Genetic evaluation of mastitis in dairy cattle in France

Abstract

Genetic parameters of clinical mastitis were estimated for the three main French dairy breeds: Holstein, Montbéliarde and Normande. Records were clinical mastitis events reported by farmers to milk recording technicians and the analyzed trait was the binary variable describing the occurrence of a mastitis case within the first 150 days of a lactation. Low heritability estimates were found: between 2 and 4 % depending on the breed but the trait has significant genetic variance despite its low heritability: efficient genetic improvement is possible.

Genetic correlations with other traits were estimated, showing large correlations (often >0.50, in absolute value) between clinical mastitis and somatic cell score (SCS), longevity and some udder traits. Correlation with milk yield was moderately large and unfavorable (r=0.26 to 0.30). High milking speed was genetically associated with less mastitis in Montbéliarde (r = -0.14) but with more mastitis in Holstein (r=0.18). Interbull genetic correlations are very high with Nordic countries, where much stricter recording systems exist (r =0.94). They were lower (around 0.80) with countries supplying SCS as a proxy for the international evaluation on clinical mastitis.

Clinical mastitis has been included since 2010 in routine evaluations using a multiple trait animal model. Mastitis estimated breeding values (EBV) are combined with somatic cell scores EBV into an udder health index which receives a weight of 14.5% to 18.5% in the new French Total Merit Index (ISU) of the three breeds.