Effects of vitamin E and C supplementation on performance, in vitro lymphocyte proliferation, and antioxidant status of laying hens during heat stress

Vitamin E (dl-alpha -tocopheryl acetate) was evaluated for its effects on p erformance, lymphocyte proliferation, and antioxidation in layers during he at stress. In Trial 1, 25, 45, or 65 IU of vitamin E/kg were fed to four re plicated pens (five hens/cage) of DeKalb Delta or Hy-Line W-36 per treatmen t starting at 20 wk of age. At 34 wk of age, hens were heat-stressed at diu rnal temperature ranging from 21 C to 35 C for 3 wk. The performances of he ns not exposed to heat stress were not influenced by supplemental vitamin E . Supplemental vitamin E did not affect egg production; however, egg mass w as greater (P < 0.05) with supplementation of 65 IU of vitamin E/kg during heat stress. Egg yolk was significantly increased (P < 0.04) when hens were fed 45 and 65 IU/kg compared with the control vitamin E level (25 IU/kg). Haugh units were higher (P < 0.01) for hens fed 65 IU of vitamin E/kg compa red to 25 and 45 IU/kg. Lymphocyte proliferative responses to concanavalin A (Con A) and Salmonella typhimurium lipopolysaccharide (LPS) were greater (P < 0.0001) in hens fed 45 and 65 IU of vitamin E/kg during heat stress. S train had no effect on any of the parameters measured. In Trial 2, a 2 x 2 factorial was designed to test effects of vitamin C in drinking water (0 an d 1,000 ppm) and dietary vitamin E (25 and 65 IU/kg). Eight replications pe r treatment with four hens per replication cage were heat-stressed at const ant temperature of 35 C for 3 wk. Egg production and egg mass were higher w hen hens were fed 65 IU of vitamin E/kg than when hens were fed 25 IU/kg (8 1.5 vs. 75.9%, P < 0.03 and 48.2 vs. 44.6 g, P < 0.03, respectively). Yolk solids weight for the 65 IU vitamin E/kg group was higher (P <less than> 0. 01) compared to the 25 IU/kg group. ConA and LPS mitogenic responses were g reater in hens fed 65 IU of vitamin E (P < 0.001 or P < 0.003, respectively ) or 1,000 ppm of vitamin C (P < 0.001 or P < 0.002, respectively). The com bination of 65 IU vitamin E/kg and 1,000 ppm vitamin C showed the highest C onA and LPS mitogenic responses among the treatments. No interaction effect s of the two vitamins on production measurements or lymphocyte proliferativ e responses were observed. TBA values in egg yolk and plasma of hens fed 65 IU of vitamin E/kg were lower (P < 0.0001) than those of hens that receive d 25 IU of vitamin E/kg. These results suggest that vitamin E supplementati on at 65 IU/kg diet may enhance production, induction of in vitro lymphocyt e proliferation by ConA and LPS, and antioxidant properties of egg yolks an d plasma of White Leghorn hens during heat stress and that supplementation of 1,000 ppm vitamin C may further enhance in vitro lymphocyte proliferativ e responses of hens during heat stress.