BOVINE PHYSIOLOGICAL RESPONSES TO TOXIC FESCUE AND RELATED CONDITIONS FOR APPLICATION IN A BIOASSAY

Physiological responses were observed in 85 male Holstein calves in mostly paired comparisons for the ultimate development of a suitable bioassay technique for fescue toxicity. The effects of environmental temperature, level of feed intake, ergotamine tartrate, and extracts of both toxic fescue and nontoxic orchardgrass on skin temperature of the distal portion of the tail were recorded. The 80% ethanol extract from toxic fescue caused a significant decrease in tail temperature, whereas nontoxic orchardgrass did not. Some differences in heart and respiration rates occurred. Multiple correlation and regression analysis indicated that room temperature and level of feed intake explained 57% of the variation in daily mean skin temperature of the tails of the animals in a room with continuous air movement. Complete removal of feed from the animals for two meals before obtaining measurements also caused reduced tail temperature, heart rate, and respiration rate. The most consistent response differences between presumably toxic and nontoxic extracts were obtained the day of treatment for intraperitoneal administration and the day following treatment for oral administration. The assay procedure described employing skin temperature appears to be the most discriminating for detecting reduced blood flow resulting from the administration of extracts of toxic fescue. © 1969, American Dairy Science Association. All rights reserved.