AAEP Convention Topics Preview: Reproduction

The latest information on scores of topics is presented at the AAEP convention; we can't report on them all, but we do try to bring you a representative sampling. This year, many of the topics can be grouped into five categories: fighting infection, reproduction, lameness/ injury, medicine, and predicting performance. In-depth coverage following the convention will be in our AAEP Wrap-Up (mailing with the February 2002 issue) and online at www.thehorse.com/aaep2001 after Nov. 24.

Stallion Fertility

Veterinarians with an interest in reproduction will find the Nov. 27 program filled with topics that will broaden their intellectual horizons. They range from the basic to the sophisticated, with the two opening presentations on the sophisticated side.

Moderators will include Michelle LeBlanc, DVM, Dipl. ACT; and Dickson Varner, DVM, MS, Dipl. ACT, of Texas A&M University. Varner will also be the lead speaker, discussing "Subfertility in Stallions Associated with Spermatozoal Acrosome Dysfunction."

He will be followed by colleague Charles Love, DVM, PhD, also of Texas A&M, who will speak on the topic, "The Relationship Between Chromatin Quality and Fertility of Chilled Stallion Semen."

The two topics are closely linked; both deal with highly important ingredients of each individual spermatozoon. The head of each spermatozoon contains, among other things, the acrosome and nucleus. The acrosome contains enzymes essential to its functions--penetrating and fertilizing the egg or ovum. The nucleus of the head contains DNA.

Ejaculated spermatozoa undergo certain sequential cellular changes that render them capable of penetrating the ovum (egg) and fertilizing it. This capacitation reaction is followed by acrosomal reaction, which occurs when the acrosomal membrane fuses with the plasma membrane that covers it. This fusing allows proteins on the plasma membrane of the head to bind to receptors on the ovum and later to the ovum's plasma membrane during fertilization.

In some stallions with low fertility, Varner says, the acrosomal reaction fails to occur. When this happens, the spermatozoon is unable to penetrate the ovum.

Varner will describe a test that has been developed at Texas A&M to identify spermatozoa that fail the acrosomal reaction process. More research in this area is needed, Varner says, but the testing procedure at Texas A&M has already identified seven or eight stallions which are low in fertility because of a dysfunctional acrosomal reaction process.

Varner will enlighten his listeners on what happens when acrosomes don't function as they should, and how to determine when dysfunction is occurring. The result of acrosomal dysfunction often is infertility, even though a sufficient number of sperm might appear to be healthy and demonstrate excellent motility.

Love also will be discussing a test that can identify a cause for low fertility. He will be telling veterinarians at the convention how the flow cytometer has added another dimension to the testing of cooled and stored semen capability and survivability.

A flow cytometer can quickly evaluate the DNA of individual sperm that have been stained with a material that's "excited" with a laser beam. Green fluorescence is emitted when the stain binds to normal double-stranded DNA, and red fluorescence appears when the stain is bound to denatured or damaged single-stranded DNA. A high rate of DNA damage coincides with low fertility.

This test can be an important one because sperm that show normal motility and morphology might still be infertile because of unstable or damaged DNA within the nucleus of the head.

Flow cytometers have been used in the past in human medicine as an aid in evaluating blood. They are relatively new in the field of stallion semen evaluation, Love says.

Preventing Estrus

Reporting on reproduction research that sounds more like a wives' tale than research wisdom will be Gary Nie, DVM, MS, PhD, of Auburn University. Nie will tell veterinarians about a technique aimed at preventing mares from coming into heat that involves a common marble being placed inside the uterus. Nie says he first heard about the technique on the Internet from a veterinarian in the Netherlands, who reported that it had been passed on to him by an older veterinarian.

Nie says the marbles used were about 35 millimeters in diameter--about the size of the shooter's marble in a marble game. Smaller marbles of 25 millimeters were also tried, he says, but a number of them failed to remain in the uterus. The marbles were left in place for four cycles, then removed.

The procedure was successful in preventing 40% of the mares from coming into heat, Nie says, but he isn't sure why it worked. However, he does have some theories. The mares in which the procedure was successful were kept from coming into heat for about 90 days each.

During his presentation, Nie will offer his theories on why the procedure worked in the successful cases. The use of a marble to prevent the mare from coming into heat, he says, provides an alternative to administering cattle hormone implants or human drugs to mares, which pose the danger of negative side effects.

There was nothing sophisticated about the marbles, Nie says. They were white and purchased for one dollar each on the Internet.

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