Masters Theses

Date of Award

8-1983

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

M. C. Bell

Committee Members

James K. Miller, Michael H. Sims

Abstract

Young Holstein calves were used as models for lactating beef cows to better understand the etiology of hypomagnesemia. The objectives were to produce hypomagnesemia in the calves and to determine the effects of excess potassium (K) on magnesium (Mg) metabolism. Procedures included evaluating oral repletion of 50 or ICQ ml of 30% MgCl2-6H20 solution on plasma and cerebrospinal fluid (CSF) and collection of tissues 48 hours post dosing for mineral analysis. The calves were randomly assigned to one of four different diets. Diet one was Mg deficient, diet two was adequate in Mg, diet three was Mg deficient plus supplemental K, and diet four contained adequate Mg plus supplemental K. When calves fed the low Mg diets became sufficiently deficient in Mg, a five day collection period was conducted in which intake, feces, and urine were measured and aliquots were obtained for analyses. A balance study was conducted consisting of three separate trials in which only 19 of the total 24 calves were utilized due to calf losses. Calves fed Mg deficient, Mg deficient plus supplementak K, and the adequate Mg plus supplemental K diets excreted .009, .010, and .095 g per day of Mg in the urine, respectively compared to .219 g per day of Mg for calves fed the diet adequate in Mg. Concentrations of K in calves fed diets supplemented in K were higher (P<.05) for K intake and urinary excretion. Fecal excretion of K remained unchanged across treat-ments. There was a higher (P<.05) K balance in calves fed the diet adequate in Mg plus supplemental K than calves fed the Mg deficient diet. Calcium (Ca) balances did not differ across treatments. Repletion data were obtained from 19 of the 24 calves immediately following the balance period. Plasma and CSF samples were obtained at 0, 5, 15, 30, 60, 120, and 180 minutes. Con-centrations of Mg in plasma of calves fed the Mg deficient diet increased from a baseline level of .44 mg/dl to .62 mg/dl 180 minutes after repletion with 50 ml of 30% MgCl2-6H20 solution. Oral Mg solutions had no effect on plasma Mg in calves on other treatments. Concentrations of Mg in CSF decreased (P<.05) from a baseline of 1.76 mg/dl to 1.14 mg/dl at 180 minutes after oral dosing with Mg in calves fed the Mg deficient plus supplemental K diet. However CSF Mg remained fairly constant over the 180 minute period in calves on other treatments. Tissue samples collected included lung, heart, brain, liver, spleen, kidney, skeletal muscle, and rib. Concentrations of Mg in brain, heart, liver, spleen, skeletal muscle, kidney, or lung were not influenced by dietary intakes of Mg or K. There was a reduction of over 30% (P<.05) in rib Mg of calves fed no supplemental Mg when compared to calves fed Mg supplemented diets.

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