Plasma zinc status of dairy cattle in the periparturient period

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Abstract
Extract There is increased interest in the possible role of zinc in a number of physiological and pathological situations. Amongst these is the possibility of some association between zinc status and events occurring during pregnancy or at parturition. Apgar ( 1968 Apgar, Jean . 1968. Effect of zinc deficiency on parturition in the rat. Am. J. Physiol, 215: 160–163. [Google Scholar] ), working with purified diets, reported very significant effects of zinc deficiency on parturition in the rat where changes occurred in actual parturition behaviour and also in the form and viability of the foetuses. Egan ( 1972 Egan, A. R. 1972. Reproductive responses to supplemented zinc and manganese in grazing Dorset Horn ewes. Aust. J. exp. Agric. Anim Husb., 12: 131–135. [Google Scholar] ) reported improved reproductive performance of sheep following oral feeding of zinc to ewes. Although frank deficiency of zinc has not been clearly demonstrated in cattle under New Zealand conditions, the possibility has emerged that there may be some association between the incidence of dystocia and body zinc status. There is some suggestion that plasma zinc levels are affected during pregnancy. Anon. ( 1973 Anon. Tracing and Treating Mineral Disorders in Dairy Cattle Centre for Agricultural Publishing and Documentation Wageningen, , The Hague 1973 [Google Scholar] ) stated that zinc concentration in plasma of healthy cows is 0.60 to 1.40 mg/litre, and that immediately after calving values may fall to about 0.50, whilst Hickey ( 1974 Hickey, F. 1974. Zinc in nutrition. N.Z. Agriculturist, 20(4): 4–5. [Google Scholar] ) stated that blood zinc concentration falls by approximately one third during pregnancy, though neither author reported the detailed data upon which these conclusions were based. J. Dufty (pers. comm.) details a mean fall from conception to 261 days of pregnancy of 11%.

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