Doctoral Dissertations

Date of Award

3-1985

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

James K. Miller

Committee Members

John P. Hitchcock, James B. McLaren, Monty J. Montgomery, Robert S. Dotson

Abstract

Sixteen Finnish cross bred ewes were used as models of cows on pasture in two experiments to investigate relationships between dietary magnesium (0.04 and 0.24% Mg), previous Mg status, potassium (0.7 and 3.5% K) and platelet function during pregnancy and lactation. In the first experiment, 12 ewes were assigned to four diets which contained either deficient or adequate Mg supplemented with adequate (diet 1 and 2) or high K (diet 3 and 4). In the second experiment eight ewes from the first experiment and eight ewe lambs born to ewes from the first experiment were fed either deficient (diet 1) or adequate Mg (diet 2) to investigate the effect of previous Mg status, either in utero or as an adult ewes, on later performance. Plasma Mg was higher (P<.05) in ewes fed diet 2 than in those fed diet 1. Supplementing diets with high K (diet 3 and 4) increased (P<.05) plasma K in ewes over those fed adequate K (diet 1 and 2) and lowered (P<.05) plasma Mg in ewes fed Mg-adequate (diet 4) but not Mg-deficient diets (diet 3). Ewes fed adequate Mg plus adequate K (diet 2) had lower (P<.05) systolic and diastolic blood pressure than those fed deficient Mg plus adequate K (diet 1). When K was high systolic, diastolic and mean arterial pressures were lower (P<.05) in ewes fed a deficient Mg diet (diet 3) than in those fed the adequate Mg diet (diet 4). In vitro platelet delay time was longer and % aggregation velocity was higher (P<.05) in ewes during the preliminary than the gestation periods. In vitro platelet reactivity measurements were not affected by Mg or K treatments in ewes after parturition or during lactation. Thromboxane B21α concentration was not affected. Previous Mg deficiency lowered (P<.05) plasma K and increased (P<.01) packed cell volume but had no effect on plasma Mg and Calcium (Ca). There was no effect of previous Mg deficiency in ewes on blood pressures or heart rate. In the second experiment feeding adequate Mg diets resulted in similar effects which were observed in the first experiment. Plasma K and blood glucose in ewes fed experimental diets were lower {P<.01) during the second than in the first experiment and the ewes developed abnormal health problems before parturtion in the second experiment. The problem was recognized as copper (Cu) toxicity due to high Cu content of corn gluten meal and possibly low molybdenum (Mo) in the diets.

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