In this article, we will be discussing about the induction and synchronization of oestrus and ovulation in the first unit, while in the second unit under this module, you will study multiple ovulation and embryo transfer (ET) technique while the 3rd unit under this module deals with pregnancy diagnosis.
We will also cover the induction and synchronization of oestrus, its advantages and means of synchronization. Also control of ovulation, and its uses as means of improving livestock productivity will be studied.
Induction and Synchronization of Oestrus and Ovulation
Synchronization of Oestrus
Is a term used to indicate the process of bringing groups of animals into heat together in response to some form of treatment.Such animals should therefore conceive at closely similar times, proceed through pregnancy together and produce their offsprings in or within a short period.
Advantages
It enables regulation of time of heat and possibly ovulation.
Enables uniform group feeding, supervision, cross fostering, batch weaning, fattening and marketing.
Enables rationalization of the use of labour, buildings and other resources.
Approaches to Synchronization
Synchronization of oestrus involves 2 approaches.
Inducing regression of the corpus luteum (CL) so that all animals in an appropriate group enter the follicular phase and return to oestrus at a closely similar time.
Suppression of ovarian follicular development so that after removing the hormonal or pharmacological blockade, animals rebound into a compact follicular phase followed by a synchronized oestrus.
Means of Synchronizing Oestrus
The means of synchronizing oestrus is varied and has been mostly done for cattle but the trend applies to all animals with varied successes. They include:
Injection of a solution of progesterone (to mimic the activity of the CL).
Feeding synthetic forms of progesterone (i.e. oral progestagens).
Implanting silicone rubber capsules of progesterone under the skin.
Inserting intra-vaginal sponges or coils containing progestagens.
Use of PGF2α or analogues of PGF2α to cause spontaneous regression of CL. Their response to PGF2α will depend on the stage in their cycle. Those with a CL younger than five days or those already in the follicular phase, will not respond to the injection.
However, a second injection given 10-12 days later should find 90-95% animals with mature CL sensitive to the lytic influence of PGF2α. The animals return to heat 2-3 days after the injection.
Control of Ovulation
Control of ovulation aims to regulate the precise time of ovulation and/or the number of follicles ovulating. These objectives are achieved most directly by injection of gonadotropic hormones.
Advantages
Enables AI at the optimum time, with or without detection of oestrus.
Improves conception rates and avoids the deleterious effects of aging of the gametes.
Enables accurate calculation of the time of fertilization and developmental stage of embryos, which are necessary in transplantation studies.
Hormone Preparation
Hormone preparations for influencing ovarian follicular development fall into two main categories:
Those rich in follicle stimulating hormone (FSH) like activity e.g. Pregnant Mare Serum Gonadotropin (PMSG) – should be used at onset of follicular phase.
Those rich in LH like activity e.g. Human Chorionic Gonadotropin (hCG) – should be used at proestrus.
If the response to the injection in terms of the number of follicles ovulating is significantly above the normal ovulation rate for the species or breed in question, then this is referred to as Superovulation.
Time of ovulation refers to the moment of follicular collapse with release of egg(s).
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