MANAGEMENT OF HYPERINSULINAEMIA
the ingestion of sand or gravel and horses should be monitored closely to identify and prevent unwanted behaviours. Feeding of soaked hay has been demonstrated to reduce the gly-
caemic and insulinaemic response in both ID and normal ponies and might be a useful strategy to implement, especially if the nutritional analysis is unavailable (Carslake et al., 2018 ; Müller et al., 2016 ). It is important to note that the temperature of the water, the soak time and the volume of water used for soaking will impact the amount of sugars leeched from the hay (Argo et al., 2015 ; Longland et al., 2014 ; Müller et al., 2016 ). One study demonstrated that soaking hay at ambient temperature for 7–16 h decreased WSC and other nutrients by 24%–43% and was associated with more than double the loss of body weight compared with feeding the equiv- alent amount of dry hay (Argo et al., 2015 ). Concerns over micro- bial growth have been raised during long soaks with warm water (Moore- Colyer et al., 2014 ) and laboratory studies advocating the use of shorter soaks with larger volumes of water might be a suit- able alternative to reduce levels of microbial contamination while still reducing WSC levels (Argo et al., 2015 ; Longland et al., 2014 ; Watts, 2004 ). The authors typically recommend soaking hay in tap water for 6–8 h prior to feeding, while also advising owners that this may not reliably lower the NSC to below 10%. Soaking also reduces the dry matter and mineral content of hay (Longland et al., 2011 , 2014 ; Moore- Colyer et al., 2014 ) and a low- calorie ra- tion balancer should always be included in the diet of these animals (Rendle et al., 2018 ). The addition of straw might be a suitable alter- native (Dosi et al., 2020 ) in situations where low WSC hay cannot be sourced or soaking is not practical. A study performed in the UK with native breeds of ponies demonstrated that feeding a 50:50 mixture of hay and straw was safe and effective at inducing weight loss (Dosi et al., 2020 ). Strategies to motivate owners to combat obesity are outside the scope of this review but are discussed in more detail elsewhere (Furtado, 2023 ). Horses exhibiting the lean EMS phenotype are, in the authors '
opinion, oftentimes the most difficult cases to manage as a balance needs to be struck between weight gain or maintenance without elic- iting an exaggerated post- prandial insulin response. Specific dietary protocols for lean EMS animals have not been established, but the provision of extra calories in the form of oils and highly digestible fi- bres (e.g. unmolassed beet pulp) has been recommended to maintain body weight without exacerbating hyperinsulinaemia (Harris, 2023 ). In these lean EMS types, dietary strategies alone may not be suf- ficient to limit hyperinsulinaemia, and judicious use of medications carefully balanced against calorie intake may need to be considered to prevent the development of HAL. Pasture high in non- structural carbohydrates has been shown
to exacerbate hyperinsulinaemia in ponies and strategies to restrict pasture intake should be implemented in animals with ID (Treiber et al., 2006 ). Horses with HAL should be removed from pasture im- mediately; but long- term management of horses with hyperinsuli- naemia may include some grazing, as long as the ID is under control (Durham et al., 2019 ). Access to pasture is desirable as it allows the expression of normal horse behaviour, but it is important to note
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that pasture intake is very difficult to estimate (Rendle et al., 2018 ). Grazing in the early hours of the morning when the sugar content of grasses is at its lowest and removal from pasture by mid- morning has been recommended previously (Geor, 2009 ). However, stress fac- tors such as frost, application of herbicides and low soil fertility re- strict pasture growth resulting in the accumulation of sugars within plants (Geor, 2009 ). Gradual introduction to pasture is advised but restricting access has been shown to increase intake over a short timeframe (Ince et al., 2011 ). When first re- introducing the horse to pasture, it is recommended that insulin concentrations are mea- sured after 1–2 h of grazing in order to determine the insulinaemic response to grass (EEG, 2022 ). Alternative grazing systems such as tracks or turnout into scrub
or woodland could be implemented to reduce pasture intake, with recent studies demonstrating that owners are motivated to invest in these systems to promote weight loss as they associate a posi- tive welfare benefit with their use (Cameron et al., 2021 ; Furtado et al., 2022 ). However, in these systems, forage (either on the ground or as browse) is generally freely available and weight loss is unlikely. Grazing muzzles can also be utilised to reduce pasture intake and may limit dry matter intake between 30% and 80%, but their ef- fectiveness varies between design and horses (Glunk et al., 2014 ; Longland et al., 2016a , 2016b ). Owner guides and videos on the proper use of grazing muzzles can be found on the National Equine Welfare Council website: https:// newc. co. uk/ advice_ artic les/ healt hy- weigh t- bcs- alter nativ e- grazi ng- syste ms/ . Regardless of the dietary strategy implemented,
the post-
prandial insulin response to diet and pasture is variable between horses and measuring pre- and 60–90- min post- ingestion (Macon, Harris, Bailey, et al., 2022 ; Macon, Harris, Barker, & Adams, 2022 ) or post- grazing insulin is advisable to determine the individu- al ' s response to their current feed. This will inform future dietary recommendations.
Exercise
Exercise is an effective interventional strategy to improve insu- lin sensitivity in people with diabetes and is recommended for horses with EMS who are not showing signs of lameness (Durham et al., 2019 ; Kumar et al., 2019 ). A recent study demonstrated that regular, low- intensity exercise combined with dietary modification improved insulin sensitivity and decreased serum amyloid A in obese ponies compared to dietary restriction alone (Bamford et al., 2019 ). Previous studies have yielded conflicting results on the effects of exercise on insulin dynamics (Carter et al., 2010 ; de Laat, Hampson, et
al., 2016 ; de Laat, McGree, & Sillence, 2016 ; Schmengler
et al., 2013 ; Stewart- Hunt et al., 2006 ). It is imperative that when ex- ercise programmes commence, the intensity is gradually increased, and horses with a history of HAL are closely monitored for evidence of lameness (Durham et al., 2019 ). There is little evidence upon which to base recommendations, however, a 2019 consensus docu- ment (Durham et al., 2019 ) advised:
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