Remarkable increases in the production of dairy animals have negatively impacted their tolerance to heat stress (HS). The evaluation of the effect of HS on milk yield is based on the direct impact of HS on performance. However, in practical terms, HS also exerts its influence during gestation (indirect effect). The main purpose of this study was to identify and characterize the genotype by environment interaction (G × E) due to HS during the last 60 days of gestation (THI_g) and also the HS postpartum (THI_m) over first lactation milk production of Brazilian Holstein cattle. A total of 389 127 test day milk yield (TD) records from 1572 first lactation Holstein cows born in Brazil (daughters of 1248 dams and 70 sires) and the corresponding temperature–humidity index (THI) obtained between December 2007 and January 2013 were analyzed using different random regression models. Cows in the cold environment (THI_g = 64 to 73) during the last 60 days of gestation produced more milk than those cows in a hot environment (THI_g = 74 to 84), particularly during the first 150 days of lactation (DIM). The heritabilities (h2) of TD were similar throughout DIM for cows in THI_g hot (0.11 to 0.20) or (0.10 to 0.22), while the genetic correlations (rg) for TD between these two environments ranged from 0.11 to 0.52 along the first 250 DIM. The h2 estimates for TD across THI_m were similar for cows in THI_g hot (0.07 to 0.25) and THI_g cold (0.08 to 0.19). The rg estimates ranged from 0.17 to 0.42 along THI_m between TD of cows in cold and hot THI_g. The results were consistent in demonstrating the existence of an additional source of G × E for TD due to THI_g and THI_m. The present study is probably the first to provide evidence of this source of G × E; further research is needed because of its importance when the breeding objective is to select animals that are more tolerant to HS.

在生产奶牛的显着增加，其耐受性热应激（造成了负面影响HS）。HS对牛奶产量的影响评估基于HS对生产性能的直接影响。但是，实际上，HS在妊娠期间也会发挥作用（间接作用）。这项研究的主要目的是通过妊娠最后60天（THI_g）以及HS产后（HSI_m）在巴西荷斯坦奶牛首次泌乳的过程中的HS引起的环境相互作用（G×E）来鉴定和表征基因型。牛。总共389,127个试验日的产奶量（TD）使用不同的随机回归模型分析了2007年12月在巴西出生的1572头第一胎荷斯坦奶牛（1248头大坝和70头公母）的记录以及相应的温湿度指数（THI）。在妊娠的最后60天中，处于寒冷环境中（THI_g = 64至73）的母牛比处于炎热环境中（THI_g = 74至84）的母牛产生的牛奶更多，特别是在哺乳期的前150天（DIM）。在THI_g高温（0.11至0.20）或（0.10至0.22）的母牛中，整个DIM中TD的遗传力（h 2）相似，而遗传相关性（r g），这两个环境之间的TD沿前250个DIM的范围从0.11到0.52。在THI_g热（0.07至0.25）和THI_g寒冷（0.08至0.19）的母牛中，跨THI_m的TD的h 2估计值相似。在冷热THI_g中，沿着奶牛TD的THI_m的r g估计值范围为0.17至0.42。结果一致表明，由于THI_g和THI_m，TD还存在G×E的其他来源。本研究可能是第一个提供这种G×E来源的证据。由于在育种目标是选择对HS耐受性更高的动物时，它的重要性非常重要，因此需要进一步的研究。