The use of frozen semen in horse breeding is becoming much more common. Two studies were presented at last year's AAEP convention concerning frozen semen. For artificial breeding with fresh semen, it has long been accepted that the minimum number of sperm to be inseminated is 500 million progressively motile sperm. However, the number of frozen thawed motile sperm to yield optimal pregnancy has not been studied until recently. Dr. Elizabeth Metcalf recently performed a study with 90 mares that were bred with frozen semen with concentrations from less than 100 million to greater than 800 million. Her findings indicated that when breeding with frozen semen, using 600 to 800 million sperm resulted in an 88% pregnancy rate which was the highest in the study. However, in many cases, these high sperm numbers are not possible with some stallions.
Because of this, two techniques have been developed to aid in breeding mares with lower numbers of sperm. One of these techniques is to place the semen deep in the uterine horn on the side of the ovulation by visualizing the oviductal opening with an endoscope. The other method of artificial breeding was by passing a flexible catheter and manipulating the catheter rectally to the tip of the uterine horn adjacent to the ovulating ovary. In contrast to the previous study in which it was determined that 600 to 800 million sperm were required with frozen semen, both techniques that placed sperm closer to the ovulating ovary used only 50 to 150 million sperm. A pregnancy rate of around 50% was achieved with these techniques, even though the number of sperm was much less than that recommended when sperm was placed only in the uterine body.
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