Effect of high stocking density on performance, egg quality, and plasma and yolk antioxidant capacity in laying hens supplemented with organic chromium and vitamin C

This study was conducted to investigate the effects of dietary supplementation of chromium-methionine (CrMet) and vitamin C on performance, egg quality measurements, and plasma antioxidant capacity in laying hens subjected to high stocking density. A total of 360 Hy-Line W-36 laying hens, 26 wk of age, were used in a 2×2×3 factorial arrangement of treatments consisting of 2 cage densities [5 or 7 hens/cage (40×45 cm2)], 2 supplemental vitamin C levels (0 and 500 mg/kg as l-ascorbic acid), and 3 supplemental Cr levels (0, 500, and 1000 μg/kg as CrMet) with 5 replicate cages per treatment. The hens were kept in wire-floor cages in an environmentally-controlled room. After a 2-wk adaptation, the 70-d study was initiated and it was divided into two 35-d periods (28-33 and 33-38 wk of age). Results showed that although subjecting hens to high stocking density had no effect on egg production percentage during 28-33 wk of age, it decreased (P=0.031) during the 33-38 wk of age, resulting in a marked reduction (P=0.038) in egg mass. Dietary Cr supplementation (500 and 1000 μg/kg) increased (P<0.01) egg production and egg mass during both 35-d periods, and improved (P=0.005) feed conversion ratio (FCR) during the first 35-d period. There was a stocking density×vitamin C interaction (P=0.018) for FCR values during the first 35-d period, so that supplemental vitamin C improved FCR to a greater extent in high stocking density-challenged hens. Dietary CrMet supplementation (500 and 1000 μg/kg) increased (P=0.001) feed intake during the second 35-d period. Shell thickness was greater (P=0.015) in hens under high stocking density challenge during the second 35-d period. Subjecting hens to high stocking density decreased (P=0.007) plasma vitamin C concentration, while plasma vitamin C level was increased (P<0.05) as the result of dietary supplementation of vitamin C. Dietary supplementation of CrMet (500 and 1000 μg/kg) increased plasma vitamin C level only in high stocking density-challenged hens, resulting in a stocking density×Cr interaction (P=0.039). Although high stocking density increased (P<0.05) plasma and yolk concentrations of malondialdehyde (MDA), supplemental vitamin C decreased (P<0.05) plasma and yolk MDA contents. Similarly, dietary inclusion of CrMet (500 and 1000 μg/kg) decreased (P=0.046) plasma MDA level. The present findings indicate that dietary CrMet supplementation could increase antioxidant capacity in stressed hens, which improve production performance of laying hens.