AAEP 2002: Reproduction
The reproduction session at the annual AAEP meeting in Orlando, Fla., was something of an A to Z seminar with an international flavor. It started with speakers from North America presenting discussions on endometrial echotexture (ultrasound results) and using computer analysis to determine when a mare will ovulate, or has ovulated, and along the way included a French researcher describing how to turn an unbred female that has not given birth into a nurse mare capable of producing enough milk to sustain a foal until weaning time.
The moderator for the session was Dickson Varner, DVM, Dipl. ACT, a reproductive specialist at Texas A&M University.
Ultrasound to Predict Ovulation
Elaine Carnevale, DVM, PhD, of Colorado State University, reported on the use of computer-assisted analysis of follicles to determine the interval before and after ovulation. She said that ultrasound images of the follicles come in some 256 shades of gray, but that the human eye can discern only a limited number of shades while the computer can analyze all 256. There are differences in the shades of gray as the mare approaches ovulation and after she has ovulated.
By analyzing the changing shades of gray with a computer, Carnevale said, it is possible to more closely determine when a mare will ovulate and, if she already has ovulated, determine when the ovulation occurred. With this knowledge in hand, she said, the veterinarian can make a more accurate decision as to when to breed the mare.
The only problem with the technique at Colorado State and for practitioners in general, she said, is that the images had to be transmitted via internet to a laboratory equipped for image analysis. She said it would likely be a few years before the procedure can be routinely used by veterinarians in the field.
More on Ultrasound
Natalie Bragg Wever, DVM, MSc, of the University of Saskatchewan in Saskatoon, told her listeners that significant changes in endometrial echotexture occur in the uterine body when a mare comes into estrus, and that these changes are influenced by hormonal treatment. Endometrial echotexture was evaluated using computer-assisted image analysis. She said this is very important as edema patterns have been evaluated previously via a subjective grading system, but this study was novel as it evaluated edema objectively using a customized computer imaging program (as was mentioned above, with the ability to analyze 256 shades of gray).
By monitoring these changes, she said, the clinician can better determine when the mare will ovulate.
Claire Card, DVM, PhD, of the University of Saskatchewan, reported on the persistence of the uterine reaction of mares which are either susceptible or resistant to endometritis after infusion with bacteria, frozen semen, or extender. Both susceptible and resistant mares, Card said, have a similar mild inflammatory reaction (neutrophil percentages and numbers) to frozen semen and extender. Differences between susceptible and resistant mares were reported when the mares were treated with bacteria even at 96 hours post-infusion. Using conventional ultrasound examination of the uterus, the susceptible mares were more likely to have intrauterine fluid at 24 and 96 hours after treatment with bacteria, but not frozen semen or extender. For mares which are resistant to endometritis, Card said, mild post-treatment inflammation--even after bacterial infusion--is a temporary condition and clears up before the embryo arrives at about Day 5 post-breeding. However, the susceptible mares only had persistent inflammation (high neutrophil counts) following treatment with bacteria, but not frozen semen or extender. This inability to get rid of the bacteria makes it impossible for the embryo to survive, Card said.
“We believe that in a clinical situation, aggressive post-breeding inflammation in mares after breeding with frozen semen suggests the presence of bacterial infection, because frozen semen and extender only induce mild inflammation"
Card reported in conclusion. "Bacterial infection may be the result of pre-existing conditions, such as chronic infectious endometritis. There may be an additional or synergistic effect on endometrial inflammation when bacteria and frozen semen are concurrently present in the uterus. Pre-breeding treatments to ameliorate pre-existing conditions such as chronic infectious endometritis may be important in minimizing the post-breeding endometrial inflammatory response in susceptible mares."
Laser Removal of Endometrial Cysts
A joint presentation of the use of a laser to remove endometrial cysts was given by Richard Griffin, DVM, and Scott Bennett, DVM, of Equine Surgical Hospital, Simpsonville, Ky.
Bennett said he began using the laser approach in 1986, and today it has become an almost routine procedure at his hospital. The cysts, he said, often develop in older mares which have produced foals on a regular basis. When the cysts develop, he said, the mare frequently becomes barren.
The approach in determining whether cysts are present, Bennett and Griffin pointed out, involves insufflating or filling the uterus with air, then examining it with an endoscope. Once the cysts have all been located, the laser is passed through the biopsy port of the endoscope and the cysts are systematically destroyed with the laser.
The treatment approach with the laser, they said, has been highly successful for them. To prove their point, they provided the results of a review involving 55 mares which had been barren for at least one season, with endometrial cysts being blamed for the condition. The 55 mares, they said, had a total of 269 cysts, all of which were removed or photoblated (destroyed) with the laser in 2000 or 2001. The age range of the mares was from 13 to 24, with the mean age being 18.
Twenty-nine of the mares were treated in 2000. Of this number, 25 were located for follow-up. Eighteen of the 25 had conceived in 2000 or 2001. These mares, the two practitioners reported, were bred an average of 2.3 cycles per conception.
Follow-up data on the mares treated in 2001 was obtained for 14 mares. Of that number, eight were known to have conceived. The eight were bred 1.4 cycles per conception.
Interestingly, mares which conceived had an average of seven cysts, while those which did not had an average of four cysts.
In answer to a question concerning cost of treatment, Bennett replied that his hospital charges approximately $500 for the entire procedure, but that it could vary at other locations. In answer to another question, Bennett said the laser causes virtually no scarring if used properly.
Terry Blanchard, DVM, MS, Dipl. ACT, presented research performed by Drs. Konnie Wendt, Kelly Stich, and himself at Texas A&M University. The presentation involved the effects of Ovuplant administration (and removal after ovulation was confirmed) to mares in foal-heat (i.e., the first post-partum estrus).
Ovuplant was approved for use in the United States in 1999 and was highly successful in inducing predictable ovulation. However, there was one drawback. If the mare didn't become pregnant, there sometimes was a delay in return to estrus. This was shown to be due to suppressed follicle stimulating hormone (FSH) production by the pituitary gland that results, in turn, in suppression in follicular growth for several days--thus delaying the onset of the next estrus. That problem was solved by implanting the drug in vulvar mucosa and removing it two days later.
The research conducted by Wendt and her colleagues was aimed at determining whether Ovulplant would produce a predictable ovulation in mares which were in foal heat, usually occurring sometime between birth and Day 20 post-partum. Mares were teased daily, and were examined three days weekly beginning five days after foaling, to determine time of breeding. Most breedings were by natural cover. Pregnancy rates in control (non-treated) and Ovuplant-treated mares treated on foal heat did not differ, and were normal (approximately 70%). Ovuplant-treated mares had shorter intervals to ovulation and required fewer breedings than control mares. The researchers did not find an association between number of covers, or day post-partum on which ovulation occurred, and pregnancy outcome.
Here is the conclusion of the researchers: "In summary, placement of desorelin (Ovuplant) implants in the vulvar mucosa was an easily performed, safe procedure that reliably induced ovulation in foal-heat mares within two days of treatment. Normal pregnancy rates were achieved with deslorelin-induced ovulations on foal-heat. Removal of the implants two days after insertion avoided follicular suppression and delayed return to estrus."
Involved in the study were 39 foal-heat mares maintained on pasture in southeast Texas. Twenty of them served as controls and 19 were treated with Ovuplant. Mares were bred by natural service. Fourteen of the 19 mares treated with Ovuplant became pregnant compared to 16 of the 20 control mares. The Ovuplant-treated mares averaged 1.3 covers after treatment, compared to 2.1 covers for the control mares. All of them were crossbreds of the Quarter Horse type.
Equine Embryo Storage
The French connection at the session was provided by Peter Daels, DVM, PhD, Dipl. ACT, ECAR, of Equitech, Le Mesnil Vicomte, France. His first presentation was given on behalf of a colleague who could not be there. It concerned a comparison of three holding solutions for cooled storage of equine embryos.
Equine embryos, he said, traditionally have been transported in a solution called Hams F10. While it has worked well, there are some drawbacks, one of which is that it must be gassed with carbon dioxide before being used. The research conducted in France utilized Emcare Holding Solution and ViGro Holding Plus, as well has Hams F10.
The results, he said, indicate that both of the other solutions are as effective as Hams F10 and are easier to use.
Non-Foaling Nurse Mares
It was the second presentation by Daels that piqued the most interest of the afternoon and produced numerous questions. The title of the talk was intriguing to say the least: “Induction of Lactation and Adoption of Foals by Non-Parturent Mares.”
The research involved a number of experiments, but the upshot of all of them was that milk production could be induced in mares which had previously borne a foal. Administered daily for two weeks to achieve milk production in the initial experiment were progesterone, estrogen, and a dopamine D2 antagonist (sulpiride or domperidone).
While the mares began producing milk as a result of the treatment protocol, it was not high in colostrum, Daels said. He recommended that a milk replacer also be offered to the foals in the first days after birth if they are placed with a mare which has had lactation induced because her milk production during that initial week will be less than that from a mare which has given birth. The daily growth rate of foals nursing lactation-induced mares was less during the first month when compared to those nursing normally lactating mares, Daels said, but by weaning time, it had evened out and there was no significant difference in growth rate or weight.
He said that when sulpiride was administered to the mares on Day 23 of lactation, milk production received a significant boost. Seven days after treatment (Day 30), milk production had increased a great deal. “In the non-treated (non-lactation-induced) mares,” he reported, “milk production had increased about 11% in contrast to 75% in mares treated with sulpiride.”
Used in the experiments were Welsh pony mares. An important part of the experiments was to determine whether these mares, after lactation was induced, would adopt the foals presented to them. They all wound up accepting the foals, Daels said, but a technique that involved manual stimulation of the vagina and uterus while the foal was being held close to the mare’s head made the process quicker and less traumatic. The mares which were stimulated, he said, showed little or no aggression toward the foal, while those which were not stimulated showed aggression in the early stages of presentation.
“Taken together,” Daels concluded, “the results of the studies described indicate that lactation can be induced in mares that have foaled in previous years. These mares are able to adopt a foal and nurse it until weaning age. The initial difference in daily growth rate is likely the combined result of the lesser milk production at the onset of an induced lactation versus a post-partum lactation and the abrupt ending of hormonal treatment only three days after adoption. Experimental data suggest that the prolonged treatment with sulpiride may help to overcome the initial insufficient milk production.”
Treating EPM with Ponazuril
The final paper of the session was presented by Steven Brinsko, DVM, MS, PhD, Dipl. ACT, of Texas A&M University. His talk involved the effects of ponazuril (a treatment for EPM), marketed under the trade name of Marquis, on the reproductive function of stallions. Twice the recommended dosage was administered to stallions in the experiment, Brinsko said. There were no negative effects even when the drug was administered at double the dosage for the recommended 28 days called for in a normal treatment protocol, he said.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
POLL: University Equine Hospitals