Relationships among clinical mastitis test-day records, somatic cell counts, and linear udder conformation traits in Czech dairy cows

This study evaluated test-day records of clinical mastitis (CM), somatic cell count, and nine udder conformation traits. Somatic cell count was log-transformed into somatic cell score (SCS) in 10 periods, each 30 days long and overall, for the first lactation. CM is a complex disease closely connected with somatic cell count. The optimum udder conformation traits significantly affect dairy cattle health. The CM binary trait was monitored in seven periods throughout lactation, each 50 days long, and for the whole lactation. A logistic regression model was used to estimate the risk of CM. The model included a fixed effect of herd-year-season, age at first calving, and a fixed effect of the linear type traits of the random effect of the animal. The phenotypic correlations for udder conformation traits, CM, and SCS ranged from -0.13 to 0.69 and standard errors were 0.01-0.99. The highest CM incidence and SCS were observed for the medial ligament scores 1-2: convex base of the udder. According to the logistic regression assessment, the medial ligament scores 1-2: convex base of the udder and the CM incidence to 50 days in milk reported a 3.79 times higher probability of the CM incidence at the reference level (extremely deep medial ligament) at the same stage of the lactation. CM incidence and SCS significantly decreased with decreasing udder depth. Udder depth below the hock was associated with the highest risk of CM. For udder depth and the whole lactation, the CM ODDS ratio was 1.00-2.56, CM least squares means were 0.18-0.44, and SCS least squares means were 3.20-4.10. Our study confirmed that the start of lactation is critical for the onset of CM, and somatic cell count is manifested throughout lactation. The effect of the udder conformation is then observable in somatic cell count and CM during the whole lactation.