From Breeding to Birth
Testing innovative techniques and brushing up on common procedures are the lifeblood of advancing any medical specialty, and the field of equine reproduction is no exception. Veterinarians are always looking for new ways to improve procedures they use every day in their clinical practices, and there's no better time to convene than in late fall, which is the "calm before the storm" that precedes foaling and breeding season.
Seasoned equine theriogenologists (specialists in reproduction) presented the latest advancements in mare, stallion, and fetal care at the Hagyard Bluegrass Equine Reproduction Symposium in Lexington, Ky., on Oct. 18-21, 2006. Hagyard Equine Medical Institute presents the symposium annually, alternating its focus between emergency/critical care and reproduction.
The 2006 program boasted 23 speakers--11 were from Hagyard's roster of veterinarians, and 12 other scientists and veterinarians were invited from universities and clinics across the country and around the world. The symposium began with a day of wet labs that gave participants opportunities to learn and practice techniques, and the subsequent 2½ days of classroom sessions spanned topics from evaluating a prospective breeding stallion to new procedures for preventing twinning and treating mare cycling problems.
The following are highlights from the conference.
Reproductive evaluation When a veterinarian is considering a stallion's suitability for breeding, the horse's history, current physical condition, and libido are as important as his semen quality.
"It's not just the semen we're looking at, it's the whole package," said Steven Brinsko, DVM, MS, PhD, Dipl. ACT, associate professor at Texas A&M University.
A satisfactory breeding prospect has no significant abnormalities and no physical, heritable, or behavioral faults.
The stallion should be able to produce a minimum of one billion progressively motile, morphologically normal sperm in the second of two ejaculates that are collected one hour apart.
Sixty percent of his sperm are progressively motile, 60% have normal morphology, and he has a minimum of 8 cm of scrotal width.
If the stallion has the requisite semen quality and a good libido, he should be able to attain a 75% seasonal pregnancy rate for a full book of mares (generally natural cover of 40 mares or artificial insemination of 120 mares).
For more information see www.TheHorse.com/emag.aspx?id=8193.
Developments in nutrition Early stallion supplements were considered ineffective by veterinarians, "but now it appears there are some products that have the potential to increase fertility," said Brinsko.
Central to sperm quality are lipids (fats), which are highly concentrated in the sperm and sperm membranes. "These lipids dictate how the membrane is going to function, and how it reacts to different situations (such as cooling or freezing)," Brinsko explained. Sperm lipids contain high levels of polyunsaturated fatty acids (PUFA, which are straight-chained fatty acids with multiple double bonds). The distribution of PUFAs in stallion sperm makes it have low tolerance to cold shock, so it freezes poorly.
Two compounds, docosahexaenoic acid (DHA, an Omega-3 fatty acid) and docosapentaenoic acid (DPA, an Omega-6 fatty acid) are major PUFAs in semen. Studies have shown that by increasing the ratio of DHA to DPA in boar semen, you can increase the fertility and quality of the sperm. Brinsko and his colleagues fed horses a DHA supplement and found that the treated horses' sperm swam straighter and faster, and after 48 hours there were improvements in total motility, progressive motility, and rapid motility.
Also, "for the marginal coolers (stallions whose semen doesn't cool well), there was a significant increase in the progressive motility of these horses' sperm." said Brinsko. "We need to change the way we feed horses and make sure they have diets that favor DHA formation versus DPA formation. And we must make sure we maintain a balance without affecting metabolism of other feed ingredients."
For more information see www.TheHorse.com/emag.aspx?id=8194.
Breeding-induced endometritis Modern breeding management and assisted reproduction might actually exacerbate the issue of mating-induced endometritis, according to Mats Troedsson, DVM, PhD, Dipl. ACT, a professor of equine theriogenology at the University of Florida's College of Veterinary Medicine. Researchers used to think that bacteria were the only cause of equine endometritis, but Troedsson said the scientific community has learned that semen can also be a cause. He said semen that has been stripped of most of its natural plasma (as it is when frozen) is more likely to cause persistent inflammation in the uterus than fresh semen. Additionally, it appears that specific seminal plasma proteins help live sperm safely reach the oviduct even in the presence of inflammation.
For more information see www.TheHorse.com/emag.aspx?id=8195.
Fetal sex determination and the mare Accurate determination of fetal sex can have a profound impact on the broodmare management practices of horse owners and breeders, said Richard Holder, DVM, of Hagyard. While the gender of a foal influences its value, it also influences the value of the gravid (pregnant) mare. Knowing fetal sex prior to foaling allows horse owners and breeders to make timely, informed management decisions, including those related to foaling location and subsequent mating of the mare. Demand for equine fetal sex determination among horse owners has risen significantly in the past decade, and it likely will continue to increase.
For more information see www.TheHorse.com/emag.aspx?id=8203.
Abortion Careful management of pregnant mares and preparation for parturition are essential to help prevent cases of equine abortion--losses of pregnancy between 150-300 days of gestation. Karen Wolfsdorf, DVM, Dipl. ACT, a Hagyard veterinarian, discussed isolation protocols, the importance of knowing the aborting mare's history, and the physical and reproductive examination.
Fairfield T. Bain, DVM, MBA, Dipl. ACVIM, ACVP, ACVECC, a veterinarian at Woodside Equine Clinic in Ashland, Va., stressed the laboratory component of investigating abortion. He said the clinical evaluation of the animal, premises, and history are vitally important to the diagnostic process, along with diagnostic laboratory evaluation.
For more information see www.TheHorse.com/emag.aspx?id=8197.
Postpartum complications in the mare If your mare experiences complications following foaling, it's important to note when they arise, said Walter Zent, DVM, of Hagyard's group. Veterinarians can help differentiate between similar conditions based on not only the clinical signs the mare is exhibiting, but also how much time has passed after foaling until those signs appear.
For more information see www.TheHorse.com/emag.aspx?id=8201.
Lactation induction in the non-pregnant mare Poor milk production or the loss of a mare in the peripartum period (in the last month of gestation or the first few months after delivery) can jeopardize the health and viability of the foal.
To provide the foal with an alternate source of milk, the horse owner might opt to hand-rear the foal using a milk replacement formula, or pair the foal with a lactating nurse mare.
While the use of a nurse mare generally is preferred to ensure proper socialization and nutrition of the foal, many horse owners do not have access to nurse mares, said John V. Steiner, DVM, Dipl. ACT, of Hagyard. He discussed a practical, affordable protocol to induce lactation in non- pregnant mares with reliable results.
For more information see www.TheHorse.com/emag.aspx?id=8204.
Systemic therapy in the high-risk mare Several conditions can threaten pregnancy in the late gestational mare. C.S. Bailey, DVM, who is completing a theriogenology residency at the University of Florida with Hagyard, said some of these conditions might warrant the use of therapeutic agents, in spite of limited knowledge about their efficacy or their ability to penetrate fetal membranes.
Current information regarding the effects of antibiotics and anti-inflammatory agents in the gravid mare is based on a model of experimentally induced placentitis in the research setting. While the optimal treatment for equine placentitis is not yet defined, combined therapies with antibiotics, anti-inflammatory agents, and tocolytics likely are most effective.
For more information see www.TheHorse.com/emag.aspx?id=8205.
Dopamine and its evil twin ergovaline In the horse, the hormone dopamine exerts a number of effects through its actions on the pituitary gland. Both dopamine and ergovaline, a dopaminergic agonist (a drug that stimulates dopamine receptors), can significantly impact the mare's reproductive cycle, said Valerie J. Linse, MS, DVM, of Hagyard.
The effects of dopamine deficiency can be observed in horses with pituitary pars intermedia dysfunction (PPID or Cushing's disease), while the effects of a relative dopamine excess are evident in cases of fescue toxicosis. Linse discussed diagnosis and treatment of both disorders.
For more information see www.TheHorse.com/emag.aspx?id=8206.
New Techniques in Reproduction
Acupuncture in the treatment of reproductive disorders Rhonda Rathgeber, DVM, PhD, an acupuncturist certified through the International Veterinary Acupuncture Society (IVAS), said acupuncture can be used in conjunction with Western medicine prior to breeding to modify anestrus (period of sexual inactivity).
It can also be used to treat excessive behavioral estrus, retained corpus luteum (an ovarian follicle after discharge of the egg that secretes the hormone progesterone), urine pooling, uterine infection and fluid, endometritis (inflammation of the innermost lining of the uterus), and vaginitis (inflammation of the vagina).
It can also be used as an adjunct therapy to prevent abortion, retained placenta, postpartum hemorrhage, and insufficient lactation.
Acupuncture is also used to treat cryptorchid stallions (those having one or more testicles that have not descended into the scrotum), as well as those with libido problems and sore backs. She says behavioral issues can also benefit from acupuncture treatment.
For more information see www.TheHorse.com/emag.aspx?id=8196.
Another approach to equine castration The use of the Stone Henderson Equine Castration Instrument, which allows veterinarians to geld colts using an attachment on a battery-powered drill, has gained speed since its debut at the 2005 American Association of Equine Practitioners' Convention. Steiner reviewed anecdotal reports of successful use, such as how veterinarians on the 6666 Ranch in Texas reportedly used the new technique to castrate 36 colts in one day without incident. Some veterinarians in attendance perform the procedure with the horse sedated and standing.
New twin reduction procedure Wolfsdorf described a novel reduction technique that she and her colleagues have used for about four years. Veterinarians generally attempt to detect and crush the extra vesicle in a twinning case by 14 days of gestation, but if the twins are detected later than that, it can be harder to reduce the second embryo.
Wolfsdorf has been using craniocervical dislocation--dislocation of the first cervical vertebrae from the cranium--of the twin transrectally or within the abdomen to ensure twin reduction and minimize interference with the remaining fetus.
"Our rationale is to try and get to the fetus before placental formation is complete and therefore produce a single normal-sized, healthy foal that has the ability to use the entire endometrial surface and grow to its full potential," said Wolfsdorf.
For more information see www.TheHorse.com/emag.aspx?id=8200.
Buserelin use in the anestrus mare The compounded drug Buserelin has shown considerable promise in treating anestrus mares. Buserelin is a synthetic gonadotropin-releasing hormone (GnRH) analogue that is designed to alter hormone levels. Zent noted that Hagyard veterinarians have used these protocols only on mares that have been under lights (to manipulate their estrous cycles), have had time to cycle, and have not responded. They have not used Buserelin on mares in winter anestrus.
For more information see www.TheHorse.com/emag.aspx?id=8202.
When our veterinarians endeavor to learn ways to improve the health of our breeding stock, we should commend them for their efforts and learn about their progress in applying new techniques.
Follow your veterinarian's advice on management methods to assist him/her in improving the success of your breeding operation.
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POLL: University Equine Hospitals