Crossbreeding Dairy Cattle. IV. Effects of Breed Group, Lactation Production, and Pregnancy on Body Growth. Generation 1

Abstract

Data on Generation 1 females were studied for the effects of breed group, concurrent lactation, and pregnancy on rates of body growth. Measures of growth were rates of change in wither height, chest depth, body length, heart girth, paunch girth, and body weight from measurements taken at 3, 6, 12, 18, 24, 30, 36, and 48 months of age. In all periods the gain in weight for animals from Holstein dams was significantly greater than that for animals from Guernsey dams. In contrast, only during the period 12-18 months was the gain in weight of animals by Holstein sires significantly greater than that of animals by Guernsey sires. In a comparison of the relative rates of increase in body weight, the effect of breed of dam was small and inconsequential prior to 24 months of age; however, from 24 to 48 months the effect of breed of dam was considerable. The differential contributions of genetic and maternal factors could not be separated in this analysis. Differences between the effects of breed of sire and breed of dam were not extensive for the other measures. Little evidence of nonadditive genetic effects on growth rates were found, either for breeds or for individual bulls. The combination of a late stage of pregnancy and heavy production early in the first lactation, or the latter alone, acted as a severe damper on increases in all six measures of body development. Measures of flesh development were affected more by high production in early lactation than measures of skeletal development. However, considerable recovery in growth rates was achieved in the periods following the high production in early lactation. © 1967, American Dairy Science Association. All rights reserved.