Correlations Among Somatic Cell Scores of Milk Within and Across Lactations and Linear Type Traits of Jerseys

Abstract

Genetic and phenotypic correlations were estimated for means of log2 SCC (somatic cell scores) from the first 305 d, the first 75 d, the first 150 d, 76 to 305 d, and 151 to 305 d of lactation for first and second lactations using REML. Somatic cell scores from the Dairy Records Processing Center in Raleigh, North Carolina for 31,180 Jersey cows sired by 411 bulls were used for analyses. Correlations between sire evaluations for somatic cell scores from this study and linear type traits from the American Jersey Cattle Club were also calculated. The model used for analyses of the somatic cell score means included herd-year of calving, age at first calving, sire, and residual. Heritability estimates for the means ranged from .05 to .15 (.12 for 305-d mean for first lactation). Genetic correlations among the somatic cell score means within first and within second lactation were≥.79. The genetic correlation between the 305-d mean from first and second lactation was .90. The smallest genetic correlation across lactations was .68. Somatic cell scores measured at various times were under similar genetic control. Phenotypic correlations were usually much smaller than genetic correlations. Correlations were small between sire evaluations for somatic cell scores measured in first lactation and linear type traits; the largest correlations were between somatic cell scores and dairy form and between somatic cell scores and teat length. Most correlations between sire evaluations for somatic cell scores measured in second lactation and linear type traits were similar to the correlations between somatic cell scores in first lactation and linear type traits. However, in second lactation the negative correlations were larger between somatic cell scores and fore udder attachment and udder depth. Lower scores for dairy form (less angularity), shorter teats, tighter fore udders, and higher udders were associated with lower somatic cell scores, especially somatic cell scores measured in second lactation.