Ranchers in African generally prefer to keep wild grazers like zebras off the grass meant for their cattle. Worldwide savanna rangelands are managed on the premise that cattle and wildlife compete for food. It makes sense, but surprisingly there is little scientific information to support the assumption.
Researchers in Kenya grazed cattle in fenced 10-acre plots of savanna rangeland. Fences excluded wildlife principally zebras. Other groups of cattle grazed with wildlife. Cattle were weighed periodically throughout the year. During the dry season, grazing with wildlife reduced weight gain by cattle, but in the wet season, cattle actually gain more weight when they grazed with wildlife.
During the wet season, grass grows tall and quickly loses its nutritional value. Under these conditions having zebras is beneficial. Zebras are more willing than cattle to knock back the rank grass leaving higher-quality grass for cattle.
It’s not yet clear whether there is a net benefit over a whole year or series of years because conditions vary from year to year. From a management perspective, the positive effect of wildlife on weight gain by cattle during the wet season suggests that wildlife conservation is not necessarily detrimental to, and can at times be compatible with, cattle production.
Reference: Odadi, W.O., M.K. Karachi, S.A. Abdulrazak, and T.P. Young. 2011. African Wild Ungulates Compete with or Facilitate Cattle Depending on Season. Science 333:1753-1755.