Analysis of the Relationships Between Type Traits and Longevity in Croatian Simmental Cattle Using Survival Analysis

Survival analysis with a Weibull proportional hazards model was used to evaluate the effect of linear type traits on the longevity in Croatian Simmental cattle. The data set consisted of 8,212 registered Simmental cows that first calved from 1997 to 2008. Longevity was defined as the number of days between first calving to culling or censoring. Cows alive at the end of the study (13.6%) were treated as right censored. Type information consisted of 19 linear type traits (with a nine-point scoring range) scored in the first lactation. Linear type traits were classified into four groups: muscularity, size traits, form traits and udder traits. The Weibull model included the time-independent effects of age at first calving, classifier, region and each type trait. The results showed a significant effect of 12 type traits on longevity. Among the form traits, low angled pasterns and extremely straight rear leg side view showed almost 2.0 times higher culling risks than normal posture. Cows with higher scores for the muscularity were at higher culling risk levels compared to lower scores. In the group of size traits, only rump height and body depth had significant impact on longevity. Lower scores for fore udder length were associated with lower risk of culling. In contrary, cows with lower scores for udder depth, suspensory ligament, rear udder length and teats thickness had higher probability of culling than the animals with higher scores