Estimation of Genetic Effects on Milk Yield and Constituent Traits in Crossbred Dairy Cattle

Abstract

Impact of crossbreeding in two-, three-breed, and 5/8 crosses among Ayrshires, Holsteins and Brown Swiss for yields and constituent traits in first lactation was measured against weighted means of purebred contemporaries. All possible crosses and reciprocals were included. Average percents heterosis for two-breed crosses were 1.1,-15.8, 5.9, 6.3, 6.0, -1.1 for age at first calving, days open, yields (kg)of milk, fat, fat-corrected milk, and fat percentage. Effects of heterosis were significant for milk yield in crosses of Ayrshires x Holstein and Brown Swiss x Holstein and for fat yield and fat-corrected milk in crosses of Ayrshire x Holstein. Holstein dams had significant effects on milk, fat, fatcorrected milk yields, and fat percentage in crosses with Ayrshire and Brown Swiss sires. Holstein sires significantly affected fat percentage in crosses of Holstein Ayrshire and Holstein x Brown Swiss and milk yield in crosses of Holstein Brown Swiss. A large effect from Holstein as dam in two-breed crosses was observed. Percent heterosis for three-breed crosses was determined from weighted mean of purebreds and mean of true parents. In general, the former estimate exceeded the latter. Average percent heterosis dropped for milk yield to 3.8, fat percent rose to