressure during the treatment period (P > 0.05). Based on the data, exposure to low to moderate levels of ergot alkaloids during the stocker phase had a negative impact on hemodynamic responses and supplemental CP had minimal impact to alleviate symptoms. Therefore, feeding additional protein above established requirements is not expected to help alleviate fescue toxicosis.

Response of Beef Cattle Fecal Microbiota to Grazing on Toxic Tall Fescue

Tall fescue, the predominant southeastern United States cool-season forage grass, frequently becomes infected with an ergot alkaloid-producing toxic endophyte, Epichloë coenophialum Consumption of endophyte-infected fescue results in fescue toxicosis (FT), a condition that lowers beef cow productivity. Limited data on the influence of ergot alkaloids on rumen fermentation profiles or ruminal bacteria that could degrade the ergot alkaloids are available, but how FT influences the grazing bovine fecal microbiota or what role fecal microbiota might play in FT etiology and associated production losses has yet to be investigated. Here, we used 16S rRNA gene sequencing of fecal samples from weaned Angus steers grazing toxic endophyte-infected (E+; n = 6) or nontoxic (Max-Q; n = 6) tall fescue before and 1, 2, 14, and 28 days after pasture assignment. Bacteria in the Firmicutes and Bacteroidetes phyla comprised 90% of the Max-Q and E+ steer fecal microbiota throughout the trial. Early decreases in the Erysipelotrichaceae family and delayed increases of the Ruminococcaceae and Lachnospiraceae families were among the major effects of E+ grazing. E+ also increased abundances within the Planctomycetes, Chloroflexi, and Proteobacteria phyla and the Clostridiaceae family. Multiple operational taxonomic units classified as Ruminococcaceae and Lachnospiraceae were correlated negatively with weight gains (lower in E+) and positively with respiration rates (increased by E+). These data provide insights into how E+ grazing alters the Angus steer microbiota and the relationship of fecal microbiota dynamics with FT.IMPORTANCE Consumption of E+ tall fescue has an estimated annual $1 billion negative impact on the U.S. beef industry, with one driver of these costs being lowered weight gains. As global agricultural demand continues to grow, mitigating production losses resulting from grazing the predominant southeastern United States forage grass is of great value. Our investigation of the effects of E+ grazing on the fecal microbiota furthers our understanding of bovine fescue toxicosis in a real-world grazing production setting and provides a starting point for identifying easy-to-access fecal bacteria that could serve as potential biomarkers of animal productivity and/or FT severity for tall fescue-grazing livestock.

Performance-enhancing technologies for steers grazing tall fescue pastures with varying levels of toxicity1

The objective of this study was to evaluate a combination of best management practices strategy for steer calves grazing tall fescue pastures with a range of toxicity. The experiment was conducted over 2 grazing seasons (fall 2015 for 91 d and spring 2016 for 84 d). Steers (n = 80 within season, body weight [BW] = 197.0 ± 15.43 kg [fall] and 116.9 ± 4.88 [spring]) were stocked at 2.45 and 4.1 calves/ha in fall and spring, respectively, to 16 pastures with varying levels of toxicity based on interim ergovaline (EV) concentration within season. Pastures were assigned to either mineral (MIN, n = 8) only management (MGMT) or a cumulative MGMT (CM, n = 8). The CM treatment included an implant containing 40-mg trenbolone acetate, 8-mg estradiol, and 29-mg tylosin tartrate (Component TE-G with Tylan, Elanco Animal Health, Greenfield, IN), 150 mg/calf daily monensin (Elanco Animal Health), and 1% BW of a 50:50 corn gluten feed:soybean hull supplement (as-is basis). Data were analyzed within season using pasture as the experimental unit. For fall and spring, the EV concentration was 1,476 ± 883.2 and 1,173 ± 620.6 ppb, respectively, and ranged from 90 to 2,180 ppb. During the fall, forage allowance did not differ (P = 0.76) between CM and MIN. In the spring, however, forage allowance only differed for the month of June (P ≤ 0.05, 2.55 vs. 3.22 ± 0.177 kg DM/kg BW, for MIN and CM, respectively). In the fall, average daily gain (ADG) responded to the simple effects of EV (P = 0.01) and MGMT (P < 0.001), and ADG for MIN steers was explained by ADG = 0.41 - 0.000064 × EV, whereas ADG for CM was explained by ADG = 1.05 - 0.000064 × EV. In the spring, there was an EV × MGMT interaction (P = 0.03) for ADG. For MIN, ADG = 0.80 - 0.000278 × EV, whereas for CM, ADG = 0.94 + 0.000001835 × EV. In spring, the ADG response to CM relative to MIN increased as EV increased. The CM strategy resulted in lower blood urea nitrogen than MIN in fall and spring (P < 0.01), but prolactin and serum Cu were not affected by MGMT in either season. In conclusion, performance was improved within the fescue belt by implementing feeding strategies using implants, ionophores, and supplementation, but a detailed economic analysis is warranted. Further research is needed to evaluate CM programs under varied stocking rates and in combination with dilution of endophyte-infected fescue pastures with nontoxic grasses or legumes.

Global warming: Impact, adaptation and amelioration strategies for bovine under tropical climatic conditions

Livestock are exposed to different climatic extreme events such as high air temperature, humidity, flood, drought, desert, heat wave, feed, fodder and water scarcity etc. which now seems to be very common in the tropical and subtropical climatic conditions. The climate change scenario is assumed to be a major threat to animal production systems under tropical climate. The demand of food or the food security issue compel us to undertake holistic approach to sustainable livestock production system that may be one of the remedies for fulfilling the demand of fast growing population. The objective of this review is to focus on the major effect on dairy production system and different strategies to overcome the adverse effect of heat stress under tropical climatic conditions. The identificationof unique adaptive traits between and within breeds and their propagation seem to be essential in near future in respect of climate change scenario. The management and feeding strategies proved to be beneficial for relieving adverse effects of heat stress for maintaining the productivity of dairy animals. Nevertheless, decision makers, extension services and research institutions have to support and encourage livestock activities to enhance the animal productivity under changed climate scenario.

Toxin-producing Epichloë bromicola strains symbiotic with the forage grass Elymus dahuricus in China

Cool-season grasses (Poaceae subfamily Poöideae) are an important forage component for livestock in western China, and many have seed-transmitted symbionts of the genus Epichloë, fungal endophytes that are broadly distributed geographically and in many tribes of the Poöideae. Epichloë strains can produce any of several classes of alkaloids, of which ergot alkaloids and indole-diterpenes can be toxic to mammalian and invertebrate herbivores, whereas lolines and peramine are more selective against invertebrates. The authors characterized genotypes and alkaloid profiles of Epichloë bromicola isolates symbiotic with Elymus dahuricus, an important forage grass in rangelands of China. The endophyte was seed-transmitted and occasionally produced fruiting bodies (stromata), but its sexual state was not observed on this host. The genome sequence of E. bromicola isolate E7626 from El. dahuricus in Xinjiang Province revealed gene sets for peramine, ergot alkaloids, and indole-diterpenes. In multiplex polymerase chain reaction (PCR) screens of El. dahuricus-endophyte isolates from Beijing and two locations in Shanxi Province, most were also positive for these genes. Ergovaline and other ergot alkaloids, terpendoles and other indole-diterpenes, and peramine were confirmed in El. dahuricus plants with E. bromicola. The presence of ergot alkaloids and indole-diterpenes in this grass is a potential concern for managers of grazing livestock.

Cows exposed to heat stress during fetal life exhibit improved thermal tolerance

Maternal heat stress during late gestation affects calf function during postnatal life. The objective of the present study was to evaluate whether calves that experience heat stress in utero have altered thermoregulatory responses to acute heat stress later in life. Specifically, the hypothesis was that heat stress in utero would improve the response to acute heat stress at maturity. Females were born to dams exposed to heat stress or cooled during late gestation preceding their birth. All animals were raised postnatally under identical management. Twelve lactating Holstein cows that were exposed to in utero heat stress (HT) and 12 that were exposed to in utero control (CON) were used. A heat stress challenge was conducted in 3 blocks using 4 HT and 4 CON cows matched according to milk yield, stage of lactation, and parity. Each challenge consisted of transfer from a barn with shade and evaporative cooling to one with shade but no additional cooling for 48 h. The challenge was replicated twice for each block. Sweating rate, respiration rate, rectal temperature (RT), and skin temperature were measured on each cow at 0900, 1100, 1300, 1500, and 1700 h for 2 consecutive days. Mean ambient temperature across 6 challenge days was 26.15 ± 4.75°C. Tendencies for differences at 1700 h were observed between treatments for RT (HT: 39.5 ± 0.1; CON: 39.6 ± 0.1°C; = 0.065), however, there was no difference in respiration rate (HT: 77.6 ± 1.6; CON: 79.5 ± 1.6 bpm; = 0.85). Sweating rate for shaved skin (HT: 29.4 ± 2.0; CON: 36.0 ± 2.0 g/mh; = 0.057) and for non-shaved skin (HT: 22.5 ± 1.5; CON: 29.2 ± 1.2 g/mh; = 0.01) differed between groups. However, there was no effect on skin temperature at the shaved location (HT: 36.2 ± 0.2; CON: 36.0 ± 0.2°C; = 0.81), but there was a tendency for differences for the non-shaved area (HT: 35.4 ± 0.2; CON: 34.9 ± 0.2°C; = 0.097). Cows that underwent in utero heat stress had greater skin temperature at 1700 h vs. in utero control cows, which may be because HT cows increased skin perfusion, and consequently greater cooling via conduction. In utero HT cows would then have higher heat loss and reduced core body temperature, which results in lower rectal temperature and lower sweating rate when exposed to heat stress. These results support the hypothesis that heat stress in utero in late gestation increases heat tolerance at maturity by increasing capacity to dissipate heat to maintain core body temperature.

Hepatic thyroid signaling of heat-stressed late pregnant and early lactating cows

During the transition between late gestation and early lactation, dairy cows experience severe metabolic stress due to the high energy and nutrient requirements of the fetus and the mammary gland. Additional thermal stress that occurs with rising temperatures during the ongoing climate change has further adverse implications on energy intake, metabolism and welfare. The thyroid hormone (TH)-mediated cellular signaling has a pivotal role in regulation of body temperature, energy intake and metabolic adaptation to heat. To distinguish between energy intake and heat stress-related effects, Holstein cows were first kept at thermoneutrality at 15°C followed by exposure to heat stress (HS) at 28°C or pair-feeding (PF) at 15°C for 6 days, in late pregnancy and again in early lactation. Herein, we focused on hepatic metabolic changes associated with alterations in the hypothalamic-pituitary-thyroid axis in HS and PF animals. T₃ and T₄ levels dropped with HS or PF; however, in HS animals, this decline was more pronounced. Thyroid-stimulating hormone (TSH) levels remain unaffected, while plasma cholesterol concentrations were lower in HS than PF animals. Hepatic marker genes for TH action (THRA, DIO1 and PPARGC1) decreased after HS and were lower compared to PF cows but only post-partum. Proteomics data revealed reduced hepatic amino acid catabolism ante-partum and a shift toward activated beta-oxidation and gluconeogenesis but declined oxidative stress defense post-partum. Thus, liver metabolism of HS and PF cows adapts differently to diminished energy intake both ante-partum and post-partum, and a different TH sensitivity is involved in the regulation of catabolic processes.

Activities and Effects of Ergot Alkaloids on Livestock Physiology and Production

Consumption of feedstuffs contaminated with ergot alkaloids has a broad impact on many different physiological mechanisms that alters the homeostasis of livestock. This change in homeostasis causes an increased sensitivity in livestock to perturbations in the ambient environment, resulting in an increased sensitivity to such stressors. This ultimately results in large financial losses in the form of production losses to livestock producers around the world. This review will focus on the underlying physiological mechanisms that are affected by ergot alkaloids that lead to decreases in livestock production.

Regional differences in the fescue toxicosis response of Bos taurus cattle

Cattle of the same breed from different regions of the USA may have altered responses to heat stress and fescue toxicosis. Angus steers from Missouri (MO ANG, n = 10, 513.6 ± 13.6 kg BW) and Oklahoma (OK ANG, n = 10, 552.8 ± 12.0 kg BW) were fed a diet containing either endophyte-infected (E+, 30 μg ergovaline/kg BW/day) or endophyte-uninfected (E-, 0 μg ergovaline/kg BW/day) tall fescue seed for 23 days. Diet treatment began on day 2. Animals were maintained at thermoneutrality (TN, 19-22 °C, days 1-8) and then exposed to heat stress (HS, cycling 26-36 °C, days 9-22). On day 23, ambient temperature was returned to TN and used as a recovery day. Feed intake (FI) was measured daily, with rectal and skin temperatures determined six times daily. Feed intake reduction from pretreatment levels was greater (P < 0.01) for E + (13.9 ± 0.9 versus 11.9 ± 0.3 kg/day) compared to E - (12.6 ± 0.9 versus 12.4 ± 0.3 kg/day) steers over the entire TN period, regardless of Angus group. During HS, E + cattle had reduced FI (P < 0.02; 6.9 ± 0.2 versus 8.4 ± 0.2 kg/day) compared to E - animals, independent of region of origin. A greater decrease in FI (P < 0.01) was observed for OK (12.1 ± 0.3 versus 6.2 ± 0.2 kg/day) compared to MO ANG (12.2 ± 0.3 versus 7.9 ± 0.2 kg/day) when ambient temperature was increased from TN to HS. On day 13 and days 15-22, OK ANG (E+) had reduced FI (P < 0.01, -2.21 kg) compared to OK ANG (E-), while there was no effect on MO ANG. From day 12 to day 22 of HS, daily minimum temperatures for ear, rump, and tail skin were less for E + (P < 0.05) when compared with E-treated steers, signifying peripheral vasoconstriction in E + animals. This was supported by reduced shoulder and lower tail temperatures (P < 0.01) for E + compared to E-treated OK ANG on the recovery day. In summary, regional differences in the response to fescue toxicosis exist, with peripheral vasomotor effects becoming most evident when animals are subjected to rapid changes in their environment.

Effect of fescue toxicosis on whole body energy and nitrogen balance, in situ degradation and ruminal passage rates in Holstein steers

This study was designed to examine alteration of ruminal kinetics, as well as N and energy balance during fescue toxicosis. Six ruminally cannulated Holstein steers (bodyweight (BW) = 217 ± 7 kg) were weight matched into pairs and pair fed throughout a crossover design experiment with a 2×2 factorial treatment structure. Factors were endophyte (infected, E+ vs. uninfected, E−) and feeding level (1100 (L) or 1800 (H) kJ/kG BW.75). During each period, after 8 days of feeding level adaptation, animals were ruminally dosed twice daily with ground fescue seed for the remainder of the period. One steer per pair was dosed with ground endophyte infected fescue seed (E+), the other with ground endophyte free fescue seed. In situ degradation of ground alfalfa was determined on Days 13–16. Total faecal and urinary collections were performed on Days 17–21, with animals placed into indirect calorimetry head-boxes during Days 20 and 21. Heat production (HP) was calculated using the Brower equation. Retained energy (RE) was calculated as intakeE – (faecalE + urinaryE + gaseousE + HP). Liquid and particulate passage rates were evaluated using Cr:EDTA and iADF respectively on Days 22 and 23. There was no difference (P > 0.9) in dry matter intake (DMI)/kg.75 between endophyte treatments, and DMI/kg.75 was different (P < 0.01) between H and L intake by design. Animals on H feeding had higher (P < 0.01) water, N and energy intakes. Energy and N excretion, as well as retained DE, ME, RE, and HP were higher (P < 0.03) for H versus L. There was no difference in retained N, DE, ME, or HP (P > 0.15) between endophyte treatments. Neither rate nor extent of in situ degradation was altered by intake level or endophyte treatment (P > 0.3). DM percentage and DM weight of rumen contents were increased (P < 0.01) by E+ dosing. Particulate passage increased (P = 0.0002) during H intake and decreased (P = 0.02) with E+ dosing. Ruminal liquid passage decreased (P < 0.03) with H feeding, while liquid flow rate tended to be reduced (P < 0.14) with E+ dosing. Total VFA concentration increased with both H feeding (P < 0.01) and E+ dosing (P < 0.0001). Despite these differences, the N and energy balance data indicate that the reductions in weight gain and productivity seen during fescue toxicosis are primarily due to reduced intake.

Physiological responses to known intake of ergot alkaloids by steers at environmental temperatures within or greater than their thermoneutral zone

Two studies separated effects of dietary ergot alkaloids from effects of feed intake or ambient temperature on respiration rate (RR), heart rate (HR), surface temperature (ST), rectal temperature (RT), blood pressure (BP), serum hormone, and plasma metabolite concentrations in beef steers. The balanced, single reversal design for each experiment used 8 beef steers fed tall fescue seed [2.5 g/kg body weight (BW)] with (E+) or without (E−) ergot alkaloids as part of a 60:40 switchgrass hay: supplement diet. Periods were 35 days with 21 days of preliminary phase and 14 days of feeding fescue seed once daily. Measures of dependent variables were collected on d 20, 25, 29, and 35 of each period at 0730 (before feeding), 1230 and 1530. In Experiment 1 steers weighed 286 kg, gained 0.61 kg BW/day, E+ supplied 2.72 mg ergot alkaloids including 1.60 mg ergovaline per steer daily, and mean minimum and maximum daily ambient temperatures were 23.6 and 32.3°C. In Experiment 2 steers weighed 348 kg, gained 1.03 kg BW/day, E+ supplied 3.06 mg ergot alkaloids including 2.00 mg ergovaline daily, and mean minimum and maximum daily ambient temperatures were 11.9 and 17.4°C. Dry matter intake was not affected by fescue seed treatment (P < 0.20) in either experiment. In both experiments, E+ reduced HR (P < 0.01) and increased insulin (P = 0.07). Systolic BP minus diastolic BP decreased (P < 0.05) for E+ in both experiments, due to increased diastolic BP in Experiment 1 (P < 0.03) and decreased systolic BP in Experiment 2 (P < 0.07). In Experiment 1, above the thermoneutral zone, E+ increased (P < 0.05) RR, RT, and left side ST in comparison to E−, but in Experiment 2, within the thermoneutral zone, E+ and E− did not differ (P < 0.18). Ergot alkaloids from fescue seed affect the cardiovascular system of steers separately from effects of feed intake or environmental temperature. Ergot alkaloids interact with ambient temperatures above the steers' thermoneutral zone to exacerbate the symptoms of hyperthermic stress.

Body temperature and respiratory dynamics in un-shaded beef cattle

In this study body temperature (BT, °C) and panting score (PS, 0-4.5; where 0 = no panting/no stress and 4.5 = catastrophic stress) data were obtained from 30 Angus steers housed outside over 120 days Steers were implanted with a BT transmitter on day -31, BT was recorded at 30-min intervals to a data logger and downloaded each day to a database. The cattle were housed in ten outdoor un-shaded pens with an earthen floor, eight of which had a pen floor area of 144 m2 (three transmitter steers plus five non-transmitter steers; 18 m2/steer) and two had an area of 168 m2 (three transmitter steers and six non-transmitter steers; 18.7 m2/steer). Only data from the transmitter steers were used in this study. The PS of the steers was obtained daily (± 15 min) at 0600 hours (AM), 1200 hours (MD) and 1600 hours (PM). At the same times climate variables (ambient temperature, black globe temperature, solar radiation, relative humidity, wind speed and rainfall) were obtained from an on-site weather station. PS observations were made from outside the pens so as not to influence cattle responses. The two closest BT values to the time when PS was obtained were downloaded retrospectively from a logger and averaged. A total of 8,352 observations were used to generate second order polynomial response curves: (AM) y = 39.08 + 0.009 x + 0.137x2 (R2 = 0.94; P < 0.001) (MD) y = 39.09 + 0.914x − 0.080x2 (R2 = 0.89; P < 0.001) and (PM) y = 39.52 + 0.790x − 0.068x2 (R2 = 0.83; P < 0.001) where y = BT (°C) and  x PS. These data suggest that PS is a good indicator of body temperature. The BT at MD corresponded to slightly lower PS compared with PM, e.g., for PS 1; BT at MD = 39.1 ± 0.05 °C whereas BT at PM = 39.5 ± 0.05 °C. However during AM, BT was lower (P < 0.05) at PS 1, 2 and 2.5 compared with MD and PM. For example, when PS was 2.5 the BT at AM was 40.2 ± 0.04 °C, at MD it was 40.9 ± 0.04 °C and at PM BT was 41.1 ± 0.04 °C. When PS was 0 the BT at AM and MD were similar. The AM response curve suggests animals attempt to increase heat dissipation during the cooler AM period relative to MD and PM. Morning observation of cattle (before feeding) are crucial for effective heat load management especially on days when high heat load is expected. The MD and PM observations provide a good indication of the impact of high environmental heat load on cattle. Differences in PS between AM and PM observations suggest that more research is needed to determine the effect of night time conditions on BT, PS and overall respiratory dynamics of cattle during periods of hot weather.

Use of different levels of ground endophyte-infected tall fescue seed during heat stress to separate characteristics of fescue toxicosis

Studies of fescue toxicosis using whole seed diets show reduced feed intake and thermoregulatory ability, but much of the seed passes undigested through the animal. Cattle were fed ground tall fescue seed at different levels to potentially facilitate digestion and absorption of toxins and identify toxin sensitivity for major characteristics of the condition [i.e., hyperthermia, reduced feed intake (FI), reduced blood prolactin]. Steers (n = 18; 350 kg BW) were housed in the Brody Climatology Laboratory at thermoneutrality (TN; 19°C) and randomly assigned to daily diet treatments with either ground endophyte-infected [E+; low and high doses at 20 and 40 μg ergovaline/(kg BW/d), respectively] or endophyte-free [E-; control at 0 μg ergovaline/(kg BW/d)] tall fescue seed. After 12 d at TN, animals received 2 d of transition to heat stress (HS; 36°C daytime, 25°C nighttime) and maintained for 14 more days. Cattle were fed twice daily at 0800 and 1600 h, with water ad libitum. Feed intake was measured at 0700 h, with skin and rectal temperatures, and respiration rate at 0600, 1100, 1600, and 2100 h. Blood was sampled on selected days for prolactin and leptin determinations. Steers fed ground E+ diet decreased (P ≤ 0.0001) FI below controls at TN, with no dose effect. Maximum FI reduction with E+ treatment was 25% at TN, with an additional 46% decrease during HS (P ≤ 0.05). By the end of HS, E+ FI increased (P > 0.05) to that of E-, suggesting recovery. Prolactin was reduced (P ≤ 0.05) in high E+ cattle below controls at study end. Leptin blood concentrations were unaffected by E+ treatment (P > 0.05) but was reduced (P ≤ 0.05) by the end of HS. Pattern of rectal temperature response to HS showed a more rapid initial increase and decline for both E+ groups compared with controls (P ≤ 0.05). Skin temperature was the only variable that identified E+ dose differences. Although there were no treatment differences at TN, skin temperature was lower (P ≤ 0.05) for high E+ steers compared with controls during HS when air temperature was reduced each day. In general, FI was more responsive to E+ toxins than body temperature or blood prolactin, declining even at TN and exhibiting dynamic activity during HS. Although body temperature response to E+ toxins appears to stabilize during HS, this is misleading as rapid change in air temperature exposes effects on skin temperature.

Effects of selected endophyte and tall fescue cultivar combinations on steer grazing performance, indicators of fescue toxicosis, feedlot performance, and carcass traits

Five tall fescue [Lolium arundinaceum (Schreb.)] pastures [wild-type 'Kentucky-31' with 78.0% of plants infected with ergot alkaloid-producing endophyte Neotyphodium coenophialum (KY31 E+), 'Jesup' AR542 endophyte-infected contaminated with 30.3% tall fescue containing ergot alkaloid producing-endophyte (Jesup AR542 E+); 'GA-186' AR584 endophyte-infected contaminated with 11.8% tall fescue containing ergot alkaloid producing-endophyte (AGRFA 140); 'PDF' AR584 endophyte-infected contaminated with 5.5% tall fescue containing ergot alkaloid producing-endophyte (AGRFA 144); and 'KYFA 9301' AR584 endophyte-infected contaminated with 10.0% tall fescue containing ergot alkaloid producing-endophyte (AGRFA 150)] were compared for steer growth performance, toxicity, feedlot performance, and carcass traits. Steers (mean initial BW=322 kg) grazed pastures for 84 d in spring and 56 d in autumn for 2 yr. Steers were shipped after grazing in Prairie, MS, to Macedonia, IA, for finishing. Mean herbage mass was not different (P=0.15) among pastures. Posttreatment (d 28+) serum prolactin concentrations were depressed (P=0.013) on KY31 E+. Steers grazing KY31 E+ had greater (P<0.01) posttreatment rectal temperatures during spring. Spring hair coat scores were greatest (P<0.01) on KY31 E+ at d 56 and 84. Steer ADG was least (P<0.01) on KY31 E+ in spring and depressed (P=0.014) on KY31 E+ and Jesup AR542 E+ in autumn. Spring grazing ADG was greater (P=0.049) on AGRFA 150 than Jesup AR542 E+ and AGRFA 140. No BW differences (P=0.09) among pastures were seen at reimplant during feedlot finishing. Pasture had no effect on ADG after reimplant (P=0.68), days on feed (P=0.56), or final BW (P=0.55). Exposure to fescue toxicosis did not affect (P≥0.19) carcass traits. Hair coat price discounts applied for spring-grazed steers on KY-31 E+ affected (P<0.01) initial steer monetary values. There were no pasture differences for finishing costs (P≥0.61) or final carcass value (P=0.59). Elite tall fescue cultivar and novel endophyte combinations improve growth performance of grazing calves over KY31 E+. Producers whose calves graze KY-31 E+ tall fescue should consider retaining ownership of these cattle through feedlot finishing to avoid market discounts and capture value from compensatory BW gains during finishing.

Evaluation of a ruminally dosed tall fescue seed extract as a model for fescue toxicosis in steers

Tall fescue (Lolium arundinaceum) toxicosis research is often complicated by a reduction in intake of infected forage or seed, making treatment comparisons difficult. This study was conducted to develop a fescue toxicosis model that would allow for variations in DMI without altering the quantity of alkaloids consumed over the course of the experiment. Ground tall fescue seed and a tall fescue seed extract were used in two 2-period crossover experiments to determine the effectiveness of ruminal dosing of a tall fescue seed extract to induce fescue toxicosis. This experiment used 4 growing Holstein steers (BW = 337 ± 24 kg) surgically fitted with ruminal cannulas. Steers were maintained on a diet of endophyte-free fescue hay fed ad libitum throughout the experiment. Endophyte-infected (E+; 4.1 mg/kg of ergovaline) and uninfected (E-; 0.0 mg/kg of ergovaline) KY-31 tall fescue seed was ground and dosed or extracted with ethanol, concentrated, and lyophilized before ruminal dosing. Ergovaline concentration of the final extract was 102 mg/kg. Animals were given a minimum of a 3-wk washout period between treatments. Physiological indicators were measured over 7 d at 22°C (d 1 to 3) and 32°C (d 4 to 7) during both seed and extract dosing. Seed and extract E+ dosing reduced serum prolactin concentrations such that they were not different from zero (P < 0.10). Treatment with E+ reduced feed intake (P < 0.05) and heart rate (P < 0.001), and increased respiration rate (P < 0.01) and core temperature (P < 0.05) during both seed and extract dosing. Increasing environmental temperature from 22 to 32°C reduced total intake (P < 0.05) and increased core temperature (P < 0.001) and respiration rate (P < 0.001) during both seed and extract dosing. Diastolic blood pressure tended (P < 0.09) to be increased during E+ extract dosing and reduced during heat stress. These physiological alterations are consistent with those reported for cattle grazing or consuming seed from endophyte-infected tall fescue. These data indicate that a ruminally dosed ethanol extract of tall fescue seed is efficacious in inducing fescue toxicosis in cattle.

Diminished reproductive performance and selected toxicants in forages and grains

This article discusses reproductive toxicants as the potential, primary causes of observed reproductive abnormalities and other variables that can affect reproductive performance in ruminants. The causes of diminished reproductive performance in ruminants are often multifactorial. It is critical that producers and their veterinarians understand the potential effects of physiologic and genetic predispositions and nutritional, environmental, infectious, and toxic stressors, as well as interactions involving management. The recognition and prevention of the adverse reproductive effects of these enzootic toxic stressors are essential for optimal ruminant reproductive performance and profitability of a ruminant production system.

Haemodynamics of lambs grazing perennial ryegrass (Lolium perenne L.) either infected with AR6 novel, wild-type endophyte, or endophyte-free

AIM

To compare vasoconstriction of the auricular artery and characteristics of blood flow in the carotid arteries between lambs grazing perennial ryegrass that was either infected with the AR6 novel endophyte (AR6), wild-type endophyte or endophyte-free.

METHODS

Sixteen Coopworth lambs, mean 23.7 (SD 1.8) kg, were randomly assigned to graze three, 0.10-ha pastures of perennial ryegrass (cultivar Extreme) located in Lincoln, New Zealand, that were infected with either the AR6 novel endophyte (n=5) or wild-type endophyte (n=6) or were endophyte-free (n=5), for 18 days until 16 March 2009. Lambs on AR6 pasture were then switched to endophyte-free pasture, and those on endophyte-free were switched to AR6 pasture, for 18 days. Lambs continued grazing the wild-type ryegrass during both phases of the study. Colour Doppler ultrasonography was used to monitor cross-sectional area of lumina in the auricular and carotid arteries as measurements of vasoconstriction, and to measure pulsatility indices, heart rate, systolic and diastolic velocities, and mean velocity in the carotid artery. Urine was sampled once during each phase, to measure the concentration of urinary alkaloids. A heat challenge (32°C) was imposed on the last day of the experiment, to determine treatment effects on rectal temperature and respiration rate.

RESULTS

Vasoconstriction was detected in the auricular arteries of lambs grazing AR6 and wild-type pastures. Areas of lumina declined linearly over 9 days in lambs that were switched from endophyte-free to AR6 pastures (p<0.05), and areas increased linearly in lambs that were switched from AR6 to endophyte-free pasture (p<0.001). Resistance to blood flow in the carotid arteries decreased linearly in the 9 days after lambs were switched from AR6 to endophyte-free pasture(p<0.05), and tended to increase after lambs on endophyte-free pasture were switched to AR6 (p<0.10). The concentrations of urinary alkaloids decreased after switching lambs from AR6 to endophyte-free pasture, and increased after switching from endophyte-free to AR6 pasture (p<0.05). The concentrations of urinary alkaloids of lambs on wild-type pasture were similar between the conditioning and experimental phases. There were no treatment effects on rectal temperature and respiration rate during the heat challenge.

CONCLUSIONS

These results indicated that management approaches are needed to overcome potential vulnerabilities to heat stress for sheep grazing AR6 perennial ryegrass. Furthermore, following grazing such pasture, lambs will need to graze endophyte-free ryegrass for >18 days, to completely clear ergot alkaloids from their vasculature, assuming that complete clearance can be achieved.

Effects of body condition on measures of intramuscular and rump fat, endocrine factors, and calving rate of beef cows grazing common bermudagrass or endophyte-infected tall fescue

Multiparous beef cows were managed to achieve marginal (BCS = 4.7 ± 0.07; n = 106) or good (BCS = 6.6 ± 0.06; n = 121) body condition (BC) to determine the influence of forage environment on BW and BC changes, intramuscular fat percentage (IMF), rump fat (RF), and serum hormones during 2 yr. Cows within each BC were randomly assigned to graze either common bermudagrass (CB; n = 3 pastures/yr) or toxic endophyte-infected tall fescue (EI; n = 3 pastures/yr) during a 60-d breeding season. Blood samples were collected at d 0, 30, and 60 of the breeding season, and serum concentrations of prolactin (PRL), IGF-I, and cortisol (CORT) were quantified; PRL and progesterone (P(4)) also were quantified 10 d before the breeding season (d -10). Body weight and BCS were recorded during the breeding season (d 0, 30, and 60). Cow IMF and RF were measured via ultrasonography at the start and end of the breeding season. Cows with increased (>1 ng/mL) P(4) at the beginning of the breeding season (cyclic) had greater (P < 0.02) concentrations of PRL on d 30 and 60 compared with anestrous cows. A forage environment × BC interaction tended (P = 0.07) to influence PRL. Cows grazing CB independent of BC had increased PRL compared with cows grazing EI. Prolactin was decreased in good-BC cows grazing EI compared with cows grazing CB, and cows in marginal BC grazing EI had the least concentrations of PRL. Concentrations of IGF-I were similar (P > 0.10) among good- and marginal-BC cows grazing CB, as well as good-BC cows grazing EI; however, marginal-BC cows grazing EI had reduced (P < 0.04) concentrations of IGF-I compared with all other groups. Cows in marginal BC grazing CB gained (P = 0.02) the most BW during the breeding season, whereas good-BC cows grazing EI gained the least amount of BW. Marginal-BC cows grazing CB tended (P = 0.06) to increase BC during the breeding season, whereas good-BC cows grazing either CB or EI lost BC. Rump fat tended (P = 0.07) to increase during the breeding season in marginal-BC cows compared with cows in good BC. Calving rates were similar (P > 0.10) among good- (82%) and marginal- (84%) BC cows grazing CB, and good-BC cows grazing EI (79%); however, marginal-BC cows grazing EI had a reduced (P = 0.04) calving rate (61%). Cattle grazing EI during the breeding season lost BC. That reduction in BC may be communicated to the pituitary via hormones that include IGF-I or PRL or both, resulting in decreased calving rates.

Impact of water troughs on cattle use of riparian zones in the Georgia Piedmont in the United States

Cattle use of riparian areas may lead to stream water contamination with nutrients, pathogens, and sediments. Providing alternative water away from the stream may reduce the amount of time cattle spend near streams and therefore reduce contamination. We conducted this study to 1) evaluate the effect of providing water troughs outside of the riparian zones on the amount of time cattle spend in riparian zones, and 2) evaluate if environmental factors such as temperature and humidity affect the impact of water trough availability on the amount of time cattle spend within riparian and nonriparian locations. Global positioning system (GPS) collars were used to document cow locations every 5 min in 2 mixed tall fescue/common bermuda-grass pastures of the Georgia Piedmont in the United States. We found that when the temperature and humidity index (THI) ranged between 62 and 72, providing cattle with water troughs outside of riparian zones tended to decrease time cattle spent in riparian zones by 63% (52 min x d(-1); P = 0.11). When THI ranged between 72 and 84, nonriparian water availability did not have a significant impact on the amount of time cattle spent in the riparian zone or in riparian shade. These results suggest that water troughs placed away from unfenced streams may improve water quality by reducing the amount of time cattle spend in riparian zones when environmental conditions as evaluated by THI are not stressful.

Influence of toxic endophyte-infected fescue on sperm characteristics and endocrine factors of yearling Brahman-influenced bulls

Sixteen (mean age = 1.1 +/- 0.1 yr; mean BW = 478 +/- 34 kg) Brahman-influenced bulls were used to determine the influence of fescue type on sperm characteristics and serum concentrations of prolactin, cortisol, and testosterone. Bulls were blocked by BW, scrotal circumference (SC), and pregrazing sperm characteristics and randomly assigned to graze toxic endophyte-infected (EI; 4 bulls/pasture; 2 pastures) or novel endophyte-infected (NE; 4 bulls/pasture; 2 pastures) tall fescue for 121 d. Semen was collected by electroejaculation, and SC was measured and blood samples collected monthly. Sperm were evaluated for motility and morphology with an integrated visual optical system. Overall mean concentration of prolactin was decreased more (P < 0.01) in EI bulls than NE bulls from May to August. Scrotal circumference was not affected by fescue type (P = 0.58); overall SC averaged 36.7 +/- 2.3 cm. Percentage of live sperm was not different (P = 0.24) between NE bulls (80%) than EI bulls (67%) in July and August. Bulls grazing NE fescue had more (P < 0.06) motile sperm than EI bulls in July and August. Percentages of progressive (57 vs. 38%, NE and EI, respectively; P < 0.06) and rapid (67 vs. 46%, NE and EI, respectively; P = 0.04) sperm were greater from bulls grazing NE than EI bulls in July and August. Average velocity of the smoothed sperm path and progressive velocity in a straight line from the beginning to the end of the sperm track were slower (P < 0.09) in EI bulls than NE bulls and were slower (P = 0.04) in August compared with July. Mean width of head oscillation as the sperm swims was less (P < 0.06) in August than July. Concentrations of cortisol and testosterone were not (P > 0.10) influenced by fescue type. Semen from bulls grazing EI had reduced motility and morphology than bulls grazing NE. Detrimental effects of toxic fescue may not be mediated by cortisol, testosterone, or both. Semen quality of bulls grazing toxic EI tall fescue was decreased with increased maximum ambient temperatures.

Hemodynamic responses of the caudal artery to toxic tall fescue in beef heifers1

Color Doppler ultrasonography was used to compare blood flow characteristics in the caudal artery of heifers fed diets with endophyte (Neotyphodium coenophialum) infected (E+) or noninfected (E-) tall fescue seed. Eighteen crossbred (Angus x Brangus) heifers were assigned to 6 pens and were fed chopped alfalfa hay for 5 d and chopped alfalfa hay plus a concentrate that contained E-tall fescue seed for 9 d during an adjustment period. An 11-d experimental period followed, with animals in 3 pens fed chopped alfalfa hay plus a concentrate with E+ seed and those in the other 3 pens fed chopped hay plus concentrate with E E- seed. Color Doppler ultrasound measurements (caudal artery area, peak systolic velocity, end diastolic velocity, mean velocity, heart rate, stroke volume, and flow rate) and serum prolactin were monitored during the adjustment (baseline measures) and during the experimental period. Three baseline measures were collected on d 3, 5, and 6 during the adjustment period for comparison to post E+ seed exposure. Statistical analyses compared the proportionate differences between baseline and response at 4, 28, 52, 76, 100, 172, and 268 h from initial feeding of E+ seed. Serum prolactin concentrations on both diets were lower (P <0.001) than baseline beginning at 4 h from the start of the experimental period. However, trends in serum prolactin concentrations for heifers on the E- diet suggested ambient temperature was affecting these concentrations. Caudal artery area in E+ heifers had declined (P <0.10) from baseline by 4 h and was consistently lower (P <0.05) for the remainder of the period. Heart rates for E+ heifers were lower than the baseline rate from 4 (P <0.10) to 100 (P <0.001) h, but were similar (P >0.10) to the baseline for 172 and 268 h measures. Blood flow in E+ heifers was consistently lower than the baseline from 4 (P <0.05) to 172 (P <0.001) h, but was similar to the baseline at 268 h when heart rate was similar to the baseline rate. Caudal artery areas for the E- diet were similar to baseline areas except at 100 h when it was greater than baseline. Heart rates and flow rates for E- heifers did not differ (P >0.10) from baseline measures during the experimental period. Results indicated that onset of toxicosis was within 4 h of cattle exposure to E+ tall fescue and is related to vasoconstriction and reduction in heart rate.

Influence of stocking rate and steroidal implants on growth rate of steers grazing toxic tall fescue and subsequent physiological responses

An 84-d grazing experiment was conducted in 2 growing seasons to evaluate interactions of stocking rate and steroidal implants with BW gain and symptoms of toxicosis in yearling steers grazing endemic endophyte-infected (E+) tall fescue (Festuca arundinacea Schreb.). A 4 x 2 factoral design was used to evaluate 4 stocking rates (3.0, 4.0, 5.0, and 6.0 steers/ ha) with or without steroidal implants (200 mg of progesterone + 20 mg of estradiol benzoate). Treatment combinations were randomly assigned to eight 1-ha pastures of E+ Kentucky-31 tall fescue (i.e., treatments were not replicated). Treatment effects were analyzed for ADG, total BW gain per hectare, forage availability, and hair coat ratings. At the conclusion of grazing in the second year (22 June), steers were placed on a bermudagrass [Cynodon dactylon (L.) Pers.] pasture, and rectal temperatures and serum prolactin concentrations were monitored for 10 d to assess carryover effects of stocking rate and steroidal implants on recovery from toxicosis-related heat stress. Forage availability differed (P < 0.001) between years, but there were no year x treatment interactions (P > 0.10). There was an implant x stocking rate interaction (P < 0.05) on ADG. Differences between the slopes in the regression equations indicated that ADG responded to implantation when stocking rates were low, but the response diminished as stocking rate increased. Stocking rate did not influence (P = 0.89) postgraze rectal temperature, but the regression intercept for implanted steers was 0.4 degrees C greater (P < 0.05) than for nonimplanted steers, and the difference was consistent across the entire 10-d fescue-free grazing period. Concentrations of prolactin increased during the 10-d fescue-free grazing period, but trends differed due to an implantation x stocking rate interaction (P < 0.05). Results indicate that implantation with progesterone + estradiol benzoate increases ADG with lower stocking rates, but the effect diminishes with increased grazing intensity. Implantation with steroid hormones increased rectal temperatures, but during a fescue-free grazing period rectal temperatures and serum prolactins for implanted and nonimplanted steers returned to values indicative of a stable and healthy status in a 192- to 240-h (i.e., an 8- to 10-d) period. However, because the treatments used in this study were not replicated, these observations need to be confirmed with replicated studies.

Fertility aspects in yearling beef bulls grazing endophyte-infected tall fescue pastures

During a 2-year study, yearling beef bulls were used to determine the effects of grazing on endophyte-infected tall fescue on endocrine profiles, semen quality and fertilisation potential. Bulls were allotted to graze tall fescue pastures infected with Neotyphodium coenophialum (E+; n = 20 per year) or Jesup/MaxQ (Pennington Seed, Atlanta, GA, USA; NTE; n = 10 per year). Bulls were grouped by scrotal circumference (SC), bodyweight (BW), breed composites and age to graze tall fescue pastures from mid-November until the end of June (within each year). Blood samples, BW, SC and rectal temperatures (RT) were collected every 14 days. Semen was collected from bulls every 60 days by electroejaculation and evaluated for motility and morphology. The developmental competence of oocytes fertilised in vitro with semen from respective treatments was determined. Bulls grazing E+ pastures had decreased BW gain (P < 0.01), increased overall RT (P < 0.01) and decreased prolactin (P < 0.01) compared with animals grazing NTE pastures. Neither percentage of normal sperm morphology nor motility differed between bulls grazed on the two pasture types. Semen from E+ bulls demonstrated decreased cleavage rates (P = 0.02) compared with semen from NTE bulls. However, development of cleaved embryos to the eight-cell and blastocyst stages did not differ between the two groups. In conclusion, semen from bulls grazing E+ tall fescue resulted in decreased cleavage rates in vitro, which may lower reproductive performance owing to reduced fertilisation ability.

A model of fescue toxicosis: Responses of rats to intake of endophyte-infected tall fescue1,2

A study was conducted to develop a model for fescue toxicosis using rats fed a diet containing endophyte-infected tall fescue seed (E+). Rats implanted with telemetric transmitters to continuously monitor core body temperature (Tc) and activity were housed at thermoneutrality (21 degrees C) and were fed a diet containing endophyte-free fescue seed (E-). After 2 wk, they were assigned to either E+ or E- diets and initially maintained at thermoneutrality (preheat) for 8 d. They were then exposed to heat stress (31 degrees C) for 22 d, followed by 1 wk of recovery at thermoneutrality (post-heat). Body weight and feed intake were measured daily. Rats receiving the E+ diet showed decreased feed intake (P = 0.001) and weight gains (P = 0.003) during the preheat period. The decrease in Tc from the pre-treatment level was greater in E+ than in E- rats during the preheat (P = 0.001) and postheat (P = 0.001) periods. With heat stress, both groups showed parallel decreases in feed intake. The increase in Tc from pre-heat to heat conditions was greater in E+ vs. E- rats (P = 0.001). Activity level was lower in E+ than in E-rats during heat stress (P = 0.009) and postheat (P = 0.037) periods. These results show that the rat model for fescue toxicosis is extremely useful because many of the observed responses to E+ diet are similar to those noted for cattle, and additional variables that are difficult to measure in cattle, such as activity, can be easily evaluated.

Effects of short-term early gestational exposure to endophyte-infected tall fescue diets on plasma 3,4-dihydroxyphenyl acetic acid and fetal development in mares

Consumption of wild-type (toxic) endophyte-infected tall fescue (E+) by horses during late gestation is known to adversely affect pregnancy outcome; however, little is known of the potential disruptive consequences of E+ consumption by mares during the critical phases of placentation and fetal development in early pregnancy. The objective of this study was to evaluate the detrimental effects of feeding E+ to mares during early gestation. Mares (n = 12) paired by stage of gestation (d 65 to 100) were assigned to diets (six per diet) consisting of endophyte-free (E-) or E+ tall fescue seed (50% E- or E+ tall fescue seed, 45% sweet feed, and 10% molasses fed at 1.0% of BW/d). Mares also had ad libitum access to E+ or E- annual ryegrass hay, and were fed diets for 10 d. Following removal from the tall fescue diet on d 11, mares were placed on common bermudagrass pasture and monitored until d 21. Morning and evening rectal temperatures were recorded and daily blood samples were collected for progesterone and prolactin (PRL) analyses, whereas samples for 3,4-dihydroxyphenyl acetic acid (a catecholamine metabolite) analysis were collected on alternate days. For clinical chemistry analysis, blood samples were collected on d 0, 5, 10 and 21. Daily urine samples were collected for ergot alkaloid analysis, and ultrasonography was performed for presence of echogenic material in fetal fluids. Rectal temperatures (E+ 37.76+/-0.03; E- 37.84+/-0.03 degrees C) and serum PRL concentrations (E+ 14.06< or =0.76; E- 12.11+/-0.76 ng/mL) did not differ (P = 0.96) between treatments. Measuring the change in basal serum concentration from d 0 over time, progesterone concentrations did not differ (-0.64 +/-1.49 and -0.55+/-1.47 ng/mL for E+ and E- mares, respectively). There was no negative pregnancy outcome, and ultrasonography indicated no increase in echogenic material in fetal fluids. Plasma 3,4-dihydroxyphenyl acetic acid concentrations decreased (P < 0.05) in E+ compared with E- mares (2.1+/-0.14 and 4.4+/0.43 ng/mL, respectively). Urinary ergot alkaloid concentration was greater (P < 0.01) in mares consuming E+ compared with E- (532.12+/- 52.51 and 13.36+/-2.67 ng/mg of creatinine, respectively). Although no fetal loss was observed during the current study, elevated concentrations of urinary ergot alkaloid were consistent with depressed endogenous catecholamine activity, suggestive of an endocrine disruptive effect of hypothalamic origin.

Effects of endophyte-infected tall fescue on indicators of thermal status and growth in Hereford and Senepol steers

Poor growth often occurs in cattle consuming ergot alkaloids associated with endophyte-infected (EI) tall fescue. Hyperthermia may contribute significantly to poor growth resulting from fescue toxicosis. This study examined indicators of thermal status and growth in Hereford (n = 30; heat-sensitive Bos taurus; H) and Senepol (n = 28; heat-tolerant Bos taurus; S) steers fed EI tall fescue (TF) or orchardgrass (OG) in 2 x 2 factorial experiments. Respiration rates, daytime shade use, tail skin temperatures, and body weights were measured during the summer and fall of 2000 (Exp. 1) and 2001 (Exp. 2). Experimental diets consisted of hay and seed for 12 wk in 2000, hay for 6 wk during the summer of 2001, and hay plus seed for 6 wk during the fall of 2001. In Exp. 1, EI tall fescue increased (P < 0.01) respiration rates, shade use, and skin temperatures in both breeds. Breed x diet affected (P < 0.01) 12-wk ADG in Exp. 1. Growth rate was lower for H-TF (262 g/d) than for S-TF, S-OG, and H-OG (475, 497, and 524 g/d, respectively). In Exp. 2, Senepol had lower (P < 0.01) respiration rates, shade use, and skin temperatures compared with Hereford, but diet did not alter (P > 0.14) these indicator traits in either breed. Breed x diet affected (P < 0.01) summer growth rates. Growth rate was lower for H-TF (88 g/d) than for H-OG, S-TF, and S-OG (508, 555, and 566 g/d, respectively). Adding seed to the diets in Exp. 2 decreased (P < 0.01) ADG for both breeds on TF during the fall. Thermal status indicator traits in Senepol and Hereford steers were similarly altered by TF; however, only Hereford showed consistently poor growth. Senepol showed resilience in their capacity for growth under conditions of fescue toxicosis. Senepol influence may enhance cattle performance in production systems that use EI tall fescue as the base forage.

Physiological and cellular adaptations of zebu cattle to thermal stress

During their separate evolution from Bos taurus, zebu cattle (Bos indicus) have acquired genes that confer thermotolerance at the physiological and cellular levels. Cattle from zebu breeds are better able to regulate body temperature in response to heat stress than are cattle from a variety of B. taurus breeds of European origin. Moreover, exposure to elevated temperature has less deleterious effects on cells from zebu cattle than on cells from European breeds. Superior ability for regulation of body temperature during heat stress is the result of lower metabolic rates as well as increased capacity for heat loss. As compared to European breeds, tissue resistance to heat flow from the body core to the skin is lower for zebu cattle while sweat glands are larger. Properties of the hair coat in zebu cattle enhance conductive and convective heat loss and reduce absorption of solar radiation. At the cellular level, genetic adaptations to resist deleterious effects of elevated temperature result in preimplantation embryos from zebu being less likely to be inhibited in development by elevated temperature than are embryos from European breeds. The zebu genotype has been utilized in crossbreeding systems to develop cattle for beef and dairy production systems in hot climates but success has been limited by other unfavorable genetic characteristics of these cattle. An alternative scheme is to incorporate specific thermotolerance genes from zebu cattle into European breeds while avoiding undesirable genes. Once specific genes responsible for thermotolerance in zebu have been identified or mapped, breeding strategies such as marker-assisted selection and transgenics can be applied to further the exploitation of the zebu genotype for cattle production systems.