Abstract: The aim of this study was to investigate the effects of Schizochytrium fermented product level in the diet of laying hens on production performance, egg quality, serum biochemical parameters, yolk docosahexaenoic acid (DHA) content and cecal microflora. A total of 960 healthy 40-week-old Hyland Brown hens of uniform body weight were randomly divided into 4 groups of 6 replicates each, with 40 hens in each replicate. The control group was fed the basal diet, and the experimental groups I, II, and III were fed with the diets supplemented with 0.25%, 0.5% and 1% of fermented fungus of Schizochytrium, respectively. The pre-test was 7 days and the formal test period was 30 days. The results showed that: 1) The addition of Schizochytrium fermentation to the diet had no significant effect on the egg production rate, feed-to-egg ratio and egg breakage rate (P＞0.05). 2) The addition of Schizochytrium fermentation had no significant effect on egg shape index, eggshell strength, egg white height, Hastelloy unit, yolk colour, eggshell colour and eggshell thickness (P＞0.05). 3) The analysis of the serum biochemical indicators showed that the addition of Schizochytrium fermentation product had no significant effects on total serum cholesterol, triglycerides, low-density lipoprotein, total superoxide dismutase activity and malondialdehyde (P＞0.05), but the addition level of 0.25% Schizochytrium fermentation significantly increased catalase activity (P＜0.05), 0.5% addition level significantly increased total antioxidant capacity, catalase and glutathione peroxidase activities (P<0.05), and serum glutathione peroxidase activity was significantly higher in the 1% Schizochytrium fermentation group than in the control group (P<0.05). 4) The addition of Schizochytrium fermentation to the diet of laying hens significantly increased the levels of DHA, total ω-3 and ω-6 polyunsaturated fatty acids in egg yolk (P<0.05) and significantly decreased the ω-6/ω-3 ratio (P<0.05). 5) The addition of Schizochytrium fermentation to the diet of laying hens increased the abundance of cecum microorganisms. In summary, the addition of Schizochytrium fermentation under the conditions of the current experiment could increase the antioxidant capacity of laying hens, improve the balance of intestinal flora, promote the deposition of DHA in egg yolk, and reduce ω-6/ω-3. In comprehensive consideration, 0.5% Schizochytrium fermentation addition to the diet increased the DHA content and had no adverse effects on the production performance and egg quality of the hens.

Key words: laying hens, Schizochytrium, egg quality, DHA, cecum microorganism