Some Genetic Aspects of Gestation Length, and Birth and Weaning Weights in Hereford Cattle

Length of gestation, birth weight and weaning weight were studied in 351 calves from eight different sires born in the same season. Neither sex, age of dam nor date of birth had a significant influence on the length of gestation, but all had a significant influence (P<.01) on birth and weaning weights. Adjustment factors were used to adjust the data for birth weight and weaning weight before a genetic analysis was made. The heritability estimates for length of gestation, birth weight, and weaning weight, based on paternal half-sib correlations, were 54, 67 and 11%, respectively. The heritability estimate for intrauterine growth was 63%, whereas for growth from birth to weaning it was only 3%. The genetic correlations were 0.44±0.28 for gestation length and birth weight, 0.41±0.42 for gestation length and weaning weight, 0.99±0.01 for birth weight and weaning weight and 0.93±0.07 for intra-uterine growth and growth from birth to weaning. It was concluded that many of the same genes responsible for variations in growth from conception to birth are also responsible for variation in growth from birth to weaning.