A study of factors which influence birth and weaning weight in lambs.

303 birth and weaning weights of West African (WA), Black-headed Persian (BP) West African crossbred .(WAC) and Dorset Horn crossbred (DHC) lambs were analysed by Least Squares. The lambs came from the flock in the Agronomy Faculty. They were kept indoors from birth to three weeks old ant were supplemented with grass and concentrate. The effects of breed, sex, month of birth, year of birth, litter size, single and twin and the covariable ewe weight at parturition were studied. Analysis of Variance indicated a significant (P < 0.01) effect of breed, sex, year, litter size and ewe weight on weaning weight. Adjusted means were 2.33, 2.41. 2.50, 2.96 for birth weight and 12.79, 12.18, 13.67 and 15.78 kg for weaning weights in breeds WA, BP, WAC and DHC. Birth and weaning weights for the ram lambs were 2.61 and 14.55 kg, while for ewelambs they were 2.49 and 12.74 kg; for single 2.83 and 14.55 kg ant for twin births 2.27 and 12.74 kg respectively. Mean ewe weight was 33.69 kg with regression coefficients of 0.60 and 0.50 with birth and weaning weights respectively. The importance of sheep production as a source of animal protein in Venezuela has been increasing during recent years. The relationship of birth weight to weaning weight and weaning weight to slaughter weight is economically very important in lamb production and is affected by genetic, physiological and environmental factors. These factors have been studied in temperate breeds under environmental and management conditions very different to our own but there is very little information available relating to tropical sheep breeds. The objectives of this work were to study the effects of breed, sex, month of birth, year of birth, litter size and ewe weight at parturition on birth weight and weaning weight in lambs of tropical breeds, and their crosses with temperate breeds, maintained under intensive production systems.