The warning came as Narok County held celebrations to mark the third World Wildlife Day, which aims to draw attention to the threats facing endangered species in Kenya.
Mr Robert Ndetei, Species Manager for the World Wide Fund for Nature (WWF), said it was shocking that tens of hundreds of cattle encroach into the reserve every night when tourists are safely out of sight.
Kenya's lion population has declined from 20,000 to less than 2,000 in 50 years, with about 300 in the Maasai Mara Reserve.
Wildlife officials and communities around the Maasai Mara game reserve must do more to prevent human wildlife conflict, a wildlife expert has said.
The warning came almost three months after a world famous pride of lions was poisoned by herdsmen inside the reserve, leading to the death of three animals. The lions from the Marsh Pride are believed to have eaten a cow carcass which had been laced with poison on December 6 last year.
