Genetic and environmental relationships of body weight, milk yield and litter size in Damascus goats

Abstract

Data from two experimental stations over several years were studied for genetic and environmental relationships between adult body weight, milk yield and litter size. They comprised 844 parturition and lactation records of 295 3-year-old and older goats from 94 sires (set No. 1; two stations, used for genetic analyses), and 557 records of milk yield, litter size and litter weight extending over two successive lactations (set No. 2; one station, used for environmental relationships). Postkidding body weight averaged 70.3±9.1 kg. During suckling goats lost 4.8±6.6 kg and then gained 3.4±6.5 kg until mating. Body weight increased curvilinearly, weight loss to weaning increased and weight gain after weaning decreased linearly with advancing age. Year, litter size and kidding interval were also significant sources of variation in body weight. Heritabilities and repeatabilities were 0.20±0.11 and 0.65±0.03 for postkidding body weight; 0.29±0.12 and 0.49±0.04 for 90-day milk yield after weaning; 0.35±0.13 and 0.46±0.04 for total postweaning milk yield; and close to zero for litter size and weight traits. Genetic and phenotypic correlations of body weight with 90-day milk yield were 0.14±0.31 and 0.08, with total milk yield of 0.03±0.09. Each kg of net weight gain during pregnancy accounted for 2.4 kg more milk and extended lactation by 0.77 days, while each kg of body weight loss during suckling was associated with 1.05 kg more milk after weaning. Milk production after weaning was hardly affected by postkidding body weight. The latter appears to be important for milk yield by reflecting differential body condition at kidding time. Body weight at mating time was linearly related with litter size and weight at subsequent kidding. Each kg of body weight accounted for 0.013 and 0.010 more kids and 0.054 and 0.205 kg higher litter weight at birth and at weaning, respectively. It was concluded that non-genetic factors are more responsible for relationships between body weight, milk yield, litter size and litter weight than genetic factors. 90-day milk yield was genetically highly correlated to total postweaning milk yield and can be used as an alternative selection criterion.