Abstract
Previous studies have found that weaned lambs from Coopworth sheep selected for low (lean) backfat depth have higher mean plasma growth hormone (GH) levels and heavier pituitary glands than those selected for high (fat) backfat depth. This study examined whether these differences between genotypes occurred in young suckling lambs. Six ewes from each genotype which were suckling a male/female set of twins were kept indoors. Four weeks after birth, ewes and lambs were blood‐sampled for 6 hours at 10 minute intervals and plasma GH levels measured. Lambs were then slaughtered and carcass composition determined. Subcutaneous fat depth was lower in lean than fat lambs at four of the five different sites measured (P < 0.05). Lean lambs and ewes had greater mean and basal plasma GH concentrations and a greater amplitude of GH pulses than fat sheep (P < 0.05). Plasma IGF‐I levels did not differ (P < 0.05) between genotype for either ewes or lambs. Pituitary glands were heavier (P< 0.001) in lean than fat genotype lambs (0.29 versus 0.19, SED = 0.017 g). It is concluded that differences between genotypes in body composition, plasma GH, and pituitary gland weight occur at an early age. An investigation of foetal development patterns may be required to elucidate the relationship between these parameters.
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