Immunosuppression in Cattle with Fescue Toxicosis

Abstract

Anecdotal observations suggest that cattle entering feed lots after grazing endophyte-infected tall fescue have increased morbidity and mortality (Purdy et al.,1989). The morbidity and mortality has been interpreted as resulting from reduced immune functions in animals with fescue toxicosis. Rats fed endophyte-infected seed diets had lower serum antibody titers to sheep red blood cells than rats fed endophyte-free seed diets. In addition, spleen cells from rats on the endophyte-infected seed diets bad reduced mitogen response (Dew et al.., 1990). A consistent physiologic change associated with fescue toxicosis is hypoprolactinemia (Thompson et al., 1987). There is an increasing body of literature that indicates that prolactin functions as a co-factor in the regulation of the immune response (Reber,1993). Based on these observations the hypothesis was developed that cattle with fescue toxicosis would have decreased ability to produce antibodies to a protein antigen.