Diet key to insulin resistance in horses

New research on the pharmacological management of insulin-resistance in horses and ponies has suggested that diet (and exercise) are still key in any management plan.

Insulin resistance (IR) is regarded as a diminished ability of a given concentration of insulin to exert its normal effect on glucose dynamics in particular, causing the body to keep releasing more and more insulin in order to elicit an effect. This may be one of the most predictable factors that determines whether a horse or pony could be more susceptible to laminitis.

An important goal for owners and vets is to prevent IR from developing, or to manage it before it contributes in turn to the development/progression of other potentially life-threatening conditions. While the correct management of energy intake and exercise levels is thought to be essential, in some cases medication is also considered, especially when increased exercise is not possible. With no licensed drugs currently available for the treatment of IR in horses and ponies, off-label medications used for IR in humans are sometimes prescribed.

The trial was conducted by the School of Animal and Veterinary Sciences, Charles Sturt University in New South Wales, Australia and the Department of Clinical Studies, New Bolton Centre, University of Pennsylvania, PA, USA, in collaboration with the WALTHAM Equine Studies Group. Its intention was to confirm the positive effect of metformin on insulin and glucose dynamics in insulin-resistant ponies so that this treatment could be used as a positive control in other studies.

Six insulin resistant, non obese ponies were repeatedly monitored by means of a frequently-sampled intravenous glucose tolerance test (FSIGT). Metformin, a drug reported to enhance insulin sensitivity of peripheral tissues in humans without stimulating insulin secretion, was administered twice-daily (15mg/kg BW BID) to three of the ponies for 21 days, while the control group, comprising the remaining three ponies, received a placebo. After a wash out period the treatments were crossed over. An FSIGT was conducted to evaluate the level of insulin resistance before and after each treatment. Their body weight, body condition score and cresty neck score were also assessed and did not alter during this study.

No change in insulin sensitivity or glucose dynamics was seen under the control conditions or in response to the dose of metformin given in this study to these ponies.

Clare Barfoot RNutr and the research and development manager at SPILLERS® said: “Although clinical trials with metformin are ongoing, this trial was consistent with our previous work showing that the bioavailability of metformin in horses is poor, and chronic dosing at these levels may not achieve therapeutic blood concentrations.”

She continued: “On this basis it would seem that a fibre based diet, that is low in starch (found in cereals) as well as sugar and fructans (found in grass), in conjunction with regular exercise if possible, is still the safest and most effective way to manage insulin-resistant ponies. It is important to recognise that, even if other doses of metformin are shown to be beneficial in the future for certain sub-groups of animals, full consideration to diet and management should remain a key tactic.”