Effects of administration of ergotamine tartrate on fertility of yearling beef bulls

Sixteen Angus crossbred bulls were used to investigate effects of ergotamine tartrate administration on semen parameters, endocrine profiles and the use of in vitro fertilization as a means of predicting developmental competency of oocytes fertilized with sperm from bulls fed ET. Bulls, approximately 350 kg body weight and 270 days of age, were assigned to one of two groups. Within each group, bulls were allotted by breed, weaning weight, hip height, scrotal circumference, and age. All bulls were fed a diet of cracked corn, corn silage, and soybean meal. Bulls restricted to this diet served as controls (CON, n = 8). Additional topdressing of 40 /yg/kg body weight of ergotamine tartrate (ET) was provided to the treatment group (ET, n = 8). ET dose remained constant throughout experimental period. In order to maintain dosage of 40 µg/kg body weight, amount of ET administrated was altered as body weight increased. Administration of ET began in mid-November and continued through the end of June. Blood samples, body weight, and rectal temperatures were recorded every two weeks beginning at ET administration and continued through experimental period. Semen samples were collected from all bulls approximately every sixty days by electroejaculator. During May and June, testicular core temperatures were measured by scrotal thermography. From both groups, collected semen from bulls (n = 2 trt) having the largest and smallest scrotal circumference was extended at the location and returned to the laboratory for further assessment such as performance of sperm using in vitro fertilization (IVF). Comparisons between ET and CON for IVF parameters were determined using PROG FREQ procedure. All other variables were analyzed by the Mixed procedure. Administration of ergotamine tartrate increased rectal temperature (39.3 + 0.05 °C) compared to CON bulls (39.1 + 0.05 °C; P = 0.02). However, concentrations of prolactin did not differ between ET (79.7 + 9.5 ng/mL) and CON bulls (56.2 + 9.6 ng/mL; P = 0.10). Neither scrotal circumference (P = 0.68) nor serum concentrations of testosterone (P = 0.17) differed throughout the experimental period between groups. Semen motility and morphology were similar in bulls administered ergotamine tartrate and controls (P = 0.83; P = 0.51, respectively). However, bulls exposed to ergotamine tartrate had a significant decline in testicular core temperatures (31.4 + 0.3 °C) compared to CON bulls (33.0 + 0.3 °C; P = 0.004). Cleavage rate of oocytes cultured with sperm from bulls fed ergotamine tartrate 51% was reduced compared to CON (69%; P = 0.001). Ability of cleaved embryos to develop to 8-16 cells (P = 0.11) or to blastocyst (P = 0.96) did not differ between groups. In conclusion, extended exposure of bulls to ergotamine tartrate appears to reduce fertilization ability of sperm; possible through the vasoconstrictive action associated with the treatment.