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 quality, 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 mu g/kg) of Cr in a 2 x 2 factorial arrangement with six replicates. The daily temperature in the house was maintained at 17 degrees C for 10 weeks (30-40 wks of age) and afterward (41-45 wks of age) increased instantly to 32 degrees 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). Increased 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, before 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.