INDEX SELECTION USING MILK-YIELD, SOMATIC-CELL SCORE, UDDER DEPTH, TEAT PLACEMENT, AND FOOT ANGLE

Milk yield, somatic cell score, udder depth, teat placement, and foot angle were evaluated in an index (sire index with 50 daughters) to improve an aggregate genotype that included milk yield, clinical mastitis, milking labor, and laminitis. Parameters and economic values were from the literature when available. Sensitivity analysis was conducted for various parameters. Selection for milk yield, somatic cell score, udder depth, teat placement, and foot angle would improve efficiency of response in the aggregate genotype by 1 to 4% over selection for milk yield alone. Most improvement in efficiency of indexes compared with selection for milk yield alone came from adding either somatic cell score, udder depth, or both. Standardized index coefficients for milk yield were three to four times the sum of the standardized coefficients for somatic cell score, udder depth, teat placement, and foot angle when all were included in the index. Index coefficients were always negative for somatic cell score and positive for udder depth, teat placement, and foot angle. Selection for lower somatic cell scores, higher udders, and closer teat placement would help to reduce or to eliminate undesirable correlated responses in milking labor and mastitis associated with selection for increased milk yield.