Development of an Udder Health Index for Sire Selection Based on Somatic Cell Score, Udder Conformation, and Milking Speed

Abstract

Genetic parameters,of subjectively,scored,milking speed,and,somatic,cell score,were,estimated,using REML and a sire model. Approximately 250,000 records,were,used. Heritabilities were,0.15 for milk- ing speed,and,0.14 and,0.16 for lactation,mean,so- matic cell score (SCS) for first and second lactations, respectively.,Genetic,correlations,between,milking speed,and SCS were,0.41 and,0.25 for first and,second lactations, respectively, indicating that faster milking was,associated,with,increased,SCS. Genetic parameters for milking speed, SCS, and udder confor- mation,were,estimated,using,REML and,an,animal model. Records from approximately 120,000 cows were,used. Genetic correlations,were,greatest,for ud- der depth,(‐0.26) with,SCS and,for width,of rear udder,attachment,(‐0.24) with,milking,speed. An udder,health,index,for use in sire selection was,devel- oped,for an aggregate,genotype,that included,subclin- ical mastitis in lactations 1 and ≥2, clinical mastitis in lactations 1 and ≥2, and milking time. Respective economic weights were ‐$12, ‐$31, ‐$15, ‐$59, and ‐$11 per,genetic,standard,deviation. Traits in the selection index were milking speed, udder conforma-