Effects of massive ovulation on oxidation state and function of the ovaries in laying hens

Modern laying hens show fast reduction in egg production rate after 60 weeks of age, which is associated with the decline in ovarian function. The aim of this study was to examine the influence of massive ovulation on the oxidation state and ovarian function in hens. In total, 48 Jing Hong hens aged 17 weeks were randomly divided into high ovulation (HO) and low ovulation (LO) groups. The LO hens were exposed to 6 h of light per day (6 L: 18 D) up to 32 weeks to delay the initiation of egg production and then were switched to 16 L: 8 D. The HO hens were reared at 16 L: 8 D from 19 weeks. The treatment effects were analyzed by the independent samples t-test using SAS 9.0 software (SAS Institute, Cary, NC, USA). At 36 weeks, there were no significant differences in body weight (P > 0.05) between the two groups and the egg production rate of both groups reached 98%; however, the cumulative egg number in the HO group was much higher than that in the LO group (71.3 versus 18.5, respectively; P < 0.001). The following parameters decreased in the HO hens compared with the LO hens: the number of small yellow follicles (SYFs, P < 0.001) and large white follicles (LWFs, P < 0.01), mRNA expression of luteinizing hormone receptor (P < 0.001), and follicle-stimulating hormone receptor (P < 0.001), while the atretic rates of SYFs and LWFs increased (P < 0.001 and P < 0.01, respectively). In addition, compared with the LO group, the HO hens had reduced activity of superoxide dismutase (plasma: P < 0.01; liver: P < 0.001; ovary: P < 0.001) and glutathione peroxidase (plasma: P < 0.01; liver: P < 0.01; ovary: P < 0.01), while the levels of methane dicarboxylic aldehyde (plasma: P < 0.01; liver: P < 0.001; ovary: P < 0.001) and mRNA expression of mitochondrial transcription factor A (P < 0.001) in granulosa cells were higher. These results indicated that massive ovulation aggravated oxidative stress and had adverse effects on ovarian function in laying hens.