THE LIVE WEIGHT OF BEEF COWS AS INFLUENCED BY AGE AT FIRST CALVING AND WINTERING PLANE OF NUTRITION

Shorthorn heifers were bred to calve either at 24 months or at 36 months. During the wintering period when they were between 18 months and 2 years of age, they were fed either hay and grass silage or the same roughage with.5 kg of concentrate per 100 kg liveweight.Calving at 2 years of age significantly decreased the body weight of the cows by 88 kg at the age of 30 months, and by 54 kg at 42 months, as compared with calving for the first time at 3 years of age. By the time the cows were [Formula: see text] years old, the difference had diminished to a non-significant level of 28 kg. These differences in bodyweight were not explainable by different number of calvings under the various treatments, or by the culling of lighter cows in certain groups.Feeding meal during the second wintering period significantly increased the weights of the cows by 57 kg at the end of the treatment. The difference decreased to 38 kg 6 months later, and became negligible at subsequent weighings.

COMPARATIVE GROWTH RATES OF SHORTHORN AND CROSSBRED BEEF CALVES FROM BIRTH TO 1 YEAR OF AGE

During the 3 years 1959, 1960, and 1961 the purebred Shorthorn herds at the Experimental Farms at Ottawa, Lennoxville, and Kapuskasing were randomly bred to Shorthorn, Angus, Hereford, and Charolais bulls. Three bulls per breed were used each year. Birth weights and rate of gain from birth to 1 year of age were measured in the 254 calves produced. Breed of sire, sex, year of birth, and age of dam were found to be significant sources of variation contributing to weight at birth, but only breed of sire was a significant source of variation in the rate of gain from birth to 1 year of age. Charolais-sired calves were heaviest at all ages, and Hereford next heaviest at all ages. Angus-sired calves were lightest at birth two years of three, but at weaning they were heavier than the purebred Shorthorn calves. The purebred Shorthorns were lightest at weaning and at 1 year of age.