Combination of test day somatic cell count and incidence of mastitis for the genetic evaluation of udder health

Genetic parameters were estimated in a joint analysis of somatic cell count (SCC) and mastitis (MAS) in Holstein/Friesian cows for the first three parities using a random regression model (RRM). There were 67,175, 30,617, and 16,366 cows with records for SCC in parities 1, 2 and 3, respectively. The incidence of MAS was 14, 20, and 25% in parities 1, 2, and 3, respectively. Average daily heritability estimates ( h 2) were 0.11, 0.14, and 0.15 for SCC in parities 1, 2, and 3, respectively. Corresponding estimates were 0.05, 0.07, and 0.09 for mastitis as a binary trait (MAS) and 0.06, 0.07, and 0.12 as a count trait (NMAS). Genetic correlations (rg) between parities were different to one; thus indicating that separate parities should be treated as separate traits. Genetic correlations between SCC at days in milk (DIM) and MAS within parities were generally medium in value, varying from 0.41 to 0.74. It is intended that the new parameters will be used in setting up a national evaluation system for the joint analysis of SCC and MAS.