Interaction of Zinc and Polyunsaturated Fatty Acids in the Chick

Abstract

Three experiments were performed to investigate the physiological relationships between zinc and polyunsaturated fatty acids (PUFA) in the chick. Chicks were fed diets low in zinc, PUFA or both; the growth rates and tissue fatty acid profiles were determined and correlated with the severity of skin lesions and leg abnormalities. The basal diets contained isolated soybean protein, approximately 6 ppm zinc and 0.03% of linoleic acid (18:2_ω6). The control diets contained 100 ppm zinc and approximately 2.5% of 18:2_ω6. A 2 × 2 factorial design was used: low Zn:low PUFA; adequate Zn:low PUFA; low Zn + PUFA, and adequate Zn + PUFA. In experiment 1, the basal diet contained 5% hydrogenated coconut oil (HCO); in experiment 2, no added fat; in experiment 3, a mixture of free fatty acids simulating HCO. The control diets contained soybean oil, corn oil or free fatty acids simulating soybean oil. When the diets were zinc-deficient, low PUFA supported a significantly higher growth rate and decreased the dermatitis. With adequate zinc, HCO and soybean oil were equivalent in support of growth. The foot skin of zinc-deficient chicks had a fatty acid profile different from that of the ad-libitum-fed controls, but the percentages of linoleic acid and arachidonic acid were similar to those of weight controls. In the physiological interaction between zinc and PUFA in the chick, PUFA aggravates the signs of zinc deficiency. This effect is opposite to the effect previously observed in the rat, but in both species a higher than normal proportion of arachidonate was found in the fatty acids of zinc-deficient skin.