Crossbreeding Dairy Cattle. I. Some Effects of Crossbreeding on the Birth Weight and Gestation Period of Dairy Cattle

Data for this study consist of the birth weights and gestation periods of 1,004 live, single-born calves in the Illinois crossbreeding project. First-generation crossbreds were 1.90 kg heavier than their purebred contemporaries, three-fourths-bred calves averaged 0.28 kg heavier, and the five-eighth-calves averaged 2.44 kg heavier than the purebreds. For all generations, crossbreds averaged 37.56 kg, whereas purebreds averaged 36.02 kg; thus, crossbreeding increased birth weight by 4.3%. The general lack of significant interactions for sires within breeds by breed of dam does not support the idea of nicking for specific sires in crossbreeding. Male calves were 2.48 kg heavier than females, calves by Holstein sires were 2.5~ kg heavier than those by Guernsey sires, and for each increase of one-eighth-Holstein in the genotype of the dam, the birth weight of the calf increased 0.78 kg; thus; calves out of Holstein dams were 6.22 kg heavier than those out of Guernsey dams. The 6.22 kg difference associated with breed of dam compared with the 2.54-kg difference associated with breed of sire is evidence for a breed, maternal effect on birth weight. Tbe gestation period of crossbreds was only 0.5 day shorter than that for purebreds. Male calves were carried 1.2 days longer than females, calves by Holstein sires were carried 4.5 days less than those by Guernsey sires, and for each increase of one-eighth-Holstein in the genotype of the dam the gestation period of the calf decreased 0.33 day; thus, Holstein dams carried their calves 2.6 days less than Guernsey dams. A comparison