ABSTRACT Research was conducted to evaluate the sensitivity of Bos indicus and Bos taurus cattle to a tall fescue ergopeptine alkaloid by assessing vital sign responses. Eight Polled Hereford and seven Red Brahman steers received bolus i.v. injections of ergotamine tartrate and saline vehicle in a simple cross-over design. Physiological traits measured 30 min and immediately before and 30, 60, and 90 min after treatment were respiration rate, rectal temperature, skin temperature at the tailhead and tail tip, systolic and diastolic blood pressure, and heart rate. Blood samples were collected immediately before and 105 min after treatments to determine plasma prolactin and cortisol concentrations. Steers were fed a fescue-free diet in drylot. Ambient temperature and relative humidity averaged 31°C and 55%, respectively, during data collection. No breed × treatment × time interactions were apparent for vital signs. The treatment × time interaction was significant (P < .05) for blood pressure and skin temperature. Ergotamine increased (P < .01) blood pressure and decreased (P < .01) skin temperature. The breed × treatment × time interactions were significant for prolactin (P < .1) and cortisol (P < .01). Ergotamine decreased plasma (P < .01) prolactin and increased (P < .01) cortisol concentrations in both breeds, despite some breed variation. Across all traits, Brahman and Hereford steers responded similarly to acute ergotamine exposure, indicating that the breeds are alike in acute sensitivity to a systemically administered ergopeptine alkaloid associated with fescue toxicosis.
Implications
Fescue toxicosis causes significant economic losses to cattle producers because of reduced cattle performance. Vital signs are altered similarly in cattle grazing endophyte-infected tall fescue or exposed to ergotamine. Taking advantage of genetic diversity in the cattle population may lessen performance problems in herds consuming endophyte-infected tall fescue. It was proposed that physiological responses to ergotamine would be lower in heat-tolerant cattle than in heat-sensitive cattle. Data reported here indicate that Brahman and Hereford steers were similarly sensitive to ergotamine upon initial exposure and tend to support a viewpoint that endophyte-infected tall fescue would adversely affect heat-tolerant cattle as it does heat-sensitive cattle. Physiological studies with these genotypes involving chronic exposure to ergopeptine alkaloids will be needed to define the utility of heat-tolerant breeds for minimizing fescue toxicosis in cattle.
Key Words: Cattle Breeds, Heat Stress, Festuca Poisoning, Ergot Alkaloids,
Cardiovascular System, Thermoregulation
© 2000, by the American Society of Animal Science. All rights reserved.
J. Anim. Sci. 2000. 78:124-130
| Search PubMed MEDLINE and PubMed are registered trademarks of the U.S. National Library of Medicine. |