Journal of Animal Science, Vol 76, Issue 9 2464-2473, Copyright © 1998 by American Society of Animal Science

JOURNAL ARTICLE

Effects of frequency of supplementation on dry matter intake and net portal and hepatic flux of nutrients in mature ewes that consume low-quality forage

C. R. Krehbiel, C. L. Ferrell and H. C. Freetly
Roman L. Hruska U.S. Meat Animal Research Center, ARS, USDA, Clay Center, NE 68933, USA.

Our objective was to determine the effects of frequency of soybean meal (SBM) supplementation on forage intake and net portal-drained viscera (PDV) and hepatic flux of nutrients in ewes that consume low-quality forage. Six Polled Dorset ewes (BW+/-SD = 82+/-9 kg) fitted with hepatic venous, hepatic portal, abdominal aortic, and mesenteric venous catheters were used in a replicated 3 x 3 Latin square design. Ewes consumed bromegrass hay (7.5% CP; DM basis). Treatments were no supplement (control), SBM fed once every 24 h, or SBM fed once every 72 h. In the SBM treatments, SBM was fed to provide 80 g/d of CP. Blood flow and net flux measurements were made on the 3rd d of each period so that ewes supplemented every 72 h were sampled the day of, the day after, and 2 d after supplementation. Arterial concentrations of alpha-amino N (AAN) and ammonia N were lower (P < .01) when SBM was fed, whereas arterial concentrations of urea N and oxygen were higher (P < .01). Feeding SBM increased net PDV release of AAN and ammonia N, net PDV removal of urea N, and oxygen consumption. A SBM x sampling day interaction (P < .05) occurred and resulted in greater net PDV absorption of AAN and ammonia N on the day after SBM supplementation when ewes were fed SBM on a 72-h interval. Net hepatic removal of AAN, ammonia N, and oxygen, and net hepatic release of urea N were greater (P < .01) with feeding SBM. The results indicate that the interval of SBM supplementation may affect the pattern of absorption without affecting the net absorption of nutrients.

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