Utilization of the vegetation on Gabbro by Burchell's zebra and blue wildebeest in the Timbavati area

Abstract

The food selection pattern of zebra and blue wildebeest in terms of quality and quantity was studied in the Northern Province Lowveld on a site originating from gabbro geological formations. At the same time a comparison was drawn between the two species. The botanical composition of the grass layer in the study area was determined, the dominant species being Heteropogon contortus, Themeda triandra, Panicum maximum and Enneapogon spp. Forage selection and grass species utilized by the zebra and blue wildebeest were determined through the measurement of forage before and after grazing. The grass species P. maximum, H. contortus and Urochloa mosambicensis were mostly utilized by both zebra and blue wildebeest. Forage and faeces samples were hand collected. Regression equations were used to calculate intake from the average amount of grass species utilized (difference before and after grazing). The monthly dry matter intake as calculated through the plant based technique, did not compare well with the monthly dry matter intake as calculated through the animal based technique with an R2 value of 0.48. Although monthly differences in quality parameters of forage occurred, the same quality and quantity of forage were available for both animal species at a specific time during the sampling period. The mean lignin (ADL) content of the available forage utilized was 8.04 % for zebra and 8.17% for blue wildebeest with the mean in vitro digestibility of organic matter of the forage being 44.2 % (zebra) and 43.1% (blue wildebeest) respectively. There was a significant (p<0.05) difference in the mean intake (expressed as % of body weight) between zebra (2.58%) and blue wildebeest (1.80%). The mean in vivo digestibility of the dry organic matter (DOM) for the zebra (42.2%) was significantly (p<0.05) lower than that of the blue wildebeest (47.9 %) as well as the fibre (NDF) digestibility (respectively 38% and 49%). The climatologically dry conditions under which the study was done did not represent a typical year, and therefore the results were not used to test the carrying capacity equivalents that are officially being used for game animals. The quantitative results, however, confirmed contentions of other literature.