| To solve the remarkable confliction between ecological restoration and economic income for herdsman, we have proposed an ecological model of "Replacing livestock with poultry" in grassland ecosystem. Based on this model, we investigated the growth patterns and feedstuff demands from free-range chicken farming in Hunshandake sandland, Zhenglan Banner, Inner Mongolia. The relationship between selective feeding and forage nutrients of free-range chicken in grassland was explored through the control experiment. We applied the community ecology methods to identify the impacts of free-range chicken on community structure, and plant diversity. The specific results are as follows:1) Free-range chickens could grow as normal in Hunshandake sandland where the weather is typically cold temperate. The growth rate of the brooding chickens was stable after one week adaptation which maintained on a high level for a long time. The relationship between growth rate and week-age was regressed as quadratic. Under free-range conditions, the simulation limit weight of'Laiwu-black'chicken was 1727.2g, but not significantly different from cage-raisiing chickens. Compared with other growth environments, the growth inflection point of free-range chickens appears later in Hunshandake Sandland area, which was probably due to the low temperature in the grassland. In addition, compared with cattle and sheep, the reasonable breeding cycles of grassland free-range chickens were about 150 days. So it is suitable for the short-growth period in grassland, avoiding the "thin in spring, fat in summer, while fat-losing in winter" phenomenon in traditional grassland stockbreeding. Shortening the breeding and harvest time would reduce the herdsmen's labor time and labor intensity.2) Each of grassland free-range chickens, compared with the cage-raising chickens, could save 2.6 kg feedstuff (about 20% of the total feedstuff) in the whole growth period. The feed to meat ratio of free-range chickens in grassland is 4.43:1, which is significantly lower than the cage-raising chickens (5.91:1). 3) Free-range chicken have strong selective feeding behaviors on the plant species in the grassland. Free-range chickens in grassland primarily are profered to the blade of the grasses. Even through, chickens have different selective feeding on the common plants growing in Hunshandake sandland, such as higher selective feeding on plants of the family of Chenopodiaceae, bean (Leguminosae) and Compositae, while lower selective feeding on the plants of Gramineous.In addition, free-range chicken also have different selective feeding behaviors among different species. For instance, the daily feeding of each chicken on Alfalfa approximately was 6.75 g while selective feeding on Caragana microphylla and Thermopsis lanceolata were only less than 1g. Another example might be chicken who only uptaked 7.11 g dandelion in Compositae as daily feedstuff. For all kinds of Compositae and artemisia plants, free-range chickens did not or barely uptake as daily feedstuff. We also found that grassland chicken had different selective feeding on plants growing in different habitat in Hunshandake sandland, which was higher on Chenopodiaceae growing in wetland, and lower on plant in fixed sand dunes, indicating that grassland chicken had little effects on the plants in the fixed sand dunes of grassland ecosystem in Hunshandake sandland.4) There were many factors that influence selective feeding of grassland chicken on plants, such as characteristics of chicken, plant palatability and abnormal flavor, etc. Moreover, plant nutrients had greater influences on chicken selective feeding. Cellulose was one of the biggest impact factors (R~2 = 0.754; P < 0.01), which was negatively correlated with selective feeding of grassland free-range chickens. The higher cellulose content the plant had, the lower selective feeding had. Another factor was nitrogen free extract (R~2 = 0.668 ; P<0.01), which positively correlated with selective feeding. The quantity of chickens selective feeding increased with the content of forage nitrogen free extract (NFE). Besides, forage crude protein content, crude fat content and chicken's daily herbivorous quantity also had significant regression relationship (P < 0.01). Plant water content was significantly positively related (P < 0.05) with chicken's daily herbivorous quantity. However, the forage ash and chicken's daily herbivorous quantity had no significant regressive relationship (P > 0.05). Furthermore, this research has also established the model on forage nutrient component and grassland chicken's daily herbivorous quantity. In the model, plant coarse fiber content (EE) and nitrogen free extract content (NFE) had been introduced into regression equation. Such model made a well explanation to 81.6% variance of the daily herbivorous quantity of free-range chicken in grassland. The optimal model is: Y=0.204-0.232EE+0.234NFE. Moreover, this model verified that coarse fiber content, one of indicators of many forage nutrient components, had the most significant effect on grassland chicken selective feeding, followed by nitrogen free extract (NFE).5) For grassland free-range chickens, free-range density had certain effects on community structure, biodiversity and productivity of grassland. Higher grassland chicken density (1000 / hm~2) caused a decline in community coverage, height, diversity and aboveground biomass. However, the amount of community litter increased with increasing free-range density. Lower grassland chicken density (250 / hm~2) only caused a little decline in aboveground biomass and community coverage. Vegetation height almost did not change, while abundance index, diversity index and evenness index increased. All of these results pointed out that lower grassland chicken density increased the complexity of community structure, enhanced the buffer action of their feedback system to environment, and thus remained species communities stable.
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