Masters Theses

Date of Award

12-1981

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 objectives of this research were to determine what effects high K fertilization of fescue pastures had on plasma levels of Mg, Ca and K and on the metabolism of Mg. Ca and K In beef cows In early lactation. Balance trials were conducted using beef cows with young suckling calves In February and March, 1980 and 1981. Cows were placed on one of two adjacent fescue pastures. Both pastures were fertilized with N (112 kg/hectare) and P (169 kg/hectare). One pasture received no fertilization of K and the other, 224 kg/hectare. The Internal (acid-detergent 11gn1n)-external (Cr203) Indicator technique was used to determine fecal dry matter output and dry matter consumption of the cows. Urine volume was estimated using creatinine ratios. Milk production (calf-suckle technique) was estimated and sampled for all cows. Cows on the control pasture consumed more dry matter and Mg. Cows consuming the K-fertilized pastured had reduced urinary Mg excretion. Indicating reduced absorption of the Mg. Excretion of Mg In the milk remained the same regardless of treatment. Cows on the K-fertilized pasture tended to have depressed plasma Mg values with a higher Incidence of hypomagnesemia. Nine cows on the K-fertilized pasture were hypomagnesemic compared with only four on the control pasture, although no symptoms of grass tetany were seen. This rela-tionship suggests that In a tetany-prone year, the number of cases n nn of grass tetany could be higher because of pasture fertilization with K. There were no differences between treatment in plasma Ca values, but plasma K tended to be higher in cows on the K-fertilized pasture.

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