Effect of repeated locoweed feeding on peripheral lymphocytic function and plasma proteins in sheep

Seven healthy, adult, crossbred yearling ewes were given (orally) 340 g of locoweed (Astragalus lentiginosus) every day for 10 weeks. Another 7 ewes were not fed the plant, but were housed similarly (controls). Blood samples were obtained once a week to evaluate the mitogen-induced lymphocytic responsiveness. For the locoweed-exposed ewes, there was decreased activity in the presence of phytohemagglutinin (a T-cell mitogen). This effect, although not statistically significant at all times, was consistent and became significant after 7 weeks. A similar response was observed in the blood cell cultures in the presence of pokeweed mitogen, but the differences were not statistically significant at most time points. For the locoweed-exposed ewes there also were gradual numerical decreases in total leukocyte and lymphocytes in peripheral blood. Peripheral leukocytes had cytoplasmic vacuolation. The results indicated that a selective effect may occur on cell-mediated immune responses. Serum proteins and gamma-globulins were not affected by locoweed treatment. Locoweed, certain species of Astragalus and Oxytropis, causes considerable economic loss to the livestock industry of western United States. Locoweed consumption by livestock can result in neurologic problems, emaciation, habituation, and reproductive alterations. The reproductive alterations include abortions, birth defects, and some interference with spermatogenesis and oogenesis. Signs of poisoning are CNS depression, rough dry coat, dull eyes, irregular gait, and excitement when stressed. The microscopic lesions are neurovisceral cytoplasmic vacuolations. Microscopic lesions are also observed in the fetuses and newborns of dams which were fed locoweed.(ABSTRACT TRUNCATED AT 250 WORDS)