Wildlife and Cows can be partners, not enemies, in search for food

Princeton researchers are leading an effort to put to pasture the long-held convention of cattle ranching that wild animals compete with cows for food. Two studies offer the first experimental evidence that allowing cattle to graze on the same land as wild animals can result in healthier, meatier bovines by enhancing the cows’ diet. The findings suggest a new approach to raising cattle that could help spare wildlife from encroaching ranches, and produce more market-ready cows in less time.

The reports stem from large-scale studies conducted in Kenya wherein cows shared grazing land with donkeys in one study and, for the other, grazed with a variety of wild herbivorous animals, including zebras, buffalo and elephants. The lead author on both papers was Wilfred Odadi, a postdoctoral research associate in the lab of Daniel Rubenstein, the Class of 1877 Professor of Zoology and chair of Princeton’s Department of Ecology and Evolutionary Biology.

Rubenstein and Odadi reported in the journal Evolutionary Ecology Research in August 2011 that cattle paired with donkeys gained 60 percent more weight than those left to graze only with other cows. The researchers proposed that the donkeys — which were chosen as tamer stand-ins for zebras and other wild horses — ate the rough upper-portion of grass that cows have difficulty digesting, leaving behind the lush lower vegetation on which cattle thrive.

In a second study, Odadi and his co-authors reported in the journal Science in September 2011 that other grazers, especially zebras, did remove the dead-stem grass layer and that cattle indeed seemed to benefit from sharing land with wild animals. Cows in mixed grazing pastures took in a more nutritious diet and experienced greater daily weight gain — but this effect was limited to the wet season. Cattle competed with wild species for food in the dry months.

Nonetheless, the studies help counter an enduring perception that wildlife is an inherent threat to the food supply of livestock, Rubenstein explained. These results could prove crucial to preserving animals that are increasingly threatened as the human demand for food drives the expansion of land used to raise cattle. Zebras and wild horses are especially vulnerable to the spread of pastures because of their abundance.

“These experiments suggest that in certain cases cattle can actually experience considerable advantages in terms of growth when allowed to graze with other species,” Rubenstein said. Odadi has presented his findings to local farmers, but understands the difficulty of overturning long-held views about the livestock/wildlife competition. “The farmers we have presented these findings to are generally surprised that zebras and other wildlife can facilitate cattle,” Odadi said.

Rubenstein conducted the experiment reported in Evolutionary Ecology Research with Odadi, who is based at Kenya’s Mpala Research Center — with which Princeton is a partner — and co-author Meha Jain, who earned her bachelor’s degree from Princeton in 2007 and whose senior thesis was the basis of the project. The work was supported by grants from the National Science Foundation (NSF), the Keller Family Trust and Wageningen University in the Netherlands.

For the second study, Odadi worked with ecology professor Truman Young of the University of California-Davis; Moses Karachi of Egerton University in Kenya; and Shaukat Abdulrazak, chief executive officer of the National Council for Science and Technology in Kenya. The study was supported by grants from the NSF, the National Geographic Society, the U.S. Fish and Wildlife Service, and the International Foundation for Science.