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Journal of Dairy Science Vol. 78 No. 7 1489-1497
© 1995 by American Dairy Science Association ®
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Long-Term Somatotropic and Galactopoietic Effects of a (1-30) Ethyl Amide Analog of Growth Hormone-Releasing Factor

H. A. Tucker 1, A. L. F. Terhune 1, L. T. Chapin 1, M. J. Vandehaar 1, B. K. Sharma 1, and W. M. Moseley 1

1 Department of Animal Science, Animal Reproduction Laboratory, Michigan State University, East Lansing 48824 and The Upjohn Company, 7921-25-4, Performance Enhancement Research, Kalamazoo, MI 49001

Thirty-five lactating Holstein cows (165 ± 8 DIM) received the following treatments for 96 d: uninfused controls; i.v. infusion of .9, 2.7, or 8.1 mg/d of Ile2, Ser8,28, Ala15, Leu27, Hse30-bovine growth hormone-releasing factor (1–30) ethyl amide; or i.v. infusion of 12 mg/d of recombinant Leu27, Hse45-bovine growth hormone-releasing factor (1–45) lactone. Concentrations of somatotropin in serum and SCM yield of cows infused with 1–30 releasing factor increased quadratically as the dose increased. Responses for somatotropin and SCM yield were quantitatively similar for cows infused with 2.7 and 8.1 mg of 1–30 or 12 mg of 1–45. While concurrently infused with the 1–30 or 1–45 as described, cows retained their ability to release somatotropin following an acute i.v. injection of 10 nmo1/100 kg of BW of either growth hormone-releasing factor 1–30 or 1–45. Mean concentrations of IGF-I in serum increased similarly in magnitude for cows infused at all doses of 1–30 or 1–45. The 1–30 releasing factor generally increased IGF-binding protein-3, but had little effect on IGF-binding protein-2. The 1–45 releasing factor did not significantly affect either binding protein. Yield of SCM was correlated with serum concentrations of somatotropin, but not with IGF-I. Concentrations of NEFA in serum were elevated through 36 and 50 d in response to the highest doses of 1–30 and 1–45, respectively. Treatment did not affect DMI, BW, or body condition score. In conclusion, continuous i.v. infusion of 2.7 and 8.1 mg/d of 1–30 and 12 mg/d of 1–45 similarly increased yield of SCM, somatotropin, and IGF-I without inducing refractoriness in the ability of the anterior pituitary gland to release somatotropin in response to a concurrent, acute challenge with 1–30 or 1–45.

Key Words: growth hormone-releasing factor • somatotropin • milk yield

Submitted on October 12, 1994
Accepted on February 22, 1995






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