PJB-2007-125
SEASONAL DYNAMICS OF ZINC IN SOIL, DIETARY FACTORS AND GRAZING SHEEP FROM SOUTHWESTERN, PUNJAB, PAKISTA
ZAFAR. I. KHAN1*, M. ASHRAF2, KAFEEL AHMAD1, EHSAN ELAHI VALEEM3 AND L.R. McDOWELL4
Abstract
Abstract:This study has been conducted in a sheep farm to determine the zinc status in a semiarid region of south western Punjab, Pakistan, during two different seasons. The purpose of this was to investigate as function of the season and the sampling period, the transfer of Zn from soils and forages to sheep grazing in this semiarid region in order to evaluate if the Zn requirement of the grazing sheep was met or if Zn deficiency occurred. The final goal was to maximize the production of animals by adopting if necessary, an adequate and balanced Zn supplementation. Soil, forage, water and feed samples as well as blood, urine, milk and faeces from lactating/ non-lactating and male grazing animals have been taken fortnightly, 4 times during summer and 4 times during winter. Zn concentrations of the samples were determined by atomic absorption spectrometry. Extractable soil Zn concentrations were found adequate for normal plant growth during both seasons. Non-significant effect of season but significant effect of sampling periods was observed on soil zinc level and was slightly higher in winter than that in summer. Forage zinc level was affected both by the season and fortnights and also found above the requirements of the ruminants only in winter. However, the level in summer was considered slightly deficient for growing and lactating animals. No effect of seasons or fortnights was observed on water Zn and that of feed zinc was affected only by the seasonal variation. Zinc content in dietary sources was higher in summer than that in winter. In summer, the plasma contained higher zinc only in non-lactating sheep than that in other two groups. Plasma zinc showed a response to the diet zinc content in summer in non-lactating sheep while the higher zinc concentration in the diet during summer remained ineffective increasing the plasma zinc levels in lactating and male sheep. The milk zinc concentration was higher in early lactation period than late lactation. The levels of faeces and urine zinc were not affected by the seasonal variation. The zinc content of faeces has reflected its pasture levels in all classes of sheep. Only plasma and milk zinc was affected by seasonal changes and urine zinc by the sampling period only in lactating sheep. Relationships between soil, forages and plasma Zn levels and the seasons and period of sampling have been discussed. Based on this study it is concluded that supplementation of grazing sheep should be done on this ranch with a specifically tailored mixture of high bioavailability to maximize the animal potential.
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