Ruminal Solubilization of Selected Macrominerals from Forages and Diets

¹ Animal Physiology and Nutrition Research Unit, USDA-ARS and Department of Animal Sciences, University of Missouri, Columbia 65211

Dry matter disappearance and ruminal solubility of Ca, P, Mg, and K from samples of forages and diets containing these forages were measured. Forages included alfalfa hay (Medicago sativa L.), fescue hay (Festuca arundinacea Schreb.), bromegrass hay (Bromus inermis L.), and corn (Zea mays) silage. Diets were from lactating cow trials conducted by this laboratory and were formulated using the forages listed so that most of the dietary Ca would be supplied by forage. Mineral solubility and DM disappearance were measured in ruminally cannulated cows; nylon bags with samples were incubated for 0. 3, 12, 24, and 48 h. The 0-h bags were only washed with distilled water. For the 0-h samples, more than 60% of the P, Mg, and K in forages and diets was solubilized. However, 45% of the Ca in forages was soluble compared with 36% for diets. Magnesium solubility increased 22% with time for both forages and diets; otherwise, mineral solubilities at 3 h were not different from 0 h. Time for maximum solubility varied; K solubility was maximized by 0 h, Mg and P by 24 h, and Ca by 48 h. Across forages and diets, K was most soluble (99%) followed by Mg (92%), P (72%), and Ca (71%). Ruminal solubilities of K, Mg, and P were similar for forages and diets and averaged 93, 85, and 70%. respectively. Solubility of Ca from forages averaged 63% and was 12 percentage units greater than that of diets. These data indicate that rumen solubilization is not a factor limiting the ruminant's ability to absorb these macrominerals.

Key Words: forage • mixed diets • macromineral • solubilization

Submitted on August 13, 1990
Accepted on December 6, 1990