Effect of bovine growth hormone administered in various patterns on nitrogen metabolism in the Holstein steer

Understanding the relationship between the components of the growth hormone (GH) secretory pattern and metabolism may provide a basis for designing studies aimed at exploring how to manipulate GH secretion to stimulate protein gains. In a 4 X 4 Latin square design with one additional period to replicate the first treatment period, eight Holstein steers, 195 kg, were assigned to receive the following treatments: 1) 10-day iv infusion (1) of GH; 2) 10 d of six iv pulse injections (P) of GH daily; 3) 10-d combination of infusion and pulses (IP) and 4) controls (C) receiving no injections or infusions. The GH dose was 48 micrograms/kg-1.d-1. Daily feed, total urine and total fecal collections were made for nitrogen (N) determination. Individual samples for d 3 through 6 (collection A) and d 7 through 10 (collection B) were pooled for analysis. Concentrations of GH were determined in blood samples collected on d 10. In collection A, and N metabolism measures were similar among all treatment groups; however, in collection B, treatment of steers with exogenous GH increased the apparent digestion coefficients for dry matter (P less than .01) and dietary N (P less than .01) and also increased the percentage N retained (P less than .01) and the retention of metabolizable N (P less than .05). Metabolic responses were similar among the different patterns of administration. The positive effects on metabolism during collection B not found in collection A were due to length of treatment with GH, as indicated by the fact that none of the measures of metabolism were changed with time in the controls. Serum concentrations of GH were increased (P less than .001) in GH-treated steers compared with controls. These results support the hypotheses that treatment of normal, growing steers with exogenous GH stimulates nitrogen accretion and that pattern of administration does not significantly affect the N response.