Doctoral Dissertations

Date of Award

12-1979

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

M. C. Bell

Committee Members

K. M. Barth, R. H. Feinberg, R. R. Johnson, J. B. McLaren, J. K. Miller

Abstract

The major objectives of this experiment were (1) to study the free magnesium and calcium concentrations in plasma« milk, urine and fecal ultrafiltrates and examine relevant variables associated with their variations in normal and hypomagnesemic beef cows; (2) to compare the absorption of magnesium and calcium in hypomagnesemic and normal lactating beef cows; (3) to study methods of producing hypomagnesemic tetany in 30 lactating Angus beef cows under experimental conditions. The three dietary regimens imposed were: tetany prone hay, tetany prone pasture and normal hay. Both tetany prone hay and tetany prone pasture were from pastures heavily fertilized with N and K. Studies on cows fed tetany prone hay and normal hay were conducted in metabolism stalls while cows on tetany prone pasture were allowed to graze the stockpiled pasture. Total collections of samples were made in metabolic stalls. The internal (acid-detergent lignin)-external (Cr₂O₃) indicators were utilized to estimate dry matter consumption and fecal dry matter output of the cows maintained on the pasture. Creatinine ratios technique was used to estimate the urine volume of cows on pasture. Milk production of the cows on the three treatments were estimated by calf weighing before and after nursing. Cows on pasture were found to have absorbed less magnesium than the cows on tetany prone hay or normal hay. The plasma total magnesium averaged 1.45, 1.28 and 1.74 meq/L for cows on tetany prone hay, tetany prone pasture and normal hay, respectively. The plasma ionic magnesium averaged .57, .46 and .71 meq/L for cows on tetany prone hay, tetany prone pasture and normal hay, respectively. The mean plasma total and Ionic magnesium among the three treatments were significantly different (p̲ < .01) . Plasma total calcium averaged 4.96, 4.85 and 5.11 meq/L for tetany prone hay, tetany prone pasture and normal hay groups, respectively. Plasma ionic calcium averaged 2.2, 2.07 and 2.25 meq/L for tetany prone hay, tetany prone pasture and normal hay groups, respectively. Excretion of both total and free magnesium and calcium were essentially the same among the three treatments regardless of the dietary treatment. Milk total magnesium averaged 6.57, 7.53 and 7.01 meq/kg of milk for tetany prone hay, tetany prone pasture and normal hay groups, respectively, The milk ionic magnesium averaged 1.15, 1.28 and 1.06 meq/kg for tetany prone hay, tetany prone pasture and normal hay groups, respectively. No differences were found between milk total calcium levels of the tetany prone hay and pasture cows, but milk total calcium level of control cows was significantly lower. However, milk ionic calcium levels were significantly (p̲ < .01) different among the treatments. Urinary excretions of both total and ionic magnesium were exceedingly low (p̲ < .01) for cows on the tetany prone pasture. No differences were found for urinary ionic calcium among the three treatment groups. Fecal excretion of total magnesium was highest (p̲ < .01) for cows on tetany prone hay and lowest for cows on tetany prone pasture. Fecal ionic magnesium was highest (p̲ < .01) for cows on normal hay and lowest (p̲ < .01) for cows on tetany prone pasture. Fecal total calcium was highest (p̲ < .01) for cows on normal hay. No differences were found between fecal ionic calcium of the tetany prone hay and pasture cows, but fecal ionic calcium levels of normal hay fed cows were significantly higher (p̲ < .01) These results suggest that the relationship between the free and stable magnesium can be altered in disease conditions. In contrast, total and ionic calcium are subject to minor variations compared to magnesium.

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