EFFECTS OF GROWTH HORMONE-RELEASING FACTORS AND COTTONSEED MEAL ON HORMONES AND METABOLITES IN PLASMA FROM LAMBS FED LUCERNE CHAFF AD-LIBITUM

This study was part of an experiment on the effects of cottonseed meal (CSM) and growth hormone-releasing factor (GRF) on growth in lambs fe d lucerne chaff. Forty-eight crossbred lambs were fed lucerne chaff ad libitum, alone or with a cottonseed meal supplement (CSM; 300 g/day). Eight lambs from each group were injected twice daily with recombinan t or synthetic GRF (rGRF and sGRF respectively; 30 mu g per kg body we ight/day) or excipient only for 28 or 30 days. Jugular blood samples w ere obtained on days 0, 7, 14, 21 and 28. On day 29, blood samples wer e taken from selected lambs (n = 2/group) at 0, 20, 40, 60, 80, 100, 1 20, 160 and 240 min after injection. Supplementation of lucerne chaff with CSM generally increased glucose and urea concentrations in plasma , reflecting improved energy and protein status. However, concentratio ns of growth hormone, insulin-like growth factor-1 and insulin were un affected by CSM, as were plasma proteins, triacylglycerols and non-est erified fatty acids. Injection of rGRF and sGRF stimulated secretion o f growth hormone (GH), insulin-like growth factor-1 (IGF-1) and insuli n. Peak GH concentrations (20 min) following injection of GRF appeared to be higher in lambs fed CSM than in those receiving lucerne chaff a lone. In contrast, maximal concentrations of IGF-1 were seen after 14 days of treatment. These changes were accompanied by increased plasma glucose, with no changes in triacylglycerols, non-esterified fatty aci ds and protein. Plasma urea was reduced by GRF, indicating that amino acids were diverted away from catabolism towards protein synthesis. Th ese two sources of GRF were very similar in their endocrine and metabo lic effects. This confirms similar observations regarding their effect s on growth performance and carcass composition.