Genotypes and phenotypes of telomere length in Holstein cattle, actors or reporters

Abstract

Selection programs aiming at improving health and survival in cattle are complicated by low heritability estimates, the fact that true herd life and carcass quality is not known until the end of an animal's life, and that many health conditions manifest late in life. Young animals are now heavily favored in breeding programs because low generation intervals accelerate the rate of genetic progress, which means selection decisions must be made before phenotypic observation of health and survival is feasible. Moreover, profitability is compromised when livestock producers raise animals that fail to produce due to health failure or that do not meet quality standards. Telomere length (TL) was hypothesized as a biomarker that could be recorded early in life, be associated with health and survival, and have higher heritability than other measures of health. Thus, our research aims were to: 1, determine associations of TL with health, wellbeing and production in Holsteins raised for dairy or beef purposes; 2, determine TL heritability, genetic variance, and genetic correlations with cow health and performance; and 3, map quantitative trait loci affecting TL and provide TL genomic predictions to industry partners and breeders. There were not significant changes made to the research plan during the project, but the timeline of the project was not met. Laboratory processing of samples was significantly delayed due to Covid along with some sample collection. TL measurements from >1100 animals across the US and Israel are available to date. TL declines modestly with age, in agreement with observations from other species. A genomic analysis was conducted using a single-step approach and TL had a moderate heritability estimate of 20% across age groups. The initial genome-wide association-analysis indicated that TL is a quantitative trait whose expression is influenced by effects across the genome. Moreover, there is a strong association of calf and dam TL at birth. Genetic relationships with health and survival were ascertained through correlations of genomic estimated breeding values (gEBV) for TL with gEBV for other traits routinely recording in national genetic evaluations. Higher TL is genetically associated with longer herd-life, a greater likelihood that cows will avoid premature on-farm death, and reduced disease incidence. The relationship appeared to be strongest when TL was measured during the first two years of life. Based on genotyping different cell types, there was evidence that maternal and colostral derived cells are present in newborns, which could bias TL measurements during the first weeks of life to a small degree. The implications of this research are that TL is a promising trait to include in multiple trait selection programs because it is heritable, available early in life, and correlated with longevity and health. Our TL reference population is currently being expanded, and genomic estimated breeding values will be disseminated to industry partners upon completion of the reference population so that they can evaluate the utility of incorporating TL into their breeding programs.