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THE USE OF DIETARY VITAMIN E AND POTASSIUM CHLORIDE TO ALLEVIATE THE EFFECTS OF HEAT STRESS ON THE PERFORMANCE OF LAYING HENS

The present study was carried out to investigate the possibility of alleviating the adverse effects of heat stress on productive performance and egg quality of laying hens exposed to heat stress during the summer season, by means of dietary supplementation with potassium chloride (KCl), vitamin E or their combinations. Three hundred and sixty, 20-week-old Hy-Line W-36 pullets were assigned to twelve equal experimental groups of 5 replications of 6 birds each. All birds were kept in community battery cages (6 birds per cage), set up in an open-sided laying house, and exposed to a daily photoperiod of 16 hr and managed similarly. Twelve mash experimental diets containing 4 levels of KCl (0.0, 0.8, 1.6 and 2.4%) and 3 levels of vitamin E (0.0, 150 and 300 mg/kg diet), in a 4×3 factorial arrangement of treatments, were formulated and used. All experimental diets were formulated to contain an average of metabolizable energy (ME) of about 2840 kcal/kg and crude protein (CP) of about 18.7%, and offered to pullets during the summer season from 20 to 32 weeks of age. Then, hens were switched to feed the control diet until the end of study, at 68 weeks of age. The criteria of response were productive performance (feed intake, hen-day egg production rate, egg weight, egg mass and feed conversion efficiency), change in body weight, mortality rate, economic efficiency of production and certain measurements of egg quality. The most important results could be summarized as follows: Apart from the effect of dietary vitamin E supplementation, feeding the KClsupplemented diets during the heat stress period (20-32 weeks of age) significantly decreased mortality rate and improved the productive performance and change in body weight of laying hens; similar improvements in their productivity, survivability and economic efficiency of production were observed during the whole experimental period, with no significant differences among the different levels of supplemental KCl in most cases. In addition, hens fed the KCl-supplemented diets during the heat stress period produced eggs of superior quality (as measured by egg weight, egg shell quality and Haugh units) compared with those of the control hens, with no significant differences among the different levels of supplemental KCl in most cases.; however, yolk percent, albumen percent, egg shape index, yolk index and yolk color were not affected. Regardless of the effect of dietary KCl supplementation, feeding the vitamin E-supplemented diets during the heat stress period significantly reduced mortality rate and improved the productive performance of laying hens, with no significant differences between the two levels of supplemental vitamin E. Change in body weight of hens was also improved proportionally to the supplemental level of vitamin E; however, daily feed intake was not affected. Dietary vitamin E supplementation during the heat stress period, independently from the effect of supplemental dietary KCl, produced similar positive carry-over effects on the productive performance, survivability and economic efficiency of production of laying hens during the whole experimental period, with no significant differences between the two levels of supplemental vitamin E. Also, feeding the vitamin E-supplemented diets during the heat stress period brought about significant improvements in egg weight and its