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Journal of Animal Science, Vol 71, Issue 11 3033-3042, Copyright © 1993 by American Society of Animal Science

JOURNAL ARTICLE

Changes in serum somatotropin, somatotropin mRNA, and serum and follicular insulin-like growth factor-I in response to feed restriction in cows actively immunized against growth hormone-releasing factor

C. J. Kirby, J. D. Armstrong, B. G. Huff, R. L. Stanko, R. W. Harvey, E. P. Heimer and R. M. Campbell
Department of Animal Science, North Carolina State University, Raleigh 27695-7621.

Cyclic cows immunized against growth hormone-releasing factor (GRFi, n = 19), human serum albumin (HSAi, n = 10), or not immunized (CON, n = 18) were used to investigate the effects of feed restriction on serum and pituitary somatotropin (ST), pituitary ST mRNA, and serum and follicular IGF-I. Cows were either fed 2.7 kg/d cottonseed hulls (R) or given ad libitum access to feed (AL) for 15 d. Ovaries bearing the largest follicle and pituitaries were collected on d 14, at 44 to 45 h after injection of prostaglandin F2 alpha. Data from CON and HSAi cows were similar; thus, data were combined (represented as CON). Serum ST (nanograms/milliliter) on d 13 was greater (P < .09) in CON-R (5.3) than in CON-AL (3.9), whereas ST in GRFi-AL (1.1) and GRFi-R (1.1; pooled SE = .4) were similar. Hemipituitary weight (grams) and ST mRNA (arbitrary units) were greater (P < .05) in CON (1.5 +/- .1 and 135 +/- 25) than in GRFi (1.0 +/- .1 and 90 +/- 18) cows. Across immunization, ST mRNA and pituitary ST concentration (mg/100 mg of tissue), respectively, were greater (P < .06) in R (152 +/- 22 and 22.5 +/- 1.9) than in AL (73 +/- 16 and 17.3 +/- 1.8) cows. Immunization and diet decreased (P < .05) serum IGF-I (nanograms/milliliter) on d 13 (CON, 176 +/- 7 vs GRFi, 42 +/- 8; AL, 120 +/- 7 vs R, 98 +/- 8). Concentrations of IGF-I in follicular fluid (FFL) from the largest follicle were lower in GRFi (29 +/- 3) than in CON (102 +/- 6) cows; however, IGF-I in FFL was similar in AL (70 +/- 9) and R (71 +/- 10) cows. In conclusion, GRFi decreased serum ST and IGF-I, and decreased ST mRNA. Feed restriction increased serum ST and ST mRNA, and decreased serum IGF-I. Although feed restriction and GRFi decreased serum IGF-I, concentrations of IGF-I in FFL were decreased only by GRFi.


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[Abstract] [Full Text] [PDF]


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Copyright © 1993 by the American Society of Animal Science.