Net portal and hepatic flux of nutrients in growing wethers fed high concentrate diets with oscillating protein concentrations

¹ USDA-ARS, US Meat Animal Research Center, Clay Center, NE 68933-0166

^* To whom correspondence should be addressed. E-mail: ferrell{at}email.marc.usda.gov.

	Abstract

We hypothesized that oscillating dietary CP would improve N retention by increasing portal drained viscera (PDV) uptake of endogenous urea-N, compared to static dietary CP regimens. Chronic indwelling catheters were surgically implanted in the abdominal aorta, a mesenteric vein, a hepatic vein, and the portal vein of 18 growing Dorset x Suffolk wethers (44.6 ± 3.6 kg). Wethers had ad libitum access to the following diets in a completely randomized block design: 1) Low (9.9% CP), 2) Medium (Med;12.5% CP), or 3) Low and High (14.2% CP) diets oscillated on a 48-h interval (Osc). Dry matter intake was greater (P = 0.04) for Osc (1,313 g/d) than Low (987 g/d), and intermediate for Med (1,112 g/d). Nitrogen intake was not different between the wethers fed Osc (25.4 g/d) and Med (22.2 g/d), but was lower (P < 0.01) in wethers fed Low (16.0 g/d). Wethers fed Osc (6.7 g/d) retained more (P < 0.04) N than those fed Med (4.0 g/d). Arterial blood flow was not different (P = 0.81) between wethers fed Osc (31 L/h) or Med (39 L/h) but was greater (P = 0.05) in wethers fed Low (66 L/h). Net release of -amino N by the PDV did not differ (P = 0.90) between Low (37.8 mmol/h) and Med (41.5 mmol/h), nor between Osc (53.0 mmol/h) and Med (P = 0.29). Net PDV release of ammonia N was less (P = 0.05) for Low than for Med, and this was accompanied by a similar decrease (P = 0.04) in hepatic ammonia N uptake. Urea N concentrations tended to be (P = 0.06) less in arterial, portal, and hepatic blood in wethers fed Low compared to those fed Med. Wethers fed Osc tended (P = 0.06) to have a greater PDV uptake of urea N than those fed Med, but there was no difference between Osc and Med (P = 0.72) in hepatic urea N release. Net PDV uptake of glutamine tended to be greater (P < 0.07) in wethers fed Low (6.7 mmol/h) than those fed Med (2.7 mmol/h). These data indicate that oscillating dietary protein may improve N retention by increasing endogenous urea N uptake by the gastrointestinal tract.

Key Words: metabolism, nitrogen, oscillation, wethers

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