Postprint version. Published in Domestic Animal Endocrinology, Volume 10, Issue 4, October 1, 1993, pages 315-324.
Copyright © 1993 Elsevier.
NOTE: At the time of publication, the author Jeffrey D. Armstrong was not yet affiliated with Cal Poly.
The definitive version is available at https://doi.org/10.1016/0739-7240(93)90035-A.
Feed restriction often increases serum somatotropin (ST) and decreases insulin-like growth factor-I (IGF-I) in ruminants; however, the mechanisms responsible for this change in ST and IGF-I are not well defined. We investigated the effects of feed restriction on serum ST, IGF-I, IGF binding proteins (IGFBP), insulin and nonesterified fatty acids (NEFA) in cyclic Angus and Charolais heifers (n=15) previously immunized against growth hormone releasing factor (GRFi) or human serum albumin (HSAi). Cows were fed a concentrate diet ad libitum (AL) or were restricted to 2 kg cotton seed hulls (R) for 4 d. Each heifer received each dietary treatment in a single reversal design. As anticipated, GRFi decreased ST, IGF-I and insulin (P