Performance and Adverse Response of Sheep During Grazing of Four Legumes

Abstract

Heifers (Bos taurus) may exhibit severe photosensitization and low gains when they consume ‘Monarch’ cicer milkvetch (Astragalus deer L.). We wanted to determine whether grazing lambs (Ovis aries) also would display these problems when they consumed Monarch cicer milkvetch compared to ‘120’ alfalfa (Medicago sativa L.), ‘Norcen’ birdsfoot trefoil (Lotus corniculatus L.), or ‘Arlington’ red clover (Trifolium pratense L.). A controlled, light grazing pressure (5 to 6% of body weight in leaf‐plus‐flower tissue dry matter per day) was used in pastures that had a Waukegan silt loam (flne‐silty over sandy, mixed, mesic Typic Hapludoll) soil. Lambs confined to the least palatable legume (cicer milkvetch) gained as well as or better than those confined to each of the other three species, even though animals often exhibited photosensitization exclusively on cicer milkvetch. Mean average daily gains during the 3 yr were 215, 228, 217, and 224 g Iamb‐' for alfalfa, birdsfoot trefoil, red clover, and cicer milkvetch, respectively. Even though red clover was leafier and had superior digestibility of stems and total forage, it usually did not promote different animal gains. Bloat of lambs occurred infrequently and only on alfalfa. Lamb product per hectare was influenced more by legume carrying capacity than by daily gains. The first‐year carrying capacity advantage of red clover progressively declined until it was lowest during the third year. We conclude that legume nutritive value variation had no consistent significance for lamb performance, and that earlier intake and gain problems by cattle that grazed cicer milkvetch were not repeatable with lambs. The excellent long‐term pasture persistence, carrying capacity, nutritive value, and lamb gains attributable to cicer milkvetch indicate that more research and breeding improvement are merited with this species even though it can cause photosensitization. Poorer persistence, but excellent initial carrying capacity, nutritive value, and lamb gains from red clover and birdsfoot trefoil indicate that breeding specifically to develop longer stand life would greatly enhance their pasture potential.