Immunization against gonadotropin-releasing hormone in dairy cattle: Antibody titers, ovarian function, hormonal levels, and reversibility

摘要

Suppression of cyclic activity in cattle is often desired in alpine farming and for feedlot cattle not intended for breeding. A cattle-specific anti-GnRH vaccination (Bopriva, Zoetis Australia Ltd., West Ryde, Australia) is approved for use in heifers and bulls in New Zealand, Australia, Mexico, Brazil, Argentina, Turkey, and Peru. Eleven healthy, cyclic Swiss Fleckvieh cows were included in the study and vaccinated twice with Bopriva 4 wk apart. Injection site, rectal body temperature, and heart and respiratory rates were recorded before and 3 d following each vaccination. Blood samples were taken weekly for progesterone and estrogen analysis and to determine GnRH antibody titer. Ovaries were examined weekly, using ultrasound to count the number of follicles and identify the presence of a corpus luteum. Thirty weeks after the first vaccination, the cows were subjected to a controlled internal drug-releasing device-based Select-Synch treatment. The GnRH antibody titers increased after the second vaccination and peaked 2 wk later. Estrogen levels were not influenced by vaccination, and progesterone level decreased in 7 of 11 cows up to 3 wk after the second vaccination and remained low for 10 to 15 wk following the second vaccination. The number of class I follicles (diameter ≤5 mm) was not influenced by vaccination, whereas the number of class II follicles (diameter 6-9 mm) decreased between 7 and 16 wk after the first vaccination. Class Ⅲ follicles (diameter ＞9 mm) were totally absent during this period in most cows. The median period until recurrence of class III follicles was 78 d from the day of the second vaccination (95% confidence interval: 60-92 d). After vaccination, all cows showed swelling and pain at the injection site, and these reactions subsided within 2 wk. Body temperature and heart and respiratory rates increased after the first and second vaccinations and returned to normal values within 2 d of each vaccination. The cows in our study were not observed to display estrus behavior until 30 wk after the first vaccination. Therefore, a Select-Synch protocol was initiated at that time. Ten cows became pregnant after the first insemination (the remaining cow was reinseminated once until confirmed pregnancy). Bopriva induced a reliable and reversible suppression of reproductive cyclicity for more than 2 mo. The best practical predictor for the length of the anestrus period was the absence of class Ⅲ follicles.