Abstract
ABSTRACT The aim of experiment was to investigate the effect of feeding high level of zinc on cow production, and health and immunity of calves. The cows in each period of pre and post calving were allocated to two treatments containing 75 and 150 mg/kg Zn, respectively, as control, and containing 110 and 250 mg/kg, respectively, as second treatment. On days −25, −5, 7 and 21 relative to parturition, blood samples were obtained from 24 cows per each treatment. High level of zinc in the diet increased serum zinc, leptin and insulin in both periods but serum glucose was constant. Serum non-esterified fatty acids (NEFA) was increased by high Zn in diet, but beta hydroxybutyrate (BHBA) decreased on day 7 of lactation. In compared to the control, milk Zn on days 1 and 7 of lactation had a significant increase. High level of Zn increased colostrum IgG, calves serum IgG and total protein. Obese cows had more serum leptin and NEFA but BHBA was higher only on day 7 of lactation. In conclusion, increased serum Zn increases leptin and insulin before and after calving. It seems that their cumulative effect in spite of an increase in NEFA had a beneficial effect on milk production and calves immunity.
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