IN-DEPTH: ENDOCRINOLOGY IN GERIATRICS


sequently horse owners can be encouraged to moni- tor and record these monthly.


PPID Endocrine Monitoring


Endocrine monitoring should include both monitor- ing of PPID as well as monitoring for the risk of laminitis. Testing for endocrine disease in the middle-aged and older horse is covered in detail in a companion paper in this in-depth session, but mon- itoring is achieved by repeating the endocrine test- ing used for diagnosis. For example, if basal ACTH was used for diagnosis, this value can be used as the baseline ACTH for follow-up evaluation of response to treatment. The first follow-up for a horse start- ing treatment for PPID should be within 4–6 weeks.13,16 At this time, ACTH values should have decreased substantially (e.g., by at least 50%) or be within the normal reference range, bearing in mind the seasonal increase in ACTH from late sum- mer.22,23 Although clinical signs may take longer to respond, most owners will detect an improved, brighter demeanor of their horse within this first time frame.16 If clinical or endocrine improve- ments are not noted, increase the dose of pergolide by 0.001–0.002 mg/kg BW/day, to a maximum of 0.01 mg/kg. Each increment in dose should be monitored with follow-up assessments of clinical signs and endocrinological testing similarly (within 1–2 months) until the horse stabilizes. If clinical signs have stabilized for more than 3 months on a dose higher than 0.002 mg/kg/day pergolide, a de- crease of the pergolide dose by 0.001 mg/kg BW/day can be attempted, with the aim to reduce the dose back down to 0.002 mg/kg BW/day, bearing in mind that lower doses can result in treatment failure.13 Once a suitable dose has been determined, fol-


low-up monitoring can decrease to 1–2 times a year. Where twice-yearly monitoring is able to be per- formed, one of these follow-up tests should be timed to occur during September when there is peak ACTH and maximal sensitivity for diagnostic test- ing,23 bearing in mind the natural stimulation may push even a well-controlled horse a little outside of the seasonal reference range.


Monitoring for the Risk of Laminitis


In addition to monitoring PPID, it is also worthwhile to measure insulin dysregulation, either basally or dynamically, and this is imperative in horses with a prior history or current laminitis, including the presence of laminitic hoof changes. In horses with PPID, hyperinsulinemia is highly associated with laminitic lesions24 and laminitis.7 The presence of hyperinsulinemia is an important prognostic indica- tor for PPID survival overall,25 and the degree of insulin dysregulation provides a good indication of the risk of laminitis. Basal or dynamic (response to oral glucose or corn syrup) tests for hyperinsulin- emia are recommended.13,16 The timeframe for monitoring hyperinsulinemia can usually fit in with ACTH monitoring, but in some cases with poorly


190 2018  Vol. 64  AAEP PROCEEDINGS


controlled laminitis, yet well-controlled ACTH, it may need to be more frequent.


Management of the Insulin-Dysregulated PPID Horse (at Risk for Laminitis)


Insulin-dysregulated horses should be managed to reduce hyperinsulinemia, but care should be taken not to treat them exactly the same as horses with equine metabolic syndrome (EMS) without PPID. Prognosis is better in horses with controlled insulin dysregulation, even if this is unable to be completely normalized.25 However, some advanced cases of PPID with insulin dysregulation can prove difficult to manage, even in the face of normalization of ACTH concentrations. In these cases, manage- ment of the insulin dysregulation by using careful dietary control is advised.


Dietary Considerations


Tailored dietary restriction and exercise has been shown to improve insulin dysregulation in horses with EMS26 but can be less effective in horses with both PPID and insulin dysregulation.27 In one study, horses with both PPID and insulin dysregu- lation had a greater degree of insulin dysregulation and poorer response to dietary management than horses with insulin dysregulation only.27 Horses with PPID are already at risk for muscle atrophy, most likely as a result of muscle catabolism,28 so dietary consideration should focus on the insuline- mic response to feeds rather than on management of obesity and weight loss. In the author’s opinion, even in obese PPID-affected horses, weight loss should be carefully monitored and reductions of 0.25–0.5% BWT per week should be the maximum. Where persistent hyperinsulinemia exists, basally or dynamically, it is important to focus on the carbohydrate content of the diet, especially the non- structural carbohydrate content of the forage com- ponent, which often forms the bulk of the diet. Soaking hay is a good way to reduce water-soluble carbohydrate content of hay and produces dramatic reductions in the insulinemic responses to forage in both normal and insulin-dysregulated ponies (with- out PPID),29 but soaking also results in leaching of water-soluble minerals (especially sodium, chloride, potassium, calcium, phosphorus, magnesium, and sulfur),30 so careful attention to appropriate balanc- ing of the diet is recommended. Similarly, al- though protein is not lost by soaking hay,30 where horses are on a forage-only diet where protein con- tent can be marginal, careful attention to protein (especially high quality amino acid supplementa- tion) and vitamin and mineral supplementation is important to prevent and reverse muscle loss and atrophy.28 In horses with more marked weight loss or unable


to cope with long fiber, for example, due to dental disease, low-glycemic short fiber or complete rations can be purchased. Higher fat rations provide a


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