Flushing & Embryo Classification

Post Date: April 5, 2012
Embryo Classification
I am often asked why elevate the head end of the donor? Embryos and eggs are in the tip of the uterine horn next to the utero-tubal junction. In order to wash them out the medium has to completely fill the uterus all the way to the end. In heifers and young cows the uterus is in the pelvic cavity and easily within reach for manipulation during the filling and emptying process. But in mature donor cows the uterus is frequently partly or entirely in the abdominal cavity and must be pulled back into the pelvic cavity for efficient and safe flushing.

This can be accomplished by retracting the uterus by the inter-cornual ligament easily located at the base of the dividing horns, and then it must be held there during the flushing process in order to assess how full the uterus is with medium. Obviously if the donor is elevated at the front it is easier to maintain the pelvic position and the operator can estimate if the two horns are filling as required and avoid over filling and a ruptured wall of the uterus.

There are several methods of elevating the cow at the front, for example for large cows two square hay bales may be used with plywood as a platform, or a step can be placed in the squeeze chute, or you can build a sloping floor to the chute, or simply raise the front of the chute with a farm jack and then place blocks under the chute (whichever method you choose to elevate the cow, make sure it is stable in order to avoid injury). Obviously donors are flushed without this aid but elevating the head end of the donor will improve results, and in time it will help avoid rotator cuff damage in the shoulder.

Often student embryologists are rightly concerned about differentiating eggs and embryos and then grading embryos. The following suggestions should be of some help. Before searching for embryos knowing the number of days after estrus is helpful. For instance, on day 6 there is the possibility of eggs and morulae and late on day 6 early blastocysts. On day 7 there is the possibility of eggs, morulae and blastocysts. On day 8 there is the possibility of eggs, even the occasional morula, blastocysts and expanded blastocysts. Once an embryo has been identified then it is usually graded. The International Embryo Transfer Society has advised on 3 grades: 1 is excellent, 2 is good, and 3 is fair. Grading is based on several features, for example stage of development in relation to morphology (appearance), color, shape, extruded cells, broken membranes et cetera, all of these factors are collated and a grade given.

The reason for grading is to estimate the expected pregnancy rate so the embryo should be judged on its appearance and not what was expected. For instance following freezing and thawing the trophoblast layer of a blastocyst will frequently collapse leaving the appearance of a small, dark morula, therefore it should be graded as such. Obviously grading is subjective and in many cases there is very little difference between the success of embryos graded 1 or 2 especially between two operators.

Dr. Peter Elsden

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