Breed and sex differences in equally mature sheep and goats 1. Growth and food intake

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Abstract
Genetic size-scaling accounts for most of the variation found among mammalian species in food intake and growth rate, with food conversion efficiency independent of the body size of the species. Is the same true of breeds and strains within species?Animals from Soay, Welsh Mountain, Southdown, Finish Landrace, Jacob, Wiltshire Horn and Oxford Down sheep breeds and from a breed of feral goats were grown to 0·40, 0·52, 0·64 or 0·76 of the mean mature weight of their breed and sex. Food was offered ad libitum and individually recorded.Allometric growth coefficients were obtained for fleece weight, femur weight and femur length. Fleece was late maturing and femur early.Breed and sex size-scaling coefficients, obtained by regression of breed and sex means on mature size, were similar to those found at the species level for age from conception to slaughter, time taken to mature and food conversion efficiency. Coefficients were higher than expected for total and daily food consumption, especially at early stages of maturity. Most breed coefficients were close to expectation while sex coefficients were somewhat higher than expected.There were significant breed deviations: Welsh Mountain, Oxford Down and probably Soay sheep required less time and Jacob sheep and feral goats required more time to mature than expected from differences in mature size. Soay and Welsh Mountain sheep appeared to be more efficient and feral goats and Jacob sheep less efficient food converters over the same maturity interval.