So, when an embryo is collected, it is graded and scored. Based on that grade, the best ones are frozen (if not enough recips) and the poor ones are implanted or thrown away. The first number is based on the grade, with 5 being the best. We have had great luck implanting 4 and 5 stage embryos. Almost no one freezes a 7 or higher, or lower than a 3, that I know of. Most embryos are sold with a guarantee, buy three and they guarantee one pregnancy. No one wants to refund money, so the best are set up to sell. Here is a chart that is really good:
The second number represents the quality of the embryo; how the zona pellicuda looks and such. A 1 is best, but a two is acceptable. We have put in 2's with good luck. It is said that a 2 will more likely be a heifer, but looking back at my data that is not necessarily true. Here is another good picture:
Here is an actual microscope pic of what they look like, at different stages:
So, you can see, the 6 and 7 are earlier maturing, and further along in development. It is my embryologists opinion that those need to go in cows that are on day 8, not day 7. This is our first season dealing with this, since 99% of the embryos I buy and put in are a 4 or 5, stage 1 or 2. I have the same conception on a 4-2 as I do on a 5-1. I bought some embryos that have came in as 6-1 and 7-1, in conventional, my vet said that is acceptable (but not desirable). In IVF, we need to be more picky about the recips and where they are in the cycle (day 8 versus 7).
Until this fall, I never messed with IVF, and really do not want to. I bought one set of eggs, knowing they were IVF, but have a great relationship with the seller (I have bought and put in numerous conventional embryos from them). They arrived as 5-1s. We put one in in December, and it stuck. I bought two sets from a dispersal sale the fall (same cow, different sires), advertised as conventional. When the embryos arrived, there was no paperwork (most come with the collection paperwork so you know what you are getting). They were sold as conventional, however when we put one in, the straw identified it as IVF. Not only that, it was a 7-2! Of course, it did not stick. I called up the company that made the embryos, and got the collection sheets (one set was IVF, one set was conventional). ALL of the embryos in that IVF lot (6 of them) are either 6 or 7, and quality 1 or 2. SO, any future recip I put those in will need to be on day 8 for our best chances.
That was probably WAY more information than what you wanted to know!
