Genetic determination of the onset of heat stress on daily milk production in the US Holstein cattle

Abstract

Existence of individual variation in the onset of heat stress for daily milk yield of dairy cows was assessed. Data included 353,376 test-day records of 38,383 first-parity Holsteins from a random sample of US herds. Three hierarchical models were investigated. Model 1 inferred the value of a temperature-humidity index (THI) at which mean yield began to decline as well as the extent of that decline. Model 2 assumed individual variation in yield decline beyond a common THI threshold. Model 3 additionally assumed individual variation for the onset of heat stress. Deviance information criteria indicated the superiority of model 3 over model 2. For model 2, genetic correlation between milk yield in the absence of heat stress and the THI threshold for heat stress was -0.4 (0.11) [marginal posterior mean (marginal posterior standard deviation)]. For model 3, genetic correlations were -0.53 (0.05) between milk yield and THI threshold and -0.62 (0.08) between milk yield and yield decay beyond the THI threshold. Total standard deviation (sum of additive genetic and permanent environmental standard deviations) for the THI threshold was 3.95 (0.06), and more than half of that variation had an additive genetic origin [56% (5%)]. Because of the high genetic correlation [0.95 (0.03)] between yield decay and THI threshold with model 3, using only one of them as a selection criterion for heat tolerance would modify the other in the desired direction.

Detrimental effect of selection for milk yield on genetic tolerance to heat stress in purebred Zebu cattle: Genetic parameters and trends

“…Bernabucci et al (2014), based on the negative genetic correlation of milk, protein, and fat production with heat stress in 3 lactations, claimed that selection for higher production itself leads to a decline in genetic merit for heat tolerance. Similar to the results obtained here, Sánchez et al (2009) also reported negative correlations between the intercept and slope for both additive genetic and permanent environmental effects of milk yield. As an alternative to overcome the antagonism between production and tolerance to heat stress, Carabaño et al (2014) suggested eigendecomposition of the random regression coefficient matrix to produce new variables that would prevent the antagonistic relationship between the intercept and slope of the reaction norms of animals.…”

Adaptation to hot climate and strategies to alleviate heat stress in livestock production

“…In both studies, heritabilities for performance traits (milk production or carcass weight at slaughter) were found to increase as a function of THI. In another approach, a hierarchical Bayes model has been proposed, where both threshold of heat stress at which performance start to decrease and rate of decline from heat stress could be estimated (Sá nchez et al, 2009). On the basis on Holstein milk production data, they found that both parameters are heritable traits (0.32 to 0.56, respectively), suggesting that selective improvement of such characters is possible.…”

Modeling heat stress under different environmental conditions

“…The pattern of individual deviations is expected to be determined by differences in the HS threshold and the magnitude of the negative effect of HS among cows. Estimation of individual thresholds under BL models has been proven to be cumbersome (Sánchez et al, 2009) because of the complexity of the needed models. Again, polynomial functions have been used to describe individual deviations to avoid these drawbacks (Brügemann et al, 2011;Hammami et al, 2013;Carabaño et al, 2014).…”