There has been considerable interest recently in the use of growth hormone (somatotrophin) to enhance growth, carcass leanness and milk yield in a number of species. Despite the similarity of bovine and ovine growth hormone, the administration of exogenous somatotrophin to lambs has produced disappointing results. Conceivably, stimulation of endogenous GH secretion may be more beneficial, and in this communication we present our preliminary results on the effective doses and rates of administration of growth hormone releasing factor in a study of the neuroendocrine regulation of growth hormone secretion in sheep. Sheep were housed indoors on a complete pelleted diet and were fitted with jugular vein catheters. Some sheep were also fitted with cannulae placed in a lateral ventricle of the brain. Bovine GRF was given at different doses to the sheep either intravenously (iv), intracerebroventricularly (icv) or intramuscularly (im) and plasma GH levels monitored. There was a dose-dependent increase in GH levels when the GRF was given iv, with both 30 and 3 ug being effective, while im administration was only effective at 30 ug. Central administration (icv) was also effective at both dose but did not stimulate GH release at 300 ng. Further studies are required to elucidate the mechanisms underlying GRF stimulation of GH release, but the efficacy of GRF as a growth promoter can be investigated using intramuscular administration.
Proceedings of the New Zealand Society of Animal Production, Volume 50, , 55-58, 1990
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