Selectivity in large generalist herbivores: feeding patterns of African ungulates in a semi-arid habitat

Feeding habits of free-ranging wildebeest and zebra were monitored in a semi-arid nature reserve, bordering the southwestern part of Kruger National Park, South Africa. The purpose of study was to distinguish and define the feeding niches of two roughage grazers that occur in similar habitat types. The monthly compositions of diets were evaluated by direct observations of feeding bouts over a period of two years when rainfall patterns were average and animal populations were stable. Other analyses evaluated the standing biomass of grass species in the reserve during the wet summer and dry winter seasons. A considerable overlap of grass species composition was found in the diets of wildebeest and zebra. Ordination of bi-monthly records of the diet composition showed greater variations in scores of grasses in zebra diet in comparison to wildebeest. Seasonal patterns were more apparent in the wildebeest diet. Preference ranking of grass species indicated that zebra diet remained constant in winter and summer. Wildebeest diet however, alternated with seasons, showing high preferences during the winter months for grass species which were rejected during summer. The combined assessment of results from three separate statistical methods analysing temporal patterns and preferences in diet composition revealed contradictory trends. The solution, however, relied on the initial assumptions posed. Hence, wildebeest and zebra are essentially generalist feeders which show a limited amount of preference in their choice of diet.     

Sheep grazing vs. cutting: regeneration and soil nutrient exploitation of the grassland weed Rumex obtusifolius

Broad-leaved dock (Rumex obtusifolius L., Polygonaceae) is an agronomically important perennial weed causing decreases in pasture yields and fodder quality. Non-chemical control measures for dock are often limited to frequent pulling and cutting, additionally it is usually avoided by grazing animals. Here, the regeneration of R. obtusifolius in a Rumex-infested grassland grazed by a sheep breed that explicitly feeds on dock (Ovis aries L. cv. East Prussian Skudden) was compared to cutting. Therefore, regeneration of 90 R. obtusifolius plants of three different size classes was monitored in three plots during three grazing and cutting cycles. Plant height and number of fruit-stands of regrown R. obtusifolius was significantly lower, number of leaves significantly higher after grazing than after cutting, while plant diameter was unaffected. Initially medium and large-sized plants (>40 cm diameter) were significantly more sensitive to grazing or cutting than initially smaller sized plants. Soil nitrate and ammonium concentrations in the vicinity of R. obtusifolius correlated with some regrowth parameters but were not affected by grazing or cutting. Sheep-grazed grassland communities comprised fewer legumes (p = 0.002), more grasses (p = 0.010) and fewer sward gaps (p = 0.025) than cut grassland. At the end of the experiment, abundance of R. obtusifolius in sheep grazed plots was lower than in cut plots (p = 0.089) suggesting that regrowth potential of this weed was depleted by continuous grazing and higher sward density. In conclusion, these data suggest that sheep could be considered in grassland management schemes to both directly and indirectly control Rumex infestations.     

东北农牧交错区绵羊的自由放养与设计饲养

探讨了在草地自由放养基础上的家畜饲养方式,提出在东北农牧交错区要进行设计饲养。即在利用草地草、农田残茬、林带草和树木落叶自由放养的基础上。按着动物的生长规律设计增重要求,同时利用能量和蛋白质饲料进行补饲,这种日常计划饲养方式有利于草地管理及家畜生产,是我国草地畜牧业的改进发展方向,在东北农牧交错区。当年生羔羊羯羊日粮中若加入20％的豆科牧草,当年体重可以增加40％～65％,即达到52～61kg．这不仅会满足商品畜当年出栏的高标准要求,缩短家畜的存栏期,增进畜牧业效益,同时也必将减轻放牧家畜对草原次年的压力。