Masters Theses

Date of Award

3-1986

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

M.C. Bell

Committee Members

R.N. Heitmann, J.K. Miller, S.P. Oliver

Abstract

The objectives of this research were to compare potassium (K) fertilization and oral administration of KCl as sources of excess K and to determine the effects of K sources on plasma, milk, fecal and urine minerals. Four pasture trials two weeks in length, using beef cows with suckling calves were conducted in February, March and April of 1984 and 1985. Cows were placed on one of two adjacent tall fescue pastures. Both pastures were fertilized with 39 kg/ha of nitrogen (N). One pasture received no fertilization of K and the other 112 kg/ha. One half the cows on each pasture received an oral dose of KCl on days 0, 2, 4, 7, 9, and 11 of each trial. Plasma, milk, fecal and urine samples were collected over a 160 minute period on the days cows were dosed.

The KCl dose on days 0 and 2 of trial 1 consisted of 28Dg of KCl administered by stomach tube. On day 4 the KCl dose was changed to 280g of KCl given via gelatin capsule, due to the death of one cow on day 2. The death of the cow appeared to be the result of K toxicity. On day 4 two cows were treated with 30% magnesium chloride enema for K toxicity. As a result of this toxicity the KCl dose was changed to 220g given by gelatin capsule, where it remained throughout the rest of the study. The levels of K given during trial 1 were below the levels of K listed in the literature as necessary to cause K toxicity.

Cows grazing the K fertilized pasture had depressed plasma and urine concentrations of magnesium (Mg) and calcium (Ca), indicating a reduction in absorption of Mg and Ca. Plasma sodium (Na) and K and urine K concentrations were not affected by pasture fertilization. Effects of pasture fertilization on milk minerals were inconsistent. Cows receiving KCl had reduced plasma Mg and increased plasma K and Na concentrations. Effects of KCl treatment on plasma Ca were variable. During the trials conducted in 1985, KCl dosed cows had reduced concentrations of Mg and Ca in their urine. Administration of KCl resulted in an increase in urine K concentration. KCl dosed animals had elevated concentration of milk Mg. Milk K and Ca concentrations tended to be higher for KCl bolused animals than for their control counterparts. Effects of KCl bolusing on milk Na were inconsistent. These results suggest that dietary K may be more toxic when administered to cattle grazing early spring pasture. It also appears that oral administration of K and K fertilization interfere with the metabolism of Mg and that the incidence of grass tetany may be increased by both.

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