The term “advanced breeding” or “advanced reproductive technologies” (ART) covers a range of techniques in cattle, including artificial insemination (AI), embryo flushing, in vitro fertilisation (IVF; also known as IVP) and embryo transfer (ET). The fundamental goal of all ARTs is to improve reproductive efficiency and genetic improvement by producing more calves from the best dams and sires available.
Artificial insemination and genomic assessment
Artificial insemination (AI) pioneered more rapid genetic improvement by allowing superior bulls to sire many thousands of calves, introducing the best genetics available worldwide into any herd in a cost-effective and biosecure manner. However, the bull is only half of the reproductive equation, and embryo technologies have a lot of benefits to offer by leveraging the best female genetics as well.
Genomic assessment […] allows producers to identify animals with the most genetic potential at an early age and consider the benefits more selective breeding could achieve
The introduction of the genomic assessment of dairy cattle and its development in several beef breeds allows producers to identify animals with the most genetic potential at an early age and consider the benefits more selective breeding could achieve. This ranges from choosing to breed replacement heifers from the top end of their herd using sexed semen, to amplifying the number of calves produced from their very best cattle by using flushing or IVF to generate embryos and implanting these into some of their lower-genetic-merit animals. One additional benefit of genomic testing is the identification of animals with good fertility but poor production – ie those that make for ideal embryo recipients.
These benefits speed up the genetic progress of a herd, with some studies suggesting around seven years of genetic progress can be achieved through AI only within a year using these methods (Kaniyamattam et al., 2017).
Embryo flushing and transfer
“Flushing” cows and the subsequent ET into recipients was the first method developed to improve the number of offspring a quality heifer or cow could produce. The first ET calf was born in the 1950s and commercial ET work started in the 1970s.
Donor animals are supplemented with follicle-stimulating hormone (FSH) from around day 11 of their cycle, stimulating a group of antral follicles to develop together rather than a single follicle achieving dominance. Ovulation of these follicles is induced with a prostaglandin injection and the removal of a progesterone device inserted earlier in the programme.
Insemination (either by a bull or, more commonly, by two to three artificial inseminations over 24 hours) leads to fertilisation and early embryo development. These embryos are retrieved from the tip of the uterine horns seven days later at the morula or blastocyst stages.
The flushing procedure involves the trans-cervical insertion of a foley-type catheter into each horn, in turn. The cuff is inflated to seal the tip of the horn, and a specially designed flush medium is alternately instilled and recovered from the horn tips, carrying (flushing) the embryos with them. This fluid is passed through a filter to produce a clear aspirate containing the embryos that can be searched for under a microscope.
In vitro techniques
Ovum pick-up
More recently, we have started producing embryos by in vitro methods. In a process similar to IVF in humans but carried out in normally fertile animals, the oocytes are collected directly from the ovaries through an ultrasound-guided needle in a process called ovum pick-up (OPU).
Oocytes are collected directly from the ovaries through an ultrasound-guided needle in a process called ovum pick-up
OPU involves the insertion of an ultrasound probe vaginally while the ovaries are gently manipulated per rectum into apposition with the probe through the vaginal wall. A needle, which passes through the probe and is connected to a vacuum pump, is introduced through the vaginal wall into the ovary and punctures each unovulated follicle in turn.
The oocytes are then collected, along with follicular fluid, in a collection tube. The aspirate is filtered to allow the oocytes to be searched for under a microscope and transferred to a maturation medium in an incubator overnight. These are then fertilised and cultured for a week under highly controlled laboratory conditions while they develop into embryos suitable for either immediate fresh transfer or freezing.
There are generally two methods of preparing donors for collection. The first involves collection once or twice a week without using drugs. The second is more controlled, with donors first being synchronised by the controlled removal of any large or dominant follicles to leave a homogenous group of antral follicles before being given low doses of hormones to stimulate follicles to develop prior to collection (carried out fortnightly). This second method leads to a greater number of better-quality embryos and improved pregnancy rates.
In vitro fertilisation
While IVF was initially used similarly to human medicine – as a technique to help with reproductive disorders – it is now used as a first-line breeding tool for breeders seeking to improve their herds. IVF is well established in North and South America and has become increasingly popular in Europe. Since 2017, more embryos have been produced by this method worldwide than by the more traditional flushing technique.
While IVF was initially used similarly to human medicine – as a technique to help with reproductive disorders – it is now used as a first-line breeding tool for breeders seeking to improve their herds
The increasing popularity of IVF over flushing is due to several key benefits:
- Heifers can be collected at an earlier age (from seven months of age)
- Collections can be carried out in pregnant animals without affecting the pregnancy
- Expensive semen can be used to fertilise oocytes from several donors with a single straw, while flushing requires multiple doses per donor
- IVF can produce more embryos to a greater selection of bulls over time
IVF can also be used to produce embryos from animals sent to the abattoir in a process known as genetic recovery.
Embryos produced by IVF and flushing can be stored in liquid nitrogen or transferred fresh into prepared recipients.
Embryos are transferred one week after standing oestrus of the recipient by a method similar to that of AI but using a longer gun. The longer gun allows the embryo to be transferred deep into the uterine horn ipsilateral to the corpus luteum formed following ovulation seven days previously. Flushing, OPU and ET are all carried out under standing epidural anaesthesia and are extremely well tolerated, with cattle showing no signs of distress.
IVF can also be used to produce embryos from animals sent to the abattoir in a process known as genetic recovery
Embryo biopsy
It is also possible to perform biopsies of embryos, recovering a few cells for DNA analysis, allowing their genomic evaluation before transfer. Expansion of this technique will make it possible for a breeder to buy sexed embryos with the specific traits they are looking to develop in their herd, whether disease resistance, production potential, live weight gain and/or improved sustainability, etc.
Final thoughts
Similarly to what we have seen with semen sales and distribution for AI, more and more embryos are now being produced and traded, with more breeders looking to these technologies to bring new genetics safely into their herds and to breed future generations.
In conclusion, embryo production and transfer technologies allow breeders to further increase the rate of genetic improvement in their herds. Use of IVF and ET is growing rapidly, with its importance increasing domestically and internationally. Production animal vets are ideally placed to engage and advise on embryo transfer with their clients, supporting them as they develop their herds.
