Relationship between somatic cell count and functional longevity assessed using survival analysis in Italian Holstein–Friesian cows

Abstract

The relationship between somatic cell scores (SCS) and longevity was assessed for Italian Holstein–Friesian dairy cows using survival analysis. The data of somatic cell count (SCC) test day information of 512 979 cows were provided by nine provinces from Northern Italy. Pedigree information was extracted from the national herd book. Two survival models were run: a model similar to the one used for genetic evaluation on length of productive life, and a second one adding the phenotypic level of ten classes of test-day SCS of the cow. A cow with a test-day in the highest class of phenotypic level for SCS had more than three times greater risk of being culled when compared to risk for the class with the lowest SCS level. The genetic correlation between the risk of being culled and SCS was estimated to be 0.31, based on the correlation between sire EBV. The rank of bulls resulting from the genetic evaluation on survival did not change significantly with the inclusion of SCS in the model (rank correlation of 0.98). It is concluded that the phenotypic level of SCS plays an important role in culling decision of farmers of Italian Holstein–Friesian dairy cows and SCS is genetically associated to the functional longevity of cows.