2024 AAEP Convention Research Highlights

This article originally appeared in the Spring 2025 issue of EquiManagement. Sign up here for a FREE subscription to EquiManagement’s quarterly digital or print magazine and any special issues.

What We’re Learning About SGLT2 Inhibitors 

The use of SGLT2 inhibitors has exploded in human medicine for treating obesity and diabetes. Equine researchers are studying these medications’ potential for managing obesity and endocrine disorders in horses to reduce laminitis risk. David Rendle, BVSc, MVM, CertEM (IntMed), DECEIM, FRCVS, spoke about this research during the 2024 American Association of Equine Practitioners ­Convention.  

Researchers predict a horse’s risk of developing laminitis within four years by evaluating the plasma concentration of resting insulin:

• Low risk (6% incidence): Horses with insulin < 21.6 uU/ml. 
• Medium risk (22% incidence): Horses with insulin 21.6-45.2 uU/ml. 
• High risk (69% incidence): Horses with insulin > 45.2 uU/ml.

Some horses struggle to lose weight, even with a controlled diet and low-NSC forage. In other cases, a horse might be thin but still hyperinsulinemic. SGLT2 medications have the potential to: 

• Lower plasma glucose.
• Elicit urinary calorie loss and subsequent weight loss.
• Lower adiponectin and leptin.
• Lower plasma volume and blood pressure.
• Reduce adipocyte-mediated ­inflammation.
• Shift to ketone metabolism.
• Reduce oxidative stress.
• Lower uric acid.
• Reduce glomerular hyperfiltration and albuminuria.
• Suppress glycemic end product signaling that could lead to inflammation, oxidative stress, and chronic disease.

Rendle discussed the use of ertugliflozin (0.025-0.05 mg/kg) for its potential to promote urinary glucose excretion. When horses’ blood glucose is reduced, they secrete less insulin from the pancreas. Candidates for this medication are horses that experience “weight loss resistance” or remain hyperinsulinemic despite weight loss. It can also be useful in scenarios when horses don’t lose weight because owners don’t comply with veterinary diet and exercise recommendations. Horses with acute laminitis as a result of hyperinsulinemia and those refractory to weight loss despite diet and management changes might also benefit from the medication.

After only 30 days of treatment, horses experience dramatic improvements in comfort. During this recovery, owners must take care to limit laminitic horses’ movement due to structural changes in their feet. In many cases, they are also on non-steroidal anti-inflammatory drugs, which mask pain.  

This medication’s side effects include polyuria, polydipsia, excessive weight loss, dullness, and potential skin disease, such as perineal necrosis. Hyperlipidemia did not occur in any horses. To reduce risk, Rendle recommends judicious use and dosing, using the smallest amount for the shortest time. The medication is not recommended for use in pregnant mares. Horses on SGLT2 inhibitors should not be on significantly restricted diets. 

Take-Home Message

The studies Rendle cited stipulate that SGLT2 inhibitors appear to be very effective at lowering insulin concentrations, promoting recovery from hyperinsulinemia-associated laminitis (HAL), and promoting weight loss. Long-term safety data are lacking in horses, he said, but the possibility of laminitis in refractory cases likely outweighs the risks. He stressed that monitoring is important, including pretreatment laboratory testing and regular checks. Overall, he said ertugliflozin does not replace appropriate diet, management, and farriery but, rather, is an adjunctive therapy to manage obese and/or hyperinsulinemic horses.

Vitamin E Assessment and Correction

Many horse owners assume the hay and supplemental feeds they give their horses contain sufficient vitamins and minerals, but this is not always the case. Carrie Finno, DVM, PhD, DACVIM (LAIM), of the University of California, Davis, School of Veterinary Medicine, discussed vitamin E and the effects of a deficiency.

Horses get vitamin E from fresh pasture. Finno said horses must spend 12 hours per day for six months a year on irrigated pasture to obtain ample vitamin E storage in their systems. The greener the grass, the more vitamin E it has. Once grass is cut and dried to hay, vitamin E oxidizes.

Young horses with vitamin E deficiencies can develop equine neuroaxonal dystrophy (eNAD) or equine degenerative myeloencephalopathy (EDM) proprioceptive ataxia. These syndromes are difficult to reverse. Vitamin E deficiency takes a different form in middle-aged horses, causing myopathy specific to muscle fibers rather than neurologic deficits. Older horses with vitamin E deficiency can develop equine motor neuron disease. 

Serum vitamin E concentrations should be at least 2 ug/ml—ideally 3-5 ug/ml. Horses grazing in a natural setting usually have levels of 3-6 ug/ml. Serum concentrations of 1.5-2 ug/ml are marginal, while < 1.5 ug/ml is considered deficient. At low levels, horses might demonstrate clinical signs. For young horses without pasture, especially during droughts, signs might not appear until they are older. 

The nomenclature of vitamin E has been revised. Alpha-tocopherol is the crucial vitamin E for horses, but the RRR stereoisomer is also important, said Finno. An α-tocopherol deficiency can cause clinical disease.

The classic way to assess vitamin E levels is by collecting serum in a red top separator tube. Finno recommended discarding hemolyzed samples, as they can yield a falsely low evaluation. Wrap samples in aluminum foil to avoid light degradation, and keep them refrigerated, she said. Spin down as soon as possible.

Many vitamin E supplements are available, but Finno said synthetic forms (designated as di- rather than d-) do not elevate vitamin E levels in deficient horses. Natural powder or pellets with d-α-t­ocopherol take 8-10 weeks to raise serum concentrations. Natural liquid d-α-­tocopherol or RRR-α-tocopherol can double the serum concentration within 24 hours and raise concentrations to appropriate levels in 2-3 days. If the horse has neuromuscular disease, Finno recommends using the natural liquid form. If the horse has clinical signs but serum levels are just over 2 mg/ml, she recommends doing a tailhead biopsy and putting the horse on the liquid supplement.

Finno said vitamin E and selenium deficiencies are separate issues. With selenium deficiency, the horse will have a poor hair coat, poor immune system, and white muscle disease. ­Supplementation with an E-Se product will provide horses with absorbable selenium, but the vitamin E included to buffer selenium is a synthetic form and will not elevate serum vitamin E levels.

Finno’s suggestions for monitoring and treatment based on a baseline vitamin E sample include:

• If the horse has no neuromuscular disease and serum levels are ≥ 2 mg/ml, continue to monitor. 
• If there is no evidence of clinical disease but levels are < 2 mg/ml, use liquid vitamin E at 6 IU/kg or supplement with 10 IU/kg natural powder or pellet per day. With a powder or pellet supplement, wait a few months and recheck. She suggests not exceeding 5,000 IU per day because excess vitamin E can interfere with the horse’s vitamin K and cause bleeding issues. 
• If levels are > 10 mg/ml, reduce the dose by half and reassess. 
• For deficient horses with levels < 2 mg/ml, she advises immediate use of the liquid form at 10 IU/kg/day; recheck in a few weeks. 
• If a pregnant mare is deficient, start liquid vitamin E immediately, and check the foal at birth and at three months. A mare on pasture should have sufficient vitamin E stores that go into the colostrum.  
• Some horses don’t absorb vitamin E well. If their levels remain < 3 mg/ml with supplementation, increase the dose by 50% and reassess. Reasons for poor absorption include eosinophilic enteritis, malabsorption of fat vitamins, or fecal parasites.

The Rider’s Impact on Horse Movement

Maria Engell, DVM, PhD, CEO of Rider in Balance (RiB), discussed an important element of equine welfare and performance: the effect of the rider. A rider with asymmetry and positional aberrations can profoundly affect a horse’s movement and even contribute to or exacerbate lameness. In Engell’s experience, optimal performance comes from decreasing variations in movement as much as possible. 

Besides evaluating a horse for soundness, Engell said it is important to analyze the horse and rider connection and interaction. Sometimes problems lie not just with the horse but also or exclusively because of the rider (and vice versa).

A rider’s position in the saddle has consequences for how a horse moves. Each of the rider’s body parts has its own mass and can affect other parts of the body. Engell recommends watching horse and rider from multiple views, including from the front, the side, and above. With equine lameness, veterinarians often consider vertical transitional movements, such as roll, yaw, and pitch. Humans have even more degrees of freedom, including roll, yaw, pitch, forward, backward, and sideways transitional segments. Each tilt or twist of the body is likely to cause a reaction in the horse. The horse might stiffen, lean, or move away from pressure to overcome a rider’s lack of balance. 

A rider generally comes to a veterinarian with a complaint about a horse’s performance issues and/or “laterality,” such as leaning more to one side or not able to bend to one side. Engell said veterinarians must consider, “Does a rider affect the horse negatively, or is it just a problem with horse?” In her practice, she analyzes the horse’s motion using a clinical exam and objective tools like inertial sensor technology. She also evaluates the segmental position of the rider’s trunk, head, and pelvis tilt when unmounted and while walking, standing, and then sitting on a balance chair that moves right and left.

Engell recommends assessing the rider’s momentary effect on a horse. Does the horse’s movement change with and without the rider or when wearing a weighted surcingle?

The following evaluations can help veterinarians determine the rider’s long-term role in how the horse is moving: 

• Have the rider’s actions contributed to asymmetrical loading in the horse over time? 
• Has lameness developed because of prolonged uneven loading? 
• Are the same symptoms recurring, even across multiple horses ridden by this rider? 

Engell incorporates the rider’s biomechanical profile into her rehab program with the objective of promoting better performance for both horse and rider with reduced risk of recurrence. While most equine practitioners will not be able to retrain the rider, they can at least bring recognition to the issue and perhaps steer the rider toward professional training. With improvements in a rider’s skills, it is easier to attain Engell’s “Sports Goal”: To replicate perfect performance again and again, the rider must focus on minimizing variation. Riding correctly and in good balance and synchrony with the horse yields the most promising success.

Recent Developments in EGGD Treatment

To improve treatment and management outcomes for equine gastric glandular disease (EGGD), we need to identify medications that do a better job suppressing stomach acid. Rendle presented new EGGD treatment developments.

For acid suppression, he suggests two newer medications besides oral omeprazole: esomeprazole and extended-­release injectable omeprazole (long-acting injectable omeprazole, or LAIO). 

Esomeprazole, administered orally at least one hour prior to feeding, resulted in 85% healing of EGGD compared to 59% healing with oral omeprazole. Esomeprazole also improved squamous healing.

Extended-release omeprazole has demonstrated more profound results than the oral form. Extended release achieves a higher pH above 4 for a longer duration compared to daily oral dosing. Researchers in Australia (Sykes) tested this treatment in 24 Thoroughbred racehorses, 12 of which received two injections seven days apart and 12 of which served as controls. EGGD resolved at two weeks in 75% of the horses that received ­extended-release omeprazole, and the other 25% improved by at least one grade. All horses with equine squamous gastric disease (ESGD) resolved in two weeks with the injectable omeprazole. In another study (Gough, Hallowell, and Rendle), EGGD healed in 82% of horses that received LAIO compared to 50% given daily oral omeprazole.

In a prospective, randomized, blinded clinical trial of endurance horses (Rendle and Hallowell), 89 had EGGD lesions ≥ 2/4, and 100 had ESGD ≥ 2/4. The horses continued in training throughout the study. Forty-four horses received oral omeprazole (4 mg/kg) for 28 days, and 45 received four IM doses of LAIO (4 mg/kg) at seven-day intervals for 28 days. Rendle reported that EGGD lesions healed in four times as many horses treated with LAIO compared to oral omeprazole. In addition, half as many horses in the LAIO group required treatment. 

For ESGD treatment, 49 of the endurance horses received daily oral omeprazole, and 51 received the LAIO IM treatment (both dose and frequency are as described in the previous study). ESGD lesions healed in four times as many horses with LAIO. Horses administered daily oral omeprazole were five times as likely to require further treatment.

Rendle also reported on a retrospective study from the Netherlands (Lieuwke, Kranenburg, Ludin), which found that LAIO significantly improves lesion scores for both ESGD and EGGD even when these lesions had not previously responded to treatment with oral omeprazole. The authors recommended against treating EGGD with oral omeprazole alone.

In another study (Dundra, Kelty, Rendle) comparing five- and seven-day dosing intervals of LAIO for treatment of ESGD and EGGD, the percentage of time gastric pH is > 4 did not tail off until around Day 5. Treatment with the LAIO IM every five days results in better outcomes than a seven-day interval: 89-93% healing occurred at five days compared to 38-63% healing at seven days. 

Rendle recommended other therapies beyond acid suppression: 

• Promote mucosal barrier function with sucralfate, misoprostol, pectin/lecithin, or corn oil. 
• Suppress inflammation with sucralfate, misoprostol, or glucocorticoids. 
• Modify gastric flora/fauna with probiotics, prebiotics, and judicious use of antimicrobials. 
• Surgical excision of nodular EGGD lesions, especially those resistant to medical treatment; this might not be a long-term solution. 

Researchers have studied the use of sucralfate combined with oral omeprazole. In a study of 204 sport and leisure horses medicated with 4 mg/kg oral omeprazole and 12 mg/kg sucralfate, healing occurred in 63%, and 81% improved by one or more grades. To date, there is no clinical data for using sucralfate with injectable omeprazole, but Rendle suggests it could avoid the potential negative impact on bioavailability and improve owner compliance for treatment. 

Misoprostol is licensed for refractory gastric disease in humans. As a prostaglandin E analogue, it increases mucosal blood flow, reduces pepsin and gastric acid production, directly inhibits parietal cells, enhances mucosal resistance to injury, and increases mucus-producing cells. Rendle said misoprostol is superior to combined omeprazole-­sucralfate for treatment of EGGD. In one study comparing different uses of misoprostol with an oral omeprazole and sucralfate combination, researchers found that misoprostol resulted in 73% healing compared to 22% of horses treated with omeprazole-sucralfate.  

Take-Home Message

In closing, Rendle provided the following takeaways about treating EGGD and ESGD:  

• Oral omeprazole monotherapy is not recommended for EGGD.
• Responses to esomeprazole appear superior to omeprazole, but this drug is not registered, and data are limited. 
• The best and most consistent responses occur with LAIO. 
• Risk of injection site reactions with LAIO is present but low. 
• A five-day dosing interval for LAIO produces better results than a ­seven-day interval.  
• Veterinarians should exercise caution regarding limitations of unregistered (compounded) medicines. 
• Misoprostol merits further ­investigation. 
• There is weak evidence for the use of sucralfate even when combined with oral omeprazole. 
• There is no evidence for antimicrobial use unless infection is present.
• Pectin/lecithin seems to prevent lesions from worsening. 
• Oil, acid buffers, and probiotics have marginal benefits.
• Select cases of EGGD might require corticosteroids or surgery.

Systemic Absorption and Endocrine Effects of Triamcinolone 

Many surveys and journal papers suggest the one-time use of corticosteroids does not induce laminitis. However, Kimberly Hallowell, DVM, DACVIM-LA, of North Carolina State University, believes this is not always the case. “Corticosteroid-­induced laminitis is not an acceptable complication of an
otherwise routine procedure,” she said.

Hallowell and colleagues aimed to determine if systemic absorption of triamcinolone (TA) varies between intrasynovial and extrasynovial injection sites and whether systemic absorption of TA impacts glucose, insulin, cortisol, and ACTH.

Twenty healthy horses that had received no corticosteroids in the previous six months each received 18 mg of TA. They were split into groups of 10, with one group receiving an intrasynovial injection in the radiocarpal joint and the other receiving an extrasynovial injection in the sacroiliac joint. Researchers collected blood samples repeatedly for 72 hours postinjection. Comparing the intrasynovial to the extrasynovial joints yielded interesting findings: 

• Both groups had significantly higher levels than baseline for all time points, and TA was still detectable at 72 hours. There was increased absorption of intrasynovial TA for 8-36 hours postinjection. Peak absorption was the same for both groups at 8 hours, with the intrasynovial injection reaching higher peak levels than the extrasynovial injection (1.61 vs. 0.7 ng/ml). 
• Glucose levels were not significantly different between either group. Yet, both had higher glucose levels over baseline from 1-72 hours postinjection. 
• Insulin showed a similar trend to glucose, with increases from 10-72 hours postinjection. Many horses had not returned to baseline by 72 hours.
  • During data evaluation, 11 horses had baseline insulin > 20 uU/mL. These were considered an “elevated baseline insulin” group. This group had higher elevations when they reached peak insulin following TA injection.
  • Nine horses had baseline insulin < 20 uU/ml, referred to as the “normal baseline insulin” group.
  • Following TA injection, the normal baseline insulin group measured 50-150 uU/ml peak insulin; the elevated baseline insulin group had widespread values, with one horse as high as 400 uU/ml. The normal baseline insulin group reached a peak insulin of 90 uU/ml, while the elevated baseline group peaked at 197 uU/ml.
• Cortisol was suppressed in both groups, especially from 4-72 hours postinjection. Many horses had no detectable cortisol levels on the assays.
• The ACTH suppression trend showed no significant differences between groups at any point. From 4-72 hours, ACTH levels decreased significantly for both groups. 

Hallowell reported that TA absorption from extrasynovial sites differs from intrasynovial sites. Plasma TA is higher in the intrasynovial group by 8-36 hours postinjection. The peak extrasynovial absorption (0.70 ng/mL) of TA is lower than intrasynovial absorption (1.61 ng/mL). Extrasynovial absorption is similar to but still higher than the effects of an IM injection, previously reported as 0.34 ng/mL. 

TA absorption has significant impacts on metabolic parameters:

• Hyperinsulinemia developed in all horses but was most severe in those with elevated baseline insulin levels.
• Three of 20 horses had sustained insulin > 208 uU/mL that led to histopathologic laminitis. This highlights the risk of corticosteroid-associated laminitis, especially in hyperinsulinemic horses.
• The study revealed sustained cortisol concentrations after one corticosteroid injection, plus decreases in ACTH. This poses a concern for hypothalamic-pituitary-adrenal axis suppression following repeated doses of steroids. 

In another presentation, Allen Page, DVM, PhD, of the University of Kentucky, compared the effects of intra-articular TA to APS, which is an autologous blood product. Researchers administered 9 mg of TA in a front fetlock to five metabolically normal horses aged 4-9 years. This was a three-way crossover design with identical 28-day treatment blocks. After 14 days of sampling, the horses had a 14-day stand-down period between the next treatment.

The results showed significant increases in glucose for up to 48 hours and insulin increases lasting seven days in some horses. Cortisol and resting ACTH showed significant suppression from the single dose of TA. None of these unfavorable effects were identified with APS treatment.

Take-Home Message

The risk of HAL increases as plasma insulin concentrations increase. This study demonstrates that TA elicits notable metabolic changes, and insulin increases even in horses with normal insulin levels prior to corticosteroid treatment. Page said it might become standard in the future to perform pretreatment testing with an oral sugar test and/or TRH test to monitor horses for insulin dysfunction prior to administering corticosteroid injections.

Respiratory Pathogens in Horse Show Stalls  

Nicola Pusterla, DVM, PhD, DACVIM of the University of California, Davis, School of Veterinary Medicine, described a method of evaluating subclinical shedding of respiratory pathogens in horse show stalls by pooling samples.   

Infectious disease outbreaks can occur because of subclinical shedding that a variety of parameters can affect: Demographics, season, and a horse’s vaccination status that might reduce severity of clinical signs to a subclinical infection that contributes to silent transmission. Young performance horses during winter and spring are expected to display the highest rate of subclinical shedding, said Pusterla. He estimates the rate of subclinical shedders to be as high as 4% depending on the horse population and the pathogen.   

A study he presented looked at determining the frequency of selected respiratory pathogens in environmental samples from sport horses attending a 15-week equestrian event from October 2022 to March 2023. Biosecurity protocols for horses at the event included vaccination against EHV-1, a health certificate for entry, daily rectal temperature monitoring, separation of febrile horses, and enhanced stall cleaning and disinfection.   

Samples were taken from 2,500 stalls in 39 barns, with 10 stalls per 3-by-1.5-inch 3-M sponge. Stalls were swabbed along the front corners, the inside of the stall door, and the inside grill. Samples were collected at Weeks 0, 8, 17, and 22 and tested with qPCR for selected respiratory pathogens, particularly EHV-1, EHV-4, EIV, ERBV, and S. equi. Because 20-60% of horses carry EHV-2 and S. zooepidemicus, these commensal pathogens serve as great markers for environmental buildup.   

The pooled samples showed a cumulative effect of positive tests over time. Ten percent tested positive the first week, 23% by Week 8, 48% at Week 17, and 58% by the end of the show. At least one respiratory pathogen was identified in 35% of 333 sponges.    

Of 464 swabs taken of individual stalls, 37% were positive for a pathogen: S. zooepidemicus 32%; EHV-2 12%; and EHV-4 and EHV-1 both 0.65%. In the first week, 6% of swabs were positive; 34% were positive by Week 8; 35% by Week 17; and 71% by Week 22. This demonstrates a similar cumulative effect to the results from the pooled samples.   

Pusterla’s ­observations included:  

• Pooled sponge sampling allows veterinarians to successfully detect respiratory pathogens in the environment.   
• EHV-2 and S. zooepidemicus were frequently detected from horse stalls with a cumulative effect over time. These are good markers of overall hygiene and pathogen buildup.   
• The low frequency (2.2%) and lack of clustering of true pathogens likely reflects an absence of active transmission. This might indicate the required steps the venue took to limit transmission were effective.   
• Pooling of samples with the sponges allowed monitoring of a large number of stalls with good agreement between pools and individual samples. Environmental monitoring saves time and money and might help contain an outbreak.  

It is often challenging to identify silent carriers of S. equi without scoping every horse. So, with an outbreak of sporadic cases, especially with silent carriers, instead of swabs and lavage, Pusterla recommends screening the environment and focusing on horses that test positive.  

He stressed that environmental monitoring is not a replacement for proper biosecurity! With high-risk populations, this pooled sample strategy helps determine what horses have shed over several days, especially as they spend 95% of their time stalled.

Related Reading

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• Impact of Bridle and Bit Fitting on Equine Performance
• Important Elements of Saddle Fit Veterinarians Should Know

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