Induction and Synchronization of Oestrus and Ovulation; Multiple Ovulation and Embryo Transfer Technique
In this article, you will be studying multiple ovulations, embryo transfer and its uses as means of improving livestock productivity.
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 a compact 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 at onset of follicular phase.
Those rich in LH like activity e.g. Human Chromonic Gonadotropin (hCG) – should be 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).
Embryo Transplantation and Storage
This technique requires recovery of embryos by flushing fluid through the reproductive tract of the donor animal (which may or may not have been super ovulated), examination of the embryos under a binocular microscope, and then their insertion into the reproductive tract of the recipient or foster mother using a glass pipette.
The recovery and transplantation procedure may involve abdominal surgery under full or local anesthesia, or they may gain access to the uterus of conscious animals through the vagina and cervix as in AI.
Supply of Embryos
A supply of suitable embryos is essential and procedures of superovulation are usually applied to the donor animal. The superovulated donor is bred naturally or if by AI with an increased number of spermatozoa and usually 2 or 3 inseminations.
Embryos may be transplanted in the fresh condition shortly after examination under a dissecting microscope, or they may be used after storage on a temporary or long-term basis.
Read Also: Guide to Proper Artificial Insemination in Farm Animals
Synchronization of Donor and Recipient
Successful transplantation of embryos depends on close synchronization of the oestrous cycles of donor and recipient animals, for 2 reasons:
Growth of the embryo is tightly programmed in terms of its requirements from the uterine secretions.
The chemical nature of these secretions is changing progressively with the time elapsing from ovulation.
In practice, ±1 day in cattle ±2 days in sheep are compatible with establishment of pregnancy.
Site of Recovery and Transfer
Although embryos can be recovered from the oviducts during abdominal surgery, it is more convenient in most circumstances to wait until the embryos have entered the uterus, 3 or so days after ovulation. Recovery can be by surgical or non-surgical procedures.
In either case, the uterine lumen is flushed with a sterile physiological solution that is collected through a rubber catheter with a balloon cuff into a round- bottomed glass dish. A physiological medium is introduced through the catheter, flushed around the uterine horn, and returns through the catheter to a collection dish.
If a single embryo is being transplanted to an unbred recipient, it must be introduced into the horn of the uterus adjoining the ovary with a Corpus Luteum (CL). If an embryo is being added to an animal already mated or inseminated, then this is deposited in the uterine horn opposite the ovary with the CL.
In the case of transplantation of two embryos, it is essential to deposit one per horn, since there is little intra-uterine migration in cattle, and competition between growing embryos may lead to death of one or both.
Uses of Embryo Transplantation
Rapidly multiplying up the number of offspring from a pedigree or exotic donor.
Increasing total calf output by means of twinning – the heritability of twinning being less than 10%.
Produces more calves from best cows in short period i.e. more female calves of high value and better bulls for AI centres.
Rapid multiplication of rare or commercially desirable breeds
In conjunction with superovulation, to speed up selection programmes.
To induce twinning i.e. either transplanting 2 embryos to unmated recipients or by adding one embryo to a mated recipient.
As part of an export programme to upgrade stock in developing countries.
To shorten the generation interval by breeding from prepuberal females.
As an experimental procedure, after deep-freezing, cloning or sexing of embryos.
In summary, embryo transplantation requires the recovery of embryos by flushing fluid through the reproductive tract of the donor animal (which may or may not have been super ovulated) examination of the embryos under a binocular microscope, and then their insertion into the reproductive tract of the recipient or foster mother using a glass pipette.
This technique is important in multiplying offspring of parents with desired traits. The process of this technique has been shown in this article.
Read Also : Micro Farming: Comprehensive Guide and Benefits
