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Portal Blood Flow and Net Absorption of Ammonia-Nitrogen, Urea-Nitrogen, and Glucose in Nonlactating Holstein Cows¹

Ruminant Nutrition Laboratory, Animal Science Institute, Agricultural Research Service, US Department of Agriculture, Beltsville, MD 20705

ABSTRACT

Portal blood flow was measured in nonlactating Holstein cows by primed, continuous infusion of para-aminohip-puric acid into a mesenteric vein and periodic collection of blood from the portal vein and femoral artery. Cows ranged in age from 2 to 4 yr; average body weight was 472 kg. They were fed ad libitum orchardgrass-red clover silage. Results of Experiment 1 in which portal blood flow was measured in four cows at 10-min intervals over 3 h indicate that flow can vary by a factor of three in a given cow. In Experiment 2, portal blood flow and net absorption of ammonia-nitrogen, urea-nitrogen, and glucose were measured in cows for 10 to 12 h. Mean portal blood flow (liters/h) and net absorption (mmoles/h) of ammonia-nitrogen, urea-nitrogen, and glucose were 836 ± 32, 121 ± 8, —52 ± 14, and —39 ± 16.

¹ Mention of a trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the US Department of Agriculture and does not imply its approval to the exclusion of other products that may be suitable.

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