effects of dietary supplemental vitamin e and chromium on egg production, egg quality and blood parameters of laying hens under thermoneutral or heat stressed conditions

The effects of dietary supplemental vitamin e (ve) and chromium (cr) on egg production (ep), egg qual-ity, serum concentrations of cr and insulin and activity of glutathione peroxidase (gsh-px) were evaluated in lohmann lsl-lite laying hens reared under thermoneutral or heat stress (hs) conditions. a total of 144 laying hens were distributed in 24 cages and assigned to feed four diets including two levels (0 and 200 mg/kg) of ve and two levels (0 and 1200 μg/kg) of cr in a 2 × 2 factorial arrangement with six replicates. the daily temperature in the house was maintained at 17 °c for 10 weeks (30-40 wks of age) and afterward (41-45 wks of age) increased instantly to 32 °c to simulate hs. decreased feed intake was observed in hens fed the cr-supplemented diet during hs (p<0.05). supplemental ve and cr had no significant effect on egg weight, egg mass, albumen weight, specific gravity, egg shape index, yolk color and index (p>0.05). in-creased feed conversion ratio (fcr) and decreased yolk weight and shell thickness were detected in hens fed the ve-supplemental diet before hs (p<0.05). a combination of ve and cr increased haugh unit, be-fore and during hs, and also increased ep, yolk and shell weight during hs (p<0.05). no dietary effects (p>0.05) were observed on serum concentrations of cr and the activity of gsh-px at 45 wk of age (after exposure to heat stress), however, supplemental ve and cr increased serum concentration of insulin (p<0.05). in conclusion, dietary supplemental ve in combined with cr partly alleviated the detrimental effects of hs in laying hens, via improving ep and egg quality.