The ovarian follicular wave pattern and induction of ovulation in the mated and non-mated one-humped camel (Camelus dromedarius).
Ovarian follicular wave patterns were studied ultrasonographically in three groups of dromedary. Group 1 camels (n = 20) were teased daily with a vasectomized male but mating was prevented; group 2 camels (n = 8) ran freely with a vasectomized male camel for 10 h each day and group 3 camels (n = 8) were kept completely separate from any males. In a second experiment (n = 63), when the diameter of the dominant follicle reached 0.5-0.9 cm, 1.0-1.9 cm, 2.0-2.9 cm or > 3 cm, the camel was given one of three treatments to induce ovulation: (i) natural mating; (ii) 20 micrograms of the GnRH analogue, buserelin; or (iii) 3000 iu hCG. The ovaries were re-scanned regularly to monitor ovulation, and daily blood samples were assayed for progesterone and oestradiol concentrations. The follicular cycle was divisible into a growth phase (10.5 +/- 0.5 days), a mature phase (7.6 +/- 0.8 days) and a regression phase (11.9 +/- 0.8 days). The dominant follicle reached a mean +/- SEM maximum diameter of 2.0 +/- 0.1 cm (range 1.5-2.5 cm) in 34 cycles (52%) before it began to regress. In the other 32 cycles (48%), however, the dominant follicle continued to grow to 4.2 +/- 0.2 cm (range 4.0-6.0 cm) before regression commenced. Group 2 camels were mated when their follicles reached 1.3 +/- 0.1 cm in diameter and the mean interval between successive matings was 13.8 +/- 1.0 days. Mean +/- SEM serum concentrations of oestradiol reached peak values at 39.0 +/- 1.8 pg ml-1, when the dominant follicle measured 1.7 +/- 0.1 cm and, after ovulation, mean serum concentrations of progesterone reached peak values at 2.6 +/- 0.3 ng ml-1 on day 8, before decreasing to < 1 ng ml-1 by day 10 or 11. When the dominant follicle measured 0.5-0.9 cm in diameter, 70%, 60% and 60% of them ovulated in response to mating, or treatment with buserelin or hCG, respectively. These ovulation rates increased to 85% (mating), 81% (buserelin) and 67% (hCG) when the follicle measured 1-1.9 cm, but they decreased again to 12.5% (mating), 29% (buserelin) and 13% (hCG) when the diameter had increased to 2.0-2.9 cm at the time of treatment. No follicles measuring > 3.0 cm ovulated in response to any of the treatments. These results indicated that the optimum time to mate or attempt to induce ovulation in the female dromedary is when the growing follicle measures 0.9-1.9 cm in diameter.