Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2006
Publication Date: 4/1/2007
Citation: Archibeque, S.L., Freetly, H.C., Ferrell, C.L. 2007. Net portal and hepatic flux of nutrients in growing wethers fed high-concentrate diets with oscillating protein concentrations. Journal of Animal Science. 85(4):997-1005. Interpretive Summary: Feeding livestock in confined areas can lead to an accumulation of nutrients, including nitrogen, which may have undesirable environmental impacts. There has been an increased focus on developing management strategies to minimize these impacts. Previous research in our lab indicated that oscillating dietary protein was a feasible method to reduce the excretion of nitrogen from finishing cattle without impacting performance. The current study demonstrates that this improvement in the use of nitrogen is accomplished, in part, by returning nitrogen to the stomach where it can be used again, rather than being eliminated in the urine. This indicates that oscillating dietary protein for finishing beef cattle may be effective for improving nitrogen use as producers try to plan for comprehensive nutrient management.
Technical Abstract: We hypothesized that oscillating dietary CP would improve N retention by increasing urea-N recycling to the rumen, compared to static dietary CP regimens. Chronic indwelling catheters were surgically implanted in a abdominal artery, mesenteric vein, hepatic vein, and portal vein of 18 growing Dorset × Suffolk wethers (44.65 ± 3.59 kg). Wethers had ad libitum access to the following diets: 1) Low (9.91% CP), 2) Medium (Med;12.50% CP), or 3) Low and High (14.19% CP) diets oscillated on a 48 h interval (Osc). Dry matter intake was greater (P = 0.04) in the Osc (1313 g/d) than the Low (987 g/d) fed wethers, but not those fed the Med diet (1,112 g/d). Nitrogen intake was not different between the Osc (25.4 g/d) and Med (22.2 g/d) fed wethers, but was reduced (P < 0.001) in wethers fed the Low diet (16.0 g/d). Osc wethers (6.66 g/d) retained more N than either Low (P = 0.01; 3.20 g/d) or Med (P = 0.04; 3.96 g/d) fed wethers. Arterial blood flow was not different (P = 0.20) between Osc (31 L/h) or Med (39 L/h) fed wethers but was greater (P = 0.02) in Low (66 L/h) fed wethers. Net release of alpha-amino N by the portal-drained viscera (PDV) did not differ (P = 0.84) among the Low (37.8 mmol/h) and Med (41.5 mmol/h) fed wethers, nor (P = 0.33) between the Osc (53.0 mmol/h) and Med fed wethers. Net PDV release of ammonia N was lower (P = 0.02) in Low fed wethers, which was accompanied by a similar decrease (P = 0.02) in hepatic ammonia N uptake. Urea N concentrations were (P = 0.05) reduced in arterial, portal, and hepatic blood in wethers fed the Low diet compared to Med fed wethers. Wethers fed the Osc diet tended (P = 0.06) to have a greater PDV uptake of urea N, but there was no difference (P = 0.73) in hepatic urea N release compared to those fed the Med diet. Net PDV uptake of glutamine tended to be greater (P < 0.06) in the Low (6.7 mmol/h) fed wethers than those fed the Med (2.7 mmol/h) diet. While not conclusive, these data indicate that oscillating dietary protein may improve N retention by increasing urea N recycling to the gastrointestinal tract.