Optimal dietary concentration of vitamin E for alleviating the effect of heat stress on egg production in laying hens

1. The effects of different dietary concentrations of vitamin E (alpha-toco pherol acetate) were investigated on laying hens exposed to chronic heat st ress at 32 degrees C from 26 to 30 weeks of age. 2. Diets containing 5 dietary concentrations of vitamin E (a control diet c ontaining 10 mg alpha-tocopherol/kg or this diet supplemented to contain 12 5, 250, 375 and 500 mg alpha-tocopherol/kg) were fed to 335 birds. Half of the birds received the supplemented diets for only 4 weeks before the heat stress period (short supplementation duration, SSD) and were fed on the con trol diet for a further 12 weeks. The remaining birds were fed on the suppl emented diets throughout the experiment, 4 weeks before, 4 weeks during and 8 weeks after the heat stress period (long supplementation duration, LSD). 3. Egg production was significantly higher during (80.6 vs 68.9%, P<0.02) a nd after (75.3 vs 62.7%, P<0.02) the period of stress in the LSD group fed on the diet containing 250 mg vitamin E/kg compared with the group fed on t he control diet. LSD birds given 375 and 500 mg vitamin E/kg also had highe r egg production than control birds during heat stress but the differences failed to roach significance (74.6 vs 68.9% and 77.1 vs 68.9% respectively) . In the SSD groups, mean egg production of the birds given the diets suppl emented with 125 mg vitamin E/kg or more was significantly different from t he control group after heat stress (70.3 vs 62.7%, P<0.05). Egg weight and food intake were similar in all the groups. 4. Plasma and liver vitamin E concentrations were proportional to the vitam in E intake before the stress period, dropped during heat stress in the SSD groups but were maintained at concentrations closer to those observed befo re heat stress in the LSD groups. 5. It is concluded that a dietary supplement of 250 mg vitamin E/kg provide d before, during and after heat stress is optimum for alleviating, at least in part, the adverse effects of chronic heat stress in laying hens.