Prediction of Lifetime Production on Basis of First Lactation Yield and Age at First Calving for Selection of Dairy Cattle

Abstract

This paper evaluates the influence of the first lactation yield and age at first calving on lifetime production and determines the relative importance of them for selection purposes. The data refer to Tharparkar, Sahiwal, and Red Sindhi breeds and one-half Jersey × one-half Thari crossbred cows. Age at first calving had more influence on the estimation of yield up to a certain age than on certain numbers of lactations, the first lactation yield being of equal importance in both cases. Regression equations to predict total yield up to five lactations, on the basis of the first lactation yield, explained 70% of the variation in Tharparkar and Sahiwal breeds and about 42% in Red Sindhi and crossbred cows. Multiple regression equations to predict yield up to 10 yr of age on the basis of the first-lactation yield and age at first calving explained more than 75% variation in purebred cows and only 40% in crossbred cows. The latter character explained more variation. The partial regression coefficients indicate that an increase of 73 kg of milk in the first lactation yield is equivalent to a reduction of one month in age at first calving in the Tharparkar breed. Similar figures in the Sahiwal, Red Sindhi, and crossbred cows are 57, 92, and 126 kg of milk, respectively. © 1965, American Dairy Science Association. All rights reserved.