There is an opportunity to breed for improved genetic longevity due to the significant variation for the trait in the general cow population. The standard deviation for longevity in the New Zealand cow population is 141.2 days.
Fertility and production performance significantly influence a cow’s life expectancy in the herd. Many other factors also affect her chances of survival, which should be accounted for in animal breeding.
In New Zealand’s Breeding Worth (BW) index, the trait residual survival represents the genetic merit for survival in the herd beyond what is accounted for by other BW traits such as production and fertility. With a 9% weighting in BW, it incorporates some non-production traits, including those most strongly correlated with the likelihood of survival. These traits include owner opinion, milking speed, leg conformation, dairy conformation and udder overall.
The influence of the traits varies depending on the age of the cow. Body condition score and milking speed are more strongly linked with early life survival, while udder and leg traits have more connection with later-life survival.
Estimation of genetic longevity can be complex. Farmers consider many factors in the retention of a cow. The longevity trait itself also takes a long time to be fully expressed.
Predictor traits are used to help with estimations. These give a good indication of the likelihood of survival of a bull’s daughters. Predictor traits include production, health and fertility traits as well as the non-production traits previously mentioned. Advances in genomic evaluation also help improve longevity estimations.