Presentations on reproduction have long been a hallmark of AAEP gatherings, and this year was no exception. The full-day reproduction session was split into two parts–the first was of a general nature, while the afternoon in-depth session involved a discussion of techniques for the use of frozen semen.
Dickson D. Varner, DVM, MS, Dipl. ACT, of Texas A&M University, reported on research aimed at determining a reason for infertility in stallions whose sperm appear to be progressively motile and morphologically normal.
One of the reasons for infertility in these stallions, Varner said, has been spermatozoal acrosome dysfunction. The acrosome fits over the head of the sperm like a bathing cap. As the sperm travel to the oviduct to meet the ovulated egg, there is an acrosomal reaction or maturational change, which is necessary for the sperm to penetrate the egg.
In some stallions, Varner said, this reaction doesn’t occur and the result is a non-fertilized egg. At the moment, science can test sperm to determine whether acrosomal reaction occurs. However, because no one yet knows what causes the dysfunction, there is no therapy to solve the problem.
Still other reasons for infertility in apparently healthy and motile sperm, reported C.C. Love, DVM, PhD, also of Texas A&M, are irregularities in spermatozoal DNA and damage to it during the cooling process.
A flow cytometer can evaluate a great many sperm at one time for DNA abnormalities. Used in the process are red and green dyes. If the DNA in a spermatozoon is normal, the green dye will attach to it. If it is abnormal, the red dye will attach.
It was found that DNA from some sub-fertile stallions deteriorated rapidly after 24 hours at 5°C, the temperature to which semen is normally cooled for storage prior to artificial insemination. If the semen is stored at higher temperatures, Love said,