18 Aug 2026
Nicola Menzies-Gow MA, VetMB, PhD, DipECEIM, CertEM(IntMed),FHEA, FRCVS discusses the differing risk factors for each form of this common and painful condition of the horse foot
Nicola Menzies-Gow
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Laminitis is a common, painful condition of the equine foot that is now defined as a clinical syndrome associated with systemic disease (sepsis or systemic inflammatory response syndrome [SIRS] or endocrine disease) or altered weight bearing rather than being a discrete disease entity.
The three forms of laminitis are:
Several studies have investigated risk factors for sepsis-associated laminitis. In one study, laminitis developed in 28.4% of animals with duodenitis/proximal enteritis2. Increased risk of laminitis was associated with bodyweight (horses weighing more than 550kg were twice as likely to develop laminitis as those below 550kg), haemorrhagic reflux observed at admission and not receiving heparin as laminitis prophylaxis.
In another study that included all horses presenting to a single hospital across an eight-year period, only endotoxaemia was significantly associated with the development of acute laminitis3. In a study of horses with infectious colitis, 20% developed laminitis during hospitalisation. Horses with neorickettsiosis were more likely to develop laminitis than coronavirus cases and admission heart rate, total solids, band neutrophils and bicarbonate concentration were predictive of laminitis development4.
Finally, administration of low molecular weight heparin appeared to be effective in reducing the risk of laminitis following colic surgery5, while digital cryotherapy reduced the risk of laminitis in horses with colitis6.
Early studies that evaluated risk factors for laminitis did not necessarily distinguish the three types of laminitis, and the results related to signalment, height, bodyweight, health parameters, weather and seasonality were inconsistent7. It is now clear that HAL occurs in association with ID, which is a feature of all animals with EMS and a subset (25% to 50%) of animals with PPID. EMS is associated with an increased risk of laminitis and those animals with PPID that have ID are at the greatest risk of developing laminitis. Thus, the risk factors for HAL are the risk factors for ID/EMS/PPID.
Initial experimental studies suggested that a circulating insulin concentration of 200mIU/ml was the threshold above which laminitis was induced8. A cohort study determined that an increased risk of future laminitis was associated with basal serum insulin concentration greater than 21.6µIU/ml and plasma adiponectin lower than 2.5mg/ml 9.
A second cohort study determined the risk could be stratified according to basal serum insulin concentrations with low (lower than 21.6µIU/ml), medium (21.6µIU/ml to 45.2µIU/ml) and high-risk (greater than 45.2µIU/ml) categories that had estimated four-year laminitis incidences (95% confidence index) of 6% (2-9), 22% (10-33) and 69% (48-82) respectively10.
Animals could similarly be stratified according to their insulin response to an oral sugar test with low (lower than 53.4µIU/ml), medium (53.4µIU/ml to 153µIU/ml) and high-risk (greater to or equal to 153µIU/ml) categories that had estimated four-year laminitis incidences (95% confidence index) of 3% (0-6), 20% (10-29) and 73% (52-84) respectively. The risk could not be estimated from any owner-reported or physically apparent data11.
With respect to the development of ID in animals with EMS, evidence supports a role for genetics, epigenetics, obesity, diet, the gastrointestinal microbiome and endocrine-disrupting chemicals as risk factors. The development of ID in animals with PPID is postulated to be associated with the production of pars intermedia products that antagonise insulin, but their exact identity and the reasons why this only occurs in a subset of animals with PPID remains unclear. The main risk factor for PPID itself is increasing age12, and Morgan horses and ponies are thought to be at a higher risk13.
HAL appears to be triggered by the consumption of pasture, and it is likely that this is associated with the insulinaemic response to ingestion of non-structural carbohydrate (NSC). The NSC content of pasture is influenced by various weather factors including temperature, rainfall and sunshine. Thus, these are indirectly risk factors for HAL.
Corticosteroid-associated laminitis is also included within HAL. No evidence suggests corticosteroid administration is associated with laminitis in adult horses without underlying endocrine or severe systemic disease14. However, there is weak evidence of an association between administration of multiple doses of systemic corticosteroid and the onset of laminitis in adult horses/ponies with underlying endocrine disorders or severe systemic disease.
While overall the prevalence of supporting limb laminitis (SLL) is low (0.02% in a study at a large UK hospital)15,it is a relatively common complication in horses being treated for severe orthopaedic problems such as fractures and synovial sepsis. For example, 12% of horses that had a limb cast fitted across a nine-year period in one North American hospital developed SLL16. However, it has also been described as being associated with osteoarthritis and neurologic conditions that affect weight bearing.
Limited epidemiologic data is available for SLL, making risk factor identification difficult. Although severe and prolonged lameness is anecdotally considered to predispose horses to the development of SLL, only the duration of lameness17, duration of cast application and bodyweight16 have been identified as significant risk factors.
Other factors including age, breed, limb affected, heart rate and temperature at admission, clinicopathological test results, or whether a cast was applied, were not significantly associated with a greater risk. Thus, SLL can be difficult to predict, and some horses will develop SLL despite apparently mild lameness, and others with severe lameness for prolonged periods will not. Accurate prediction of SLL may require more sensitive and objective means of monitoring changes in limb weight-bearing patterns and/or perfusion than are currently available.
The risk factors for each form of laminitis are very different. Sepsis-associated laminitis risk factors include bodyweight above 550kg, haemorrhagic reflux observed at admission, heart rate, total solids, band neutrophils and bicarbonate concentration all at admission, endotoxemia and underlying disease.
Prophylactic heparin therapy and digital cryotherapy reduce the risk. HAL risk factors are the risk factors for EMS and PPID. Those for EMS include genetics, epigenetics, diet, and obesity, while the risk factors for PPID include increasing age.
HAL appears to be triggered by the consumption of pasture, and it is likely that this is associated with the insulinaemic response to ingestion of NSC.
The NSC content of pasture is influenced by various weather factors, including temperature, rainfall and sunshine. Thus, these are indirectly risk factors for HAL in animals with EMS and PPID. Corticosteroid-associated laminitis is also included within HAL, and an underlying endocrine disorder or severe systemic disease appear to be risk factors. Finally, supporting limb laminitis risk factors include the duration of lameness, duration of cast application and bodyweight.
Nicola Menzies-Gow qualified from the University of Cambridge in 1997 and, after three years in first opinion equine practice in Essex, joined the RVC, where she completed a residency in equine medicine and a PhD. Now a senior lecturer in equine medicine, Nicola’s clinical interests focus on endocrinology, cardiology and general medicine.