In Vitro Fertilisation (IVF)

Overview

The majority of IVF programs in cattle are conducted in South America, which accounts for about 85% of the IVF embryos produced globally. In Australia, the majority of embryos are produced through ET, in vivo (within the donor cow). The use of IVF is growing, particularly in the northern regions of Australia, as Bos indicus cattle breeds that dominate this region, tend to respond the best to the IVF procedures. Bos indicus cattle tend to yield more embryos than other breeds, yet tend to not respond as well to superovulatory treatments used in conventional ET. The use of IVF in Bos taurus breeds of cattle is possible, but are generally treated with some superovulation treatments to ensure a reasonable yield of oocytes.

In Australia the majority of IVF derived embryos transferred to recipient females are fresh. Some frozen transfers do occur, however due to the high variability in pregnancy rates from these embryos, most practitioners and breeders prefer to use fresh where possible.

Advantages

The reason breeders choose to use IVF is to maximise the genetic potential of elite donor females in their herd. The main advantage of using IVF in cattle is to get a higher yield of embryos in cattle where conventional ET programs are not working effectively. This generally includes cattle that do not respond well to superovulation treatments. This tends to be Bos indicus cattle, older females, or females that have reproductive disorders that won’t enable embryos to be flushed from the uterus.

As Bos indicus females tend to have a large number of follicles present on their ovaries as compared to Bos taurus breeds, they tend to yield a higher number of oocytes. In addition, the proportion of oocytes that convert to embryos are much higher in Bos indicus breeds than others.

For most IVF programs, the donor female doesn’t require any treatments to superovulate nor synchronise their ovulation. The oocytes are collected by an experienced veterinarian using a process called ‘ovum pick up’ commonly referred to as OPU. During OPU the veterinarian will use a vacuum pressured needle, passed transvaginally, to puncture any antral follicles that are present on the ovary. The needle will then extract the follicular fluid and the oocyte that is then transferred to a holding vial. After completion of OPU the oocytes are incubated and transferred to the laboratory. Up to 3 OPUs per female can be performed in a 30 to 40 day interval. Generally this means that numerous embryos may be collected from a female and also enable her to calve every 12 months.

Once the oocytes are at the laboratory, they will be matured using a process called ‘in vitro maturation’ or IVM. After the maturation process, the oocytes are fertilised with the semen preferred by the breeder. The oocytes are then cultured for a further 6 days, so that they can reach development to an appropriate embryo stage (usually morula) that will be suitable for transfer into recipients. The embryos are graded so that only suitable good quality embryos are transferred into recipients. The recipient cows are usually treated previously to synchronise their ovulation to ensure that they are at the correct stage in their cycle to receive the embryo. It is possible to preserve the embryos by freezing, however pregnancy rates to frozen IVF embryos are typically variable and can be low.

In Australia, the average conception rate to transferred fresh IVF embryos is approximately 40 to 45%. As per any assisted reproduction program, there are a variety of variables that can affect the result. Semen quality, breed and technician can significantly contribute to the outcome. The table below outlines the average results that can be expected in ‘unselected’ donor females. If you ‘pre-select’ your donor cows by choosing the ones that are most likely to yield a higher number of embryos, it is possible that these statistics will increase.

Products used

• Cue-Mate

• Folltropin