Net Absorption of Macrominerals by Portal-Drained Viscera of Lactating Holstein Cows and Beef Steers

¹ Department of Animal Science, University of Maryland, College Park 20742
² USDA, ARS, Livestock and Poultry Sciences Institute, Ruminant Nutrition Laboratory, Beltsville, MD 20705

Net absorption of macrominerals by portal-drained viscera of cattle was measured in two experiments. In Experiment 1, net portal-drained visceral and liver flux of Na, K, Ca, P, and Mg were measured in four lactating Holstein cows fed a 60:40 corn silage:concentrate diet ad libitum and milked at 12-h intervals. Twelve measurements of net flux (venous-arterial concentration difference x blood plasma flow) were obtained hourly at 4 and 8 wk postpartum. Intake of DM and milk yield averaged 15.6 and 32.2 kg/d, respectively. Excluding Na, net absorption of these macrominerals was measurable across portal-drained viscera. Flux of Na was negative at wk 4 postpartum (net removal from blood) and positive at wk 8 (net absorption into blood). Excluding Mg, differences in venous-arterial concentrations for macrominerals across the liver were not different from zero. In Experiment 2, net portal-drained visceral flux of Na, K, Ca, P, and Mg was partitioned into stomach and poststomach sections in two Hereford steers. Poststomach tissues accounted for essentially all such absorption of K, Ca, and P and, on a net basis, removed Na and Mg. Stomach tissues absorbed Mg and small amounts of K, Ca, and P. Net stomach flux of Na was positive, denoting net absorption, but highly variable. Net portal-drained visceral absorption of K increased with intake in both experiments. Net portal-drained visceral absorption of P was greater than total intake in both experiments, reflecting recycling of P via saliva and other digestive secretions.

Key Words: portal-drained viscera • minerals • absorption

Submitted on March 31, 1990
Accepted on September 10, 1990