Depending on what study you read, laminitis prevalence in horse populations ranges anywhere from 1.5% to 34%. One of the most frequently cited prevalence estimates, from a study of horses in Great Britain, is 7%. But which figure is correct? Claire Wylie, PhD, MSc, BVM&S, a veterinary epidemiologist at Rossdales Equine Hospital, in Newmarket, England, believes none of them are. So she recently set out to determine a more accurate rate of occurrence, and also to develop a clinical recording system to help veterinarians diagnose laminitis. She presented her findings at the 2013 International Equine Conference on Laminitis and Diseases of the Foot, held Nov. 1-3 in West Palm Beach, Fla.
In the first part of her three-segment study, funded by World Horse Welfare, Wylie and colleagues recruited 28 equine veterinary practices in Scotland, Wales, and England to fill out a reporting form for every lameness case they received from February to April 2009 and January 2010 to May 2011. Based on the responses, these veterinarians diagnosed 37 cases (15.5%) as laminitis and 201 (84.5%) as another form of lameness. In comparing clinical signs between laminitis and nonlaminitis cases, the team determined they were extremely variable, with no one sign present in every case.
In the second part of the study, Wylie's team sent the same practices a form to complete that would help the researchers calculate laminitis prevalence. They determined the prevalence was approximately 0.5%, meaning 1 in every 200 horses evaluated had active episodes of laminitis. They documented the highest prevalence in the months of January and June, which Wylie noted was interesting because it indicates laminitis is not just a springtime, pasture-associated disease.
Other observations the team made about these cases included:
- Laminitis occurred in all limbs;
- Laminitis developed in the forelimbs bilaterally (both limbs) most frequently (55.5%);
- Laminitis was most severe in the forelimbs; and
- Common clinical signs included an increased digital pulse, difficulty turning, and a short gait at the walk.
Courtesy Claire Wylie, PhD, MSc, BVM&S
In the final segment, the researchers conducted an epidemiological case study of laminitis risk factors. They sent the owners of horses evaluated at the clinics in the previous two parts of the study a 16-page, checkbox-type questionnaire comprised of questions based on findings in previous published studies. They received 764 usable responses divided into 105 cases and 659 controls. From these, they determined that:
- The taller the horse, the less likely he was to develop laminitis;
- Horses that gained weight in the three-month period prior to a laminitis episode were 4.2 times more likely to develop laminitis than those that did not gain weight;
- Horses were 4.1 times more likely to founder in summer and 3.6 times more likely to founder in winter compared to springtime;
- Horses with a history of laminitis were 4 times more likely to develop it again;
- Horses that were lame/sore after hoof trimming were 3.8 times more likely to develop laminitis;
- Horses with existing endocrinopathic disease (e.g., Cushing's disease, equine metabolic syndrome) were 19.6 times more likely to also develop laminitis;
- Horses that had only had access to pasture grass for four weeks or less were 4 times more likely to founder;
- Horses on stall rest were 2.8 times more likely to founder;
- Horses that had been transported in the previous week were 0.2 times less likely to founder;
- Horses receiving nutritional supplements were 0.5 times less likely to founder; and
- Most interestingly, said Wylie, was that compared to horses dewormed every one to six months, horses that had been dewormed in the past four weeks had a reduced risk of laminitis; horses that had not been dewormed in the past six months to a year were 2.5 times more likely to founder; and horses that had not been dewormed in over a year or never were 11.3 times more likely to founder. "We don't know why this is," Wylie said, "but it could be due to many things, such as a novel effect of anthelmintic drugs, an association between laminitis and gut function, or maybe it indicates better-cared-for horses (are less likely to develop laminitis)."
From these results, Wylie suggested that "endocrinopathic laminitis might be responsible for most cases. Smaller animals, those with increased body weight, and those with endocrine disease should be managed most closely." She also encouraged owners to be vigilant for laminitis year round, as their study results indicated this is not just a springtime disease.
In conclusion, Wylie cautioned owners and veterinarians to take care when interpreting these findings. "This study identified a number of novel risk factors for veterinary-diagnosed equine laminitis, including management-level factors which have not previously been studied in detail, which prioritize areas for further research," she said. "Further exploration and elucidation of these factors may lead to the future implementation of preventive measures to decrease the frequency of equine laminitis, providing a significant improvement to the welfare of animals."
Research is ongoing.
The study "Risk factors for equine laminitis: A case-control study conducted in veterinary-registered horses and ponies in Great Britain between 2009 and 2011" was published in the September 2013 issue of The Veterinary Journal and "A cohort study of equine laminitis in Great Britain 2009–2011: Estimation of disease frequency and description of clinical signs in 577 cases" was published in the November 2013 issue of Equine Veterinary Journal.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.