Heritability Estimates of Udder Disease as Measured by Various Tests and their Relationship to each Other and to Milk Yield, Age, and Milking Times

Abstract

Paternal half-sib heritability estimates of milk yield, number of quarters infected with mastitis organisms, and number of quarters showing abnormal milk were obtained from an analysis of milking and mastitis data of 2,865 Holstein cows. The within-herd heritability estimate for daily milk yield was 0.353 and that for the number of quarters infected with Streptococcus agalactiae 0.196. The heritability estimates for the number of quarters infected with organisms other than Streptococcus agalactiae, number of quarters infected, and number of quarters showing abnormal milk were all below 0.1.Within-herd correlation coefficients were calculated among daily milk yield, milking data, age, and mastitis indicators. Age, stripping time, and machine-on time were positively correlated with daily milk yield. Older cows had longer machine-stripping times and machine-on times than younger cows. Older cows also showed higher values for all indicators of mastitis.