Genetic parameters of cow functional survival and correlations with predictor conformation and farmer-opinion traits with recommendations for genetic evaluation

Abstract

Functional survival is defined as a dairy cow’s ability to be retained in the herd for functional reasons (e.g. good health) independent of milk production and fertility. In this study, we defined two sets of functional survival traits between each of the first four lactations, in which the effects of culling for production and fertility were removed, based on: (1) farmer-recorded culling reasons, and (2) a set of rules based on commonly recorded data fields for production and reproductive traits. We estimated genetic parameters of cow functional survival traits, along with predictor cow conformation and farmer’s opinion traits, and assessed predictors for their utility in genetic evaluation of functional survival. All functional survival traits had low heritability (0.002 to 0.013), with slightly lower heritabilities for rules-based functional survival traits. Body condition score (BCS) had the strongest genetic correlations with early functional survival (0.46, 0.38 with survival in the first and second parities) and weaker correlations with later functional survival (0.15, 0.19 with survival in the third and fourth parities). In contrast, udder traits had the strongest genetic correlations with later functional survival traits (0.29 to 0.40). Milking Speed was correlated with functional survival in all parities (0.28 to 0.33) as was Legs straightness (-0.14 to -0.30). The genetic correlations of rules-based functional survival traits with conformation and farmer-opinion traits were similar to those based upon farmer-recorded culling reasons. We estimated the accuracies of sire genetic evaluations of functional survival using selection index modelling for scenarios where daughter records for conformation, farmer-opinion traits, and survival became available at increasing ages. The best predictors of overall functional survival included BCS and Milking Speed (early survival) and Udder Overall and Legs (late survival). For a bull with 50 daughters recorded for all traits, conformation and farmer-opinion traits produced an accuracy of 0.48 for the prediction of overall functional survival prior to any available survival scores on a bull’s daughters, a substantial improvement over the accuracy of functional survival from first to second lactation (0.30). The prediction accuracy of overall functional survival improved to approximately 0.53 when these four predictor traits and functional survival to second lactation observations were combined. Therefore, we recommend including four predictor traits in the genetic evaluation of functional survival.