Hello Mounir. I suppose Prof Harinder Makkar, University of Hohenheim, Center for Agriculture in the Tropics and Subtropics/FAO has done a good research work on cactus. You can search with his name, i hope you will find good materiel on cactus as a fodder and beyond. Best Regards
Dear Mounir, although in Portuguese the text has a good economic analysis about cactus fields irrigated to maximize the forage production in northeast Brazil.
Article Viabilidade econômica da produção de palma forrageira irriga...