Mitigation of heat stress effects on laying hens' performances, egg quality, and some blood parameters by adding dietary zinc-enriched yeasts, parsley, and their combination.

Objective: Finding natural, handy and efficient nutritional solutions to prevent and mitigate negative effects caused by environmental heat stress and to be applied to large-scale laying hen industry.

Research Design: A 3-weeks trial was conducted on 128 laying hens TETRA-SL LL (50 weeks of age) housed in 8 cages/group, 4 laying hens/cage, 32 laying hens/group, under heat stress conditions (34±1°C). The basal diet on corn and soybean meal was formulated to be isocaloric and isonitrogenic. Compared to Control group diet (C), experimental groups E1 included 1% zinc-enriched yeast; E2 included 2% parsley and E3 included 1% zinc-enriched yeast combined with 2% parsley to minimize the heat stress effects.

Methods: The parsley and the zinc-enriched yeast were analysed for their chemical composition, total polyphenols, antioxidant capacity, minerals, vitamin E and incorporated into the ration structure. Production parameters, egg quality, biochemical and haematological profiles of blood samples were analysed during the trial.

Results: A statistically significant ( < 0.05) average egg weight was noticed on E2 and E3 compared to Control group, and also during the 1st week compared to the 2nd and the 3rd experimental weeks. Average daily feed intake values were highly significant ( < 0.001) on E3 group compared to C, E1, E2, and on the 2nd week compared to the 3rd experimental week ( < 0.021). Feed conversion rate was highly significant (p < 0.001) during the 2nd and the 3rd experimental weeks compared to the 1st week. The average daily egg production was highly significant ( < 0.001) within 1st week compared to the 2nd and 3rd weeks. A highly significant ( < 0.001) yolk coloration was noticed on E2 and E3 groups. The malondialdehyde (MDA) concentration decreased significantly ( < 0.05) to all experimental groups compared to Control group during the 14th and 28th days of storage.

Conclusion: These findings suggest that the two ingredients minimized the heat stress effects on production performance parameters with a demonstrated antioxidant capacity role by delaying the lipid peroxidation during different storage time periods.