328
| hormone (a- MSH), corticotropin- like intermediate lobe pep-
tide (CLIP), beta- endorphin and other peptides (Durham, 2016 ; McFarlane, 2011 ). An in- depth review of PPID is outside the scope of this article but can be found elsewhere (McFarlane, 2011 ). Testing for PPID by measuring basal ACTH using seasonally adjusted ranges or ACTH response to exogenous thyrotropin- releasing hormone (TRH) is easily performed in practice (Durham et al., 2014 ). TRH can be difficult to source in some countries but is available in the USA, UK and Australia as an extemporaneous preparation. However, as ACTH can be elevated by stress, transport and severe pain, interpre- tation of results should consider these factors (Stewart et al., 2019 ). As a result, interpretation of ACTH values in a severely painful horse should be done with caution. Whether PPID and EMS are linked has not been determined, and
it may be that the two conditions simply occur concurrently in older animals without any causal association (McFarlane, 2011 ). However, studies suggest that hyperinsulinaemia occurs in approximately 30– 60% of PPID cases (Horn et al., 2019 ; McFarlane, 2011 ), and animals with concurrent PPID and hyperinsulinaemia are likely at a higher risk of developing laminitis (Johnson, 2016 ). Studies have also sug- gested that increases in alpha- MSH and CLIP can increase insulin secretion and severe cases of PPID might be more likely to have ID (Marshall et al., 1984 ; Obici et al., 2001 ). Recurrent episodes of lam- initis in older horses are often associated with failure to manage the PPID alongside persistent hyperinsulinaemia (Durham et al., 2014 ). Recent reports demonstrate that the changes in lamellar pathology observed in PPID (and EMS) are consistent with those induced ex- perimentally with infusion of insulin (Karikoski et al., 2015 , 2016 ). While the link between EMS and PPID remains unclear, hyper- insulinaemia should be investigated in all PPID cases (McFarlane et al., 2016 ). Concerted effort should be made to ensure both PPID and hyperinsulinaemia are well controlled to prevent unnecessary suffering from HAL (Durham et al., 2014 ; Walsh et al., 2009 ). A re- cent study demonstrated that performing a TRH stimulation test prior to the OST on the same day did not impact the OST results and this might offer a practical and convenient protocol for clinicians to diagnose both conditions in the field (Hodge et al., 2019 ).
MANAGEMENT OF HYPER INS ULI NAE MIA As discussed above,
SUNDRA ET AL.
might be one of the most important predictors of laminitis risk (Meier, de Laat, et al., 2018 ; Meier, Reiche, et al., 2018 ), and reducing post- prandial hyperinsulinaemia is therefore paramount in preventing HAL (Macon, Harris, Bailey, et al., 2022 ; Macon, Harris, Barker, & Adams, 2022 ). If the animal presents with suspected HAL, it is essen- tial that any feeds high in non- structural carbohydrates (e.g. grain, pasture, cereal hay) that have the potential to exacerbate the sever- ity of the current episode are immediately removed (Harris, 2023 ). Horses with EMS typically, but not always, exhibit generalised or regional adiposity and weight loss is a critical component in limiting hyperinsulinaemia (Rendle et al., 2018 ). Leptin and adiponectin are biologically active hormones (adipokines) produced in adipose tissue and are reported to play a role in the development of ID in obese horses (Caltabilota et al., 2010 ; Wooldridge et al., 2012 ). In obese horses with hyperinsulinaemia, weight loss should be
achieved by restricting energy intake and increasing energy expen- diture through exercise, although this can be severely limited in laminitic animals (Shepherd et al., 2021 ). Conjecture exists between the benefits and safety of abrupt versus gradual feed restriction (Dugdale et al., 2010 ; Hughes et al., 2004 ; Weyenberg et al., 2008 ), but target weight loss rates of between 0.5% and 1% of bodyweight per week have been suggested (Argo et al., 2015 ). Due to differences in genetic predisposition to EMS and obesity, there is a marked inter- horse variability in weight loss responsiveness to the same level of dietary restriction, and nutritional advice should be tailored to ac- count for forage quality and variability between individuals (Argo et al., 2012 ). Hay should form the bulk of the ration in horses with EMS, and
the management of hyperinsulinaemia re-
volves around dietary management, exercise and corrective farriery. However, pharmaceuticals to manage hyperinsulinaemia may be considered in severe cases or those that do not respond to tradi- tional management strategies.
Dietary management
Dietary modification is a critical component in the management of hyperinsulinaemia in horses with EMS (Durham et al., 2019 ). Studies in ponies with ID suggested that the insulin response to oral sugars
the nutrient composition of forage should ideally be determined prior to feeding (Harris et al., 2017 ). Hays with low (<10%) water- soluble carbohydrate (WSC) content is recommended to limit the in- sulin response (Durham et al., 2019 ). Practical recommendations for obese horses with EMS are to feed a low WSC (<10%) hay, at 1.5%– 2% bodyweight (on a dry matter basis), divided into small meals as well as a ration balancer to provide essential vitamins, minerals and amino acids (Rendle et al., 2018 ). To account for errors in estimation, the authors routinely advise owners to weigh their feeds and hay using commercially available luggage scales. It is the authors ' opinion that in horses presenting with obesity and active HAL, more aggres- sive weight loss programmes that limit feed intake to 1% body weight as dry matter should be considered to improve insulin sensitivity and hasten recovery from laminitis if weight loss is not achieved at feeding rates of 1.2%–1.5% bodyweight. A study demonstrated that limiting forage intake to 1% body weight as dry matter can result in weight loss of 1% bodyweight per week and rapidly decreased hyperinsulinaemia without the development of permanent undesir- able behaviours (Dugdale et al., 2010 ). Owners might raise concerns that restricting forage intake increases the risk of gastric disease, however, studies have indicated that the levels of feed restriction for weight loss and overnight fasting are not associated with the development of squamous gastric disease (Bruynsteen et al., 2015 ; Husted et al., 2009 ). However, the authors have observed the devel- opment of pica in some animals during forage restriction including
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88
