Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/1998
Publication Date: N/A
Interpretive Summary: Forages such as dormant grass consumed by cattle or sheep grazing winter pastures or rangeland generally contain inadequate amounts of available protein and energy. To prevent weight loss of animals consuming those forages, supplements are generally provided to supply additional protein and energy. This experiment was conducted to determine the effects of frequency of supplementation on forage intake, nutrient supply and pattern of nutrients available to the animal. Mature ewes were offered bromegrass hay (7.5% protein) ad libitum and received either no supplement or soybean meal (82 g/d) daily or at 3-d intervals. Supplementing soybean meal increased forage intake, and protein and energy available to the animal. Although the pattern of absorption was different when soybean meal was fed every third day, net absorption of nutrients was generally not affected by frequency of supplementation.
Technical Abstract: The objective was to determine the effects of frequency of soybean meal supplementation on forage intake and net portal-drained viscera (PDV) and hepatic flux of nutrients in ewes consuming low-quality forage. Six Polled Dorset ewes (82 +/- 9 kg) fitted with hepatic venous, hepatic portal, abdominal aorta, and mesenteric venous catheters were used in a replicated 3 x 3 Latin square design. Ewes were offered brome hay (7.5% CP) ad libitum. Treatments were no supplement (control), soybean meal (SBM) fed once every 24 h, or SBM fed once every 72 h. Soybean meal was fed in amounts to provide 80 g/d of CP. Blood flow and net flux measurements were made 3 d of each period so that ewes supplemented on a 72-h interval 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 egreater (P < .01). When SBM was fed, net PDV absorption of AAN, ammonia N and oxygen consumption were greater (P < .01) than in control ewes. Net PDV removal of urea N was greater (P = .04) when SBM was fed. A SBM sampling day interaction (P < .05) occurred as net PDV absorption of AAN and ammonia N were greater the day after supplementation than the day of or 2 d after in ewes 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) in ewes fed SBM compared with control ewes. Interval of SBM supplementation may affect the pattern of absorption but does not affect net absorption of nutrients.