Least squares constants were fitted for weaning percent and pre-weaning death loss of calves resulting from 3994 pasture matings over a 15 year period. There were 3 straightbred groups of cattle including Brahman, Shorthorn and Grade Shorthorn, and 9 groups of crossbred or mixed breeding. Weaning rates for breed of bull to which cows were mated were 61.4% for crossbred, 73.8% for Brahman and 76.1% for European bulls. Among females included in a Brahman-Shorthorn crossbreeding study, weaning rates for cows classified on proportion of blood were 65.8% for pure-breds, 69.6% for 3/4 bloods, and 86.7% for first cross cows. All environmental factors studied including lactation status of cow during breeding season, age of cow, year, and pasture had significant effects on weaning percent and ranked in importance in the order given. Significant approximate interactions noted were lactation x pasture, lactation x year, lactation x breed, pasture x year, pasture x age of cow and year x breed.