Additive Nature of Sodium Bicarbonate and Magnesium Oxide on Milk Fat Concentrations of Milking Cows Fed Restricted-Roughage Rations

Abstract

Sodium bicarbonate (272 or 363 g/day) and MgO (136 or 181 g/day) alone or combined were added to the diet of 20 cows given a low-roughage–high-grain ration in a Latin-square trial. Responses were the same for the second, third, and fourth weeks of each four-week period. Both supplements increased fat test and rumen pH, but decreased molar proportion of valerate and propionate in the rumen. These effects were additive when both were fed together. Sodium bicarbonate increased daily milk and fat production, but MgO caused a slight decrease, probably due to its more pronounced effect on decreasing grain intake. Cows with the greatest level of milk and fat production had the greatest mammary uptake of glucose and acetate. Mammary uptake of plasma glucose, acetate, cholesterol, cholesterol esters, and triglycerides were positively related to arterial concentrations. Simple and multiple correlation coefficients indicated that milk fat concentration was negatively related to rumen valerate and propionate proportions, but when supplements were fed valerate assumed much more importance than propionate. The extent and sign (− or +) of several coefficients changed when MgO was fed. © 1969, American Dairy Science Association. All rights reserved.