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EMBRYO TRANSFER. WHAT IS EMBRYO TRANSFER?. It is a procedure that removes a number of embryos from a high – value female (embryo donors) and transfers them into many less- valuable females (embryo recipients) The recipients complete the pregnancies and raise the offspring.
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WHAT IS EMBRYO TRANSFER? • It is a procedure that removes a number of embryos from a high – value female (embryo donors) and transfers them into many less- valuable females (embryo recipients) • The recipients complete the pregnancies and raise the offspring. • The donor return to normal oestrus and will rebreed or be used again to produce more embryos.
Normally, the embryo donors are bought into synchronised heat using progesterone hormones. • Hormones are given to increase the number of unfertilised eggs that are ovulated. • The donor animal is bred and the eggs become fertilised and recovered using surgical procedures about 1 week later – 6 day old embryos. • The embryos must be transferred into recipient animals at the same hormone stage as the donor. • The embryos trick the recipient into believing she is pregnant from her own heat – which prevents the next heat from occurring and causes a normal pregnancy to develop.
WHY TRANSFER EMBRYOS? • Because the donors are more valuable than other animals and we use ET to increase the numbers of offspring that a donor could naturally produce. • Reasons for being more valuable include:- production record, pedigree, health status etc. • Embryos are the most efficient method for moving genetics over long distance.
Embryos are free of production diseases common to sheep and goats. • By increasing the normal number of ovulations (superovulation), ET can be used to greatly increase the number of offspring born per donor in a short period of time. • By freezing embryos, ET can be used to store embryos for future use and to move genetics between farms and regions.
WHAT IS SUPEROVULATION? • It is done with twice-daily injections of hormones for 3 days in advance of the donor’s heat. • The success of superovulation is determined by surgery – ovulation sites on the ovaries are counted (Corpora lutea)
Results vary from none to over 30. • Results are affected by age, season, body condition, breed, nutrition, lactation and stress.
Synchronization of oestrus • The successful use of all artificial breeding alternatives depends on the ability to successfully synchronise the oestrus in the ewes.
2 options- CIDR • CIDR’s are very easy to use and are the preferred method of synchronization by many breeders. • They consist of 2 wings which fold together when placed in the applicator and when released, spring out to their original position holding the CIDR in place within the vagina. • The plastic tail remains outside the vagina to allow easy removal of the CIDR. • They are without doubt the preferred method to use on maiden ewes however some breeders reported greater losses of CIDR’s in older ewes.
Sponges • Sponges are a little more difficult to use but many breeders find better retention using sponges. • The sponge is compressed into the end of the applicator which is carefully inserted into the vagina where the compressed sponge is pushed out with the plunger. • The strings are left external to provide a means of removal. • Sponges can be obtained in various progesterone strengths depending on the weight and breed of the ewe being synchronised.
Artificial Insemination • Artificial insemination is by far the most used form of artificial breeding and one that is accessible to almost every sheep breeder. • Laparoscopic AI has replaced cervical AI as the preferred means of using semen from selected sires and the use of frozen semen has greatly increased the number of potential progeny that can be gained from a single sire. • Laparoscopic AI can be performed in your shed on farm and, once the ewes are synchronized, your AI technician will perform the small operation that is required to place thawed semen into the uterus of your ewes. • Ewes are lightly sedated, placed into a cradle that enables them to be restrained and tipped up at an angle that facilitates 2 small cuts to be made where the uterus is accessed using a laparoscope and small measures of semen are injected into each horn of the uterus.
The timing of a typical AI program • DAY 0 - INSERT SPONGES/CIDR’s • DAY 12 - BEFORE 9am, REMOVE SPONGES/CIDR’s, INJECT WITH 2ml PMSG • ALLOCATE EWES TO DIFFERENT SIRES BY IDENTIFICATION WITH MARKER • DAY 14 - BEFORE 12 NOON, EWES INSEMINATED LAPAROSCOPICALLY
Artificial Insemination, as the most common form of artificial breeding conducted by most sheep breeders can also be the most variable and frustrating. • Conception rates can vary the full scale, that is from 0% (unlikely to ever happen) to 100% (hallelujah) with average conception rates around 60-65%. • Once you have it working in your favour, AI will become a very cost effective and important tool in your breeding program.
EMBRYO RECOVERY • The number of embryos recovered can range from 40% to 100% of the embryos. • Embryo recovery is affected by donor age, health of uterus, number of lambings/calvings and the experience of the surgical team.
Embryos from a single flush ready for transplanting into recipient ewes
Are all embryos suitable for transfer? • Not all embryos are transferable. • Embryos are graded on their probability of producing a pregnancy/offspring. • Only about 80% of embryos recovered are of an acceptable quality.
PREGNANCY RATES • Generally, transferring good quality embryos into good recipients should result in a pregnancy rate of about 70%.
WHAT FACTORS AFFECT THE RESULTS OF ET? • Results vary depending on the following factors:- Successful fertilization, Donor breed, Donor age, Season, Stress, Body condition, Diet, Breeding program, Recipient selection and care.
1. Successful fertilization • The hormones levels in donor animals are abnormal due to the large number of ovarian follicles activated by the superovulation drugs. • Those hormones alter the signals of heat and can affect the transport of semen through the cervix. • Instead of the normal numbers of eggs, the male animal has to fertilize a large number of eggs.
2. Donor breed • Prolific breeds respond better to superovulation drugs than terminal sire breeds.
3. Donor Age • More ovulations occur during the years of peak reproduction e.g. 2 to 5 years in sheep. • Younger or older animals produce less eggs.
4. Season • If the animal is not in its normal breeding season, then there is a drop in embryos produced and in the pregnancies in recipient animals.
5. Stress • Stress reduces fertility, therefore it will also reduce the success of an ET program. • The times most affected by stress are;- the breeding of the donors, the time of oestrus in the recipients, and the first two weeks after implantation.
6. Body Condition • Both donors and recipients need to be in good condition. • 7. Diet • Select animals that are well-conditioned, in good health and on a sensible diet for an ET program.
8. Breeding Program • Superovulated animals come into heat earlier than normal, within 18 to 24 hours of pessary removal (hormones). • Males are introduced for 36 hours or else AI is used.
9. Recipient selection and care • Selecting good recipients is critical to success. • Recipients should be young, reproductively proven, in good condition and good health. • They should be free of disease.
