Effects of recombinant bovine somatotropin (rbST) and season on plasma and milk insulin-like growth factors I (IGF-I) and II (IGF-II) in lactating dairy cows.
During two studies, effects of recombinant bovine somatotropin (rbST) on plasma and milk IGF's in cows adapted to summer (S; 12 cows) or winter (W; 12 cows) conditions were evaluated. Each study consisted of on-farm periods (30 days) followed by climatology chamber periods (CC; 30 days). Cows were given daily injections of rbST, Sometribove, USAN (25mg/day; 6 cows each study) or saline (control; 6 cows each study). During on-farm periods, blood and milk (am and pm) samples were collected once weekly. During CC periods, blood samples were collected every 2 days and milk samples (am and pm) were collected daily. Plasma IGF-I and IGF-II were increased in cows treated with rbST. A pronounced seasonal pattern in basal and rbST-stimulated plasma IGF-I but not IGF-II was detected. Higher basal and rbST-stimulated plasma IGF-I concentrations in S occurred despite large decreases in feed intake and energy balance. Milk IGF-I and IGF-II was not affected by rbST treatment or season. Although milk IGF-I and IGF-II concentrations were unaffected by rbST treatment, total IGF-output increased due to increased milk yield. The observed seasonal patterns in plasma IGF-I may be indicative of seasonal differences in the coupling of the somatotropin-IGF axis. In particular, we failed to detect an uncoupling of the somatotropin-IGF-I axis in S despite an induced negative energy balance during thermal stress.
Collier
Robert J
RJ
Department of Animal Science, University of Arizona, 204 Shantz Building, PO Box 210038, Tucson, AZ 85721, United States. rcollier@ag.arizona.edu
Miller
M A
MA
McLaughlin
C L
CL
Johnson
H D
HD
Baile
C A
CA
D000818:Animals; D002417:Cattle / Q000378:metabolism*; D003612:Dairying; D004734:Energy Metabolism / Q000187:drug effects; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D007774:Lactation / Q000097:blood / Q000187:drug effects / Q000378:metabolism; D008892:Milk / Q000187:drug effects / Q000378:metabolism*; D017440:Photoperiod; D010949:Plasma / Q000187:drug effects / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D012621:Seasons; D013312:Stress, Physiological / Q000378:metabolism; D013696:Temperature
D011994:Recombinant Proteins; C073294:growth hormone, bovine; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone