Genetic variation in growth and body dimensions of Jersey and Limousin cross cattle. 1. Pre-weaning performance

During a 5-yr period, 1994-1998, pre-weaning and weaning data were collected on 591 calves produced by mating either straightbred Jersey, straightbred Limousin or F1 (LimousinxJersey) bulls to mature purebred Jersey or Limousin cows. Traits recorded included birth and weaning weight, height, length, girth, fat depth and a measure of muscle (ratio of stifle to hip width expressed as a percentage). All traits were analyzed assuming a model with sire and dam random effects that included effects of year and date of birth, sex, breed and yearxsex interaction. Main effects were generally significant with few exceptions. Direct genetic effects were large for weight, height, girth and muscle with a breed trend from purebred Jersey (small) to purebred Limousin (large). At weaning, the maternal effect of the Jersey dam was positive for weight (10.9±4.9 kg), girth (3.7±1.0 cm) and muscle (6.0±0.9%). Heterosis was highly significant and positive only for fat depth (1.5±0.2 mm) with the F1 progeny being the fattest, followed by the backcrosses, then purebred Jersey and purebred Limousin. Also, significant (p