Synchronisation of ovarian follicular waves in the dromedary camel (Camelus dromedarius)

This study was designed to compare the efficacy of various treatments intended to synchronise follicular wave cycles in dromedary camels by removing the existing follicle of unknown size and replacing it with a follicle capable of ovulating at a known time. Camels were randomly assigned to one of five groups and treated with either (1) 5 mg oestradiol benzoate (i.m.) and 100 mg progesterone (i.m.; E/P, n = 15), (2) 20 μg GnRH analogue, buserelin (i.m.; GnRH, n = 15), (3) 20 μg buserelin (i.m.) on Day 0 (T = 0) and 500 μg prostaglandin on Day T + 7 (GnRH/PG n = 15), (4) transvaginal ultrasound—guided follicle ablation of all follicles ≥0.5 cm (ABL, n = 15) or (5) 5 ml saline (i.m; Controls n = 15). All camels were subsequently injected with 20 μg buserelin 14 days after the first treatment was given. The ovarian response was monitored daily by transrectal ultrasonography and the intervals from treatment to follicular wave emergence and also the day on which the new dominant follicle reached 1.3 cm was recorded. Amongst the treatment groups the mean interval from treatment to new follicle wave emergence and treatment to time taken for the new dominant follicle to reach 1.3 cm in diameter was shortest in the ABL group (2.3 ± 0.5 days and 8.8 ± 1.1 days respectively, P = 0.044) and longest in the E/P group (6.4 ± 0.8 days and 12.2 ± 1.0 days respectively, P < 0.001) whereas the GnRH and GnRH/PG groups were intermediate (3.0 ± 0.5 days and 11.1 ± 0.8 days GnRH; and 4.5 ± 0.5 days and 10.7 ± 0.7 days GnRH/PG). A total of 11/15 camels in both the GnRH and GnRH/PG groups had dominant follicles between 1.3 and 1.9 cm 14 days post treatment, of which 21 of the 22 follicles ovulated after GnRH injection on T + 14. The ABL, E/P and control groups however, showed greater variability in follicle size with less camels having dominant follicles between 1.3 and 1.9 cm than the GnRH and GnRH/PG groups and more in the ≥2.0 cm or follicle regressing groups, therefore fewer of these camels ovulated (ABL n = 7; E/P n = 9; Control n = 6) after GnRH injection on Day T + 14. In conclusion, two GnRH injections 14 days apart or two GnRH injections 14 days apart and PG on Day 7 after the first GnRH were the most effective methods to synchronise ovulation rate in dromedary camels at a fixed time interval of 14 days after treatment.