Abstract

The ingestion of pasture with a high infection rate of endophyte may cause a variety of pathological conditions in livestock, such as ryegrass staggers, diarrhoea, hypothermia and gangrene. This experiment was designed to ascertain the function of the immune system under such conditions. Mixed age ewes were grazed during the summer months, on either high endophyte or low-endophyte ryegrass pastures. Lymphocytes were separated from peripheral blood samples by density gradient centrifugation, and subjected to an in vitro lymphocyte proliferation (lymphoblastogenesis) assay, using the mitogens phytohaemagglutinin (PHA), lipopolysaccharide (LPS), concanavalin-A (Con-A) and intestinal nematode (Trichostrongylus colubriformis) antigen. There were significant differences (P<0.05) in the response to selected mitogens, between the group grazing high versus low endophyte pasture at 14 days (PHA) and 21 days (PHA and Con-A) after the commencement of differential grazing. The animals on high endophyte pasture showed higher stimulation indices. LPS or nematode antigen had no effect on the cultured lymphocytes. As LPS is stimulatory for Bursal-derived (B) lymphocytes and PHA and Con- A for Thymic-derived (T) lymphocytes, it would appear as if material from the high endophyte pasture affected the latter cell population. It is unknown as to whether these effects on the immune system are important, in vivo.

PH, Hemsworth, JL Barnett, and GJ Coleman

Proceedings of the New Zealand Society of Animal Production, Volume 53, , 211-213, 1993