J. Anim Sci.
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J. Anim Sci. 1969. 29:959-966.
© 1969 American Society of Animal Science
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Effects of Feeding Different Magnesium Levels to Drylot-Fed Lactating Beef Cows1

R. E. O'kelley2 and J. P. Fontenot

Virginia Polytechnic Institute, 3 Blacksburg

Abstract

Three experiments were conducted with eight lactating Angus cows to study the effects of dietary magnesium levels at early, mid- and late lactation. The individual experiments consisted of two consecutive 15-day trials. Each trial consisted of a 5-day adjustment period and a 10-day experimental period. During the experimental periods the total magnesium content of the four rations averaged 9.7, 20.6, 31.0 and 42.4 gm. per day. Blood and urine samples were taken at the end of the adjustment periods and on alternate days during the experimental periods. Generally, increasing the level of dietary magnesium significantly increased blood serum magnesium during the three stages of lactation but did not influence serum calcium or inorganic phosphorus values. In general, urinary magnesium per unit of creatinine was significantly increased as the level of dietary magnesium increased. As calculated from the regression equations obtained at each stage of lactation for the effect of dietary magnesium on serum magnesium, 20.9, 22.1 and 18.0 gm. per day of dietary magnesium would be required to maintain serum magnesium levels of 2.0 mg. per 100 ml. during early, mid- and late lactation, respectively.

Footnotes

1 Appreciation is expressed to N. O. Price for his assistance in the calcium and magnesium analyses. Chas. Pfizer and Co., Inc., Terre Haute, Indiana is acknowledged for supplying vitamin A.

2 Present address: Chas. Pfizer and Co., Inc., Terre Haute, Indiana.

3 Departments of Animal Science and Biochemistry and Nutrition






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