Masters Theses

Date of Award

6-1979

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

M. C. Bell

Committee Members

J. B. McLaren, J. W. Holloway

Abstract

The major objectives of this experiment were to determine the daily balance of magnesium, calcium and potassium in lactating beef cows under conditions of hypomagnesemia.

Three balance trials were conducted using lactating cows. Three dietary regimes were imposed: tetany-prone hay, good-quality hay and heavily fertilized fescue pasture (Treatments 1, 2 and 3, respectively). The tetany-prone hay was from pastures heavily fertilized with N and K which had produced hypomagnesemic tetany. Treatments 1 and 2 were conducted in metabolism stalls, and Treatment 3 cows were allowed to graze the tetany-prone pasture. Total collections were made in the stalls. The internal (acid-detergent lignin)-external (Cr2O3) indicator technique was used to determine fecal dry matter output and dry matter consumption of the pasture cows. Urine volume was estimated on the pasture cows using creatinine ratios. Milk production (calf-suckle technique) was estimated and sampled for cows on all treatments.

Pasture cows were found to have consumed less magnesium than the cows on tetany-prone hay or the control hay. Urinary excretion of magnesium was very low for cows on the tetany-prone hay and pasture. Excretion of magnesium in the milk remained the same regardless of treatment. Fecal excretion of magnesium was higher for cows on the two hay treatments than for cows on tetany-prone pasture. Magnesium balance was negative for both tetany-prone hay and pasture cows.

No differences were found between plasma magnesium levels of the tetany-prone hay and pasture cows, but plasma levels of control cows were significantly higher. Treatment had no effect on plasma calcium or plasma potassium levels of the cows.

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