The risks we take – an IVF story.

Most who work in the cattle IVF field as a commercial enterprise are, in some way or other, challenged every day.  However, some situations are so challenging, they are worthy of a story to be told.

An Australian Wagyu breeder enlisted a team consisting of an experienced cattle ART vet, IVF and genetics leaders, including ourselves and SpeedBreed, Gnarwarre (near Geelong, Victoria, Australia), to deliver as many calves as possible from just two straws of semen.  The genetics within those two straws was of such high value that each straw cost tens-of-thousands of Australian dollars.  And to complicate things further, we had no idea how the semen would perform under IVF conditions!  This was a BIG investment by the breeder – it had to work.  The first decision that carried a risk was to cut one straw in half, use one half for the first day’s collection and the other for a 2nd day’s collection.

Although the OPU went well on the first day of collection (29 donor cows, providing 284 good quality COCs), and the transport maturation looked fine, there were fewer cleaved embryos than expected following IVF (51%). It gave, what we would categorise as a poor, but by no means uncommon result from untested semen.  As a result, good quality embryo number was also lower than expected (56, 38% of cleaved), but this is also a characteristic of poor fertilisation.  We suspected the issue was a not-optimized IVF step.  The sperm motility was fine, but we know some bulls that have good AI fertility may be poor at IVF.  We agreed to increase the heparin level, to twice our normal dose.  This was a further risk, but we needed to boost IVF rates.  It was worth it, as the cleavage rate was 75% of COCs (304 from the same 29 cows), and good quality embryo production from cleaved was just below 60% (135 embryos).  For OPU-derived oocytes, this is at the upper end of the spectrum.

We are now awaiting the pregnancy outcomes, but this story is about the need to adjust practices, evaluating the risks and making decisions that really impact IVF success.


Cumulus Expansion During IVM – What Does it REALLY Mean?

Have you looked down your dissecting microscope and felt that the level of cumulus expansion of IVM-derived cumulus-oocyte complexes (COCs) is not as you have seen in other articles?  Maybe you have seen pictures of in vivo matured COCs (such as in human IVF) and they look much more expanded.  Do not be too concerned!

Many factors impact the degree of cumulus expansion during cattle IVM; although the composition of the matrix is mostly hyaluronic acid, the cumulus matrix composition is subtly different between in vivo and in vitro matured COCs, but this difference means a lot.  For in vivo matured COCs within the follicle post-LH surge, the extent of cumulus expansion does relate to oocyte competence. However, IVM medium composition, especially the levels of glucose and glutamine (the substrates for hyaluronic acid production), impact the degree of cumulus expansion, as does the type and concentration of hormone preparation used that initiates expansion.

These are either FSH, EGF, or the EGF-like peptides, with or without oestradiol, or combinations.  The level of serum will also affect the level of cumulus expansion, so will the density of COCs per volume of medium.   All of these factors will interact with each other, causing differences in the degree of expansion.

The ‘take-home’ message is that cumulus expansion itself during cattle IVM likely indicates helpful ‘signalling pathways’ for oocyte competence are turned on, but it shouldn’t be used as a direct measure of oocyte competence.  Each IVM medium system will likely cause differences in the extent of cumulus expansion, but it is not comparable to in vivo maturation, where the degree of maturation does reflect oocyte competence. 

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