Estimation of genetic parameters for heat stress,including dominance gene effects,on milk yield in Thai Holstein dairy cattle

Heat stress in tropical regions is a major cause that strongly negatively affects to milk production in dairy cattle. Genetic selection for dairy heat tolerance is powerful technique to improve genetic performance. Therefore, the current study aimed to estimate genetic parameters and investigate the threshold point of heat stress for milk yield. Data included 52 701 test‐day milk yield records for the first parity from 6247 Thai Holstein dairy cattle, covering the period 1990 to 2007. The random regression test day model with EM‐REML was used to estimate variance components, genetic parameters and milk production loss. A decline in milk production was found when temperature and humidity index (THI) exceeded a threshold of 74, also it was associated with the high percentage of Holstein genetics. All variance component estimates increased with THI. The estimate of heritability of test‐day milk yield was 0.231. Dominance variance as a proportion to additive variance (0.035) indicated that non‐additive effects might not be of concern for milk genetics studies in Thai Holstein cattle. Correlations between genetic and permanent environmental effects, for regular conditions and due to heat stress, were ? 0.223 and ? 0.521, respectively. The heritability and genetic correlations from this study show that simultaneous selection for milk production and heat tolerance is possible.     

A new heat load index for feedlot cattle

The ability to predict the effects of extreme climatic variables on livestock is important in terms of welfare and performance. An index combining temperature and humidity (THI) has been used for more than 4 decades to assess heat stress in cattle. However, the THI does not include important climatic variables such as solar load and wind speed (WS, m/s). Likewise, it does not include management factors (the effect of shade) or animal factors (genotype differences). Over 8 summers, a total of 11,669 Bos taurus steers, 2,344 B. taurus crossbred steers, 2,142 B. taurus x Bos indicus steers, and 1,595 B. indicus steers were used to develop and test a heat load index (HLI) for feedlot cattle. A new HLI incorporating black globe (BG) temperature ( degrees C), relative humidity (RH, decimal form), and WS was initially developed by using the panting score (PS) of 2,490 Angus steers. The HLI consists of 2 parts based on a BG temperature threshold of 25 degrees C: HLI(BG>25) = 8.62 + (0.38 x RH) + (1.55 x BG) - (0.5 x WS) + e((2.4-WS)), and HLI(BG<25) = 10.66 + (0.28 x RH) + (1.3 x BG) - WS, where e is the base of the natural logarithm. A threshold HLI above which cattle of different genotypes gain body heat was developed for 7 genotypes. The threshold for unshaded black B. taurus steers was 86, and for unshaded B. indicus (100%) the threshold was 96. Threshold adjustments were developed for factors such as coat color, health status, access to shade, drinking water temperature, and manure management. Upward and downward adjustments are possible; upward adjustments occur when cattle have access to shade (+3 to +7) and downward adjustments occur when cattle are showing clinical signs of disease (-5). A related measure, the accumulated heat load (AHL) model, also was developed after the development of the HLI. The AHL is a measure of the animal's heat load balance and is determined by the duration of exposure above the threshold HLI. The THI and THI-hours (hours above a THI threshold) were compared with the HLI and AHL. The relationships between tympanic temperature and the average HLI and THI for the previous 24 h were R(2) = 0.67, P < 0.001, and R(2) = 0.26, P < 0.001, respectively. The R(2) for the relationships between HLI or AHL and PS were positive (0.93 and 0.92 for HLI and AHL, respectively, P < 0.001). The R(2) for the relationship between THI and PS was 0.61 (P < 0.001), and for THI-hours was 0.37 (P < 0.001). The HLI and the AHL were successful in predicting PS responses of different cattle genotypes during periods of high heat load.     

Genetic evaluation of heat tolerance in Holstein cows in Japan

We used test‐day records and daily records from provincial weather stations in Japan to evaluate heat tolerance (HT) in Holstein cows according to a random regression test‐day model. Data were a total of 1,641,952 test‐day records for heritability estimates and 17,245,694 test‐day records for genetic evaluation of HT by using milk yield and somatic cell score (SCS) in Holstein cows that had calved for the first time in 2000 through 2015. Temperature–humidity index (THI) values were estimated by using average daily temperature and average daily relative humidity records from 60 provincial Japanese weather stations. The model contained herd–test‐day, with lactation curves on days in milk within month–age group as a fixed effect. General additive genetic effect and HT of additive genetic effect were included as random effects. The threshold value of THI was set to 60. For milk yield, estimated mean heritabilities were lower during heat stress (THI = 78; 0.20 and 0.28) than when below the heat stress threshold (THI ≤ 60; 0.26 and 0.31). For SCS, heritability estimates (range 0.08–0.10) were similar under all heat stress conditions. Genetic trends of HT indicated that EBVs of HT are changing in an undesirable direction.     

Ruminant heat stress: effect on production and means of alleviation

A review of the literature indicates heat stress generally causes lower milk production, decreased growth rate for cattle and lambs, but little effect on wool production. Breed and diet affects the degree of adverse response. Heat stress is caused primarily by high air temperature, but can be intensified by high humidity, thermal radiation and low air movement. Improving performance of animals under warm conditions involves breeding and management and modifying the environment. The former includes selection for heat tolerance, use of crossbred animals, diets with low heat increment in relation to energy for production and control of diseases and parasites. Environmental modifications may include provision of shades, use of water for evaporative cooling and increased air movement.     

Conception rate of Holstein and Japanese Black cattle following embryo transfer in southwestern Japan

This study aimed to quantify and compare conception rates to embryo transfer (ET) of Holstein and Japanese Black cattle in southwestern Japan. A 10‐year retrospective epidemiological survey was conducted. The recipient numbers for Holstein and Japanese Black cattle was 621 and 527, respectively. Conception rates of Holstein and Japanese Black cattle during the study period were 45.4% and 42.3%, respectively. There was no significant difference between both breeds. However, a different trend of conception rate to ET in Holstein and Japanese Black cattle was observed. In Holstein cattle, conception rate in August to October was lower than in the other months and was significantly lower (p < .05) than in April. Particularly, conception rate in October of Holstein cattle was the lowest (31.0%). In Japanese Black cattle, conception rates in December (24.2%) and January (31.3%) were lower than in the other months. Conception rate of Japanese Black cattle declined as the temperature–humidity index (THI) decreased, exhibiting significantly lower levels in the ≤45 THI class than in any other THI class (p < .05). By contrast, in Holstein cattle, no relationship was observed between conception rate and THI on the day of ET. These observations suggest the importance of appropriate management that considers seasonal reactivity in each breed.     

Effect of Heat Stress on Milk Production,Rectal Temperature,Respiratory Rate and Blood Chemistry in Holstein,Jersey and Australian Milking Zebu Cows

The effect of heat stress on changes in milk production, rectal temperature, respiratory rate and blood chemistry was evaluated in three groups of six mature Holstein, Jersey and Australian Milking Zebu (AMZ) dairy cows. These animals were subjected to a cool environment when the mean temperature-humidity index (THI) was 72+/-1.4 (dry bulb temperature of 22.2-24.4 degrees C and relative humidity of 100-60%) during the month of December. This experiment was repeated during the hotter month of July of the following year, when the mean THI was 93+/-3.1 (dry bulb temperature of 35.6-43.9 degrees C and relative humidity 95-35%). Holstein cows produced more (p <0.01) milk than AMZ and Jersey cows during the cooler months of the year and all the cows were dry during the hotter months from June until September. Heat stress increased (p<0.01) rectal temperature and respiratory rate in all three breeds. Heat stress had no effect on blood pH in Holstein and AMZ cows but lowered (p <0.01) blood pH from 7.42 to 7.34 in Jersey cows. In addition, heat stress lowered (p <0.01) blood pCO2 (kPa), bicarbonate (HCO3, mmol/L), base excess (BE, mmol/L) and plasma chloride (Cl-, mmol/L) in all three breeds. The total haemoglobin (THb, g/dl) was elevated (p <0.01) in all three breeds when they were subjected to heat stress. Heat stress increased (p<0.01) oxygen saturation (O2SAT, %) in Jersey and AMZ cows but lowered it (p <0.01) in Holstein cows. On the other hand, heat stress increased (p <0.01)pO2 (kPa) in Holstein and Jersey cows but lowered it (p <0.01) in AMZ cows. Heat stress increased (p <0.01) plasma potassium (K, mmol/L) and calcium (Ca, mmol/L) only in Holstein and Jersey cows but lowered them (p<0.01) in AMZ cows. The plasma glucose (GLU, mmol/L) increased (p<0.01) with heat stress in Holstein and AMZ cows but decreased (p <0.01) in Jersey cows. Heat stress increased (p<0.01) plasma creatinine (CR, (mol/L) but lowered (p<0.01) plasma creatinine phosphokinase (CPK, IU/L), aspartate aminotransferase (AST, IU/L) and blood urea nitrogen (BUN, mmol/L) in all three breeds. These results indicate that heat-stressed Holstein and AMZ cows were able to maintain their acid-base balance with a marginal change in their pH of 0.02 when their rectal temperatures increased by 0.47 and 0.38 degrees C, respectively. When heat stress increased the rectal temperature in Jersey cows by 0.70 degrees C, the pH decreased (p<0.01) from 7.42 to 7.34. However, even with this decrease 0.08 the pH is still within the lower physiological limit of 7.31.     

相对湿度对家禽水蒸发散热和健康的影响

相对湿度(RH)作为温热环境的重要因素之一,与温度和风速等共同影响家禽的热平衡状态。当RH适宜时,蒸发散热(EHL)达到最大;高温环境下,高湿会阻碍家禽的EHL,从而造成体温上升、呼吸加快、食欲下降,严重时导致酸碱平衡紊乱、热虚脱和呼吸性碱中毒。本文主要综述水蒸发散热(EWL)在家禽热平衡调节中的重要作用,及RH对家禽EWL的影响,并结合由此而引发的对家禽健康的影响,探讨RH在家禽实际生产中的重要作用。     

Environmental factors influencing heat stress in feedlot cattle

Data from 3 summer feedlot studies were utilized to determine the environmental factors that influence heat stress in cattle and also to determine wind speed (WSPD; m.s(-1)) and solar radiation (RAD; W.m(-2)) adjustments to the temperature-humidity index (THI). Visual assessments of heat stress, based on panting scores (0 = no panting to 4 = severe panting), were collected from 1400 to 1700. Mean daily WSPD, black globe temperature at 1500, and minimums for nighttime WSPD, nighttime black globe THI, and daily relative humidity were found to have the greatest influence on panting score from 1400 to 1700 (R2 = 0.61). From hourly values for THI, WSPD, and RAD, panting score was determined to equal -7.563 + (0.121 x THI) - (0.241 x WSPD) + (0.00082 x RAD) (R2 = 0.49). Using the ratio of WSPD to THI and RAD to THI (- 1.992 and 0.0068 for WSPD and RAD, respectively), adjustments to the THI were derived for WSPD and RAD. On the basis of these ratios and the average hourly data for 1400 to 1700, the THI, adjusted for WSPD and RAD, equals [4.51 + THI - (1.992 x WSPD) + (0.0068 x RAD)]. Four separate cattle studies, comparable in size, type of cattle, and number of observations to the 3 original studies, were utilized to evaluate the accuracy of the THI equation adjusted for WSPD and RAD, and the relationship between the adjusted THI and panting score. Mean panting score derived from individual observations of black-hided cattle in these 4 studies were 1.22, 0.94, 1.32, and 2.00 vs. the predicted panting scores of 1.15, 1.17, 1.30, and 1.96, respectively. Correlations between THI and panting score in these studies ranged from r = 0.47 to 0.87. Correlations between the adjusted THI and mean panting score ranged from r = 0.64 to 0.80. These adjustments would be most appropriate to use, within a day, to predict THI during the afternoon hours using hourly data or current conditions. In addition to afternoon conditions, nighttime conditions, including minimum WSPD, minimum black globe THI, and minimum THI, were also found to influence heat stress experienced by cattle. Although knowledge of THI alone is beneficial in determining the potential for heat stress, WSPD and RAD adjustments to the THI more accurately assess animal discomfort.     

Length of lags in responses of milk yield and somatic cell score on test day to heat stress in Holsteins

We used daily records from provincial Japanese weather stations and monthly test‐day records of milk production to investigate the length of the lags in the responses of cows’ milk yield and somatic cell score (SCS) to heat stress (HS). We also investigated the HS thresholds in milk yield and SCS. Data were a total of 17,245,709 test‐day records for milk and SCS in Holstein cows that had calved for the first time between 2000 and 2015, along with weather records from 60 weather stations. Temperature–humidity index (THI) values were estimated by using average daily temperature and average daily relative humidity. Adjusted THI values were calculated by using temperature, relative humidity, wind speed, and solar radiation. The model contained herd, calving year, month of test day, age group, days in milk, and THI as a fixed effect. THIs for each day from 14 days before the test day until the test day were used to represent the HS effects. The HS occurring 3 days, and between 8 and 10 days, before the test day had the greatest effect on the milk yield and SCS, respectively. The threshold THI values for the HS effect were about 60–65 for both traits.     

Evaluation on Air Environment of a Large Tower Type Cowshed for Dairy Cattle in Northern China

In this study, the air environment quality indicators of a large tower type cowshed for dairy cattle in North China were monitored and evaluated at all seasons of one year, including the indicators of thermal environment, the content of ammonia (NH₃), carbon dioxide (CO₂), microbe and the dust in the air. The objective was to study the change rules of the mentioned indicators, to evaluate whether this type of cowshed could meet the production requirements, and to provide theoretical basis for the design and daily management of the cowshed in the Northern region of China. The results showed that all the indicators mentioned above varied with seasons and time to some extent. The wind speed inside was below the standard of dairy cattle cowshed in summer, and the temperature in 14∶00 of summer was above 27 ℃, and THI was beyond 69, so the dairy cattle suffered slight heat stress in summer. The other air environment quality indicators monitored in any time and any space all met the standard. In conclusion, the tower type cowshed monitored was suitable for dairy cattle in North China, but some facilities should be added to decrease the temperature and the heat stress in summer.     

北方地区大型钟楼式奶牛舍空气环境的评价

试验对北方地区某大型钟楼式奶牛舍一年内不同季节舍内、外的空气环境指标,包括温热环境指标、CO₂和NH₃含量、空气中的粉尘和微生物含量进行测定,旨在了解其变化规律,评价其是否满足奶牛健康生产的要求,以便为北方地区奶牛舍的设计和日常管理提供理论依据。结果表明,所测指标随季节或时间均呈现出一定的变化规律;所监测奶牛舍夏季舍内风速低于标准,中午（14∶00）舍内温度超过27 ℃,温湿指数（THI）>69,奶牛在夏季产生轻度的热应激;除此以外,在不同时间、不同位点监测的其他各项空气环境指标均符合奶牛的饲养标准。综合测定结果,试验所监测的钟楼式奶牛舍较适合北方地区的奶牛养殖,但建议增加防暑降温措施,以减少奶牛在夏季产生的热应激。     

Dual-purpose Guzerá cattle exhibit high dairy performance under heat stress

The present study evaluated the heat stress response pattern of dual-purpose Guzerá cattle for test-day (TD) milk yield records of first lactation and estimated genetic parameters and trends related to heat stress. A total of 31,435 TD records from 4,486 first lactations of Guzerá cows, collected between 1986 and 2012, were analysed. Two random regression models considered days in milk (DIM) and/or temperature × humidity-dependent (THI) covariate. Impacts of −0.037, −0.019 and −0.006 kg/day/THI for initial and intermediate stages of lactation were observed when considering the mean maximum daily temperature and humidity to calculate THI. Heritability estimates ranged from 0.16 to 0.35 throughout lactation and THI values, suggesting the possibility to expect gains from selection for such trait. The variable trajectory of breeding values for dual-purpose Guzerá sires in response to changes in THI values confirms that the genotype × environment interaction due to heat stress can have some effect on TD milk yield. Despite the high dairy performance of Guzerá cattle under heat stress, estimated genetic trends showed a progressive reduction in heat tolerance. Therefore, new strategies should be adopted to prevent negative impacts of heat stress over milk production in Guzerá animals in future.     

北京地区泌乳牛夏季鼓膜温度昼夜节律及影响因素研究

【目的】 试验旨在揭示北京地区荷斯坦泌乳牛鼓膜温度的群体特征及其随昼夜和环境温湿度指数（temperature-humidity index,THI）的变化规律,探究中度热应激下泌乳牛鼓膜温度的影响因素及其与直肠温度的关系。【方法】 2021年8月对北京地区某规模化牧场638头荷斯坦泌乳牛的鼓膜温度、直肠温度及环境温湿度进行测定,并对其进行描述性统计;对161头荷斯坦泌乳牛6 h鼓膜温度和直肠温度进行相关性分析;利用混合线性模型分析THI、测定时间、胎次、泌乳阶段和繁殖状态等因素对鼓膜温度和直肠温度的影响。【结果】 北京地区荷斯坦泌乳牛夏季鼓膜平均温度为（39.01±0.40）℃;测定时间内THI为76.11~83.18,此时泌乳牛处于中度热应激。泌乳牛鼓膜温度昼夜变化较大,昼夜节律表现为上午低、下午和傍晚均较高且在早晨和下午出现不正常峰值,鼓膜温度的变化滞后于THI变化。鼓膜温度与直肠温度呈显著正相关关系（P<0.05,r＝0.35）,且两种体温均随着THI的升高而升高,回归系数分别为0.09（P<0.05,R²=0.09）和0.10（P<0.05,R²=0.08）。测定时间和胎次对泌乳牛鼓膜温度有显著影响（P<0.05）,胎次和泌乳阶段对泌乳牛直肠温度有显著影响（P<0.05）,且THI对两部位温度的回归均显著（P<0.05）。【结论】 本研究揭示了奶牛体温的节律变化和影响因素,鼓膜温度可有效反映奶牛实时体温,可为精细化管理牛群提供理论依据。     

Exploration of factors determining milk production by Holstein cows raised on a dairy farm in a temperate climate area

In this study, we examined factors that affected milk production by cows raised in a temperate climate area. We conducted this study on a large dairy farm containing approximately 2000 Holstein cows, located in a temperate climate area. We collected 7803 calving records for 4069 cows from 2012 to 2016. We then assessed the effect of hot weather on milk yield by examining three climate factors: season, maximum temperature (MAX), and the temperature and humidity index (THI). We found that increases in heat stress caused linear decreases in milk yield (P?<?0.05). Additionally, the effects of the three climate factors on milk yield varied depending on cow parity and days open (P?<?0.05). Thus, management procedures should consider cow parity and lactating stage to minimize the negative effects of heat stress on milk production. We also found that the lowest Akaike information criterion value was obtained in our model when using THI for 305-day milk yield. This suggests that THI is a more accurate variable for evaluating heat stress than MAX or season.

     

Effects of heat stress on reproductive efficiency in Holstein dairy cattle in the North African arid region

This work aims to study the relationship between variations of the Temperature-Humidity Index (THI) and the parameters of reproduction especially the first conception rate (FCR) and to determine the threshold THI value where cows’ fertility rate dropped in 12 Holstein dairy herds raised in the arid climatic conditions of Tunisia. THI values were calculated over 22 years (1996–2018), and the mean monthly temperature and relative humidity data were obtained from the Meteorological Institute of Tunisia. A total of 20,396 individual records (Insemination and calving dates) were extracted from the Livestock and Pasturing Office (OEP, Tunisia) with regard to the highest THI before breeding, on the breeding day, and after breeding. Statistical analysis was performed using the GLM procedure of SAS software. Results point to the fact that a summer heat stress exists in southeast Tunisia and lasts for 4 months starting from June until September with THI values fluctuating between 73 ± 2.38 and 79 ± 3.01 exceeding, therefore, THI threshold of 72. Increased THI from ≤70 to ≥80 units was associated with drops in conception rate (CR) and fertility rate (FR) of 49% and 45% giving a correlation with the THI of (r = −.72, p < .05) and (r = −.74, p < .05), respectively. When cows were inseminated on extremely hot days (THI ≥ 80) preceded by cooler temperatures, pregnancy by service (P/AI) was 7% points higher than for other cows that were exposed to high temperatures before breeding. The average number of insemination was higher (p < .05) from THI ≤ 70 (2.01) compared to THI ≥ 80 (3.41). Cows calving during an absence of heat stress (THI ≤ 70) have the shortest average calving intervals (CI: 420 ± 15.1 days). Contrastly, calving in the condition of heat stress (THI ≥ 80) has the longest CI (487 ± 12.8 days). For each point increase in the THI value above 67, there is a decrease in the first conception rate by 1.39%. In this particular arid environment, high-yielding Holstein cows’ breeding success is strongly affected by heat stress that takes place just before or after breeding.     

Utility of on- and off-farm weather records for studies in genetics of heat tolerance

Utility of weather information from on-farm and weather stations was evaluated for the application in studies on the genetics of heat stress. Daily milk yield of 31 primiparous Holstein cows was collected at Tifton, GA, from April 28 to July 19, 1993. Weather information was recorded on-farm and was available from weather stations in Georgia. Analyses used daily average of temperature–humidity index (THI). Effects of threshold of heat stress and the rate of decline in milk after the threshold were estimated. With on-farm weather data, threshold was at THI = 22 and rate of decline was − 1.12 kg of milk per unit of THI measured 2 days before milking. At the Tifton weather station, 3 km away from the farm, the threshold was THI = 20 and the rate was the same. With data from Macon, Columbus, Atlanta, and Athens stations, the threshold was at 20, 21, 20, and 20, respectively, and the rate of decline with a 2 day lag was − 0.88, − 1.02, − 0.90, and − 0.97 kg of milk per unit of THI. Subsequent analysis included 2260 test day records from the same farm from 1993 to 2003 and weather data from Tifton station. The highest rate of decline on milk yield of − 0.22 kg per unit of THI occurred at the threshold of 20 and no lag. For data restricted to 1999–2003, the threshold increased to 22 and the rate to − 0.46 kg per THI unit. Public stations provide satisfactory information for national genetic evaluation for heat stress. Critical parts in such an evaluation are modeling of test days and accounting for changes among farms and weather stations over time.     

Annual Dynamic Research of Thermal Environment of Dairy Cowshed in Free Stall-feeding with Window

The objective of this study was to investigate the annual dynamic of thermal environment of dairy cowshed in free stall-feeding with window. Through continuous detection of the dairy cowshed for 12 months of air temperature, relative humidity and wind speed, the annual variations in these 3 parameters were analyzed. The results indicated that the indoor air temperature was high at noon and low in both the morning and evening, while the opposite tendency in the relative humidity was observed. The indoor air temperature was above 25℃ for 7.5 to 10 h daily in summer, especially in June, the indoor air temperature was higher than outdoor air temperature. In December, the indoor wind speed was almost 0 m/s. From the comprehensive index analysis, during the period of 09:30~19:30 in summer, the temperature humidity index (THI) was above 72, which made dairy cows suffer from mild heat stress. The wind chill temperature (WCT) was not below -10℃ in winter, and the dairy cows did not suffer from cold stress. In conclusion, not only heatstroke prevention in summer but also ventilation enhanced in winter for this dairy cowshed should be paid more attention.     

舍饲散栏有窗奶牛舍温热环境的年动态研究

为研究寒区奶牛舍温热环境的年动态变化,试验选择河北省承德市某规模化奶牛场一栋散栏有窗奶牛舍,连续12个月监测舍内外的气温、相对湿度和风速并分析其规律。结果表明,全年奶牛舍内、外气温均表现为中午高、早晚低的规律性变化,相对湿度则表现出相反的规律。夏季（6~8月）每天有7.5~10 h舍内气温高于25℃,且在6月出现了舍内气温高于舍外气温的现象。12月舍内风速几乎全天为0 m/s。从综合指数分析,夏季每天09∶30~19∶30（10 h）舍内温湿指数（THI）均超过72,奶牛处于轻度热应激状态;冬季的风寒温度（WCT）均未低于－10℃,奶牛不遭受冷应激。综合以上结果,对于寒区散栏有窗奶牛舍,夏季应加强防暑降温措施,冬季加强通风换气。     

Evaluation of Thermal Environment of Cowshed and Correlation Analysis Between Thermal Parameter and Physiological Parameter of Dairy Cows in Central Plain of Hebei

The purpose of this study was to evaluate thermal environment of cowshed in four seasons in central plain of Hebei,and analyze the correlation between the temperature parameters and physiological indexes of dairy cows.Three dairy cow houses with different building structures were selected,the thermal parameters (ambient temperature (Ta) and relative humidity (RH)) and physiological parameters (respiratory rate,rectal temperature and body surface temperature) were detected.The results showed that the Ta,RH and index of temperature and humidity (THI) changed significantly in four seasons (P<0.05),the average daily temperature in summer was the highest (28.59 ℃),and the average daily temperature in winter was the lowest (1.55 ℃).In summer,dairy cows were suffering from mild heat stress for 15.5 h every day,and from moderate heat stress for 6.0 h.In winter,dairy cows were under mild cold stress for an average of 12.0 h per day.The Ta and THI of three cowsheds in each season had no significant differece (P>0.05),except for that in winter.Compared with the cowshed with low wall or roller blind,the average Ta in the cowshed with only roof was 0.80-1.27 ℃ higher in summer and 1.36-1.84 ℃ lower in winter.In addition,the physiological parameters of dairy cows were extremely significantly higher in summer than those in other seasons (P<0.01).The respiration frequency or rectal temperature of cows among cowsheds in summer were significantly different (P<0.05),and the seasonal difference in body surface temperature was significant (P<0.05).Correlation analysis of thermal parameters and cow physiological parameters showed that the respiratory frequency,rectal temperature and body surface temperature were positively correlated with THI and Ta (P<0.05).However,there was no significant correlation between physiological parameters and RH (P>0.05).The results provided scientific basis for environment evaluation of cows,and physiological status of dairy cows were inferred according to environmental thermal parameters,which provided data for occurrence and early warning of stress.     

冀中平原奶牛舍温热环境评价及温热参数与生理指标的相关性分析

试验旨在评价冀中平原地区四季奶牛舍的温热环境，并分析温热参数与奶牛生理指标的相关性。选择3栋不同建筑结构的奶牛舍，对各舍温湿度和奶牛的呼吸频率、直肠温度和体表温度等生理指标进行检测。结果显示，奶牛舍四季环境温湿度和温湿指数（THI）变化显著（P<0.05），其中夏季日均温最高，为28.59 ℃；冬季日均温最低，为1.55 ℃。奶牛夏季每天平均15.5 h遭受轻度热应激，6.0 h遭受中度热应激；冬季每天平均12.0 h遭受轻度冷应激。除冬季外，各季节不同牛舍的温度和THI均未表现出显著差异（P>0.05）。相比带矮墙或卷帘的棚舍，仅设顶子的棚舍夏季平均温度要高0.80~1.27 ℃，冬季低1.36~1.84 ℃。另外，夏季奶牛各项生理指标极显著高于其他季节（P<0.01），且夏季不同舍奶牛的呼吸频率和直肠温度均表现出显著差异（P<0.05），体表温度各季节差异均达显著水平（P<0.05）。从环境温湿参数与奶牛生理参数的相关性分析可看出，各项生理参数（呼吸频率、直肠温度和体表温度）与THI、环境温度均呈显著正相关（P<0.05），但与湿度未表现出显著相关性（P>0.05）。本研究可为奶牛舍环境的评价提供科学依据，并通过环境温热参数的检测推断奶牛生理状况，为应激的发生及预警提供数据。