Determinants of birth weight and its size as an onset representative of growth potential in goat and sheep meat production
Keywords:Birth weight, Genotype, Non-genetic factors, Goats, Sheep
Birth weight is an important growth trait in goats and sheep which is of remarkable productive and economic interest for efficient meat production. Birth size in goats and sheep follows the pattern of prenatal growth and development, which is determined by genetics and a variety of environmental factors. Information on determinants of birth weight is of concern to producers, over and above the animal breeders, because birth weight has much influence on kid/lamb weaning weight hence later the overall flocks’ meat production. Paternal and maternal genotypes are important sources of variation on birth weight in goats and sheep. By way of illustration apart from breed effect, environmental factors influencing birth weight include nutrition, dam age and parity, season and year, sex and birth type. These factors and their interactive forces proffer the overall impression as explanatory variables for birth weight variation in goats and sheep. Males have superior birth weight as compared to females and this can be perpetuated up until weaning age. The kidding/lambing season greatly influence birth weight due to its bearing on availability of forage, hence it is suggested that mating schedules for dams should be designed in a manner where pregnancies should coincide with adequate grazing in order to attain optimal birth size. The differential pattern of feed resources from season to season or month to another might affect dam’s nutrition throughout their pregnancy consequently the birth outcome. Kids/lambs of primiparous ewes/does have a birth weight disadvantage, hence producers should consider alternatives for managing underweight birth on an individual flock basis. A pronounced effect of litter size, with compromised birth size in kids/lambs born as triplets being lower as compared with those born as twins, which in turn is lower than that in kids/lambs born as singles. Interactions of determinants of birth weight are important in goats and sheep namely breed by parity, breed by birth type and birth type by parity. The point to note is that birth weight is highly correlated to anticipated future weights until mature or slaughter weight which can presumably influence meat production. An understanding of the determinants of birth weight will warrant modifications in the breeding and management schedules to minimize influences, which reduce meat production efficiency. The present review is undertaken to give an insight on the determinants of birth weight for instance age of dam, type of birth, sex, year and month of birth.
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