IT’S been less than a hundred years since Artificial Insemination (AI) was first successfully carried out in cattle, writes Paragon Vet, Rob Simmons. Since then it has become a mainstream breeding tool, especially among Dairy and pedigree Beef breeders. The ease with which semen can be moved around the world, allowing a much greater choice of sires than is available through natural service, and the opportunity to use the best bulls available in a biosecure way to maximise herd improvement has, no doubt, underpinned its success. The bull is only half of the story, however, and whilst getting as many offspring from an outstanding bull is great, there are also many heifers and cows with fantastic potential and only getting one calf a year from them is a great limitation.

‘Flushing’ cows, and subsequent embryo transfer into recipients was the first method developed to improve the number of offspring a quality heifer or cow could achieve. The first calf was born through embryo transfer in the 1950’s, but it wasn’t until the 1970’s that this became a truly commercial offering. The concept behind it is reasonably simple: hormone injections given to the donor stimulate a group of follicles to develop and ovulate together, meaning a number of oocytes (eggs) are released into the uterus rather than just a single one, as occurs normally in cattle. Insemination (either by a bull or, more commonly, by AI) of these eggs leads to a number of embryos starting to develop. These can be ‘flushed’ from the uterus after 1 week and either transferred into recipient animals immediately, or frozen to be transported (often globally), or implanted later.

More recently embryos have started to be produced by in vitro methods. 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 Oocyte PickUp (OPU). These are then fertilised and allowed to grow for a week under highly controlled laboratory conditions until they become embryos suitable for either freezing or transferring. There are, generally, two methods of doing this. The first is without using drugs and carrying out collections once or twice a week. The second is more controlled, with donors being synchronised, and given low doses of hormones to stimulate follicles to develop before collection, which is carried out fortnightly. This second method leads to better quality embryos and better pregnancy rates, so is our preferred method. IVF is becoming increasingly popular in Europe, having become well-established in both North and South America in recent years. The increasing popularity of IVF over flushing is due to its ability to produce many more embryos over time, reduced use of expensive semen, and the more regular collections allow good donors to produce embryos to a number of different sires in a short space of time. In addition, heifers can be collected at an earlier age, and collections can be carried out in pregnant animals without affecting the pregnancy. IVF can also be used to produce embryos from animals destined for slaughter.