Temporal pattern of insulin-like growth factor-I response to exogenous bovine somatotropin in lactating cows.
The effect of exogenous bovine somatotropin (bST) treatment on the temporal pattern of insulin-like growth factor-I (IGF-I) in serum of four multiparous Holstein cows was examined. Cows (190 +/- 24 days postpartum) were treated with daily subcutaneous injections of recombinant bST (40 mg) or excipient for 12-day periods in a crossover experimental design. During excipient treatment, concentrations of IGF-I in serum were relatively constant throughout the day and averaged 70 ng/ml. Following the first bST injection, serum IGF-I began increasing after a lag of 5 to 7 hr and progressively increased over the first 2 days of treatment. Serum IGF-I levels were approximately 2-fold greater than control values at the end of day 1 of bST treatment, with a 3-fold elevation observed at the end of day 2. Concentrations of IGF-I in serum plateaued by day 3 of bST treatment. Serum concentrations of IGF-I did not follow the oscillating pattern of bST in serum resulting from daily bST injections. Milk yield (3.5% fat-corrected) plateaued after 6 days of bST treatment and was increased 61% (+15.3 kg). Both IGF-I and milk yield remained essentially constant across days for the remainder of treatment. Following cessation of treatment, serum IGF-I and milk yield gradually declined, returning to control values after approximately 4 days. The temporal pattern of circulating concentrations of IGF-I is consistent with a role for IGF-I in mediating a portion of the effects of exogenous bST in lactating cows.
Cohick
W S
WS
Department of Animal Science, Cornell University, Ithaca, NY 14853-4801.
Plaut
K
K
Sechen
S J
SJ
Bauman
D E
DE
D000818:Animals; D002417:Cattle / Q000502:physiology*; D004032:Diet; D002149:Energy Intake; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000097:blood / Q000378:metabolism*; D007774:Lactation / Q000187:drug effects*; D008892:Milk / Q000032:analysis / Q000378:metabolism; D011247:Pregnancy; D013002:Somatomedins / Q000378:metabolism*
D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone