What Role for the Rice Straw in the Dry Season Diet of Zebus in Sahel Irrigated Area? Case of the Senegal River Delta

During the dry season, transhumant zebu cattle herds used to graze on the Senegal River delta wet areas. Since the 1960s, agricultural colonization and rice cultivation caused major changes in cattle management and feeding. The feeding behavior of three herds was observed from May to July 2000 and from January to July 2001. Rice straw was the main feed, consumed from the ground after harvest by herds moving through the rice areas. From January to May 2001, more than 70% of the feeding activity was concentrated on straw. Then, from May to July, the straw being scarce, substitution forages were grazed or browsed: Typhaceae and Cyperaceae on river banks, and also grasses, a few legumes and Chenopodiaceae from the remaining pastoral areas. Diets simulated by hand plucking of the rations and by animal observation, and samples of the main fodders consumed were analyzed and tested for enzymatic degradability. From April to July, swampy plants and grasses showed low nitrogen and high parietal constituent levels, and, often, lower degradability than rice straw. Only Salsola baryosma, Indigofera suffruticosa and Salvadora persica seemed able to increase digestibility of diets based on rice straw, but their proportions within the rations remained low. Alternatives for feeding resource management and for improving fodder resources are discussed with an aim to increase milk production. They will be challenged by the hold social groups have on the land, as well as on agricultural and/or pastoral use