title: The effect of dietary nitrogen and protein on feed intake, nutrient digestibility, and nitrogen flux across the portal-drained viscera and liver of sheep consuming high-concentrate diets ad libitum.
abstract: Our objectives were to determine the influences of supplemental nonprotein N or protein on feed intake, digestibility, and postabsorptive N metabolism in sheep fed a high-concentrate diet for ad libitum consumption. Nine Romanov-sired, crossbred wethers (13 mo old; 52 kg) were fitted with catheters in a mesenteric artery, mesenteric vein, portal vein, and hepatic vein. Wethers consumed a 95% concentrate diet ad libitum. Treatments consisted of control (no supplemental N; 6.6% CP) or supplemental urea (11.4% CP), soybean meal (SBM; 11.2% CP) or ruminally undegradable protein (BFM; 11.2% CP; 50:50 blood meal and feather meal). Intake or apparently digested intake of DM, OM, and energy did not differ between control and N-supplemented (P > 0.40), or between urea- and protein-supplemented (P > 0.40), but were greater (P < 0.05) in SBM- than in BFM-supplemented wethers. Intake and apparently digested intake of N were less (P < 0.01) in wethers fed the control diet than in those receiving N supplementation but were less (P = 0.03) in BFM- than in SBM-supplemented wethers. Neither portal nor hepatic venous blood flows differed (P > 0.15) among treatments. Net portal release and hepatic uptake of alpha-amino N and ammonia N and hepatic release of urea N were greater (P < 0.05) in wethers supplemented with N than in controls, but portal-drained viscera (PDV) uptake of urea N did not differ (P > 0.40) among diets. Splanchnic release of a-amino N and ammonia N did not differ from 0 or among diets (P > 0.10), but net release of urea N was less (P = 0.05) for control than for sheep receiving N supplementation. No differences (P > 0.10) in blood concentration within vessel or net flux across PDV, hepatic, or splanchnic tissues of alpha-amino N, ammonia N, or urea N were observed among wethers receiving supplemental N. Net uptake of oxygen by the PDV did not differ among diets, but hepatic uptake was less (P < 0.05) in control and urea-supplemented sheep than in sheep receiving SBM or BFM. These observations suggest that the source of supplemental N had no large effects on the overall N economy of the animals used in this study.
authors.affiliation: Roman L. Hruska U. S. Meat Animal Research Center, USDA, ARS, Clay Center, NE 68933-0166, USA. ferrell@email.marc.usda.gov
authors.forename: C L
authors.initials: CL
authors.lastname: Ferrell
authors.forename: H C
authors.initials: HC
authors.lastname: Freetly
authors.forename: A L
authors.initials: AL
authors.lastname: Goetsch
authors.forename: K K
authors.initials: KK
authors.lastname: Kreikemeier
mesh_terms: D000818:Animals; D004032:Diet / Q000662:veterinary*; D004044:Dietary Proteins / Q000494:pharmacology*; D019587:Dietary Supplements; D004063:Digestion; D002149:Energy Intake / Q000187:drug effects*; D008099:Liver / Q000378:metabolism*; D008297:Male; D009584:Nitrogen / Q000378:metabolism*; D011168:Portal System; D012756:Sheep / Q000378:metabolism*; D013048:Specimen Handling / Q000662:veterinary; D014508:Urea / Q000494:pharmacology; D014781:Viscera
chemical_list: D004044:Dietary Proteins; D014508:Urea; D009584:Nitrogen