Modeling heat stress effect on Holstein cows under hot and dry conditions: Selection tools

Abstract

Data from milk recording of Holstein-Friesian cows together with weather information from 2 regions in Southern Spain were used to define the models that can better describe heat stress response for production traits and somatic cell score (SCS). Two sets of analyses were performed, one aimed at defining the population phenotypic response and the other at studying the genetic components. The first involved 2,514,762 test-day records from up to 5 lactations of 128,112 cows. Two models, one fitting a comfort threshold for temperature and a slope of decay after the threshold, and the other a cubic Legendre polynomial (LP) model were tested. Average (TAVE) and maximum daily temperatures were alternatively considered as covariates. The LP model using TAVE as covariate showed the best goodness of fit for all traits. Estimated rates of decay from this model for production at 25 and 34°C were 36 and 170, 3.8 and 3.0, and 3.9 and 8.2g/d per degree Celsius for milk, fat, and protein yield, respectively. In the second set of analyses, a sample of 280,958 test-day records from first lactations of 29,114 cows was used. Random regression models including quadratic or cubic LP regressions (TEM_) on TAVE or a fixed threshold and an unknown slope (DUMMY), including or not cubic regressions on days in milk (DIM3_), were tested. For milk and SCS, the best models were the DIM3_ models. In contrast, for fat and protein yield, the best model was TEM3. The DIM3DUMMY models showed similar performance to DIM3TEM3. The estimated genetic correlations between the same trait under cold and hot temperatures (ρ) indicated the existence of a large genotype by environment interaction for fat (ρ=0.53 for model TEM3) and protein yield (ρ around 0.6 for DIM3TEM3) and for SCS (ρ=0.64 for model DIM3TEM3), and a small genotype by environment interaction for milk (ρ over 0.8). The eigendecomposition of the additive genetic covariance matrix from model TEM3 showed the existence of a dominant component, a constant term that is not affected by temperature, representing from 64% of the variation for SCS to 91% of the variation for milk. The second component, showing a flat pattern at intermediate temperatures and increasing or decreasing slopes for the extremes, gathered 15, 11, and 24% of the variation for fat and protein yield and SCS, respectively. This component could be further evaluated as a selection criterion for heat tolerance independently of the production level.

Genetics of heat tolerance for milk yield and quality in Holsteins

“…Consequently, selection for higher MY, F% or P% may result in a poor response of the poorly adapted animals to heat stress. A genetic antagonism between general production level and specific ability to respond to heat stress has also been reported in other studies on dairy cattle (Aguilar et al, 2009;Carabaño et al, 2014;Santana et al, 2016). The genetic trends show that, for MY, there was considerable genetic progress in the general production level over the years studied in all three lactations.…”

“…These authors reached the same conclusion in the case of severe heat stress (THI > 90). Carabaño et al (2014) reported a reduction in SCS with increasing average temperature for Spanish Holstein cows. In contrast, Brügemann et al (2012) and Hammami et al (2013) found that SCS tended to increase at both low and high THI in Holstein cows raised in the maritime region of Germany and in Luxembourg, respectively.…”

“…The latter authors concluded that SCS is sensitive to hot conditions in temperate climates. On the basis of the correlation between SCS at low and high temperatures, Carabaño et al (2014) concluded that G × E are strong for this trait in Spanish Holstein cattle. This trait therefore typically exhibits strong G × E due to heat stress.…”

“…Aguilar et al (2010) estimated the genetic trends for milk yield (MY) of cows in the United States and observed that the genetic merit of the animals for MY increased consistently over the years, whereas the genetic tolerance to heat stress decreased. Another relevant factor related to heat stress is G × E. Carabaño et al (2014) and Hammami et al (2015) identified G × E due to heat stress for milk production and milk quality traits of primiparous Holstein cows raised in Spain and Belgium, respectively. In both studies, changes in the genetic correlations within some traits were observed across the environmental scale (THI or only temperature).…”

Review: Towards the agroecological management of ruminants, pigs and poultry through the development of sustainable breeding programmes: I-selection goals and criteria

“…Indeed, Hammami et al (2013) showed that the heat stress thresholds under a continental temperate climate (Luxembourg) for production traits and somatic cell counts in Holstein cows were really lower (18°C v. values between 23°C and 30°C) than other estimates under tropical or Mediterranean climate conditions. Carabano et al (2014) showed for Holstein cows bred in Southern Spain in hot but dry conditions that their comfort thresholds could differ markedly depending on the production trait: about 29°C for milk yield, 18°C for protein yield and only 15°C for fat yield and somatic cell count. Selection criteria other than those which target production levels are now being sought in order to better evaluate the heat resistance of ruminants.…”