Plasma Profiles of Insulin-like Growth Factor-I for 24 Hours and after Injection of Bovine Growth Hormone in Dairy Heifers

Plasma concentrations of insulin-like growth factor-I(IGF-I) and growth hormone(GH) in four Holstein-dairy heifers were measured. Secretory patterns of IGF-I for 24 hours were less pulsatile than those of GH. Individually calculated average concentrations of plasma GH of heifers for 24 hours were 3.1±2.2, 5.0±4.3, 7.0±6.0 and 9.5±1.1.7ng/ml, whereas 24 hour average concentrations of IGF-I for the corresponding heifers were 34.3±5.5, 36.5±6.7, 41.2±11.0 and 48.6±6.1ng/ml respectively. Heifers with higher averages of plasma GH for 24 hours showed higher averages of plasma IGF-I. On the other hand, plasma concentrations of GH and IGF-I for dairy heifers were also measured after a single subcutaneous injection(500μg/kgBW) of recombinant DNA derived bovine growth hormone(rbGH). Plasma GH levels increased to peak around 4-6 hours(154±47ng/ml at 4 hours, and 155±56ng/ml at 6 hour safter rbGH injection) and they recovered to basal levels within 32 hours after the injection. Plasma IGF-I concentrations began to increase 6 hours after the rbGH injection and statistical higher levels(p