Background: Cage-rearing in laying ducks, as a novel rearing system, not only fundamentally solves the pollution problem of the duck industry and improve bio-safety and product quality but also exhibits more benefits by implementing standardized production compared with the floor-rearing. Of course, this system also brings some welfare problems and stress injuries to layers due to lack of water environment and limited activities in the cages. However, the effects on the factors of antioxidant defense and inflammatory injury in the early cage stage are not well-understood.
Results: In this study, eighty Shaoxing layers were reared on floor and in cages from 12 weeks of age. The ducks were caged 1, 2, 4, 7, and 10 days, the factors of antioxidant defense and inflammatory injury were investigated. The results showed that the caged ducks suffered liver injury to a certain extent when the ducks were just put into the cages. Analysis of antioxidant enzyme activities indicated that the different rearing system could not affect the change of antioxidant capacities, while the liver malondialdehyde (MDA) level was significant higher in the 2-d, 7-d, and 10-d ducks compared with the 1-d ducks during the change of days, while catalase (CAT) activity showed the opposite results. Additionally, quantitative real-time PCR (qRT-RCR) revealed that the relative mRNA levels of endoplasmic reticulum (ER) stress-related gene (CHOP and GRP78) were significantly upregulated in cage rearing ducks compared to that of the floor rearing ducks. Moreover, the mRNA levels of inflammatory cytokines including cycloxygenase-2 (COX-2), nitric oxide synthase (iNOS), Interleukin 1 beta (IL-1β), Interleukin 2 (IL-2) and Interleukin 6 (IL-6), were also increased significantly in caged layers.
Conclusions: Taken together, although antioxidant defense has no obvious effect on cage stress, the stress levels of laying ducks vary greatly in the early cage stage, which not only caused liver tissue damage to some extent, but also resulted in increases in the expression of the factors of inflammatory injury. Therefore, we recommend that anti-stress agents should be added in the feed to alleviate the stress in the early cage stage.
Keywords: Antioxidant enzymes; Cage rearing; Duck; Inflammatory cytokines.