EFFECT OF DIETARY ENERGY-INTAKE AND EXOGENOUS PORCINE GROWTH-HORMONE ADMINISTRATION ON CIRCULATING PORCINE GROWTH-HORMONE CONCENTRATION ANDRESPONSE TO HUMAN GROWTH HORMONE-RELEASING FACTOR ADMINISTRATION IN GROWING SWINE

In a 2 x 2 treatment array (n = 4 pigs/treatment), the effects of feed intake (ad libitum vs. restricted to 60% ad libitum) and the daily ad ministration of excipient buffer or porcine pituitary-derived growth h ormone (GH) at a dose of 100 mu g/kg body weight per day on serum GH p rofile and human growth hormone-releasing factor (hGRF) response were examined in barrows weighing 55 kg. Feed intake treatment was implemen ted from 25 to 55 kg live weight. Buffer or GH treatment was implement ed for 10 d before sampling. After GH treatment, the integrated serum GH concentration area was 25% greater in barrows fed restrictively. Da ta are consistent with the suggestion that GH dose to improve the effi ciency of lean tissue deposition be adjusted according to feeding regi men. The serum GH response to hGRF was also altered by level of feed i ntake. The ad libitum feeding of buffer-treated animals resulted in a monophasic serum GH response to hGRF, whereas barrows fed restrictivel y had a biphasic response to hGRF. Together, these data suggest that f eed intake pattern alters GH secretion and as such could influence the practical implementation of somatotropin as a metabolism modifier in swine.