Heat Stress In Dairy Cows Research Articles

Developing a new thermal comfort prediction model and web-based application for heat stress assessment in dairy cows

Precise evaluation and prediction of heat stress on animals are largely studied, given their importance for reducing economic losses and improving animal welfare. There are serials of thermal comfort index models that attempt to quantify the severity of heat stress imposed on dairy cows. However, few index models involved the heat exchanges between cows and the environment. There is also no relevant online prediction and assessment tool for heat stress in dairy cows. The objective was of this study was to develop a new thermal comfort indicator, referred to as Skin Temperature Index for Cows (STIC), based on the heat balance equations and an integrative tool to predict and assess heat stress in dairy cows. Environmental and physiological data from a previous study was divided into the validation set (N = 902, accounting for 30%) and the evaluation set (N = 2103, 70%). We first derived the explicit expression for the theoretical model (Predicted Skin Temperature, PST) by simplifying the theoretical model and using nonlinear regression analysis. As verified by the validation set, the PST model showed an acceptable accuracy with the root mean square error of 1.165 °C, the mean absolute error of 0.918 °C, and the mean absolute percentage error of 2.62%. Then, the STIC model was obtained based on the upper and lower limits of skin temperature and the PST model. The results indicate that the determination of coefficient (R 2 ) of STIC for rectal temperature, respiration rate, skin temperature, eye temperature were 0.48, 0.71, 0.73, and 0.42, respectively. The STIC showed significantly higher prediction with the physiological responses than other thermal comfort indices (p < 0.05) with respect to rectal temperature (r = 0.69), skin temperature (r = 0.86), and eye temperature (r = 0.65). In addition, the STIC thresholds and the adjustments of cow-related factors (body posture, average daily milk yield, and stage of lactation) to the critical threshold were established based on temperature-humidity index thresholds. Further, we developed a web-based application, the Heat Stress Indicator Tool, for thermal comfort index calculation and visualization of the level of heat stress imposed on dairy cows. Overall, the PST and STIC models incorporate air temperature, relative humidity, solar radiation, wind speed and consider the interactions of environmental parameters based on the heat exchange theory. They are powerful in assessing the heat stress of cows and have great potential for serving as precise environmental control criteria in cow buildings. Moreover, the online tool is practical for researchers and dairy farm managers. • A thermal index, Skin Temperature Index for Cows (STIC), was developed. • STIC was based on the simplified heat balance model. • STIC includes air temperature, relative humidity, wind speed and solar radiation. • Through verification, STIC predicted the thermal comfort of dairy cows well. • A web-based app, the Heat Stress Indicator Tool, was developed.

SOD1 Gene Silencing Promotes Apoptosis and Suppresses Proliferation of Heat-Stressed Bovine Granulosa Cells via Induction of Oxidative Stress.

Heat stress (HS) compromises dairy cattle reproduction by altering the follicular dynamics, oocyte maturation, and normal physiological function of ovarian granulosa cells (GCs), eventually resulting in oxidative damage and cell apoptosis. To protect the cells from oxidative damage, the Superoxide dismutase-1 (SOD1) degraded the hydrogen peroxide (H2O2) to oxygen (O2) and water. The objective of the current study was to investigate the impact of SOD1 silencing on intracellular ROS accumulation, cell viability, MMP, hormone synthesis (P4, E2), cell proliferation, and apoptosis in GCs under HS. The mechanistic role of SOD1 regulation in the heat-stressed GCs was explored. SOD1 gene was successfully silenced in GCs and confirmed at both transcriptional and translational levels. We found that silencing of SOD1 using siRNA under HS aggravated intracellular accumulation of reactive oxygen species, apoptosis, disrupted the mitochondrial membrane potential (MMP), altered transition of the cell cycle, and impaired synthesis of progesterone (P4) and estrogen (E2) in GCs. The associative apoptotic, steroidogenic, and cell cycle genes (BAX, Caspase-3, STAR, Cyp11A1, HSP70, PCNA, and CyclinB1) were used to confirm the results. These results identify a novel role of SOD1 in the modulation of bovine ovarian GC apoptosis, which provides a target for improving the fertility of heat-stressed dairy cows in summer.

504 Late-Breaking: Automatic Monitoring Systems to Detect Behavioral and Productive Variations during Heat Stress in Dairy Cows

Abstract Aim of the project was to evaluate behavioral and productive variations of dairy cows detected by automatic monitoring systems, during different seasons. Environmental data (Temperature (T, °C), Relative Humidity, (RH, %) and Temperature and Humidity Index (THI)), were recorded inside the pens by electronic probes during 4 periods over 2 years, for a total of 473 days. Fans and sprinklers were activated at THI &amp;gt;60. Hundred lactating and dry cows were equipped with monitoring tag (Heatime-Pro, SCR Engineers Ltd.) that recorded continuously time (min/d) spent ruminating (RT), panting (PT) and feeding (FT). Daily PT and FT data were recorded as group average [lactating (LC) or dry], while RT and milk production were extracted as individual data. Four classes of environmental stress were identified based on maximum THI: comfort (C, THI &amp;lt; 60, 101d), moderate stress (MS, 60&amp;lt; THI &amp;gt;69, 92d), stress (S, 70&amp;lt; THI &amp;gt;75, 102d), severe stress (SS, THI &amp;gt;75, 178d). Behavioral and productive data were compared between classes. Data were analyzed by mixed model with repeated measures, with environmental class, group (dry or lactating), parity and interactions as fixed effect. Cow was included as random effect for RT and milk production. Means comparison was performed by Tukey post hoc test. All behavioral outcomes were influenced by heat stress (P &amp;lt; .001, table 1). Panting increased linearly with maximum THI recorded, being highest during SS days in LC (49.6 min/d, P &amp;lt; .001). FT and RT (min/d) were lowest (P &amp;lt; .001) during S days (206.9, FT and 473.1, RT) and RT reached the lowest values in cows within 15 DIM (456.4). Milk production was affected in multiparous cows, with a linear reduction from C to SS days (P &amp;lt; .001). Heat stress deeply affected cows behavior and performances, despite cooling systems. Automatic monitoring of these parameters can effectively help in detecting heat stress and consequently adopt strategies to improve animal welfare.

PSX-B-27 Physiological changes in grazing dairy cows at increasing temperatures under moderate climate conditions

Abstract The continuous direct exposure to solar radiation, coupled with their own metabolic heat production, make grazing dairy cows on pasture particularly susceptible to heat stress. Heat stress can impair performance, animal welfare, and health. The objective of the present study was to identify physiological indicators of heat stress in dairy cows in a pasture-based production system under moderate climate conditions. The study was performed with 24 lactating Holstein dairy cows during summer 2018 and 2019 at the experimental farm of Agroscope (Posieux, Switzerland). Cows grazed full-time using a set stocking system. Climate conditions were recorded every min and were used to calculate the comprehensive climate index (CCI), which reflects the felt temperature in °C. The vaginal temperature (VT) of each cow was measured every 10 minutes with temperature loggers and was used as a physiological indicator of heat stress. Blood and milk were sampled once daily in the afternoon before and during milking, respectively. The concentrations of thyroxine (T4) and triiodothyronine (T3) were analyzed in blood plasma and cortisol concentration was analyzed in milk. Data from 12 periods of up to 3 consecutive days with increasing CCI was analyzed. Analysis were performed with the averaged CCI and the maximal VT recorded between 0830 and 1430 h. The VTmax was positively correlated with CCIaverage (P &amp;lt; 0.001). The T4 and T3 concentrations decreased with increasing CCIaverage and VTmax (P &amp;lt; 0.01). Cortisol concentrations were positively correlated with CCIaverage and VTmax (P &amp;lt; 0.05). Changes in VT and hormones showed that cows responded to increasing environmental temperature and may have perceived the rising heat load as a stressor.

Evaluation of Thermal Indices as the Indicators of Heat Stress in Dairy Cows in a Temperate Climate.

Simple SummaryWhen the ambient temperature exceeds the upper limit of a certain temperature range, heat stress is triggered and then negatively affects the production, reproduction, health, and welfare of livestock animals. Due to the limitations of ambient temperature alone as a representative measure of the thermal environment, heat stress is commonly assessed by thermal indices, which contain two or more environmental parameters representing the influence of heat exchanges between the animal and its environment. To understand and utilize the thermal indices better, we evaluated several thermal indices commonly used in the heat stress assessment of dairy cows. We found that the comprehensive climate index (CCI), which includes air temperature, relative humidity, wind speed, and solar radiation, showed a better relationship with the animal-based indicators (i.e., rectal temperature, skin temperature, and eye temperature) of heat stress. According to the results of this study, the CCI has the potential to replace the temperature–humidity index in quantifying the severity of heat stress in dairy cows.Many thermal indices (TIs) have been developed to quantify the severity of heat stress in dairy cows. Systematic evaluation of the representative TIs is still lacking, which may cause potential misapplication. The objectives of this study were to evaluate the theoretical and actual performance of the TIs in a temperate climate. The data were collected in freestall barns at a commercial dairy farm. The heat transfer characteristics of the TIs were examined by equivalent air temperature change (ΔTeq). One-way ANOVA and correlation were used to test the relationships between the TIs and the animal-based indicators (i.e., rectal temperature (RT), respiration rate (RR), skin temperature (ST), and eye temperature (ET)). Results showed that the warming effect of the increased relative humidity and the chilling effect of the increased wind speed was the most reflected by the equivalent temperature index (ETI) and the comprehensive climate index (CCI), respectively. Only the equivalent temperature index for cows (ETIC) reflected that warming effect of solar radiation could obviously increase with increasing Ta. The THI and ETIC showed expected relationships with the RT and RR, whereas the CCI and ETIC showed expected relationships with the ST and ET. Moreover, CCI showed a higher correlation with RT (r = 0.672, p < 0.01), ST(r = 0.845, p < 0.01), and ET (r = 0.617, p < 0.01) than other TIs (p < 0.0001). ETIC showed the highest correlation with RR (r = 0.850, p < 0.01). These findings demonstrated that the CCI could be the most promising thermal index to assess heat stress for housed dairy cows. Future research is still needed to develop new TIs tp precisely assess the microclimates in cow buildings.

Development and evaluation of thermal models for predicting skin temperature of dairy cattle

Heat stress significantly impacts dairy production. Skin temperature (Tskin) is demonstrated to be critical to the thermal comfort of animals. The predictive models for Tskin of dairy cattle have great potential in guiding climate control systems in dairy barns to mitigate the heat stress of dairy cows efficiently. This study aimed to develop thermal models to predict the Tskin of dairy cows. Ten models were constructed based on integrating the existing models and formulas associated with the heat production and loss from the body surface and respiratory systems. The models were categorized into the two-layer and the three-layer models according to whether the core layer is included or not. The models were also categorized into the thermoregulatory and the mechanistic models based on the sub-model outside the skin surface. The prediction performances of the models were quantitively evaluated by comparing the predicted values with the Tskin measured by infrared thermography. 85 Holstein cows were included, and 453 infrared images that contained the mean and maximum Tskin were collected in this study. The root mean squared error (RMSE), mean absolute error (MAE), and coefficient of determination (R2) were adopted as the performance metrics. The results show that the two-layer mechanistic model, including the actual core-body temperature, performed best for the mean Tskin with RMSE, MAE, and R2 of 0.649, 0.516, and 0.891, respectively. The two-layer thermoregulatory model, incorporating the estimated core-body temperature, provided satisfactory prediction performance for the maximum Tskin with RMSE, MAE, and R2 of 0.770 °C, 0.580 °C, and 0.793, respectively. The models generally performed better under heat stress conditions of the temperature-humidity index ≥ 72, with all the performance metrics considered. Besides, in comparison to the mean Tskin, the maximum Tskin is less sensitive to environmental parameters but more correlated with the core-body temperature. It seems that the maximum Tskin is a more appropriate representation of skin temperature in dairy cattle than the mean Tskin.

Jejunal mucosa proteomics unravel metabolic adaptive processes to mild chronic heat stress in dairy cows

Climate change affects the duration and intensity of heat waves during summer months and jeopardizes animal health and welfare. High ambient temperatures cause heat stress in dairy cows resulting in a reduction of milk yield, feed intake, and alterations in gut barrier function. The objectives of this study were to investigate the mucosal amino acid, glucose and lactate metabolism, as well as the proteomic response of the small intestine in heat stressed (HS) Holstein dairy cows. Cows of the HS group (n = 5) were exposed for 4 days to 28 °C (THI = 76) in a climate chamber. Percentage decrease in daily ad libitum intake of HS cows was calculated to provide isocaloric energy intake to pair-fed control cows kept at 15 °C (THI = 60) for 4 days. The metabolite, mRNA and proteomic analyses revealed that HS induced incorrect protein folding, cellular destabilization, increased proteolytic degradation and protein kinase inhibitor activity, reduced glycolysis, and activation of NF-κB signaling, uronate cycling, pentose phosphate pathway, fatty acid and amino acid catabolism, mitochondrial respiration, ATPase activity and the antioxidative defence system. Our results highlight adaptive metabolic and immune mechanisms attempting to maintain the biological function in the small intestine of heat-stressed dairy cows.

Passive envelope solutions to aid design of sustainable livestock buildings in Mediterranean climate

The dairy cattle sector is responsible of significant greenhouse gas emissions such as methane, carbon dioxide, nitrous oxide. The reduction of heat stress of dairy cows plays a crucial role in the improvement of dairy productivity and avoid greenhouse emissions. In this study a parametric analysis about several traditional or innovative passive solutions for building envelope of livestock housing is carried out, with the aim to achieve the thermal comfort of animals without active energy systems.The different energy efficiency measures designed for the building envelope are evaluated on the basis of different indexes for animal comfort, by means of the combination of the Building Energy Performance Simulations (BEPS) and computational fluid dynamics (CFD) simulations.The proposed method starts from the numerical model definition of a semi-closed, naturally ventilated, loose housing system, characterized by criteria traditionally recognized or accepted by the scientific community for designing a dairy cow housing. Different interventions, referred to the shape of the building and its envelope materials, are taken into account, such as cool materials or cross laminated timber, as well as polyurethane insulation or shading systems.Basing on the both temperature-humidity index (THI) and black globe temperature humidity index (BGHI) the optimal building envelope solutions are: opening ridge area with 1.8 m width, window to wall ratio equal to 79%, roof made by polyurethane foam with a slope of 15°. The environmental indexes calculated by means of BEPS numerical models simpler than CFD analysis bring a difference in results by a maximum of 18%.The results can support the decision-making process in the design of a sustainable barn for dairy cows taking animals welfare as reference. Moreover, the methodological approach could be easily replicated for other livestock type or other climatic zones.

Maternal heat stress reduces body and organ growth in calves: Relationship to immune status

Late-gestation heat stress of dairy cows reduces fetal growth and influences postnatal performance and immune status of the offspring. Our first objective was to evaluate the effect of in utero heat stress on overall fetal and organ growth, particularly organs associated with immune function. The second objective was to examine the cellular mechanism of altered passive immunity in neonatal bull calves after in utero heat stress. Specifically, we examined the rate of apoptosis of intestinal cells early in life, as it is associated with gut closure. Dams were dried off approximately 45 d before expected calving and randomly assigned to 1 of 2 treatments: heat stress (HT) or cooling (CL). During the dry period all cows were housed under shade in a freestall barn, where the pen for CL cows was equipped with active cooling, including water soakers and fans, whereas the pen for HT cows had no soakers or fans. Using rectal temperature and respiration rate as indicators, heat stress was severe. Average rectal temperature in HT cows was 39.3°C compared with 39.0°C in CL cows, and HT cows had a respiration rate of 66.7 breaths/min compared with 43.2 breaths/min for CL cows. Bull calves (n = 30) were immediately separated from their dams at birth, weighed, and then killed before colostrum feeding (n = 5/treatment; d 0) or at 1 or 2 d of age following colostrum feeding (n = 5/treatment per day). After slaughter, the small intestine was removed and weighed, and samples from the jejunum were fixed for immunohistochemistry. Birth weight of bulls from HT dams was 1.1 kg lower than that of bulls from CL dams. Thymus, spleen, and heart weights of HT bulls were lower relative to those of CL bulls, whereas liver weight of HT bulls tended to be lower relative to that of CL bulls. Jejunal cell apoptosis decreased with age in both HT and CL calves after birth, mirroring gut closure. However, in utero heat stress increased the apoptotic rate in the jejunum, particularly at birth. We conclude that the chronic exposure to heat strain of HT compared with CL dams in late gestation significantly affected fetal growth and immune tissue development, which may be associated with reduced immune function in early life. Also, late-gestation heat stress increased calves' intestinal apoptosis in the first 2 d of life, which might explain the decreased IgG uptake and limited passive immune competence observed in previous studies.

Heat stress in dairy cows

This review includes an analysis of the literature on various influencing factors influencing heat stress in lactating dairy cows and the way it affects milk production. Signs and symptoms of heat stress in cows are reduced feed consumption and decreased milk yield, elevated breathing rate, increased body temperature and reduced reproductive overall performance. There are other problems for example, a seasonal growth in bulk tank somatic cell counts. The birth weight is decreased in cows which have been exposed to heat stress throughout the dry length. It is established that the most critical is the heat accumulated via direct radiation from the solar. It was found out that high feed consumption results in raised metabolic heat increment. High metabolic warmness increment requires powerful thermoregulatory mechanisms to maintain body temperature in a thermoneutral area and in physiological homeostasis. It is confirmed that heat stress is complicated because the responses to heat stress have an effect on not best the energy stability, but also water, sodium, potassium and chlorine metabolism. Plasma progesterone degrees may be elevated or reduced depending on whether or not the heat pressure is acute or chronic. Water, sodium, potassium and chlorine are vital constituents of sweat, and sweating is a chief, if not the most important, thermoregulatory mechanism used to burn up extra body heat. Strategies to reduce heat stress must be evolved to enable cows to express their full genetic ability. Key words: dairy cows, heat stress, thermoregulatory mechanism, water, feed consumption, mineral elements.

Performance of roof-mounted misting fans to regulate heat stress in dairy cows.

Heat stress can negatively affect cow's physiology, behavior, and milk production. This study evaluates the effectiveness of roof mounting misting fans to improve heat and humidity index which reduces heat stress in a cowshed. Local climatic conditions were monitored and cooling system ability to control heat stress were assessed. Measurements were conducted at different cooling zones and levels comparing with shaded and open zones. The temperature and humidity index measurements outside the cowshed THIout showed that animals exposed to high degrees of heat stress during most of the day. The average value of THIout was 87.49, whereas the average value of adjusted outside temperature and humidity index THIadj was greater than THIout by 10% when solar radiation was considered. The maximum difference of hourly averages for temperature and humidity indices THIadj and THI occurred at noon when the intensity of solar radiation was highest. The average value for temperature and humidity index under misting fans THIfan was 82.27 whereas inside the cowshed under shade THIshade was 85.20. This conclude that the misting fans was able to reduce heat stress in a limited degree. Further improvement in terms of the cowshed design aspects and an increase of cooling efficiency is needed.

Spatio-Thermal Variability and Behaviour as Bio-Thermal Indicators of Heat Stress in Dairy Cows in a Compost Barn: A Case Study.

Simple SummaryThe thermal distribution inside a compost-bedded pack barn and the behavioural aspects plays an important role in terms of welfare and sustainability for dairy cows. Through a spatial variability assessment of thermal conditions in a compost barn, we found different regions with comfortable or stressful conditions based on air and bed temperature, as well as wind speed. Regarding the behaviour of cows with different number of lactations, we observed a higher probability of water intake in primiparous cows and increased walking behaviour in multiparous cows during the hottest periods. We suggest that special attention must be given to environmental control in a compost barn, mainly during hot seasons, to avoid different hot spots inside the facility. Additionally, with unbalanced environmental resources, the hierarchy of multiparous over primiparous cows might predominate the alleviation of the herd’s thermal stress.The spatial variability and behavioural aspects of compost-bedded pack barns remain unknown in subtropical regions. In this study, we investigated whether spatial variability occurs in the thermal environment of a compost barn and how the behaviour of dairy cows with different numbers of lactations differs in this system. The spatial sampling design comprised a grid of 108 locations inside the facility. At each location, we measured air temperature, relative humidity, wind speed, and bed temperature at 9:00, 12:00, and 15:00. We performed 24-h behavioural observations. Regarding spatial variability, the north face showed high air temperature values, and the distribution of relative humidity varied from the north to the south face. Kriging maps revealed a high bedding temperature trend, indicating heterogeneous ventilation management. Primiparous cows visited the water trough during the hottest hours of the day, whereas multiparous cows displayed a higher probability of walking during these periods. In conclusion, we observed a heterogeneous management of ventilation through the spatial distribution of the thermal environment inside the compost-bedded pack barn, with multiparous cows exhibiting dominance over primiparous cows seeking environmental resources.

Early embryo losses, progesterone and pregnancy associated glycoproteins levels during summer heat stress in dairy cows.

Objectives of this study were to characterize the effects of heat stress on pregnancy associated glycoproteins (PAG) and progesterone and its involvement in embryo survival. In trial 1, blood samples collected from days 29 to 36 post insemination were examined for the comparison of PAG concentrations between winter (n = 3721) and summer (n = 2388). In trial 2, embryo losses were assessed in winter (n = 144) and in summer (n = 133), in days 31 or 32 of pregnancy. Pregnancy diagnosis was carried out by ultrasonography on days 24 or 25, and it was repeated a week later; in the second occasion PAG concentration was also determined. In trial 3 the PAG and progesterone concentrations were assessed in days 33 to 36 in winter and summer. In trial 1 PAG levels did not differ between winter and summer, the conception rate and the proportion of uncertain pregnancies were higher in winter than summer. The likelihood of pregnancy was 10 to 15% higher in winter. In trial 2, the embryo death rate was higher in summer, but the PAG levels of cows that had embryo loss in summer were higher than those in winter. In both seasons, lower PAG levels were associated with higher risk of pregnancy loss, while embryo death was five times more likely to occur in summer than in winter and lower PAG concentrations were positively associated with higher risk of embryo loss. In trial 3, mean PAG levels were higher and of progesterone were lower during the summer than during the winter. We infer that despite the devastating effects of heat stress on cows' fertility, those early embryos that survive under continuous heat stress can form a well-functioning placenta; hence, the high embryo mortality rate observed during the summer months could be mainly attributed to luteal insufficiency.

Dietary supplementation of acetate-conjugated tryptophan alters feed intake, milk yield and composition, blood profile, physiological variables, and heat shock protein gene expression in heat-stressed dairy cows.

The purpose of this study was to investigate the effects of dietary supplementation of rumen-protected tryptophan (RPT) at four levels on milk yield, milk composition, blood profile, physiological variables, and heat shock protein gene expression in dairy cows under conditions of moderate-severe heat stress (MSHS, THI=80~89). Sixteen early-lactating dairy cows (body weight=719±66.4kg, days in milk=74.3±7.1, milk yield=33.55±3.74kg, means±SEM) were randomly assigned in a factorial arrangement to one of the four treatments: control group (n=4, no RPT supplementation), 15g/d RPT (n=4), 30g/d RPT (n=4), or 60g/d RPT group per cow (n=4) supplemented to the TMR. A higher dry matter intake (DMI) and milk yield were found in the 30g RPT group compared with the other groups, and the 3.5% fat-corrected milk yield, energy-corrected milk yield, milk fat, protein, β-casein, mono-unsaturated fatty acid, and poly-unsaturated fatty acid contents, and serum glucose content were observed in the 30g RPT group (p<0.05). The milk lactose concentration was significantly higher in the 30g RPT group compared with the control and 60g RPT groups (p<0.05). The plasma cortisol level was lower, while the serotonin and melatonin concentrations were higher in the 30g group compared with the other groups (p<0.05). Heat shock protein (HSP) 70 expression was downregulated in the control and 15g RPT groups, whereas the expression of HSP90 and HSPB1 remained unchanged among the groups. In particular, the 30g RPT group was considered to have an improved DMI, milk yield, and lactose concentration, as well as anti-heat stress effects due to the simulation of serotonin and melatonin during MSHS.

The effects of the ratio of pellets of wheat and barley grains to ground corn grain in the diet on sorting and chewing activities of heat stressed dairy cows.

BackgroundNormal feeding behaviours is one of the criteria of the health condition of dairy cows particularly in the condition of heat stress.ObjectiveThe study evaluated the effects of the ratio of pellets of wheat and barley grains to ground corn grain on sorting activity and chewing behaviour of lactating dairy cows managed under ambient conditions including natural heat stress events.Materials and MethodsNine multiparous cows (650 ± 56 kg Body Weight; mean ± SD) averaging 102 ± 13 days in milk and producing 54 ± 6 kg/d were randomly assigned to a triplicate 3 × 3 Latin square. During each 21‐d period, cows received one of three total mixed rations as dietary treatments. The dietary treatments were three ratio of pellets (containing 50% ground wheat and 50% ground barley): ground corn on a dry matter (DM) basis: 1) 33.3:66.6 (low); 2) 66.6:33.3 (medium); and 3) 100:0 (high). During the experiment, the ambient temperature‐humidity index was equal or more than 72, indicating that the cows were predisposed to heat stress condition.ResultsIncreasing the proportion of wheat‐barley pellets in the diet had a minimal effect on sorting index of different particles during the first 6 h of the day. However, later in the day (6‐18h), sorting against long particles (particles >19 mm) and in favour of fine particles (particles <1.18 mm) linearly increased with increasing the proportion of pellet; as a result overall daily sorting against long particles was increased with increasing the proportion of pellets. Although the average of daily eating and rumination was not affected by the treatments in the day times with high ambient THI, time spent for eating and rumination was low and eating time had more fluctuation for diet contained a high level of pellets.ConclusionIncreasing the proportion of pellets of barley and wheat grains in the diet under conditions of heat stress caused more fluctuation in daily eating behaviour and cows were predisposed to sort against long particles.

Telomere attrition rates are associated with weather conditions and predict productive lifespan in dairy cattle

Telomere length is predictive of adult health and survival across vertebrate species. However, we currently do not know whether such associations result from among-individual differences in telomere length determined genetically or by early-life environmental conditions, or from differences in the rate of telomere attrition over the course of life that might be affected by environmental conditions. Here, we measured relative leukocyte telomere length (RLTL) multiple times across the entire lifespan of dairy cattle in a research population that is closely monitored for health and milk production and where individuals are predominantly culled in response to health issues. Animals varied in their change in RLTL between subsequent measurements and RLTL shortened more during early life and following hotter summers which are known to cause heat stress in dairy cows. The average amount of telomere attrition calculated over multiple repeat samples of individuals predicted a shorter productive lifespan, suggesting a link between telomere loss and health. TL attrition was a better predictor of when an animal was culled than their average TL or the previously for this population reported significant TL at the age of 1 year. Our present results support the hypothesis that TL is a flexible trait that is affected by environmental factors and that telomere attrition is linked to animal health and survival traits. Change in telomere length may represent a useful biomarker in animal welfare studies.

Genome-wide identification and functional prediction of circular RNAs in response to heat stress in Chinese Holstein cows

Heat stress (HS) leads to substantial economic loss of dairy industry each year. The negative effect of HS in dairy cows is becoming one of the more urgent issue due to accelerating side-effects of global warming. Various genes are involved in HS response but the information about the role of noncoding RNAs, especially circular RNAs (circRNAs) is largely unknown. In our study, we aimed to investigate the different expression profile of circRNAs between HS and Non-heat-stressed condition (NC) of Chinese Holstein cow’s mammary gland. CircRNAs were identified using RNA sequencing and bioinformatics analysis. In total, 37405 circRNAs were detected and 95 were differentially expressed (DE), including 15 downregulated and 80 upregulated circRNAs in HS group compared to NC. Eight circRNAs were randomly selected to verify the RNA sequencing result. Further, Sanger sequencing validated the backsplicing site of the eight circRNAs. Moreover, results obtained from the Quantitative real time PCR (qRT-PCR) showed consistent expression trend with that of RNA sequencing. GO annotation and KEGG analysis suggested that these DE circRNAs probably involved in the energy metabolic regulation. Furthermore, we constructed ceRNA network and the result indicated that these DE circRNAs could regulate lactation through IGF1 and PRL signaling pathway.

Effects of bamboo leaf extract on the production performance, rumen fermentation parameters, and rumen bacterial communities of heat-stressed dairy cows.

ObjectiveAn experiment was conducted to evaluate the effects of bamboo leaf extract (BLE) on the production performance, rumen fermentation parameters, and rumen bacterial communities of heat-stressed dairy cows.MethodsThe experiment comprised a 14-day adaptation period and a 21-day experimental period and was conducted in a high-temperature and humidity environment (daily mean ambient temperature = 33.5°C±1.3°C; daily mean relative humidity = 64.9%±0.8%, daily mean temperature-humidity index = 86.2±0.4). Twelve Holstein dairy cows were randomly allocated into two groups. A total mixed ration supplemented with BLE at 0 (CON) and 1.3 g/kg dry matter (DM) were fed, respectively. Feed intake and milk yield were recorded daily. Milk samples were collected on 1, 11, and 21 d of the experimental period to analyze milk performance. Rumen fluid samples were collected on 21 d of the experimental period to analyze rumen fermentation parameters and rumen bacterial communities.ResultsCompared with the control group, supplementation of BLE increased milk yield (p<0.01), milk fat yield (p = 0.04), 4% fat-corrected milk (p<0.01) and milk fat content (p<0.01); reduced somatic cell count (p<0.01). No differences in DM intake and milk protein or lactose content were observed between two groups. Supplementation of BLE also increased the rumen total volatile fatty acid (p<0.01), acetate (p<0.01), butyrate (p<0.01), and valerate (p = 0.05) concentrations. However, no significant effects were observed on rumen pH, ammonia nitrogen, propionate, acetate/propionate ratio, isobutyrate, or isovalerate. Furthermore, BLE increased the rumen bacterial abundance and the diversity of the rumen bacterial community. The BLE reduced the Firmicutes/Bacteroidetes abundance ratio and increased the abundances of Butyrivibrio_2 (p<0.01) and Ruminococcus_2 (p<0.01).ConclusionThe BLE supplementation at 1.3 g/kg DM could improve production performance and rumen fermentation in dairy cows during heat stress.

85 The effects of heat exposure on the growth and developmental competence of oocytes derived from early antral follicles in dairy cows

Summer heat stress in dairy cows impairs the developmental competence of oocytes from antral follicles (2–8mm) which are used in conventional IVM and IVF systems. Moreover, summer heat stress is considered to impair the oocyte competence derived from smaller follicles; therefore, the impairment of oocyte competence possibly continues into the cooler autumn season. To investigate the thermosensitivity of early antral follicles (&amp;lt;1mm), we evaluated the effects of heat exposure on the growth and developmental competence of oocytes using invitro culture of oocyte–cumulus-granulosa complexes (OCGCs) derived from early antral follicles. OCGCs (n=315) were collected from early antral follicles (0.5–1mm) and cultured for 12 days. OCGCs in the heat shock group were cultured using a temperature cycle of 38.5°C for 5h, 39.5°C for 5h, 40.5°C for 5h, and 39.5°C for 9h, whereas those in the control group were cultured at a constant temperature of 38.5°C for 24h. The diameters of oocytes were measured before culture. Half of the culture medium was replaced every 4 days. Oestradiol-17β (E2) and progesterone (P4) production during the first, second, and third 4-day periods were measured by enzyme immunoassay; the viability of OCGCs was evaluated based on their morphology. Oocytes that survived after 12 days of culture (n=191) were subjected to IVM (38.5°C, 22h); their diameter and nuclear status were evaluated. Some oocytes (n=71) were subjected to IVF (38.5°C, 18h) and embryo culture (39.0°C, 150h). Cleavage and blastocyst rates were evaluated at 48h and 168h after IVF. Effects of treatment groups and culture periods on E2 and P4 production and diameters of oocytes were evaluated by two-way ANOVA followed by Tukey-Kramer or Student’s t-test. The viability of OCGCs, nuclear maturation, cleavage and blastocyst rates between two groups were compared by the chi-squared or Fisher’s exact test. E2 and P4 production and the viability of OCGCs were not different between the 2 groups. Although mean oocyte diameters before culture did not differ between the 2 groups, the mean diameters after IVM were significantly smaller in the heat shock group (108.0µm, n=56) than in the control group (111.7µm, n=61; P&amp;lt;0.05). The nuclear maturation rate in the heat shock group (36.4%, n=55) was significantly lower than in the control group (60.3%, n=58; P&amp;lt;0.05). Cleavage rates were similar between the control (54.5%, n=33) and heat shock groups (45.7%, n=35). However, no oocytes developed to blastocysts in the heat shock group (0%, n=35), whereas 30.3% (n=33) oocytes developed to blastocysts (cell number±s.d.; 92.4±28.4) in the control group (P&amp;lt;0.05). These findings suggest that summer heat stress in dairy cows impairs the growth, nuclear maturation, and developmental competence of oocytes derived from early antral follicles. This experimental model could be used to explore the mechanisms by which heat stress subsequently impairs oocyte competence during the cooler autumn season.

Dynamic cooling strategy based on individual animal response mitigated heat stress in dairy cows

Technological progress enables individual cow's temperatures to be measured in real time, using a bolus sensor inserted into the rumen (reticulorumen). However, current cooling systems often work at a constant schedule based on the ambient temperature and not on monitoring the animal itself. This study hypothesized that tailoring the cooling management to the cow's thermal reaction can mitigate heat stress. We propose a dynamic cooling system based on in vivo temperature sensors (boluses). Thus, cooling can be activated as needed and is thus most efficacious. A total of 30 lactating cows were randomly assigned to one of two groups; the groups received two different evaporative cooling regimes. A control group received cooling sessions on a preset time-based schedule, the method commonly used in farms; and an experimental group, which received the sensor-based (SB) cooling regime. Sensor-based was changed weekly according to the cow's reaction, as reflected in the changes in body temperatures from the previous week, as measured by reticulorumen boluses. The two treatment groups of cows had similar milk yields (44.7 kg/d), but those in the experimental group had higher milk fat (3.65 vs 3.43%), higher milk protein (3.23 vs 3.13%), higher energy corrected milk (ECM, 42.84 vs 41.48 kg/d), higher fat corrected milk 4%; (42.76 vs 41.34 kg/d), and shorter heat stress duration (5.03 vs 9.46 h/day) comparing to the control. Dry matter intake was higher in the experimental group. Daily visits to the feed trough were less frequent, with each visit lasting longer. The sensor-based cooling regime may be an effective tool to detect and ease heat stress in high-producing dairy cows during transitional seasons when heat load can become severe in arid and semi-arid zones.