WINTER SHEEP GRAZING OF ALFALFA IN THE IRRIGATED SONORAN DESERT .1. LAMB PERFORMANCE

A lamb (Ovis aries L.) grazing trial on alfalfa (Medicago sativa L.) was conducted during the winters of 1985/1986 and 1986/1987 at the Imperial Valley Research and Extension Center, to relate lamb gain to available alfalfa forage. Lambs from a commercial flock sequentially grazed the same paddocks. Non-linear regressions of lamb average daily gain on alfalfa leaf dry matter (DM) per unit of lamb body weight (R2 = 0.53) more accurately represented lamb performance during the winter grazing season in the Imperial Valley than did the regression of lamb gain on total alfalfa DM per unit of lamb body weight (R2 = 0.50). When grazing alfalfa, lambs preferentially selected the leaves over stems. Near maximum gains occurred when leaf DM was about 7% of lamb body weight or about 280 to 300 lb of leaf DM per acre. When alfalfa stubble was about 4 to 6 in. tall and devoid of leaf, lamb gains started to decline. Such information might be helpful to local graziers to plan lamb movements.