Physiological responses of Brahman and Hereford steers to an acute ergotamine challenge

Research was conducted to evaluate the sensitivity of Bos indicus and Bos t aurus cattle to a tall fescue ergopeptine alkaloid by assessing vital sign responses. Eight Polled Hereford and seven Red Brahman steers received bolu s i.v. injections of ergotamine tartrate and saline vehicle in a simple cro ss-over design. Physiological traits measured 30 min and immediately before and 30, 60, and 90 min after treatment were respiration rate, rectal tempe rature, skin temperature at the tailhead and tail tip, systolic and diastol ic blood pressure, and heart rate. Blood samples were collected immediately before and 105 min after treatments to determine plasma prolactin and cort isol concentrations. Steers were fed a fescue-free diet in drylot. Ambient temperature and relative humidity averaged 31 degrees C and 55%, respective ly, during data collection No breed x treatment x time interactions were ap parent for vital signs. The treatment x 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 x t reatment x time interactions were significant for prolactin (P <.1) and cor tisol (P < .01). Ergotamine decreased plasma (P < .01) prolactin and increa sed (P < .01) cortisol concentrations in both breeds, despite some breed va riation. Across all traits, Brahman and Hereford steers responded similarly to acute ergotamine exposure, indicating that the breeds are alike in acut e sensitivity to a systemically administered ergopeptine alkaloid associate d with fescue toxicosis.