Impact of conformation traits on functional longevity in South African Holstein cattle

Abstract

A proportional hazards model with a piecewise Weibull baseline hazard was used to determine the impact of observed scores for rump, udder, feet and leg traits on longevity. Conformation data of a total of 15 704 cows with either of or all 13 type traits for the period 1995–2013 were obtained from the Holstein Society of South Africa. Functional longevity was defined as the number of days from first calving to culling or censoring, adjusted for production. Type traits were fitted to the reference model one at a time. The model included the fixed time-dependent effect of region by year of calving, within-herd milk production class by year-season, number of lactations by stage of lactation by within-herd milk production class, protein and fat percent production class by year of calving, herd size by annual herd size change, fixed time-independent effect of age at first calving and presence of type record. Cows without type scores were 7–26% more likely to be culled than those with scores. Udder traits had the greatest impact on functional longevity. Fore teat placement had the strongest influence on functional longevity followed by udder depth, fore udder attachment, median ligament and rear treat placement. Rump and udder width had the least Chi-square contributions. Risk of culling was significantly higher for cows with very narrow chest, weak median ligament, extremely towed out teats and short rump height. There is potential for indirectly selecting animals for longevity based on udder type trait information.