Effect of Dietary Energy Source and Level on Serum Growth Hormone, Insulin-Like Growth Factor 1, Growth and Body Composition in Beef Heifers

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Abstract
Effects of fiber vs starch energy supplements on endogenous growth hormone (GH), insulin-like growth factor (IGF-1) and animal performance from weaning to breeding age were evaluated in 18, 9-mo-old beef heifers. Heifers had ad libitum access to wheat silage plus an average daily supplement intake of 1) 4.08 kg corn-soybean meal (SBM) (high energy-starch, HS), 2) 4.54 kg soyhulls (SH)-SBM (high energy-fiber, HF) or 3) 1.36 kg SH-SBM (low energy-fiber, LE). Serum samples were collected via jugular puncture every 10 d and were analyzed for IGF-1 by RIA. On d 45 and d 176, four heifers per treatment were fasted 18 h and serial blood samples collected via jugular cannulas every 15 min for 6.5 h. Arginine (.5 g/kg BW) was administered intravenously (ARG) to induce release of GH, and four additional samples of blood were collected. Samples were analyzed by RIA for GH. Mean fasted GH (6.4 ± .4, 8.3 ± .4 and 13.8 ± .4 ng/ml for HS, HF and LE, respectively) varied with energy source and level (P < .01). Mean GH following ARG was higher (P < .01) in heifers receiving LE (46.2 ± 4.7) than in those receiving HS and HF (23.5 ± 4.4 and 24.1 ± 4.6 ng/ml). Basal GH concentration and peak amplitude were higher (P < .05) in LE than in HS and HF treatments. Diet did not influence number or frequency of GH peaks. Mean IGF-1 values were similar for HS and HF heifers (P > .05) but were lower for LE heifers (P < .01). The LE heifers had lower (P < .05) ADG, backfat and ribeye area. We conclude that fiber supplements may overcome the depression in GH associated with grain feeding of heifers. Copyright © 1988. American Society of Animal Science . Copyright 1988 by American Society of Animal Science