Effect of Zinc Supplementation on Plasma Mineral Concentration in Grazing Goats in Sub-Humid Climate of Tanzania

Abstract

Tropical pastures are characterised by fast growth and early maturity during the rain seasons and a fall in nutritive value during the dry seasons. Animals should be supplemented with minerals known to be deficient. The bioavailability of common supplements and their possible undesirable effects are hardly known. This study was conducted to determine the effect of zinc supplementation on plasma zinc, calcium and inorganic phosphate in East African local goats. The goats were randomly divided into two groups of 12 each. One group was supplemented with 24 mg/Kg body weight of Zn every other day for six weeks during the rainy and dry season. The unsupplemented group was the control. Blood samples collected from goats in both groups were analysed for plasma Zn, Ca and Pi using standard methods. The concentration of plasma Zn was significantly higher (P<0.05) in Zn supplemented goats than in the control group during rainy and dry seasons.  In both groups plasma Zn concentration was above the normal minimum levels of 18 mmol/l, except towards the end of dry seasons. Plasma Ca (1.9 – 3.1 mmol Ca/l) and Pi (1.3 – 1.60 mmol Pi/l) concentrations for Zn-supplemented group were lower during all the sampling days (P <0.05) than for the control group (Ca 2.0 – 3.4 mmol/l and P (1.5 - 1.62 mmol/l) in all seasons.  It is concluded that, goats in the study area and probably areas with similar ecological conditions should be supplemented with Zn only when there is evidence of Zn deficiency during prolonged dry seasons.