4. Ovarian physiology
4.1. Follicular phase of the oÕarian cycle All camelids are induced ovulators, i.e. they ovulate after mating or the administra-
tion of a hormone with luteinizing activity. Hence, the follicular phase is constant and interrupted by a luteal phase after ovulation. If mating does not occur, follicles grow and
regress constantly in a wave-like fashion. Therefore, it is more appropriate to use the term follicular wave pattern, rather than oestrous cycle. In lamoids, follicles become
dominant when they are 6 mm in diameter. Dominance is exerted on the cohort of follicles on the ipsilateral and contralateral ovaries. A follicular wave lasts, on average,
Ž .
10–12 days range 7–14 and the dominant follicle alternates between the ovaries in Ž
. 85 of the cases Bravo and Sumar, 1989; Bravo et al., 1990 . Follicle waves overlap
Ž and this determines constant and long periods of sexual receptivity of the female San
. Martin et al., 1968; Bravo et al., 1994 .
Based on observations of follicular waves in the dromedary camel and on determina- Ž
. tions of plasma oestradiol concentrations Elias et al., 1984 , the mean duration of the
Ž .
oestrous cycle has been reported to be 17.2–23.4 days in India Joshi et al., 1978 , 24.2 Ž
. days in Egypt, 28 days in Sudan Musa and Aubusineina, 1978 , and 16–22 days in
Bactrians. However, oestrous behaviour can be difficult to detect since the female may show receptivity to the male outside the confines of oestrus when she has mature
follicles in her ovaries. The dromedary will ‘succumb’ to being mated at any stage of her ovarian cycle, even during early pregnancy and during the luteal phase that follows a
Ž .
sterile mating Arthur et al., 1985 . Studies using real time ultrasonography have shown Ž .
that these waves of follicular activity are clearly divisible into three stages: i the Ž
. Ž .
growth phase lasting a mean s.d. of 10.9 3 days; ii a mature phase of 7.6 4.2 Ž .
days; and iii a regression phase of 11.9 4.2 days with the mature follicles reaching a mean maximum diameter of 2 0.3 cm, or may in some cases continue to grow to as
Ž .
large as 6 cm in diameter Skidmore et al., 1995 . 4.2. OÕulation
There are various stimuli that induce ovulation in camelids, but the most common Ž
triggering mechanism is mating by an intact andror vasectomized male Fernandez-Baca .
et al., 1970; Marie and Anouassi, 1987 . In Bactrians, dromedaries and alpacas, mechanical stimulation of the cervix and vagina does not trigger ovulation, nor does
mounting alone. However, the presence of whole semen deposited deep in to the vagina Ž
. Ž
. induced ovulation in Bactrians Chen et al., 1985 and alpacas Rios, 1989 and even the
Ž intramuscular injection of semen, or seminal fluid provokes ovulation in Bactrians Zhao
. Ž
. Ž
. et al., 1990, 1992a . Similarly, luteinizing hormone 300 IU , hCG 100–200 IU and
Ž .
Ž GnRH analogue 250–500 mg have been shown to trigger ovulation in Bactrians Zhao
. Ž
. et al., 1990 and, in dromedaries, both hCG 3000 IU and 20 mg GnRH analogue
Ž .
Buserelin injected intravenously induced ovulation within 36–48 h after treatment in
Ž .
Ž the presence of 1–1.9 cm diameter growing follicles Musa et al., 1990; McKinnon
. and Tinson, 1992; Skidmore et al., 1996 . In lamoids, it was found that 750 IU hCG was
sufficient to induce ovulation in 100 of alpacas and 80–800 mg GnRH provoked ovulation in 80 of llamas and alpacas. In lamoids, the minimum ovulatory size follicle
has been determined as 7 mm and the follicles should be in growing phase. Ovulation cannot be induced in the presence of smaller follicles due to the lack of release of LH by
the pituitary gland and luteinization of the follicle occurs if female lamoids are bred in
Ž .
the presence of regressing follicles Bravo et al., 1991 . 4.3. Synchronisation of female camels
When preparing camels for AI, it is necessary to be able to control follicular growth and synchronise ovulation in groups of animals. This poses particular problems in the
camels due to the absence of a cyclical CL that would exist in spontaneously ovulating species such as the horse and cow, and would be lysable with PGF
or one of its
2 a
analogues. There are few published reports on the use of progestagens to control follicular growth in the camel. Treating them with PRIDS has been found to be
unreliable, because removal of the PRID may be followed very rapidly by spontaneous Ž
. ovulation in some animals Marie and Anouassi, 1987; Cooper et al., 1992 . Daily
intramuscular injections of 100 mg progesterone-in-oil for 10–15 days has been shown to limit follicular growth and is particularly effective at hastening the regression of large
Ž .
unovulated follicles McKinnon and Tinson, 1992; McKinnon et al., 1994 . However, as growth rates of individual follicles can be highly variable between different animals,
attempts to synchronise them with progesterone — so that they only have a few small follicles present at the end of treatment — is not always beneficial as it does not
necessarily mean that they will all have a mature ovulable follicle between 1 and 1.9 cm in their ovaries at the same time.
Synchronisation of female lamoids for AI has not been explored. Whenever insemina- tion was intended, sexually receptive females to vasectomised males andror intact males
have been used. Then, ovulation has been provoked by mating to a vasectomised male or administration of hCG, andror GnRH.
5. Methods of semen collection
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