Feeding strategies for sheep grazing the Inner Mongolian steppe, China

The present study was conducted within the framework of the Sino-German MAGIM-project (“Matter fluxes of Grasslands in Inner Mongolia as influenced by stocking rate”, 2004 – 2010) and the LOTGras-project (“Long-term strategies towards improved grassland productivity in semi-arid environments”, 2010 – 2013) funded by the Deutsche Forschungsgemeinschaft DFG (German Research Foundation). In the MAGIM-project, biological aspects (e.g. grazing intensity, grazing management system, vegetation productivity and species composition, and soil parameters) of the Inner Mongolian steppe ecosystem were studied with the aim of reducing the ecological problems mainly associated with overgrazing in this region. LOTGras focused on precise feed supplementation to improve sustainable animal productivity and avoid degradation of the plant community. The objectives of this study were to evaluate the effects of different feeding strategies, in particular looking at the impact of grazing intensity, grazing management system and concentrate supplementation on feed intake, digestibility of organic matter intake and live weight gain of grazing sheep and on grassland condition in a semi-arid and arid pastoral system. A grazing experiment in the Xilin River Basin (northeast Inner Mongolia) was conducted during the grazing seasons of 2005 – 2010, with two management regimes and six different grazing intensities (Very light – very heavy) and with ~ 300 female non-lactating Mongolian fat-tailed sheep. A continuous grazing management system, in which plots for grazing and hay-making were used continuously, and an alternating grazing management system, in which plots for grazing and hay-making alternated annually, were established. The first study analyzed results (2005 – 2010) of the alternating grazing system, to evaluate the impact of grazing intensity on digestibility, feed intake and live weight gain of grazing sheep. The second study in 2010 the effects of a moderate concentrate supplementation on sheep and the grassland in both grazing management systems and six different grazing intensities were analyzed. Results of the first study shows that individual animals are only marginal influenced by high grazing intensities regarding digestibility of organic matter intake, organic matter intake, metabolizable energy intake and live weight gain despite a very low herbage allowance. In contrast parameters measured per unit of land area, organic matter intake per ha, metabolizable energy intake per ha and live weight gain per ha increases with increasing grazing intensity during all years. All parameters are strongly influenced by year and significant interaction between grazing intensity and year are observed for live weight gain per animal and live weight gain per ha. Live weight gain per area of land unit is highest in very high stocking densities (9.5±0.6 sheep/ha) in most years, indicating that in short term farmers act properly from an economical point of view. Whereas, vegetation ground cover and end-of-season-standing biomass at the end of the grazing season indicate that high stocking densities in most of the study years exceed the threshold values seen as critical for a sustainable long-term grassland use. To prevent soil erosion during winter months and thus, to maintain long-term grassland productivity, it is necessary to reduce stocking densities to <2.0 – 6.4 sheep/ha, depending on climatic conditions. The ecological optimum is not congruent with the economic stocking density, but they will converge due to predicted negative changes in herbage composition in the future. Results of the second study show that concentrate supplementation strongly increases feed intake and live weight gain of grazing livestock and appears sufficient to maintain output per area even with lower stocking densities. Efficiency in the use of concentrate feed was similar for both grazing systems and over a wide range of stocking densities in our study, most likely due to a lack of differences in herbage and animal parameters between systems and grazing intensities and the adaptive feeding behavior (e.g. selection of herbage and expanded grazing time) of sheep. Concentrate supplementation restricted to selected months with high efficiency (i.e. g live weight gain/g concentrate) can be cost-effective. The considerable reduction in the herbage organic matter intake of individual animals alleviates grazing pressure and can thus contribute to maintaining long-term productivity of grasslands and similar environments.