Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/1998
Publication Date: N/A
Interpretive Summary: Tall fescue is the predominant cool season grass in the humid pasture region of the eastern United States. Unfortunately, from an animal perspective, most of the 14 million hectares are infected with a fungus that produces chemical compounds that result in reduced animal performance which results in an estimated loss of over $600 million annually. At present, there are no easy, inexpensive, management options to overcome the effects of the endophyte. A vaccine could provide such an option. Results of this study suggests that a vaccine could be developed.
Technical Abstract: Three sequential experiments were conducted with rabbits to: 1) ascertain the effect of endophyte-infected (E+) tall fescue seed upon rabbit performance and examine the effect of anti-ergot immunization on rabbit performance and protectiveness against fescue toxicosis, 2) compare immunogens designed to elicit systemic anti-ergot alkaloid antibodies, and 3) select a superior adjuvant. In Exp. 1 rabbits (n = 6/trt) fed E+ fescue seed diets (20%, 340 ppb total ergot alkaloids) had reduced (P < .05) intake and weight gain compared with endophyte-free (E-) controls, whereas apparent diet digestibility was not different between E+ and E-. Rabbits immunized against ergot alkaloids (E+ vac) with lysergol conjugated to human serum albumin (Lys-HSA) had greater (P < .05) intake compared with E+ during the first week of a 3-wk dietary challenge. In Exp. 2, rabbits (n = 4/trt) were immunized with Lys-HSA, with H100-B (ergot alkaloid hapten, H100-different protein carrier, B conjugate), or combinations of both with alum as adjuvant. Greatest (P < .001) anti-ergot alkaloid antibody (Ab) titer developed in the group immunized with H100-B. In Exp. 3, rabbits (n = 4/trt) were immunized with the immunogen H100-B in conjunction with six different adjuvants. Freund's Incomplete Adjuvant (FIA) in combination with DEAE-dextran and FIA alone gave highest anti-ergot titers. In summary, rabbit weight gain and intake were reduced by feeding E+ fescue seed diets, imunization against ergot alkaloids provided temporary improvement in intake, and H100-B conjugate with FIA or FIA + DEAE-dextran as adjuvants elicited a superior anti-ergot immune response. Therefore, it appears that the rabbit may serve as a model animal for fescue toxicosis research.