Ravagnolo O, Misztal I
Department of Animal Science, University of Georgia, Athens 30602, USA.
J Dairy Sci. 2002 Nov;85(11):3101-6. doi: 10.3168/jds.S0022-0302(02)74397-X.
The objective of this study was to examine the relationship between reproductive traits and heat stress. Nonreturn rate at 45 d (NR45) was analyzed in a fixed-effect model that included the temperature-humidity index (THI) from a nearby weather station as a measurement of heat stress. Data consisted of 150,200 first inseminations at first and later parities of 110,860 Holstein cows from 550 herds in Georgia, Tennessee, and Florida with weather information from 16 weather stations. THI on the day of the insemination, 2 d prior, 5 d prior, 5, 10, 20, and 30 d after insemination were studied as independent variables. The THI on the day of insemination showed the highest effect on NR45, followed by 2 d prior, 5 d prior, and 5 d after insemination, but no relationship was found with THI at 10, 20, and 30 d after insemination. NR45 showed a decrease of 0.005 per unit increase in THI on the day of insemination for THI >68. First and later parities presented similar thresholds but responded differently to an increase in THI, with NR45 being significantly lower and more susceptible to increases of THI in cows in their first parity than in later parities (0.008 vs. 0.005 decrease). Threshold for sensitivity to heat stress changed with the states, with Florida, Georgia, and Tennessee having thresholds of 70, 70, and 66, respectively. The decrease in NR45 per unit increase of THI was 0.007, 0.005, and 0.006 for Florida, Georgia, and Tennessee, respectively. With respect to only the Florida data, the final fixed-effect model used was NR45 = herd(year) + month(year) + month(year) + age(parity) + days in milk + 100d milk + THI + error. Animals with more than 150 d in milk (DIM) had a 0.16 lower NR45 than animals with less than 60 DIM at insemination. Lower milk-producing animals showed 0.08 higher NR45 than higher-producing animals. A difference of 0.10 in NR45 was observed between THI lower than 70 and THI 84. This variation in NR45 caused by THI changes is sufficient to merit further studies to examine genetic components of heat tolerance for this trait.
本研究的目的是检验繁殖性状与热应激之间的关系。在一个固定效应模型中分析了45天的返情率（NR45），该模型将附近气象站的温湿度指数（THI）作为热应激的度量指标。数据包括来自佐治亚州、田纳西州和佛罗里达州550个牛群的110860头荷斯坦奶牛在初产及经产时的150200次首次输精，并配有来自16个气象站的天气信息。将输精当天、输精前2天、输精前5天、输精后5天、10天、20天和30天的THI作为自变量进行研究。输精当天的THI对NR45的影响最大，其次是输精前2天、输精前5天和输精后5天，但未发现与输精后10天、20天和30天的THI存在关联。当输精当天THI>68时，THI每增加一个单位，NR45下降0.005。初产和经产呈现相似的阈值，但对THI升高的反应不同，初产奶牛的NR45显著低于经产奶牛，且对THI升高更敏感（下降0.008对0.005）。对热应激敏感的阈值因州而异，佛罗里达州、佐治亚州和田纳西州的阈值分别为70、70和66。佛罗里达州、佐治亚州和田纳西州THI每增加一个单位，NR45的下降幅度分别为0.007、0.005和0.006。仅就佛罗里达州的数据而言，最终使用的固定效应模型为NR45 = 牛群（年份）+月份（年份）+月份（年份）+年龄（胎次）+产奶天数+100天产奶量+THI + 误差。输精时产奶天数超过150天（DIM）的动物的NR45比产奶天数少于60天的动物低0.16。产奶量低的动物的NR45比产奶量高的动物高0.08。观察到THI低于70和THI为84时，NR45相差0.10。由THI变化引起的NR45的这种差异足以值得进一步研究以检验该性状耐热性的遗传成分。
