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 ofclinical mastitis (CM), somatic cell count, and nine udder conformation traits. Somatic cell count was log-transformed into somatic cell score(SCS) in10periods, each 30days long and overall, for the first lactation. CM isacomplex disease closely connected with somatic cell count. The optimum udder conformation traits significantly affect dairy cattle health. The CM binary trait was monitored inseven periods throughout lactation, each 50days long, and for the whole lactation. Alogistic regression model was used toestimate the risk ofCM. The model included afixed effect ofherd-year-season, age atfirst calving, and afixed effect ofthe linear type traits ofthe random effect ofthe animal. The phenotypic correlations for udder conformation traits, CM, and SCS ranged from –0.13 to0.69 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 ofthe udder. According tothe logistic regression assessment, the medial ligament scores 1–2: convex base ofthe udder and the CM incidence to50days inmilk reported a3.79times higher probability ofthe CM incidence atthe reference level (extremely deep medial ligament) atthe same stage ofthe lactation. CM incidence and SCS significantly decreased with decreasing udder depth. Udder depth below the hock was associated with the highest risk ofCM. 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 oflactation iscritical for the onset ofCM, and somatic cell count ismanifested throughout lactation. The effect ofthe udder conformation isthen observable insomatic cell count and CM during the whole lactation.