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The University of Georgia, Athens 30602
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.
1 Appreciation is expressed to J. Barron and the UGA Beef Center staff for care of the animals, to A. Fielding, D. Nisbet, K. McKissack and all others who helped in the collection of blood samples, to B. Barrett for his laboratory assistance, to A. Nelson for statistical assistance and to B. Mabry for preparation for manuscript.
3 USDA-ARS Richard B. Russell Res. Center, Athens.
4 Dept. of Physiol. and Pharmacol., Auburn University, Auburn, AL.
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