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

Abstract

Portal blood flow was measured in nonlactating Holstein cows by primed, continuous infusion of para-aminohippuric 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 lib orchardgrass-red clover silage. Results of experiment 1 in which portal blood flow was measured in 4 cows at 10-min intervals over 3 h indicate that flow can vary by a factor of 3 in a given cow. In experiment 2, portal blood flow and net absorption of ammonia-N, urea-N and glucose were measured in cows for 10-12 h. Mean portal blood flow (l/h) and net absorption (mM/h) of ammonia-N, urea-N and glucose were 836 .+-. 32, 121 .+-. 8, -52 .+-. 14 and -39 .+-. 16, respectively.