Study of Longevity in Dairy Cattle

This study aimed to estimate the effect of environmental factors on variation of the longevity and the ge-netic parameters of the trait in Holstein dairy cows in Iran. The records of 181738 cows in the years 2001 to 2018 were provided by the Animal Breeding Center of Iran (Karaj, Iran). Profitability in dairy herds de-pends on animal survival in the herd, which is provided by reducing involuntary culling and increasing the voluntary culling in the herd. The survival was defined as the lifespan, the lifetime milk, fat, and protein yield after first calving, and lifetime days in milk. The effect of environmental factors on traits and risk of culling was estimated using Survival kit and cmprsk statistical packages. The variance components were estimated by Gibbs sampling method based on exponential distribution, incomplete data, and survival analysis. The effects of herd, season, and age of calving on traits were significant (P<0.001). The risk of culling of cows with difficult calving was higher than others. The risk of culling of cows calved in spring was higher than in other seasons. The heritability of different traits of survival estimated to be 0.0067-0.0147. The results showed that the effect of different environmental factors on variation of longevity is significant, and the heritability of the trait is low. However, a review of the literature indicates that, despite the low heritability of the trait, it can be improved in a population through genetic selection. This approach is justified, as longevity is not only important for the farmer from the economic point of view, but it also affects the increase of animal welfare and social acceptance of the dairy sector.