Studies On Interaction Between Zinc And Vitamin A Metabolism And Adequate Requirement In Broilers

Two experiments were conducted to further elucidate the interaction between low or high levels of zinc and vitamin A metabolism in broilers, and to explore the possibility of assessment of vitamin A status in broilers using the serum vitamin A relative dose response (RDR) procedure. In experiment 1, the zinc-deficient semi-purified diet containing 4.67mg/kg zinc was mainly composed of corn starch and low zinc soybean meal. Broilers were fed four levels of dietary zinc (4.67, 9.67, v.67, 84.67mg/kg) and three levels of dietary vitamin A (0, 3000, 60001U/kg) in a 2 X 4 X 3 factorial arrangement. In addition, four zinc-sufficient pair-fed groups (PF) with the zinc-deficient groups were restricted to the average consumed by zinc-deficient groups. In experiment 2, the basic diet containing 22.61mg/kg zinc was mainly composed of corn and soybean meal. Broilers were fed five levels of dietary zinc (47.61, 87.61, 167.61, 327.61, 647.61mg/kg) and three levels of vitamin A (3000, 6000, 120001U/kg) in a 2 X 5 X 3 factorial arrangement. In addition, one control group was fed the basic diet containing 22.61mg/kg zinc and 30001U/kg vitamin A. The results indicated that zinc deficiency would result in a significant depression of serum vitamin A and retinol-binding protein (RBP) concentrations and alcohol dehydrogenase activity of liver and whole eye, and that feed intake restriction would result in an apparent decrease in serum vitamin A and RBP concentrations. A significant decrease of serum vitamin A concentration and increase of hepatic vitamin A concentration were a result of feed intake and growth restriction resulting from zinc deficiency while dietary zinc level was 9.67 mg/kg. However, a significant decrease in serum vitamin A concentration was a result of not only zinc deficiency, but feed intake restriction resulting from zinc deficiency while dietary zinc level was 4.67 mg/kg. High levels of dietary zinc above 327.61 mg/kg might also result in an apparent decrease in serum and liver vitamin A concentrations and serum RBP concentration Results also showed that vitamin A deficiency would result in a significant decrease in serum and liver vitamin A concentrations and serum RBP concentration. Serum zinc level was decreased significantly, however, hepatic zinc level was increased and tibia zinc level was not changed while vitamin A was deficient. Serum vitamin A relative dose response might be used to evaluate the vitamin A nutritional status of broilers in addition to serum and liver vitamin A concentrations. Zinc nutritional status of broilers could be reflected by serum, liver and tibia concentrations. The results suggested that the adequate requirements of zinc and vitamin A in broilers were 45 mg/kg and 3000IUIkg diet respectively. Diet containing zinc 22.61 mg/kg was referred to as marginally deficient in zinc, and diet containing zinc 167.61 mg/kg was referred to as marginally excess in zinc, and dietary zinc was excess while dietary zinc level was above 327.6lmg/kg.Diet containing 12000 lU/kg vitamin A would result in a significant increase in serum vitamin A concentration, and the result implied that there was a possibility of vitamin A excess.