The specifications and the high price of feed in organic farming require implementing forage fattening. Based on the principles of agroecology, we hypothesized that the livestock farming system performance (animal productivity, environment and level of inputs) would be improved by associating beef cattle and sheep, allowing better valorisation of forages and parasitism control for the sheep. Three suckler farming systems (cattle (CAT), sheep (SH), mixed sheep-cattle (MIX)) were managed for 5 years into separate farmlets in INRAE Herbipole experimental farm, in order to test this hypothesis and the feasibility of producing beef and sheep-meat with only grass in a context of permanent grassland at 1000-1,300 m asl. The results showed that MIX sheep took advantage of the association, with a lower use of concentrates and anthelmintics and a better lamb growth rate compared to SH. Despite a satisfactory degree of fatness, the carcass of young cattle were considered too light by the industry with poor price. The high need for conserved forages for beef fattening in winter, coupled with droughts, has generated additional costs through the purchase of hay.