Effect of Zinc supplementation and Betaine substitution to methionine on performance and blood parameters of laying hens under heat stress
To investigate the effects of dietary zinc and betaine (Bet) substitution to methionine on performance, egg quality and blood parameters in laying hens under heat stress, an experiment with 288 Hy-line W-36 leghorn (at 50 to 62 weeks old) in complete randomized design (CRD) with a 3×2×2 factorial arrangement of treatments with twelve treatments, 3 replicates and 8 hens in each replicate was performed. There were 6 dietary treatments: three doses of Bet (0, 13 and 26%) substitute to methionine combined with three levels of zinc (50 and 100 mg/kg) supplemented to the basal diets that were combined with two environmental conditions (thermoneutral (23°C constant) and heat stress ( 23.9 to 35°C cycling) conditions). The results indicated that performance parameters of laying hens and egg quality were all significantly reduced by heat stress (HS) (P<0.05). Substitution of methionine with Bet led to significantly increase of egg production (P<0.05); whereas it had no effect on egg weight and egg quality. Supplementation of the basal diets with zinc significantly increased laying performance of hens and egg quality (P<0.05). Moreover, the results of this experiment indicated that, there were significant effect of Betaine on blood cholesterol and triglyceride, (p<0.05), but no significant effect on glucose in broiler chickens. Moreover, results demonstrated that Zinc supplementation decreased cholesterol, triglyceride and glucose. The present study showed that dietary supplemental Bet and zinc at the level of 13% and 100 mg/kg resulted in an improving egg quality and performance of laying hens under heat stress.
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