Bovine embryo transfer occurs after embryo production, either through embryo flushing or in vitro fertilization (IVF). An embryo produced is transferred into the uterus of the recipient or surrogate cow where the embryo develops to a foetus and at calving the recipient will raise the calve until weaning. Embryo Transfer is seen as the aim of all assisted reproduction techniques (ART) and the advantages of embryo transfers outweighs the disadvantages
Bovine Embryo Transfer
- More calves can be produced from a genetic superior cow yearly.
- An animal of lower genetic potential can still be utilized for genetic progress (as recipient).
- Increased rate of genetics progress.
- It allows breeders to produce calves that sell for better prices (E.g. more profitable weaner production).
The high cost of embryo production and transfer is the main disadvantage. The effect of time lost with embryo flushing is taken into account by breeder societies when calculating inter calve period.
With the process of embryo transfer, the recipient cows are synchronised to be ready for embryo transfer on a specific day. This synchronisation is often scheduled to be on the same day as embryo flushing, so that fresh flushed embryos can be transferred. Fresh embryos have a conception rate of 50%, on average, with frozen (cryopreserved) thawed embryos on 40% conception rate.
Factors effecting the success rate of embryo transfer:
- Fertility – it is important to select fertile animals as recipients. Animals that show activity, cycle regularly and had no trouble getting pregnant previously. Recipient prepared more than two times are discouraged.
- Age – the age of the recipient plays a role, with a cow that calved more than three time being the best and heifers, at breeding age, as second option for embryo recipients. Females that has calved only once, is naturally more difficult to get pregnant again and not preferred to be prepared as embryo recipients.
- Breed – the breed factors can include factors like adaptability and temperament, but also the size. It is important that the recipients used are the appropriate size for the embryos that they will carry to term. This is to ensure easy calving. It is also important that the recipients used is adapted to the feed, the environment, the farm and even to handling. Animals that are not used to handling, are more likely to stress. Any kind of stress has a negative effect on embryo success. Some breeds are more temperamental, which is also a stress indicator.
- Body condition score (BCS) – body condition is scored from a 1 to 5, with 1 being lowest and 5 the highest. It is important to score the body condition so that feeding can be adapted to get the group in optimal condition. Recipients should be in a rising condition state at transfer to ensure optimal conception rates. Moving from 2.5 to a score of 3 is preferred.
- Post-partum – recipients without calves are the best, but often not available and therefore it is suggested that animals be used as embryo recipients at 80 days post calving.
- Facilities – handling facilities is preferred to be neat and enable easy handling on the day of embryo transfer to ensure less stress on the recipients.
- Environment – the weather has a major effect on embryo survival as thunderstorms, cold, extreme temperature and rain causes stress on the animals. If cover is available during cold or rain it is suggested to use is. Feed can be increased during colder, wetter weather since the body increases metabolic heat production to sustain a constant body temperature and in contrary reduces nutrients available for reproduction. Cooling options during extreme temperatures can also be used where possible.
- Season – it is best to do embryo transfer during natural mating season. This is often not possible and breeding objectives differ between farmers; therefore we only discourage embryo transfer in mid-winter and -summer.
- Management – not only is management of the synchronisation vital, but it is also important to manage the group of recipients properly after embryo transfer. Managing factors that can cause stress, like changing of feed or moving the animals from one area to the next.
Only 50%, on average, of animals prepared are used during embryo transfer. Therefor we suggest preparing two animals per embryo available. After two synchronisations we suggest artificial insemination or putting the unused females to the bull.
Embryo transfers are performed by our Veterinarian, Dr Collin Albertyn.