Genotype by heat stress interactions for production and functional traits in dairy cows from an across-generation perspective

摘要

The aim of this study was to analyze time-laggedheat stress (HS) effects during late gestation on geneticco(variance) components in dairy cattle acrossgenerations for production, female fertility, and healthtraits. The data set for production and female fertilitytraits considered 162,492 Holstein Friesian cows fromcalving years 2003 to 2012, kept in medium-sized familyfarms. The health data set included 69,986 cowsfrom calving years 2008 to 2016, kept in participatinglarge-scale co-operator herds. Production traits weremilk yield (MKG), fat percentage (fat%), and somaticcell score (SCS) from the first official test-day in firstlactation. Female fertility traits were the nonreturnrate after 56 d (NRR56) in heifers and the intervalfrom calving to first insemination (ICFI) in first-paritycows. Health traits included clinical mastitis (MAST),digital dermatitis (DD), and endometritis (EM) in theearly lactation period in first-parity cows. Meteorologicaldata included temperature and humidity from publicweather stations in closest herd distance. The HSindicator was the temperature-humidity index (THI)during dams’ late gestation, also defined as in uteroHS. For the genetic analyses of production, female fertility,and health traits in the offspring generation, asire-maternal grandsire random regression model withLegendre polynomials of order 3 for the production andof order 2 for the fertility and health traits on prenatalTHI, was applied. All statistical models additionallyconsidered a random maternal effect. THI from lategestation (i.e., prenatal climate conditions), influencedgenetic parameter estimates in the offspring generation.For MKG, heritabilities and additive genetic variancesdecreased in a wave-like pattern with increasing THI.Especially for THI >58, the decrease was very obviouswith a minimal heritability of 0.08. For fat% and SCS,heritabilities increased slightly subjected to prenatal HSconditions at THI >67. The ICFI heritabilities differedmarginally across THI [heritability (h~2) = 0.02–0.04].For NRR56, MAST, and DD, curves for heritabilitiesand genetic variances were U-shaped, with largestestimates at the extreme ends of the THI scale. ForEM, heritability increased from THI 25 (h~2 = 0.13)to THI 71 (h~2 = 0.39). The trait-specific alterationsof genetic parameters along the THI gradient indicatepronounced genetic differentiation due to intrauterineHS for NRR56, MAST, DD, and EM, but decreasinggenetic variation for MKG and ICFI. Genetic correlationssmaller than 0.80 for NRR56, MAST, DD, and EMbetween THI 65 with corresponding traits at remainingTHI indicated genotype by environment interactions.The lowest genetic correlations were identified whenconsidering the most distant THI. For MKG, fat%,SCS, and ICFI, genetic correlations throughout werelarger than 0.80, disproving concerns for any genotypeby environment interactions. Variations in genetic (co)variance components across prenatal THI may be dueto epigenetic modifications in the offspring genome,triggered by in utero HS. Epigenetic modifications havea persistent effect on phenotypic responses, even fortraits recorded late in life. However, it is imperative toinfer the underlying epigenetic mechanisms in ongoingmolecular experiments.