Stress-related hormonal alterations, growth and pelleted starter intake in pre-weaning Holstein calves in response to thermal stress

Effect of heat stress during the dry period on milk yield and reproductive performance of Holstein cows

This study aimed to determine the influence of heat stress during the dry period on milk yield and reproductive performance of Holstein cows in a hot environment. Breeding and milk production records of cows, as well as meteorological data between 2017 and 2020 from a commercial dairy herd (n = 12,102 lactations), were used to determine the relationship between climatic conditions during the dry period (average of the temperature-humidity index (THI) at the beginning, middle, and end of the dry period) and reproductive efficiency and milk yield traits. THI was divided into < 70 (no heat stress), 70-80 (moderate heat stress), and > 80 (severe heat stress). First-service pregnancy rate of cows decreased (P < 0.01) with increasing hyperthermia during the dry period (9.5, 7.3, and 3.4% for THI < 70, 70-80, and > 80, respectively). All-service pregnancy rate was highest (P < 0.01) for cows not undergoing heat stress during the dry period (60.2%) and lowest (42.6%) for cows with severe heat stress during the dry period. Cows not experiencing heat stress during the dry period required a mean ± SD of 5.6 ± 3.8 services per pregnancy compared with 6.5 ± 3.6 (P < 0.01) for cows subjected to THI > 80 during the dry period. Cows not suffering heat stress during the dry period produced more (P < 0.01) 305-day milk (10,926 ± 1206 kg) than cows subjected to moderate (10,799 ± 1254 kg) or severe (10,691 ± 1297 kg) heat stress during the dry period. Total milk yield did not differ (P > 0.10) between cows not undergoing heat stress (13,337 ± 3346 kg) and cows subjected to severe heat stress during the dry period (13,911 ± 4018 kg). It was concluded that environmental management of dry cows during hot months is warranted to maximize reproductive performance and milk yield in the following lactation.

Effects of thermal stress on calf welfare

Cold and heat stress present welfare challenges for dairy calves. The consequences of thermal stress on biological functioning have been well documented, and many housing and management strategies have been evaluated to mitigate those detrimental impacts. In cold weather, mitigation strategies have largely focused on nutritional interventions or limiting heat loss with resources such as bedding or jackets. In hot weather, heat abatement strategies such as supplemental shade, increased environmental air exchange through passive ventilation, and forced air movement through mechanical ventilation have been evaluated. Recently in Wisconsin's continental climate, our group evaluated how 2 aspects of calf welfare-the needs for thermal comfort and social contact (i.e., pair or group housing vs. individual housing)-may align or conflict in winter and summer, respectively. In both seasons, calves pair-housed in outdoor hutches preferred social proximity. When 2 calves shared a hutch, the heat load was greater than for a single calf, which may be beneficial for thermal comfort in winter. In summer, the potential detriments from the additional heat load of 2 calves was mitigated with passive hutch ventilation, which calves preferred. Nonetheless, knowledge gaps remain regarding the impacts of thermal stress on calves' affective states, and much remains unknown about their preferences and motivations for specific thermal stress mitigation resources. Future research to address these gaps could improve our understanding of calf welfare and inform best practices for calf management.

A retrospective study of thermal events on the mortality rate of hutch-reared dairy calves

Introduction

Heat stress in hutch-reared dairy calves (Bos taurus) is highly relevant due to its adverse effects on animal welfare, health, growth, and economic outcomes. This study aimed to provide arguments for protecting calves against heat stress. It was hypothesized that the thermal stress caused by high ambient temperature in summer months negatively affects the survival rate in preweaning calves.

Methods

In a retrospective study, we investigated how calf mortality varied by calendar month and between thermoneutral and heat stress periods on a large-scale Hungarian dairy farm (data of 46,899 calves between 1991 and 2015).

Results

The daily mortality rate was higher in the summer (8.7-11.9 deaths per 10,000 calf days) and winter months (10.7-12.5 deaths per 10,000 calf-days) than in the spring (6.8-9.2 deaths per 10,000 calf-days) and autumn months (7.1-9.5 deaths per 10,000 calf-days). The distribution of calf deaths per calendar month differed between the 0-14-day and 15-60-day age groups. The mortality risk ratio was highest in July (6.92). The mortality risk in the 0-14-day age group was twice as high in periods with a daily mean temperature above 22°C than in periods with a daily mean of 5-18°C.

Conclusions

Heat stress abatement is advised in outdoor calf rearing when the mean daily temperature reaches 22°C, which, due to global warming, will be a common characteristic of summer weather in a continental region.

Methods for detecting heat stress in hutch-housed dairy calves in a continental climate

Dairy calves exposed to solar radiation, elevated ambient temperature, and humidity are at risk of impaired welfare and productivity. Initial detection of thermal discomfort requires determination of optimal heat stress indicators and thresholds. Such values have recently been established in calves in chronic, subtropical, and acute continental environments but not in continuous, temperate conditions. Herein, the objectives were to determine associations between animal-based and environmental heat stress indicators and establish environmental breakpoints for hutch-raised dairy calves during a continental summer. From June to August, dairy calves (n = 63; 14 to 42 d of age) were individually hutch-housed and managed according to the dairy standard operating procedures in Arlington, Wisconsin. Calf respiration rates (RR), rectal temperatures (RT), shaved or unshaved skin temperatures (ST), and hutch internal and external air speed were measured thrice weekly at 0700 and 1400 h after a 15 min hutch restriction. Environmental indices including dry bulb temperature (T_db), black globe temperature, and relative humidity were measured every 15 min, averaged hourly, and used to calculate temperature-humidity index (THI) using 8 different equations (THI_1-8). Correlation and linear regression models were used to determine relationships within and between animal-based and environmental indicators. Environmental breakpoints were established using segmented regression models to estimate THI and T_db thresholds for abrupt changes in animal responses. There were strong, positive correlations between animal-based indicators and T_db or THI_1-8, with the strongest association observed between unshaved ST and T_db (r = 0.80). The linear regression of animal-based indicators with the best fit included T_db or T_db plus relative humidity and air speed. The threshold at which RR and RT began to rise was at a THI of 69 for both or at a T_db of 21.0 or 21.5°C, respectively. No threshold was established for ST. Together, these outcomes indicate that T_db is an appropriate measurement to detect thermal discomfort for calves in a temperate summer climate and individual hutch housing. Monitoring of calves is warranted before ambient temperature reaches 21.0°C, corresponding to RR of 40 breaths per minute and RT of 38.5°C, to promote calf comfort and reduce the risk of hyperthermia-related welfare and productivity consequences.

Effect of a 2-step probiotic program on digestive health and performance of Holstein heifer calves

Managing the composition of the bacterial communities in the digestive tract with the use of probiotics that enhance protective microflora could result in positive effects on health and performance of calves. The objective of this study was to evaluate a 2-step probiotic program (added to colostrum and milk) on the digestive health and growth of preweaning Holstein heifers. A randomized clinical trial was conducted from July to October 2020 in a calf rearing facility in Colorado. Calves were housed in pairs sharing the same treatment in 2 polyethylene hutches within a common area of 4.50 m². A total of 232 calves were enrolled at birth and randomly allocated into 2 treatment groups [control (CTR) = 116; treatment (PB) = 116] and followed until weaning (64 ± 3 d). Treatment consisted of 2 formulations of a multistrain bacterial-based probiotic added in colostrum (PBF1) and milk (PBF2). Treatment calves received 2 g of PBF1 added to each colostrum feeding, and 1 g of PBF2 added to the milk at the morning feeding 3 times per week up to weaning. Calf weight was collected at birth, at 30 d of age, and at weaning. Serum total protein was determined at age 3 ± 1 d and a health assessment was completed 3 times per week. Statistical analyses were performed using SAS, with calf considered the experimental unit clustered by housing pair. Cox proportional hazard analysis and time to event analysis were used to compare time to the first diarrhea event and time to recovery between treatment groups. The total number of diarrhea events and culling were assessed by Poisson regression and logistic regression analysis, respectively. Linear regression was performed to evaluate differences in average daily gain by treatment group. Overall, the mean (± standard error) temperature humidity index (THI) was 75 (± 0.44) units during the study period, which resulted in continuous exposure to heat stress in the day hours. No difference between treatment groups was observed in serum total protein. The overall incidence of diarrhea was 96.6% (CTR = 99%, PB = 95%); no differences were determined in the hazard of a first diarrhea episode or in the median time to the first diarrhea event (11 d in both groups). Similarly, no differences were found in the likelihood of recovery or in the median time to recovery from diarrhea (7 d in both groups). Likewise, treatment group was not associated with the number of diarrhea events, mean (± standard error, g/d) average daily gain from birth to weaning [CTR = 562.5 (13.9); PB = 570.8 (13.5)], or with the odds of culling. The most prevalent pathogen isolated from feces was Clostridium, which tended to be more frequent in CTR calves than PB calves. In conclusion, the probiotic program did not affect the incidence of enteric disease or the growth of preweaning heifer calves.

The relationships between environmental parameters in livestock pen and physiological parameters of Holstein dairy cows

There has been an increase in temperature and the incidence of extreme weather events, such as heat wave, due to global warming, which has promoted the incidence of livestock diseases. Therefore, it is important to examine the effect of changes in environmental parameters on livestock performance. The aim of this study was to examine the relationship between ambient environmental conditions in livestock pen and the physiological parameters of Holstein dairy cows. The results showed that there was a decrease in the red blood cell counts, hemoglobin concentrations, and mean corpuscular hemoglobin concentration of the cows with increasing pen temperature, wet bulb globe temperature (WBGT), and temperature humidity index (THI). Additionally, high daily variation in temperature caused a decrease in the serum albumin levels of the cows. Moreover, the lowest serum calcium, inorganic phosphorus, and magnesium concentrations were observed in November, and were negatively correlated with the 24-hr temperature, WBGT, and THI range of the pen prior to sampling. Multiple regression analysis showed a positive correlation between serum cortisol concentration and 24-hr WBGT range of the pen prior to samplings and packed cell volume. However, serum cortisol and total protein concentrations were negatively correlated. Overall, the findings of the study suggest that large variation in temperature induced stress in the cows, which could be overcome by increased water consumption and improved protein digestion and absorption by the animals, and the addition of minerals, such as calcium to the diet.

Early-life heat stress exposure impacts dairy calf feeding and thermoregulatory behavior

Heat stress has well-known influences on dairy calf physiology, but less is understood about calf behavioral responses to heat stress. Herein, we evaluated milk replacer intake, standing activity, and lying behaviors of calves exposed to prenatal or postnatal heat stress or both. Holstein calves were born to dams experiencing heat stress (HT; shade of a freestall barn) or cooling (CL; shade, fans, and soakers) during late gestation [~44 d before calving, prenatal; mean daily temperature-humidity index (THI) = 78]. They were then subsequently exposed to postnatal heat stress (shade and natural ventilation of an open-sided barn) or cooling (shade of the barn and forced ventilation by fans) from birth to weaning (56 d; mean daily THI = 77; n = 12 per prenatal × postnatal treatment). Heat stress was confirmed by elevated respiration rate and rectal temperature of the prenatal dam and the postnatal calf. Calves were group-housed with automatic milk feeders, from which milk replacer (MR) intake was assessed. Calf behavior was monitored using loggers and video. Postnatal-HT calves tended to consume less MR per hour in the late morning and drank less MR per visit relative to postnatal-CL calves. Postnatal-HT calves spent more time lying laterally and less time lying sternally in a tucked position during overnight hours. Prenatal-HT calves stood longer across the day, particularly overnight, compared with prenatal-CL calves. This study characterized behavioral responses of preweaning dairy calves exposed to chronic heat stress or active cooling during early-life developmental windows.

Evaluating the Effects of Noise Pollution on the Levels of Blood Cortisol, Testosterone, and Thyroid in Male Wistar Rats

Background: Noise pollution is a global problem causing changes in the secretion of various hormones and consequently affecting social well-being and quality of life in cities. Objectives: This study aimed to investigate the effect of noise pollution on the levels of testosterone, thyroid, and cortisol hormones in male rats. Methods: In this experimental study, a total of 70 male Wistar rats (200 - 250 g) were randomly assigned into one control and six experimental groups, with 10 rats in each group. Experimental groups were exposed to noise with different intensity (dB) and time (min) as follows: (I) 60 dB, 30 min; (II) 60 dB, 60 min; (III) 85 dB, 30 min; (IV) 85 dB, 60 min; (V) 110 dB, 30 min; (VI) 110 dB, 60 min; (VII) controls. Animals in the experimental groups were exposed to noise in an acoustic chamber designed for this purpose for 50 days. The Noise.exe software was used to generate noise, and the sound level meter (model TES 1358) was used to determine the accuracy of the intensity and frequency of sound. To determine plasma levels of the hormones, appropriate research and commercial kits were used, which were based on the ELISA method. To determine the concentration of hormones other than TSH, human assay kits were used. All statistical tests were performed in SPSS software version 21. Results: Serum levels of cortisol in the 110-dB (30 and 60 min), 65-dB (60 min), and 85-dB (60 min) groups were significantly higher than the control group (P ≤ 0.05). Also, cortisol levels in the 65-dB and 85-dB (30 minutes) groups were higher than the control group; however, the increase was not significant (P > 0.05). The levels of T4, T3, and TSH in the 60-dB and 85-dB groups were significantly lower than in the control group (P ≤ 0.05). The serum levels of T4, T3, and TSH hormones in the 110-dB group were insignificantly lower than the control group (P > 0.05). The serum level of testosterone in the 110-dB group was significantly lower than the control group (P ≤ 0.05). The mean serum levels of testosterone in the 65-dB and 85-dB groups were insignificantly lower than the control group (P > 0.05). Conclusions: Based on this study, exposure to noise pollution increased cortisol secretion and decreased T4, T3, TSH, and testosterone levels in rats. As this hormonal imbalance may create direct and indirect effects, studies and strategies are recommended to control the imbalance of hormones in the polluted environments.

ADSA Foundation Scholar Award: Early-life exposure to hyperthermia: Productive and physiological outcomes, costs, and opportunities

Global rising temperature is a considerable threat to livestock production and an impediment to animal welfare. In fact, the 5 warmest years on record have occurred since 2016. Although the effect of heat stress on lactating cattle is well recognized and extensively studied, it is increasingly evident that rising temperatures will affect dairy cattle of all ages and lactation states. However, the extent and consequences of this effect are less understood and often overlooked in the literature and dairy industry. Early-life experiences, such as exposure to hyperthermia, can have life-long implications for health and productivity. This review highlights the body of work surrounding the effects of heat-stress exposure in young dairy cattle, including the prenatal fetus (in utero), postnatal calves (preweaning), and growing heifers, which are all categories that are typically not considered for heat-stress abatement on farm. Insights into the physiological and molecular mechanisms that might explain the adverse phenotypic outcomes of heat-stress exposure at different stages of development are also discussed. The estimated economic loss of in utero hyperthermia is addressed, and the ties between biological findings and opportunities for the application of cooling management interventions on farm are also presented. Our research highlights the importance of heat-stress abatement strategies for dry-pregnant cows to ensure optimal multigenerational productivity and showcases the benefits of cooling neonatal calves and growing heifers. Understanding the implications of heat stress at all life stages from a physiological, molecular, economic, and welfare perspective will lead to the development of novel and refined practices and interventions to help overcome the long-lasting effects of climate change in the dairy industry.

Water sprinkling as a tool for heat abatement in farmed Iberian red deer: Effects on calf growth and behaviour

Climatic models predict scenarios in which ambient temperature will continue increasing worldwide. Under these climatic conditions, fitness and animal welfare of many populations are expected to suffer, especially those that live in captive or semi-natural conditions, where opportunities of heat abatement are limited. We undertook an experimental design to assess the effect of heat abatement that water sprinkling might have on Iberian red deer calf growth and behaviour from birth to weaning (135 days). One group of ten mother-calf pairs lived on plots with water sprinkling (treatment) available during summer’s hottest time of the day, while the control group (nine mother-calf pairs) occupied plots with no available water sprinkling. Treatment and control groups were fed ad libitum and swapped between plots every seven days to minimise any plot effect. Body weight was monitored weekly and individual behaviour was recorded once or twice a week at mid-day. We observed that calves had showers under the sprinklers and wallowed in mud puddles. The results clearly indicated that calves of the treatment group showed a significant increase in body weight at weaning in comparison with the control group, with no differences between sexes (treatment: male = 56.5 kg, female = 50.3 kg; control: male = 50.3 kg, female = 46.5 kg). Mother weight and mother age effects were negligible on calf body weight at weaning. The heavier the mother the faster was the rate of growth of its offspring, irrespective of calf sex. The model indicated that although males grew significantly slower than female calves in the control group, males grew faster than females when exposed to the treatment. Calves of the treatment group spent less time drinking, less time in the shade, similar time eating and more time in motion than calves of the control group. There were no behavioural differences between calf sexes of treatment and control groups. The results indicate the importance of providing animals with opportunities of heat abatement in hot environments to improve animal growth and welfare in farmed Iberian red deer.

Association between heat stress during intrauterine development and the calving-to-conception and calving-to-first-service intervals in Holstein cows

Heat stress has been widely studied in relation to its effects on the production and reproduction of dairy cattle. However, the long-term effects of heat stress during intrauterine development on adult cows have been scarcely considered. Thus, the aim of this study was to evaluate possible changes in the reproductive performance of Holstein cows gestated under different values of the Temperature-Humidity Index (THI) during their intrauterine development. Data collected from a database of reproductive and productive records of 10,790 Holstein cows from the central region of Argentina and the THI data from the agrometeorological station of the Instituto Nacional de Tecnología Agropecuaria (INTA) EEA Rafaela, Santa Fe, Argentina, were used. The gestation of the cows evaluated was divided into trimesters, in which the highest THI cycles (sum of three or more consecutive days of exposure to a THI ≥72 during each trimester) and number of days with a THI ≥ 72 were calculated. The calving-to-conception and calving-to-first-service intervals of the cows evaluated were considered as reproductive variables associated with their first lactation. Generalized Linear Mixed Models were used, considering the cow's dairy farm as a random factor within the model. The exposure of the animals to environments with a THI ≥72 during the first trimester of gestation had a negative impact on the reproductive efficiency parameters analyzed. The results obtained indicate that the exposure of pregnant females to high THI values has a long-term impact on their daughters, which may contribute to a decrease in their reproductive performance, possibly through inherited epigenetic characteristics that remain in later generations through fetal programming.

Effects of a Saccharomyces cerevisiae fermentation product on heat-stressed dairy cows

The objective of this study was to evaluate the effects of supplementing a Saccharomyces cerevisiae fermentation product (SCFP) on body temperature indices, metabolism, acute phase protein response, and production variables during heat stress (HS). Twenty multiparous lactating Holstein cows (body weight = 675 ± 12 kg; days in milk = 144 ± 5; and parity = 2.3 ± 0.1) were used in an experiment conducted in 2 replicates (10 cows/replicate). Cows were randomly assigned to 1 of 2 dietary treatments: control diet (CON; n = 10) or the CON diet supplemented with 19 g/d of SCFP (n = 10; NutriTek, Diamond V, Cedar Rapids, IA). Cows were fed their respective diets for 21 d before initiation of the study. The experiment consisted of 2 periods: thermoneutral (period 1; P1) and heat stress (period 2; P2). During P1 (4 d), cows were fed ad libitum and housed in thermoneutral conditions for collecting baseline data. During P2 (7 d), HS was artificially induced using an electric heat blanket (EHB; Thermotex Therapy Systems Ltd., Calgary, AB, Canada). Cows were fitted with the EHB for the entirety of P2. Rectal temperature, respiration rate, and skin temperature were obtained twice daily (0600 and 1800 h) during both periods. Overall, HS increased rectal temperature, skin temperature, and respiration rate (1.4°C, 4.8°C, and 54 breaths/min, respectively) relative to P1, but no dietary treatment differences were detected. Compared with P1, HS decreased dry matter intake and milk yield (36 and 26%, respectively), and the reductions were similar between dietary treatments. Relative to P1, HS increased milk fat content and milk urea nitrogen (17 and 30%, respectively) and decreased milk protein and lactose contents (7 and 1.4%, respectively). Overall, HS increased (52%) plasma cortisol concentrations of CON, but circulating cortisol did not change in SCFP-fed cows. Heat stress increased circulating lipopolysaccharide binding protein and serum amyloid A (SAA; 2- and 4-fold, respectively), and SCFP supplementation tended to decrease peak SAA (∼33%) relative to CON cows. Overall, although HS did not influence circulating white blood cells and neutrophils, SCFP increased circulating white blood cells and neutrophils by 9 and 26%, respectively, over CON in P2. In conclusion, HS initiated an acute phase protein response and feeding SCFP blunted the cortisol and SAA concentrations and altered some key leukocyte dynamics during HS.

Heat stress in dairy calves from birth to weaning

This Research Reflection collects current knowledge on the effects of heat stress in dairy calves. Chapters cover the concept of foetal programming, animal-based and environmental indicators of heat stress in the postnatal period, and methods of heat stress abatement. Conclusions for further research about economic efficiency, research methodology and an integrated approach of pre- and postnatal heat stress are also proposed.

Methods for assessing heat stress in preweaned dairy calves exposed to chronic heat stress or continuous cooling

Although dairy calves are more thermotolerant relative to mature cows, they are still susceptible to heat stress, as demonstrated by elevated physiological responses and reduced feed intake under high ambient temperature and relative humidity. However, indicators of heat stress have not been well-characterized in calves. Herein, we evaluated associations between environmental and thermoregulatory and productive animal-based indicators of heat stress in dairy calves exposed to chronic heat stress or continuous cooling in a subtropical climate. Holstein calves were exposed to heat stress (HT; shade of barn, n = 24) or continuous cooling (CL; shade of barn plus 2 fans, n = 24) from 2 to 42 d of age. Environmental indices, including ambient temperature, relative humidity, temperature-humidity index (THI), and wind speed, and animal-based indices, including respiration (RR), heart rate (HR), rectal (RT), and skin temperature (ST) were recorded thrice daily (0900, 1300, and 1900 h). Milk replacer (MI) and grain intakes were recorded daily from 15 to 42 d of age. Using segmented regression models, we then estimated THI thresholds for significant changes in physiological responses. We found a strong, positive correlation between animal-based indicators (except for HR, MI, and grain intakes) and ambient temperature and THI, with the highest correlation obtained with ST and THI (r ≥ 0.72). Ambient temperature and ST and ambient temperature or THI and MI were the only correlations that differed between treatments. The coefficient of determination (R²) obtained from regression analyses to model animal-based indicators was substantially improved by the inclusion of environmental indicators, with the greatest improvement achieved with THI. Overall, continuous cooling by fans promoted calf heat loss as CL calves had lower RR, RT, ST, and higher feed intake compared with HT calves. Temperature-humidity index breakpoints could be determined for RT (THI = 67), RR (THI = 65), and MI (THI = 82) in HT calves, and only for RR (THI = 69) in CL calves. Skin temperature variables had no detectable breakpoints in either treatment due to the strong linear relationship to THI. Collectively, our results suggest that ST is appropriate to estimate chronic heat stress and that THI is the best environmental indicator of heat stress in dairy calves raised in a shaded, subtropical environment. At a practical level, calves should be closely monitored when THI reaches 65 to 69 to minimize the risk of heat stress-related impairments.

Impact of thermal stress exposure on seminal quality, antioxidant defence system, TNF-α and TIMP-3 in Ossimi ram

Heat stress (HS) occupies huge importance nowadays as it leads to severe economic losses especially in livestock. Preserving sheep against HS is one of the governmental scopes where it represents huge percentage of global ruminant. The present research was conducted to study semen quality, some stress and inflammatory markers in Ossimi rams under both hot and mild climatic conditions. The current study was conducted on selected 46 ram samples divided into two groups during summer and winter. Semen analysis, testosterone (TES), cortisol (COR) and blood glucose (BG) levels, and lipid and protein profiles were done. Concentrations of tumour necrosis factor alpha (TNF-α), tissue inhibitor of metalloproteinase-3 (TIMP-3), nitric oxide (NO), malondialdehyde (MDA) and reduced glutathione (GSH) and specific activity of glutathione peroxidase (GPx) and superoxide dismutase (SOD) were assessed. The results in summer compared to winter revealed significant elevation of total defects and number of dead sperms; however, there was reduction in sperm total motility and concentration and external epididymal tail duct diameter. Histological study of epididymal tail lumen exhibited azoospermia. Further, TES, TIMP-3 and GSH levels were decreased and COR, TNF-α, NO and MDA were raised. Specific activities of GPx and SOD were also declined. Additionally, there was a significant increase in concentrations of BG and lipid profiles except high-density lipoprotein. Our data concluded that there were new insights into TNF-α and TIMP-3 as biomarkers can be used in diagnosis of sheep suffering from HS, but further studies are recommended to do in future work about such aspect.

Pre- and postnatal heat stress abatement affects dairy calf thermoregulation and performance

Prenatal heat stress during late gestation exerts long-term effects on growth and productivity of the dairy calf. Further, direct exposure to heat stress during the preweaning period impairs calf thermoregulation and performance. We examined the effects of heat stress abatement during the prenatal period, postnatal period, or both on calf performance. We hypothesized that calves exposed to pre- and postnatal heat stress abatement would perform most optimally in terms of thermoregulation, growth, and health responses when compared with calves that are heat-stressed at any time in the pre- or postnatal periods. Holstein calves born to heat-stressed (HT) or cooled (CL) dams during late gestation (44 ± 5 d; prenatal HT or CL) were exposed to heat stress or cooling postnatally for 56 d (postnatal HT or CL), resulting in 4 treatments: HT-HT, HT-CL, CL-HT, and CL-CL; n = 12/treatment. Calves were administered 4 L of pooled colostrum and after 2 d of age allotted 10 L/d milk replacer and up to 3 kg/d concentrate in automatic feeder group pens (n = 6/pen). Postnatal cooling was achieved by 2 fans (average wind speed 2 m/s). Thermoregulatory responses (respiration rate and heart rate; rectal, body, and skin temperature), feed intake, growth parameters including average daily gain and medication events were recorded, and blood samples were collected weekly. Thermoregulatory responses were lower in postnatal CL calves compared with postnatal HT. In the afternoon, HT-HT calves had the highest respiration rate and rectal temperature, HT-CL calves had the lowest respiration rate, and CL-HT calves had the lowest heart rate compared with the other treatment groups. Prenatal CL calves weighed more at birth and weaning with a tendency for greater average daily gain compared with prenatal HT calves, whereas postnatal CL calves had increased milk replacer and concentrate intake and a tendency for reduced fever, infection, and total medication events relative to postnatal HT. Prenatal HT calves were esophageal tube fed more often than prenatal CL. Blood hematocrit and 24-h serum IgG concentration were greater in prenatal CL calves relative to prenatal HT. Prenatal heat stress abatement improves weight gain, hematocrit, and immunoglobulin transfer, whereas postnatal heat stress abatement modulates thermoregulatory responses, feed intake, and calf health. This study is the first to characterize the combined effects of pre- and postnatal heat stress or active cooling on the dairy calf.

The impact of hair coat color on physiological variables, reproductive performance and milk yield of Holstein cows in a hot environment

Vulnerable animals to heat stress have been described as ones with dark or black hides due to increasing absorption of solar radiation. The effect of coat color in pluriparous contemporary Holstein cows in a hot environment (mean annual temperature 24.6 °C), on body surface temperature (infrared thermography), physiological and hematological variables as well as milk yield and reproductive performance was assessed using 178 Holstein pluriparous cows (74 predominantly white and 104 predominantly black). Data were collected in the morning and afternoon in July (mean temperature-humidity index 82 units). Body condition score at mid-lactation (128 ± 32 days in milk at the start of the experiment) was higher (P < 0.01) in predominantly white than in black cows (3.3 vs. 3.2). Respiration rate did not differ between groups (72 ± 23 vs. 73 ± 20 breaths/min for white and black cows, respectively, sampling time combined). In contrast, rectal temperature of black cows was 0.1 °C higher (P ≤ 0.01) than white cows, regardless of sampling time. The only significant hematologic change was a slight increase in mean corpuscular volume in black cows (54.7 fL, P < 0.01) compared to white cows (53.8 fL), but it remained within the reference range. Differences due to coat color did not alter body surface temperatures at any time of the day. Conception rates, services per conception, calving intervals and fetal losses were not associated with hair coat color, but cows with predominantly white coat produced 394 kg more (P < 0.01) fat-corrected milk in 305 days compared to cows with predominantly black coat. It was concluded that in this hot-arid environment with cows housed in facilities with extensive cooling, black hair coat moderately reduces 305-d milk yield without affecting milk composition, body surface temperature, and reproductive performance.

Exposure to heat-stress environment affects the physiology, circulation levels of cytokines, and microbiome in dairy cows

The microbiome has emerged as a new player on behavior, physiology and stress because of its significant effects on the brain-gut axis. The aim of this study was to increase our understanding of brain-gut function in dairy cows. We investigated the effects of a heat-stress (HS) environment and individual differences of heat sensitivity (IH) on bovine physiological characteristics and microbial composition. Results indicate that both HS and IH increased rectal temperature (RT) (P < 0.05). An HS environment increased plasma, as well as milk cortisol and cytokines in plasma; however, it decreased plasma, and milk oxytocin, triiodothyronine, and thyroxine (P < 0.05) levels. Exposure to an HS environment reduced the diversity of the fecal microbial population, and resulted in a higher expression of diseases, the environmental adaptation pathway, and the immune related pathway, whereas it lowered the expression of metabolic pathways (P < 0.05). High heat sensitive cows have upregulated metabolisms, environmental adaptation and cellular process pathways, and a downregulated neurodegenerative disease pathway (P < 0.05). Thus, we conclude that exposure to an HS environment modulates physiological characteristics, which may interplay with microbial activity, and in turn, alter the circulation levels of cytokines, implicating the role of the brain-gut axis in dairy cows. The HS environment affected physiological characteristics, cytokine levels, and microbial composition, but IH influenced RT and fecal microbial functions.