PRODUCTIVE LIFE EVALUATIONS - CALCULATION, ACCURACY, AND ECONOMIC VALUE

A preliminary national evaluation of productive life was computed from records of 11 million Holsteins. Data were a mixture of projected and completed months in milk by 7 yr of age. Data were analyzed with the animal model programs currently used for yield traits. Genetic trend for productive life was positive as a correlated response to past selection for yield and type traits. Phenotypic trend was slightly negative. Active Al bulls had PTA that ranged from -1.7 to +4.3 mo and mean reliability of 56%: 3-yr-old cows had mean reliability of 29%. Yield and type PTA were almost uncorrelated with productive life PTA for active Al bulls but had positive correlations (.25 to .36) for all bulls born since 1980. An index that combines yield and productive life PTA with relative weights 2.5:1 can increase economic progress by up to 4%. Nearly identical progress can result from an index that combines yield and productive life adjusted for yield. Multitrait evaluations might produce higher reliabilities for productive life by inclusion of correlated traits measured earlier in life such as yield, type, and somatic cell score.