ENDOCRINE AND METABOLIC CHANGES IN NEONATAL CALVES IN RESPONSE TO GROWTH-HORMONE AND LONG-R-3 INSULIN-LIKE GROWTH-FACTOR-I ADMINISTRATION

Postnatal growth is primarily controlled by growth hormone (GH) and in sulin-like growth factor-I (IGF-I). We have studied effects of recombi nant bovine GH (rbGH) and Long-R-3-insulin-like growth factor-I (Long- R-3-IGF-I) on metabolic and endocrine characteristics of neonatal calv es. Group GrC (control) was fed colostrum as first meal and then milk replacer up to day 7. Groups GrIGF(f), GrIGF(i) and GrGH were fed as G rC. In group GrIGF(f), Long-R-3-IGF-I (50 mu g/[kg x day], twice daily for 7 days) was fed together with colostrum or milk replacer and in g roup GrIGF(i), Long-R-3-IGF-I (50 mu g/[kg x day], twice daily for 7 d ays) was injected subcutaneously at times of feeding. Calves of group GrGH were injected rbGH (1 mg/[kg x day, s.c.], twice daily for 7 days ) at times of feeding. While orally administered Long-R-3-IGF-I had no effects, subcutaneously administered Long-R-3-IGF-I lowered plasma gl ucose and insulin concentrations (p < 0.05). In group GrGH, day-2 post prandial plasma insulin concentrations were increased more than in Lon g-R-3-IGF-I-treated groups (p < 0.05) and day-2 postprandial prolactin responses were greater in group GrGH than in controls (p < 0.05). Oth er traits (lactic acid, nonesterified fatty acids, glucagon, cortisol, thyroxine and 3.5.3'-triiodothyronine) exhibited age-dependent change s, but were not significantly affected by rbGH or Long-R-3-IGF-I. The study shows, that parenteral, but not oral, Long-R-3-IGF-I affects pla sma glucose and insulin concentrations, and that rbGH transiently infl uences plasma prolactin concentrations in neonatal calves.