Every year equine veterinarians flock to the Kester News Hour session at the American Association of Equine Practitioners (AAEP) convention for reports on research that are too brief or new to be included in the scientific program. For the past two years, the fast-paced news broadcast format has been anchored by three renowned equine experts:

  • Scott Palmer, VMD, Dipl. ABVP, hospital director/surgeon at the New Jersey Equine Clinic in Clarksburg and a past president of the AAEP, focuses on lameness and surgery topics.
  • Margo Macpherson, DVM, MS, Dipl. ACT, associate professor at the University of Florida, discusses reproduction topics.
  • Bonnie Rush, DVM, MS, Dipl. ACVIM, professor of equine internal medicine at Kansas State University, covers medicine topics.

Following are brief synopses of the studies discussed.

Medicine
Lawsonia intracellularis Rush reviewed two studies on this organism, which causes a proliferative ileitis (an intestinal disease) in horses and swine worldwide. The first study followed 57 affected horses between two and eight months of age. They showed ventral (lower belly) edema (fluid swelling, in 81% of horses) and hypoalbuminemia (low levels of albumin protein in the blood, 100% of horses), with other intestinal signs such as colic, fever, lethargy, and diarrhea to a lesser degree. The disease appeared seasonally, with these horses presenting for examination between August and January (half in November and December). A thickened small intestine (seen on ultrasound examination of the abdomen) was not present in all cases, but this finding is suggestive of the disease.

Only half of the horses tested positive for L. intracellularis on both PCR (polymerase chain reaction) and IPMA (immunoperoxidase monolayer assay) tests; the rest were positive on one or the other. Survival rate was good (93%) with antibiotic treatment (primarily oxytetracycline), but the disease did have some lasting effects; 14 affected Thoroughbred foals sold for 68% less than siblings by the same sire, presumably due to a negative impact on growth and development.

The second study found that the incidence of the disease is relatively low despite relatively high exposure. Of 102 healthy horses on farms with L. intracellularis cases, 32.3% had antibodies to the disease (seropositive, indicating exposure). None tested positive via PCR, and none had hypoproteinemia (low protein in the blood).

"Seropositivity can occur without clinical signs of infection and should not be used for definitive diagnosis by itself," Rush commented. She said the author of the second study would also be presenting a study on L. intracellularis later in the meeting (coverage of that presentation on Lawsonia intracellularis).  

REFERENCES: Frazer M.L. Lawsonia intracellularis infection in horses: 2005-2007. J Vet Intern Med 2008; 22: 1243-1248.

Pusterla, N.; Higgins, J.C.; Smith, P.; Mapes, S.; Gebhart, C. Epidemiological survey on farms with documented occurrence of equine proliferative enteropathy due to Lawsonia intracellularis. The Veterinary Record, Aug. 2, 2008.

Polysaccharide storage myopathy (PSSM) "This disease (a form of tying-up) is an important cause of poor performance in many horses," noted Palmer. Rush discussed two papers on this disease, starting with one that described the genetic mutation responsible for this form of tying-up.

In the early 1990s, PSSM was recognized as an abnormal accumulation of glycogen (a form of sugar that cells use for energy) in skeletal muscle. The authors of this study discovered that the disease results from a dominant mutation in the glycogen synthase enzyme (GYS1), which is unusual in that it causes overactivity of the enzyme, resulting in an accumulation of abnormal byproducts (most disease-causing mutations result in a loss or reduction of function). "That's why it was hard to find this defect--and it is the feature that makes this genetic mutation unique of all muscle storage diseases," Rush commented.

"The bottom line is that we have a genetic test for this mutation to help make breeding decisions."
--Dr. Bonnie Rush
A second study described the prevalence of the mutation in 17 of 36 breeds of horses with PSSM, which affects up to 36% of draft horses and 10% of Quarter Horses today. The GYS1 mutation was found in nearly half of the affected horses, from 18% of affected Warmbloods to 72% of affected Quarter Horses and a whopping 87% of affected draft horses. "This mutation isn't the only cause of PSSM, or the numbers would be 100%, but it appears to be the most important" said Rush. "There must be some other mechanism by which abnormal accumulation occurs. The bottom line is that we have a genetic test for this mutation to help make breeding decisions. There's also a newly discovered genetic point mutation in Quarter Horses that causes the most severe form of tying-up we see when paired with the GYS1 mutation."

Most owners of affected horses found an improvement in clinical signs with the recommended low-starch, fat-supplemented diet and regular daily exercise. If this disease is suspected, hair root testing and muscle biopsy can be used to confirm the disease (read more).

REFERENCES: McCue, M.E.; Valberg, S.J.; Lucio, M.: Mickelson, J.R. Glycogen synthase 1 (GYS1) mutation in diverse breeds with polysaccharide storage myopathy. J Vet Intern Med 2008; 22: 1228-1233.

McCue, M.E.; Valberg, S.J.; Miller, M.B.; Wade, C.; DiMauro, S.; Akman, H.O.; Mickelson, J.R. Glycogen synthase (GYS1) mutation causes a novel skeletal muscle glycogenosis. Genomics 2008.

Kester hosts 2008

Drs. Macpherson, Palmer, and Rush headed up the 2008 Kester News Hour.

Multinodular pulmonary fibrosis Rush reported that this disease, which causes a restrictive breathing pattern, weight loss, fever, cough, tachycardia (fast heart rate), tachypnea (fast respiratory rate), and poor body condition, was first reported 20 years ago. It strikes horses of all ages, and chest radiographs show nodules (white areas) in an interstitial pattern (overall loss of detail in the lung due to an increase of fibrous tissue). The prognosis is poor.

The disease appears radiographically similar to fungal pneumonia, but the history often helps separate these diseases (fungal pneumonia usually follows severe gastrointestinal disease), she noted. One paper found equine herpesvirus (EHV)-5 in 79% of affected horses via bronchoalveolar lavage or lung biopsy, compared to 8.7% of unaffected horses. "There's a strong relationship between EHV-5 and fibrosis; it seems to be the most important cause and it's an additional target for treatment," said Rush.

REFERENCES: Williams, K.J.; Maes, R.; Del Piero, F.; Lim, A.; Wise, A.; Bolin, D.C.; Caswell, J.; Jackson, C.; Robinson. N.E.; Derksen, F.; Scott, M.A.; Uhal, B.D.; Li, X.; Youssef, S.A.; Bolin, S.R. Equine multi-nodular pulmonary fibrosis: a newly recognized herpesvirus-associated fibrotic lung disease. Vet Pathol 2007: 44; 849-862.

Hart, K.A.; Barton, M.H.; Williams, K.J.; Flaminio, M.J.B.F.; Howerth, E.W. Multinodular pulmonary fibrosis, pancytopenia, and equine herpesvirus-5 infection in a Thoroughbred gelding. Equine Vet Educ 2008; 20(9): 470-476.

Wong, D.M.; Belgrave, R.L.; Williams, K.J.; Del Piero, F.; Alcott, C.J.; Bolin, S.R.; Marr, C.M.; Nolen-Walstob, .R.; Myers, R.K.; Wilkins, P.A. Multinodular pulmonary fibrosis in five horses. J Am Vet Med Assoc 2008: Vol 232, No. 6.

Thyroid hormone supplementation and insulin sensitivity Thyroid hormone is often given to overweight horses with a specific body type consistent with a metabolic impairment in an attempt to stimulate weight loss and avoid development of laminitis. In one study the hormone levothyroxine given to normal horses daily for 48 weeks resulted in up to a 2.4-fold increase in insulin sensitivity. Weight loss occurred along with the increase in insulin sensitivity, with 49 kg (more than 100 pounds) lost after 16 weeks. However, the effect waned a bit with a total weight loss of 43 kg at 32 weeks, and 25 kg at 48 weeks.

"This medication is not a substitute for diet and exercise; it seemed to lose its effectiveness over the course of the year," Rush noted. "It also stimulated hyperphagia (overeating). We know these horses with obesity and laminitis aren't truly hypothyroid, but thyroid supplementation does help stimulate appropriate metabolic processes in horses that can't exercise due to laminitis or can't lose weight despite a proper diet and exercise program." She noted that when it's time to stop this medication, horses should be weaned gradually.

REFERENCES: Frank, N.; Buchanan, B.R.; Elliott, S.B. Effects of long-term oral administration of levothyroxine sodium on serum thyroid hormone concentrations, clinicopathologic variables, and echocardiographic measurements in healthy adult horses. Am J Vet Res 2008; 69: 68-75.

Frank, N.; Elliott, S.B.; Boston, R.C. Effects of long-term oral administration of levothyroxine sodium on glucose dynamics in healthy adult horses. Am J Vet Res 2008; 69: 76-81.

EPM prevention Rush discussed a study in which 20 unexposed horses were inoculated with Sarcocystis neurona, the parasite that causes equine protozoal myeloencephalitis (EPM). Some were then treated with ponazuril at four times the recommended dose every seven days (starting on Day 5) or every 14 days (starting on Day 12). The first dosage regimen prevented invasion of S. neurona into the cerebrospinal fluid in three of five horses, while the second was ineffective in all horses. No horses developed ataxia (incoordination) or other clinical signs of the disease, even if untreated.

"We need a better model for recreating this disease experimentally," she noted. "Nonetheless, using the best model we have available today, ponazuril given at this dose every seven days to horses with known high exposure may prevent EPM."

REFERENCE: MacKay, R.J.; Tanhauser, S.T.; Gillis, K.D.; Mayhew, I.G.; Kennedy, T.K. Effect of intermittent oral administration of ponazuril on experimental Sarcocystis neurona infection of horses Am J Vet Res 2008; 69: 396-402.

Heart murmurs in racehorses Heart murmurs are not necessarily a problem in athletic horses, according to a study of 526 Thoroughbred racehorses (flat racers and steeplechasers) in the United Kingdom. Rush reported the more fit the horse is, the more likely he is to have a murmur. Murmurs can be a functional adaption to athleticism, as opposed to the result of a structural cardiac abnormality.

"Even when separating out horses with loud and apparently clinically relevant murmurs (ones you can feel with your hands)--there was still no negative impact on performance."
--Dr. Bonnie Rush
"In this population, 22% of the horses had murmurs, including 43% of the National Hunt horses (steeplechasers)," she said. "But even when separating out horses with loud and apparently clinically relevant murmurs (ones you can feel with your hands)--there was still no negative impact on performance." These findings do not indicate that every murmur in an athletic horse should be dismissed; however, the presence of a murmur does not necessarily indicate a structural cardiac problem.

REFERENCE: Young, L.E.; Rogers, K.; Wood, J.L.N. Heart murmurs and valvular regurgitation in Thoroughbred racehorses: epidemiology and associations with athletic performance. J Vet Intern Med 2008; 22: 418-426.

Surgery/Lameness
Biomarkers for lameness diagnosis Palmer discussed three studies on biomarkers (substances that indicate certain biological states) in joint fluid and their possible uses.

  • The first study found that while some biomarkers increase in response to exercise, others increase with arthritis (studied with a surgically created carpal or knee chip model). "We can use this information to diagnose arthritis in horses that are exercising," Palmer explained.
  • The second study found that treating horses with phenylbutazone didn't significantly affect serum biomarker levels.
  • The third found that biomarkers of bone metabolism decreased as foals aged, but the decrease was more pronounced in foals born late (after March 31) than in early foals. In this study biomarkers were not helpful to diagnose osteochondrosis in young foals.

"This is exciting new technology, but it's not quite ready for prime time yet," he commented.

REFERENCES: Frisbie, D.D.; Al-Sobayil, F.; Billinghurst, R.C.; Kawcak, C.E.; McIlwraith, C.W. Changes in synovial fluid and serum biomarkers with exercise and early osteoarthritis in horses. Osteoarthritis Cartilage 2008; Oct 16 (10): 1196-1204.

Fradette, M.E.; Celeste, C.; Richard, H.; Beauchamp, G.; Laverty, S. Effects of continuous oral administration of phenylbutazone on biomarkers of cartilage and bone metabolism in horses. Am J Vet Res 2007; 68(2): 128-133.

Vervuert, I., et al. Evaluation of the influences of exercise, birth date, and osteochondrosis on plasma bone marker concentrations in Hanoverian Warmblood Foals. Am J Vet Res 2007; 68 (12): 1319-1331.

Tendon/ligament repair "The names have changed since last year. What we once referred to as stem cells, we now call nucleated cell fractions," said Palmer with a smile. He discussed a study from Cornell University that found that injection of adipose (fat)-derived nucleated cell fractions improved fiber organization in repaired tendons ("architecturally better healing").

Another study evaluated platelet-rich plasma used to treat mid-body suspensory ligament injuries in nine Standardbred racehorses via a single injection followed by a controlled exercise program. All nine returned to racing after about 32 weeks, with at least six starts thereafter (five were still racing three years later). "Although many Standardbred racehorses can race with suspensory ligament injury, these horses had moderate to severe trauma and did pretty well with this treatment," Palmer commented.

REFERENCES: Nixon, A.J.; Dahlgren, L.A.; Haupt, J.L.; Yeager, A.E.; Ward, D.L. Effect of adipose-derived nucleated cell fractions on tendon repair in horses with collagenase-induced tendinitis. Am J Vet Res 2008; 69 (7): 928-937.

Waselau, M.; Sutter, W.W.; Genovese, R.L.; Bertone, A.L. Intralesional injection of platelet-rich plasma followed by controlled exercise for treatment of midbody suspensory ligament desmitis in Standardbred racehorses. J Am Vet Med Assoc 2008; 232 (10): 1515-1520.

Airway problems Palmer discussed four studies that described surgical techniques used to treat partial upper airway obstruction in performance horses.

  • One study of Thoroughbred and Standardbred racehorses found that horses with soft palate displacement that were treated with a laryngeal tie-forward (where the voice box is moved up and forward within the throatlatch area) were just as likely to race afterward as untreated horses. Their earnings, which were below average before treatment, increased to baseline levels after surgery.
  • The second study found that horses with soft palate displacement that were treated with a combination of tenectomy of the strap muscles attaching to the voice box and soft palate surgery experienced improved in performance and earnings postoperatively.
  • A third study evaluated partial arytenoidectomy (removal of dysfunctional or diseased cartilage of the voice box) followed by closure of the mucosal incision. When this procedure was performed on 76 Thoroughbred racehorses, 82% raced after surgery after about six months, and 63% raced at least five times. "So a Thoroughbred racehorse treated with partial arytenoidectomy with mucosal closure is likely to race after this procedure and to return to his previous performance level," said Palmer.
  • The last airway study he discussed found that sedation with either detomidine or acepromazine for endoscopic airway examination reduced a horse's ability to fully abduct the left arytenoid cartilage (move it out of the airway). Thus, "Sedation should be avoided whenever possible when evaluating a horse for normal laryngeal function to achieve a more accurate diagnosis," advised Palmer. This advantage, however, should always be weighed against the safety of either the horse or the examiner and handler.

REFERENCES: Cheetham, J.; Pigott, J.H.; Thorson, L.M.; Mohammed, H.O.; Ducharme, N.G. Racing performance following the laryngeal tie-forward procedure: A case-controlled study. Equine Vet J 2008; 40 (5): 501-507.

Dykgraff, S., et al. Sternothyroideus tenectomy combination surgery: treatment outcome in 95 Thoroughbred racehorses (1996-2006). J Equine Vet Sci 2008; 28(10): 598-602.

Parente, E.J.; Tulleners, E.P.; Southwood, L.L. Long-term study of partial arytenoidectomy with primary mucosal closure in 76 Thoroughbred racehorses (1992-2006). Equine Vet J 2008; 40 (3): 214-218.

Lindegaard, C.; Husted, L.; Ullum, H.; Fjeldborg, J. Sedation with detomidine and acepromazine influences the endoscopic evaluation of laryngeal function in horses. Equine Vet J 2007; 39 (6): 553-556.

Joint medication Several studies were discussed that looked at innovations in intra-articular (within a joint) therapy. Palmer discussed one that investigated movement of corticosteroids between the coffin joint and the navicular bursa (a fluid-filled cushioning sac between the navicular bone and the deep digital flexor tendon). The study of 32 healthy horses found that when either location was medicated, clinically significant concentrations of the medication were found in the other structure. So clinicians are justified in injecting the coffin joint to treat navicular bursitis. "This approach is much easier and safer for the horse," explained Palmer.

"Doxycycline might have a potential use for treating septic arthritis (infection in a joint) in foals. However, since doxycycline isn't a broad-spectrum antibiotic, it would not be a good choice unless the causative organisms are found to be sensitive to it."
--Dr. Scott Palmer
A laboratory study found that a commonly injected corticosteroid (triamcinolone acetonide) had protective effects on equine cartilage that were similar to that found with sodium hyaluronate injection. "In vivo (in live horses) studies are needed to demonstrate the clinical impact of these findings," Palmer noted.

Lastly, a study performed on calves found that doxycycline (an antibiotic) injected intra-articularly caused no damage and even exerted a short-term chondroprotective (cartilage-protecting) effect. For this reason, "Doxycycline might have a potential use for treating septic arthritis (infection in a joint) in foals," noted Palmer. "However, since doxycycline isn't a broad-spectrum antibiotic, it would not be a good choice unless the causative organisms are found to be sensitive to it."

REFERENCES: Pauwels, F.E.; Schumacher, J.; Castro, F.A.; Holder, T.E.; Carroll, R.C.; Sega, G.A.; Rogers, C.W. Evaluation of the diffusion of corticosteroids between the distal interphalangeal joint and navicular bursa in horses. Am J Vet Res 2008; 69 (5): 611-616.

Bolt, D.M.; Ishihara, A.; Weisbrode, S.E.; Bertone, A. Effects of triamcinolone acetonide, sodium hyaluronate, amikacin sulfate, and mepivacaine hydrochloride, alone and in combination, on morphology and matrix composition of lipopolysaccharide-challenged and unchallenged equine articular cartilage explants. Am J Vet Res 2008; 69 (7): 861-867.

Haerdi-Landerer, M. Christina et al. Intra-articular administration of doxycycline in calves. Am J Vet Res 2007; 68(12): 1324-1331.

Pain management Palmer described two studies comparing pain management strategies. The first study evaluated the use of non-steroidal anti-inflammatory drugs by comparing phenylbutazone (Bute) given alone or in combination with flunixin meglumine (Banamine) for treatment of lameness. That study found the combination improved lameness scores more than did treatment with Bute alone. However, lameness was not always completely eliminated even with the combination, and lameness did not improve at all in some cases. Additionally, one horse died of acute necrotizing colitis following administration of the combination. This paper provides additional evidence that combined use of multiple NSAIDs to treat lameness in the horse is not always successful and can have fatal complications.

"The (lameness improvement) results may attract people to use this combination to increase performance, but we must consider the potentially life-threatening toxic adverse events," said Palmer.

The second study compared oral paste firocoxib (Equioxx) to Bute and found that the two medications improved lameness to the same degree. "The firocoxib-treated horses had less pain on joint manipulation and palpation, decreased joint circumference (less swelling), and improved range of motion, but the same lameness scores," said Palmer. "There was also no significant difference in the rate of adverse events. They're fairly equivalent drugs."

REFERENCES: Keegan, K.G.; Messer, N.T.; Reed, S.K.; Wilson, D.A.; Kramer, J. Effectiveness of administration of phenylbutazone alone or concurrent administration of phenylbutazone and flunixin meglumine to alleviate lameness in horses. Am J Vet Res 2008; 69 (2): 167-173.

Doucet, M.Y., et al. Comparison of efficacy and safety of paste formulations of firocoxib and phenylbutazone in horses with naturally occurring osteoarthritis. J Am Vet Med Assoc 2008; 232 (1): 91-97.

Surgical techniques When a horse needs to have an eye removed, you don't have to knock him out to do it. That was the message of one study, which found that the procedure can be done in standing horses with proper local/regional anesthesia. "There were no long-term complications of doing the procedure standing; this approach reduces cost and eliminates the risks of general anesthesia," commented Palmer.

The second study evaluated the risks and outcomes of rectal tears, which were most common in Arabian and Miniature Horse breeds, mares, and horses older than nine years (and tended to be larger following dystocia). Tears are graded according to which tissue layers are torn. Grade 4 tears are the most severe, with tearing of all tissue layers and potential escape of feces into the abdomen. Grade 1 and 2 tears had 100% survival regardless of surgical technique used to repair them, while grades 3 and 4 had poorer success rates (38% and 2%, respectively).

Another study on rectal tears, specifically surgical repair in mares after parturition (delivery), found that four of six mares survived postpartum surgical repair of the rectal tear (two died of unrelated causes). "This study showed that in spite of the serious nature of this type of injury, rectal tears as a result of parturition can be repaired successfully with (the appropriate) surgical technique," commented Palmer.

Lastly, Palmer discussed a study that found injection of corticosteroids into the fibrous lining of subchondral (beneath the joint cartilage) cystic lesions in the stifle joint was an effective treatment for 67% of the 52 reviewed cases. He noted that treatment success rates varied with the surgeon and that the procedure was more effective for cases with cysts in one limb vs. both hind limbs and in horses without pre-existing arthritic changes in the joint. Horses generally returned to training within three months.

"This procedure is easier than debridement (cutting out the lesion) and has similar results," he noted.

REFERENCES: Claes, A.; Ball, B.; Brown, J.; Kass, P. Evaluation of risk factors, management, and outcome associated with rectal tears in horses: 99 cases (1985-2006). J Am Vet Med Assoc 2008; 233 (10): 1605-1609.

Pollock, P.J.; Russell, T.; Hughes, T.K.; Archer, M.R.; Perkins, J.D. Transpalpebral eye enucleation in 40 standing horses. Vet Surgery 2008; 37: 306-309.

Kay, A.T.; Spirito, M.A.; Rodgerson, D.H.; Brown, S.E. Surgical technique to repair grade IV rectal tears in post-parturient mares. Vet Surgery 2008; 37: 345-349.

Wallis, T.W.; Goodrich, L.R.; McIlwraith, C.W.; Frisbie, D.D.; Hendrickson, D.A.; Trotter, G.W.; Baxter, G.M.; Kawcak, C.E. Arthroscopic injection of corticosteroids into the fibrous tissue of subchondral cystic lesions of the medial femoral condyle in horses: A retrospective study of 52 cases (2001-2006). Equine Vet J 2008; 40 (5): 461-467.

Additional Topics
Protect those heads! Palmer discussed a professional liability trust study on injury insurance claims, which found that equine claims made up only 3.27% of claims, but they included some of the most severe and costly injuries. "Two of the three most expensive claims were for more than $4 million and involved brain injury," he reported. "These injuries should be considered when addressing safety measures and personal protective equipment in your practice. Consider wearing (and having your staff wear) helmets when working on horses."

Rush followed up with a review paper noting that 50% of head injuries in horseback riders require surgery, with an average hospital stay of five days and a death rate of 5-10%. "It's more dangerous than rugby, skiing, and football, based on the severity of the injuries (as opposed to frequency); head trauma risk is higher with more time spent in contact with horses," she commented. "Use chemical restraint and a helmet when indicated (when treating horses)."

Unwanted horses The presenters played a video featuring AAEP Past President Tom Lenz, DVM, chairman of the Unwanted Horse Coalition (UHC), discussing the hot topic of unwanted horses. He noted the increasing prices of hay and grain, along with the expense of disposing of euthanized horses, have resulted in an increasing number of unwanted horses in the United States. The UHC conducted an online survey in an attempt to get hard numbers on the current status of this problem.

He also related the findings of a UHC group that visited two Mexican slaughter plants, reporting that the plants were extremely clean and well-run, staff fed and watered the horses properly before slaughter, and they euthanized horses humanely with the captive bolt method.

Lenz also discussed three upcoming pieces of legislation concerning horse transportation, slaughter prevention, and prevention of equine cruelty (which would make it a federal crime to sell horses for slaughter or horsemeat in the United States.). Neither of the latter bills makes any provisions for enforcement infrastructure, he commented; thus, AAEP opposes both.

Tips of the Hat
Each year, the Kester News Hour includes several "tips of the hat" to recognize equine veterinarians and others who have made significant contributions. Following is a list of those recognized this year.

  • The AAEP's 30-plus On-Call veterinarians, who provide information to the media on equine injuries during sporting events. "These veterinarians are particularly crucial during catastrophic events such as Eight Belles' breakdown," said Macpherson.
  • Carol Clark, DVM, Dipl. ACVIM, an internist at Peterson & Smith Equine Hospital in Ocala, Fla., who recognized piroplasmosis in a horse in Florida, which triggered a foreign animal disease investigation that resulted in quarantines and euthanasia of 19 positive horses--but the disease was contained. "This is a beautiful example of everything done right," said Rush, quoting John Harvey, DVM, PhD, Dipl. ACVP, a professor of hematology at the University of Florida, amid an ovation for Clark. She continued quoting Harvey: "This is why we teach foreign animal disease in veterinary school."
  • David Foley, AAEP executive director, for 20 years of service to the organization. "We're glad for the 20 years of service and looking forward to another 20," said current AAEP President Harry Werner, VMD, as he helped present Foley with a horse sculpture by AAEP member veterinarian Doug Byars, DVM, Dipl. ACVIM.

Reproduction
Controlling estrous behavior "Owners frequently ask us for techniques for suppressing estrus in performance animals," said Macpherson. She discussed a Finnish study on the use of polypropylene balls placed in the uterus within four days after ovulation to simulate an equine conceptus, similar to the glass marble concept. The technique resulted in "surprisingly prolonged diestrus" (staying out of heat); 75% of the studied mares stayed out of heat for an average of 57 days, compared to only an average of 16 days for control (untreated) mares. The balls had limited movement throughout the uterus and caused no uterine damage.

"They were very effective for reducing estrous behavior," Macpherson commented.

Another study used oxytocin injections (twice per day for a week, starting a week after ovulation) to achieve the same goal. All six treated mares stayed out of heat for at least 30 days. A third study evaluated a long-acting synthetic progestin (medroxyprogesterone acetate) injected intramuscularly on a weekly basis for five weeks following an initial loading dose, comparing it with a daily administration of altrenogest (Regu-Mate). The researchers found that the synthetic progestin was not effective for controlling estrous behavior, while treatment with Regu-Mate was.

REFERENCES: Rivera del Alamo, M.M.; Reilas, T.; Kindahl, H.; Katila, T. Mechanisms behind intrauterine device-induced luteal persistence in mares. Animal Reproduction Sci 2008; 107(1-2): 94-106.

Vanderwall, D.K.; Rasmussen, D.M.; Woods, G.L. Effect of repeated administration of oxytocin during diestrus on duration of function of corpora lutea in mares. J AmVet Med Assoc 2007; 231(12): 1864-1867.

Gee, E.K.; McCue, P.M.; Deluca, C.A.; Stylski, J.L. Efficacy of medroxyprogesterone acetate in suppression of estrous behavior and follicular activity. Theriogenology 2008; 70(3): 588.

Late-term broodmare concerns "Generally we like to forget about late pregnant mares and put them on the back burner until they foal, but they can have some pretty significant issues," said Macpherson. She discussed a study of body wall tears (such as hernias and prepubic tendon ruptures) that found conservative management (such as pain relief and fluids) was just as effective as interventional management (such as Cesarean section or early induction of parturition/delivery) at saving the life of the mare. Foal survival was better with conservative management (seven of eight mares survived and delivered healthy foals vs. no live foals in the interventional treatment group).

"Generally we like to forget about late pregnant mares and put them on the back burner until they foal, but they can have some pretty significant issues."
--Dr. Margo Macpherson
"Give the mares a shot!" advised Macpherson. "They can survive and deliver viable foals."

Uterine torsion (twisting) was the focus of another study, which found that surgical correction of the torsion showed good survivability of both mares and foals. The technique involved "floating" the uterus with 20 liters of sterile saline to make manipulation of the uterus easier, and it had a "good success rate" (successful correction in 17/19 mares). Thirteen delivered live foals, and five had wound complications (at the incision).

Sometimes it is helpful to induce parturition in a later-term mare. Low-dose oxytocin (3.5 IU) was found to be effective for this in one study, with 69% of 148 mares responding within 20 minutes. It took more than two hours for the rest to respond. All foals were normal.

"Some may slip through the cracks and foal later, so keep watching them," said Macpherson. "It's an effective method, but mares have to be ready to foal to respond to this microdose."

REFERENCES: Ross, J.; Palmer, J.E.; Wilkins, P.A. Body wall tears during late pregnancy in mares: 13 cases (1995-2006). J Am Vet Med Assoc 2008; 232(2): 257-261.

Jung, C.; Hospes, R.; Bostedt, H.; Litzke, L.F. Surgical treatment of uterine torsion using a ventral midline laparotomy in 19 mares. Australian Vet J 2008; 86(7): 272-276.

Villani, M., and Romano, G. Induction of parturition with daily low-dose oxytocin injections in pregnant mares at term: clinical applications and limitations. Reprod Dom Anim 2008; 43: 481-483.

Foaling problems Uterine tears incurred during foaling are usually considered surgical cases, but Macpherson reported that one study showed similar survival rates for mares treated only medically (73%) and mares treated surgically (76%). There was no significant difference in treatment cost or duration of hospital stay. Future reproduction was not significantly impaired for medically managed mares in the same season; however, long-term effects on reproduction were unknown.

"This rocked my world; I always thought this was a surgical disease," she commented.

Another possible foaling complication is traumatic ventral (lower belly) herniation in foals after dystocia (difficult birth). Macpherson reported that two of four affected Thoroughbred foals in one study survived following surgical repair; the other two were euthanized. "Use only moderate traction to assist a dystocia case, and pull in concert with the mare's contractions in a downward arc so you're not fighting against the mare's anatomy," she recommended.

REFERENCES: Jasvicas, L.H.; Giguere, S.; Freeman, D.E.; Slovis, N.M. Peritonitis secondary to uterine tears in postpartum mares: retrospective comparison of surgical versus medical treatment. In Proceedings. 26th Am Coll Vet Int Med 22[3]815. 2008.

Witte, S.; Rodgerson, D.H.; Hunt, R.; Spirito, M. Traumatic ventral herniation in foals as a complication of dystocia. Compendium Equine 2008; 3(3): 137-142.

Stallion self-mutilation "This is not an overly prevalent disease, but it can have catastrophic consequences," said Macpherson. The study (by The Horse's behavior columnist Sue McDonnell, PhD, Cert. AAB, found that stallion self-mutilation occurs in about 2% of stallions and pain is the most common cause (such as from enteroliths; uroliths; or any problem in the reproductive tract). This is the most common of the three types of self-mutilation, and it's seen in mares, too; behavior includes circling, lunging, and biting or kicking at the flanks that can result in substantial damage.

Type 2 is only seen in males and describes self-directed inter-male aggression (even in herd situations) such as a stallion marking his own fecal pile or becoming aggressive to his own odor on objects. Type 3 is the least common and describes a quiet, mutilative stereotypic (rhythmic and repetitive) behavior that tends to happen at the same time of day in the same location.

"How do we treat these animals? The most important thing is to remove the underlying cause, which might require exhaustive examination," said Macpherson. Restraints are not recommended, although rubber grazing muzzles might help prevent self-damage. Social, feeding, and work changes are recommended. More information can be found on this topic.

REFERENCE: McDonnell, S.M. Practical review of self-mutilation in horses. Animal Reproduction Sci 2008; 107(3-4): 219-228.

Reproduction in deceased horses "There are lots of tidbits in the news on this," said Macpherson. She listed three studies on assisted reproduction techniques for both mares and stallions.

Vitrification of embryos (an alternative to freezing them) is currently used on embryos harvested from mares meeting an untimely death, and often on smaller embryos than those used for freezing (2-8 cells). One study found this technique resulted in five pregnancies from eight vitrified embryos. "This is a little window into the future of a technique we may be incorporating into our practice," she commented.

A study on transported ovaries found that time is critical--when oocytes are harvested within six hours after death, embryo development was 50% better. "Retrieve ovaries as quickly as possible and rush ship them in an Equitainer at room temperature to an assisted reproduction facility," advised Macpherson.

Although fertility rates of sperm harvested from deceased stallions are typically low, a Brazilian research group achieved "astounding" fertility rate of almost 70% by using a Botu-Crio extender before freezing and timed artificial insemination. "This extender isn't available in the U.S., but I imagine we'll be seeing it soon," said Macpherson.

REFERENCES: Campos-Chillon, L.F.; Suh, T.K.; Barcelo-Fimbres, M.; Seidel, J.; Carnevale, E.M. Vitrification of early-stage bovine and equine embryos. Theriogenology In Press, Corrected Proof.

Ribeiro, B.I.; Love, L.B.; Choi, Y.H.; Hinrichs, K. Transport of equine ovaries for assisted reproduction. Animal Reproduction Sci 2008; 108(1-2): 171-179.

Melo, C.M.; Papa, F.O.; Fioratti, E.G.; Villaverde, A.I.S.B.; Avanzi, B.R.; Monteiro, G.; et al. Comparison of three different extenders for freezing epididymal stallion sperm. Animal Reproduction Sci 2008; 107(3-4): 331.

Twin reduction Macpherson discussed a study of two methods for euthanizing a twin after it has become stationary in the uterus (when discovered earlier, one twin is usually manually crushed since twinning poses a health risk to both of the fetuses and to the mare). The study found that 57% of the remaining embryos survived at least 10 days after ultrasound-guided reduction of one embryo. Increased mare age, number of previous foals, and length of gestation all resulted in decreased success rates with either procedure. "Both procedures require experienced hands for success," noted Macpherson.

REFERENCE: Govaere, J.L.J.; Hoogewijs, M.K.; de Schauwer ,C.; Dewulf, J.; de Kruif, A. Transvaginal ultrasound-guided aspiration of unilateral twin gestation in the mare. Equine Vet J 2008; 40(5): 521-522.

Equine viral arteritis (EVA) in pregnant mares Macpherson discussed a small study of five late-gestation mares that were accidentally given a modified-live EVA vaccine seven to 13 weeks prior to foaling. All mares remained healthy and so did the foals (which showed antibodies to EVA after nursing). Another study that is still in progress found that three of 19 vaccinated mares aborted (one factor might have been stress from a diarrhea outbreak on the farm). "Be cautious how you use this vaccine," advised Macpherson. "The AAEP guidelines on this should be adhered to closely."

REFERENCES: Timoney, P.J.; Fallon, L.; Shuck, K.; McCollum, W.H.; Zhang, J.J.; Williams, N.M. The outcome of vaccinating five pregnant mares with a commercial equine viral arteritis vaccine. Equine Vet Edu 2008;(December): 606-616.

Holyoak, G.R.; Balasuriya, U.B.R.; Broaddus, C.C.; Timoney, P.J. Equine viral arteritis: Current status and prevention. Theriogenology 2008; 70(3): 403-414.

Stallion fertility "This was a big year for developments in stallion reproduction," she commented, leading into a discussion of four studies.

One study comparing three "nonspermicidal" lubricants found that all but one (Pre~SeedEQ) significantly decreased sperm motility at 24 and 48 hours of storage. "Motility isn't necessarily the best indicator of fertility, so use caution in interpreting this information," said Macpherson.

Another study comparing two semen cryopreservation protocols for eight stallions found that the most effective approach was to use lactose EDTA cryopreservation extender with a pre-cooling period (which is different than package instructions).

Cushioned centrifugation of semen resulted in high sperm recovery rates and satisfactory sperm function in another study. Conical-bottom tubes resulted in slightly more sperm recovered, but newer nipple-bottom tubes resulted in higher values for motility. Lastly, motility was better with an opaque extender than with a clear one. "This information may be helpful when processing dilute ejaculates," noted Macpherson.

Three studies on density gradient centrifugation of semen using silane-coated silica particles (EquiPure) was found to result in improved motility and viability compared to centrifuging without this product, resulting in improved fertility of select cases.

REFERENCES: Samper, J.C.; Garcia, A. Comparative effect of "nonspermicidal" lubricants on stallion sperm function. Animal Reproduction Sci 2008; 107(3-4): 360.

Salazar, J.; Hayden, S.S.; Waite, J.A.; Comerford, K.L.; Edmond, A.J.; Teague, S.R.; et al. Effect of cryopreservation protocol on post-thaw characteristics of stallion spermatozoa. Animal Reproduction Sci 2008; 107(3-4): 347-348.

Waite, J.A.; Mancill, S.S.; Love, C.C.; Brinsko, S.P.; Teague, S.R.; Salazar, J.L.; et al. Factors impacting equine sperm recovery rate and quality following cushioned centrifugation. Animal Reproduction Sci 2008; 107(3-4): 355.

Stoll, A.; Stewart, B.L.; Brum, A.M.; Liu, I.K.; Ball, .BA. Evaluation of cryopreserved-thawed stallion sperm before and after density gradient centrifugation with silane-coated silica particles (EquiPure). Theriogenology 2008; 70(3): 590-591.

Edmond, A.J.; Teague, S.R.; Brinsko, S.P.; Comerford, K.L.; Waite, J.A.; Mancill, S.S.; et al. Effect of density-gradient centrifugation on quality and recovery rate of equine spermatozoa. Animal Reproduction Sci 2008; 107(3-4): 318.

Varner, D.D.; Love, C.C.; Brinsko, S.P.; Blanchard, T.L.; Hartman, D.L.; Bliss, S.B.; et al. Semen Processing for the Subfertile Stallion. J Equine Vet Sci 2008; 28(11): 677-685.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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