Profiles of growth hormone and insulin secretion, and glucose response to insulin in growing Japanese Black heifers (beef type): comparison with Holstein heifers (dairy type).

Nine Japanese Black and 10 Holstein heifers ranging from 1 week (wk) to 18 months (mo) old received a single bolus intravenous injection of GH-releasing factor (GRF, 0.25-microg/kg BW), glucose (112.5-mg/kg BW) or insulin (0.2-U/kg BW) at various stages through 18 mo of age. The GH secretory response to exogenous GRF in Japanese Black heifers was lower than that in Holstein heifers at all stages of growth. While insulin secretory function was not very different in both breeds from 1 to 12 mo of age, the insulin response was much higher in Japanese Black heifers than in Holstein heifers after sexual maturation. The degree of decrease in plasma glucose following insulin injection was similar in both breeds at each stage of growth. It is concluded that compared with Holstein heifers, Japanese Black heifers have lower GH and higher insulin secretory functions, and that the two breeds have similar glucose response to insulin.