The Udder Health index is strongly correlated with NTM. The Udder Health index is a very important trait, both for dairy cows’ well-being and comfort but also for economic reasons. Mastitis is among the top culling reasons in dairy cows.
The Udder Health index describes the bull’s daughters’ genetic ability to resist mastitis and it includes breeding values for udder health in the first three lactations. The Data behind the Udder Health index is the records on clinical mastitis made by veterinarians. Cell count (first three lactations) and udder conformation (fore udder attachment and udder depth from the 1st lactation) are used as indicator traits for udder health.
What makes the Udder Health index unique is that in the Nordic countries, we register actual disease cases and don’t just rely on indicator traits, like Somatic cell count (SCC). SCC alone is not a good enough predictor for improving mastitis resistance. The Correlation between SCC and clinical mastitis is around 0.6, so it is not really the same trait. Therefore, registrations of clinical mastitis are a more accurate breeding value base. Official registrations are done for 90% of cows in Denmark, Sweden and Finland. That results in a high reliability of breeding values for udder health.
A daughter of a bull with an estimated breeding value (EBV) of 120 in Udder Health will have less mastitis than a daughter of a bull with 100 EBV which is the population average for the breed. There really is a difference between bulls! For example, VikingHolstein EBV 120 for Udder Health means 42% less cases of mastitis relative to population average.