Hot topic: association of telomere length with age, herd, and culling in lactating Holsteins.

Telomere length variation may provide a quantitative measure of the effects of dairy management and selection practices on animal stress and welfare. The objective of this study was to evaluate the association between telomere length in Holstein cattle with age, herd, and survival. A multiplex quantitative PCR (qPCR) procedure was utilized to estimate telomere length for 201 Holstein cows from 10 herds following DNA extraction from blood. Primers were designed to amplify a 79-bp telomere product and a 144-bp product of a standard reference gene (β-globin). Both primer sets were included in the same reaction well to enable the analysis of relative quantity (qT) of telomere product compared with β-globin product. Triplicate samples were run for each cow, and mixed models were used to analyze the qPCR results. Younger cows were significantly associated with higher qT, and significant variation was observed among herds for qT. Cows with short telomeres were more likely to be culled in the subsequent year than cows with above-average telomere lengths. Multiplex qPCR provides a cost-effective method of assessing telomere length. Variation in telomere length might provide insights into how management practices and genetic selection influence cow stress and physiological responses to stress.