Net Portal Nutrient Flux in Steers Fed Diets Containing Wheat and Sorghum Grain Alone or in Combination

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Abstract
Three Holstein steers (280 to 353 kg during the experiment) fitted with hepatic portal, mesenteric venous and arterial catheters were fed 90% concentrate diets containing wheat, dry-rolled sorghum grain or a 50:50 mixture of the two to determine the effect of dietary grain source on net portal nutrient flux. Steers were allotted to a six-period crossover design with treatments lasting 2 wk. Diets were fed in 12 portions daily to equal intakes across treatments. Simultaneous arterial and portal blood samples were taken four times per day for the final 3 d of the treatment period. Portal blood flow was determined by continuous infusion of p-aminohippuric acid, and net portal nutrient absorption was calculated by venous-arterial difference × blood flow. Dry matter intakes averaged 6.2, 6.1 and 6.0 kg/d for wheat, 50:50 mixture and sorghum grain, respectively. Net fluxes of glucose, lactate, NH3, urea-N or alpha-amino-N were not affected by diet. Net fluxes increased for propionate and decreased for 2-methybutyrate as the level of wheat increased (P<.10). Overall, acetate and propionate net fluxes contributed 57% to 66% of the absorbed energy on these diets, with glucose contributing a maximum of 4% on the sorghum grain diet. Copyright © 1988. American Society of Animal Science . Copyright 1988 by American Society of Animal Science