Endocrine and metabolic changes in neonatal calves in response to growth hormone and long-R3-insulin-like growth factor-I administration.

Postnatal growth is primarily controlled by growth hormone (GH) and insulin-like growth factor-I (IGF-I). We have studied effects of recombinant bovine GH (rbGH) and Long-R3-insulin-like growth factor-I (Long-R3-IGF-I) on metabolic and endocrine characteristics of neonatal calves. Group GrC (control) was fed colostrum as first meal and then milk replacer up to day 7. Groups GrIGFf, GrIGFi and GrGH were fed as GrC. In group GrIGFf, Long-R3-IGF-I (50 micrograms/[kg x day], twice daily for 7 days) was fed together with colostrum or milk replacer and in group GrIGFi, Long-R3-IGF-I (50 micrograms/[kg x day], twice daily for 7 days) 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-R3-IGF-I had no effects, subcutaneously administered Long-R3-IGF-I lowered plasma glucose and insulin concentrations (p < 0.05). In group GrGH, day-2 postprandial plasma insulin concentrations were increased more than in Long-R3-IGF-I-treated groups (p < 0.05) and day-2 postprandial prolactin responses were greater in group GrGH than in controls (p < 0.05). Other traits (lactic acid, nonesterified fatty acids, glucagon, cortisol, thyroxine and 3.5.3'-triiodothyronine) exhibited age-dependent changes, but were not significantly affected by rbGH or Long-R3-IGF-I. The study shows, that parenteral, but not oral, Long-R3-IGF-I affects plasma glucose and insulin concentrations, and that rbGH transiently influences plasma prolactin concentrations in neonatal calves.