Effects of density and feed supplement on layer production and yolk cholesterol under grazing conditions

Although the birth of ecological chicken industry was greeted with great enthusiasm, unreasonable feeding density has largely killed plant cover, exposed hill slopes bare and damaged the ecology. How to use the land resource and shade environment under trees has become a major problem requiring an urgent solution. A total of 441 healthy 45-week-old layer hens were randomly divided into 7 groups to study the effects of density and feed supplement rate on layer production and yolk cholesterol content under grazing conditions. Hens of groups 1?6 were reared under jujube/alfalfa wood. Treatments were set at feed supplement rates of 50% and 70% of free ingestion and at densities of 100, 250 and 400 hens per 667 m². The 7^th group of hens was reared in cages with free ingestion. Each plot area was 62 m², 3 replicas set up for each group and 3 plots of each group used for rotation grazing. Preliminary trial period was 7 days while normal trial period was 70 days. The results showed that while density and feed supplement interaction had significant effects on egg laying rate (P < 0.01), it had no significant effect on egg weight and feed/egg ratio. Egg weight, egg laying rate and feed/egg ratio were not significantly different between cage-reared hens with free ingestion and 70% feed supplement with density of 100 hens per 667 m² (P > 0.05). However, in cage-reared hens with free ingestion, egg laying rate was significantly higher than in other treatments (P > 0.05), egg weight significantly higher than in 50% feed supplement with density of 100 hens per 667 m² (P > 0.05), and feed/egg ratio significantly lower than in 50% feed supplement with density of 100 hens per 667 m²(P < 0.05). The interaction between feed supplement and density had no significant effect on yolk weight, yolk cholesterol content and egg cholesterol content (P > 0.05). However, hen density had significant effect on egg cholesterol content (P < 0.01). Yolk weight of cage-reared hens with free ingestion was significantly higher than that of hens reared under 50% feed supplement and density of 100 hens per 667 m² (P < 0.01). Yolk cholesterol content and egg cholesterol content of cage-reared hens with free ingestion were significantly higher than those of hens reared under 50% and 70% feed supplements and density of 100 hens per 667 m² (P< 0.05). Pasture cover was highest for treatment with 70% feed supplement and density of 100 hens per 667 m². Thus the culture mode with 70% feed supplement and density of 100 hens per 667 m² was better for layer production, yolk cholesterol content and pasture protection.