Absence of Quadratic Relationships Between Genetic Evaluations for Somatic Cell Scores and Udder Linear Traits

Abstract

Sire genetic evaluations for lactation average somatic cell scores from first and second lactation daughters were regressed in separate models on genetic evaluations for udder linear traits. Somatic cell scores were from Pennsylvania DHIA, and udder linear scores were from the Holstein Association of America classifications of first lactation cows in the northeastern US excluding Pennsylvania. The independent data files for calculation of genetic evaluations included 108,632 cows from 301 sires with udder linear scores and 58,235 cows from the same 301 sires with somatic cell scores. Sire genetic evaluations for higher udders, stronger fore udder attachments, closer teat placement, and shorter teats were associated with lower somatic cell scores. Quadratic relationships between genetic evaluations for the udder traits and somatic cell scores were not important. Quadratic components were significant only for somatic cell scores and teat length. Evaluations for intermediate teat length tended to be associated with higher somatic cell score evaluations. Selection and mating for intermediate udder depth, fore udder attachment, and front teat placement scores are not as effective in reducing somatic cell scores as selection for higher udders, stronger fore udders, and closer front teats.