Induced and Spontaneous Ovulators, An Overview:
There are two different modes of reproduction in mammals; spontaneous and induced:
- Spontaneous- ova are released without the need of copulation at specific times during an oestrus cycle
- Induced- the act of copulation stimulates the release of ova.
Most domestic/farm animals are spontaneous ovulators, but a few examples of induced ovulators are cats, alpacas and llamas, rabbits and ferrets. Essentially, this means that the females of these species can potentially become pregnant at any time (it seems it’s not just rabbits!)
How Does Induced Ovulation Work?
Unlike spontaneous species, induced mammals do not display a typical oestrus cycle (this means there are recurring, cyclical, physiological changes in the animal, like menstrual cycles in humans for example). Induced ovulation species rely on copulation to trigger a surge in LH (Luteinizing Hormone) which stimulates ovulation.
Induced ovulators are polyoestrous. Some species are seasonally polyoestrous (such as cats, which typically cycle from February to September, rabbits which usually cycle between mid-February to late summer and ferrets from March to September). Whereas other species can be mated throughout the year (such as alpacas and llamas). Therefore we can refer to these animals generally as having follicular and luteal phases.
Induced Ovulation Species: Similarities and Differences
Surprisingly, reproductive anatomy seems to be very similar between cats, alpacas and llamas; they have two uterine horns attached to a single uterine body. Ferrets differ in that their uterus is bicornuate and their ovaries are embedded with the ovarian bursa. With rabbits, the ovaries are attached to the fallopian funnel, which in turn becomes the fallopian tube and ends in the uterus.
Mating Behaviour: This also differs between species…
- Alpacas and llamas- very similar. When females are receptive they will lay down into a sternal position, and males can be quite loud. Mating can take approximately 45 minutes.
- Cats- it’s the female that becomes vocal, displaying behaviours such as rubbing, rolling and possibly seeking attention. You may also notice that she arches her back in a downwards position with her hind quarters raised. Mating is normally very quick and she may mate with multiple males.
- Rabbits- a buck will bite a doe to keep her in place, then drop off her once copulation is complete.
- Ferrets- when a Jill is ready for mating her coat will become extremely greasy and produce a strong scent and her vulva will swell. Mating can vary in time; it may last from hours to days. The hob will bite the Jill and hold the bite to stimulate the release of LH.
Ultrasound and Induced Ovulation
Ultrasound performed pre-mating may identify structures such as the ovaries developing immature follicles. With cats it can be quite difficult to identify the ovaries so ultrasonography may not yield any results. Rabbits and ferrets may also yield invalid results due to noncompliance from the animal. With Alpaca and Llama’s you can quite easily obtain good ultrasonic images of the ovaries. However, ultrasound is generally better used for pregnancy detection and monitoring after mating in most induced ovulation species.
Here are the approximate, ideal number of days post-mating for transabdominal pregnancy detection in the species mentioned:
- Cats – 28 days
- Alpaca – as early as 40 days
- Llama – as early as 40 days
- Rabbits – as early as 12 days
- Ferrets – 14 days post mating