Development of a bovine model to evaluate administration routines for endophyte-infected tall fescue

Abstract

Fescue toxicosis in cattle is characterised by a reduction in feed intake and hyperthermia during the summer in Southeast to Midwest regions of the United States. Several studies were performed using these endpoints to evaluate different administration routines that might produce a reliable model for this condition. Endophyte-infected (E+) or uninfected (E- ) fescue seed was administered in the standard diet as ground or whole seed during thermoneutral and heat stress periods to determine which seed form produced the greater response in different thermal environments. Time of administration was also tested by comparing response to whole seed administered either before or during heat stress. In each study, a high and low level of ergovaline in the diet was evaluated to identify potential dose differences. Ground E+ seed at either level produced a rapid decrease in feed intake in both environments, with no effect on core body temperature. Whole E+ seed treatment prior to heat stress resulted in a greater daily rise in core body temperature than E- with no effect on feed intake. In contrast, whole E+ seed administration during heat stress produced a dose-dependant upward shift in body temperature and reduction in daily feed intake to suggest that this is the more reliable routine for generating these characteristics of fescue toxicosis in cattle. Keywords: fescue toxicosis, cattle, heat stress