Abstract
The effects of adding vitamin A supplement (0, 6 mg retinol/kg) and sunflower oil (0, 20 g/kg) on the performance and on yolk cholesterol, fatty acid and retinol and plasma lipids, lipoproteins and retinol concentrations of laying hens were studied for 13 weeks. Pullets fed the retinol supplement had a significantly (p < 0.05) higher egg production, egg mass, plasma retinol concentration, yolk cholesterol and retinol contents and a higher daily egg cholesterol output and a lower yolk arachidonic acid concentration than pullts fed the control diet. Weight gain, feed consumption, egg weight, yolk concentration of most fatty acids and plasma lipids and lipoproteins concentrations were not significantly affected by retinol supplementation. Sunflower oil supplementation significantly (p < 0.01) increased yolk concentration of stearic, linoleic and arachidonic acids and decreased yolk concentration of palmitic and oleic acids. Production performance, yolk cholesterol, linolenic acid and retinol concentrations and plasma retinol, lipid and lipoprotein concentrations were not significantly affected by sunflower oil supplementation. There was a significant interaction between dietary sunflower oil and retinol supplements on egg weight. Sunflower oil supplementation significantly reduced egg weight of pullets fed the retinol diet, whilst sunflower oil supplementation increased the egg weight of pullets fed the control diet. The reduction in egg weight may be caused by the inhibitory effect of retinol on the synthesis of arachidonic acid from linoleic acid in the liver of laying hen.
It was concluded that hens fed a diet supplemented with retinol produced eggs with a high concentration of retinol and cholesterol and that hens fed on a diet supplemented with sunflower oil produced eggs with a high concentration of stearic, linoleic and arachidonic acids, but none of the dietary supplements affected the composition of the plasma lipoproteins.