IN-DEPTH: GERIATRIC MEDICINE/METABOLICS


weight gain is desired or for insulin-resistant horses that are in work. In these situations, the goal is to provide additional calories without exacerbating hy- perinsulinemia/insulinemic responses to feeding. One approach is to add nonmolassed sugar beet pulp to the ration, for example, 0.5 to 1.0 kg/d. Beet pulp is rich in highly digestible fibers, provides more DE when compared with most hay types, and does not elicit a marked glycemic or insulinemic response unless molasses is added at the time of processing. Beet pulp shreds should be soaked in a volume of water 3- to 4-fold higher than that of the beet pulp before feeding. The energy density of the ration also can be increased by feeding vegetable oil mixed with sugar beet pulp shreds or with hay cubes that have been softened in water. Corn and soy oils are commonly used in horse diets but must be fresh, nonrancid, and introduced gradually to the ration. One standard cup (approximately 225 mL or 210 g) of vegetable oil provides 1.7 Mcal of digestible en- ergy. Depending on energy requirements, one-half to 1 cup of oil can be fed once or twice daily (up to a maximum of 1 mL oil/kg BW). Smaller amounts (eg, one-fourth cup once daily) should initially be fed, with a gradual increase over a 7- to 10-day period. Stabilized rice bran (20% fat) is another option for increasing the energy density of the diet, provided that the calcium:phosphorus ratio of the final ration is considered. A number of commercial feeds are available that contain relatively low starch and sugar content (20–25% NSC, DM basis) and can be used to add calories to the diet of the lean EMS or PPID horse.


Pasture Access


Pasture access is another consideration in the management of the insulin-resistant, hyperinsu- linemic horse. In general, most affected horses can be allowed access to pasture after resolution of the most recent bout of laminitis, but some restric- tion of grass intake (ie, application of a grazing muzzle) is usually recommended, especially dur- ing periods when pasture forage NSC is likely to be high—during spring and early summer; after summer or fall rains that cause the grass to turn green; and when pastures have been subjected to drought or frost stress, all conditions that favor fructan accumulation.


Dietary Supplements


A number of supplements are marketed with claims for improved insulin sensitivity or reduced risk of laminitis, but evidence of efficacy is scant.32 Many products contain magnesium, chromium, and/or cin- namon. Chromium is thought to potentiate insulin action through activation of insulin receptor kinase and/or inhibition of insulin receptor tyrosine phos- phatase.33 However, the feeding of a supplement containing 5 mg/d chromium, 8.8 g/d magnesium, and other unspecified nutraceuticals for 16 weeks did not alter morphometric measurements, resting


314 2013  Vol. 59  AAEP PROCEEDINGS


serum glucose and insulin concentrations, or insulin sensitivity in obese horses with a history of lami- nitis.34 Daily supplementation with 45 g short- chain fructo-oligosaccharide (scFOS) for 6 weeks resulted in a modest improvement in insulin sen- sitivity and a decrease in resting serum insulin concentrations of obese Arabian horses fed a 50:50 grass hay and sweet feed diet.35 In EMS horses undergoing dietary restriction (1.25% of body weight as DMI); however, loss of body weight and improvement in insulin sensitivity were unaf- fected by the addition of scFOS to the diet.24 More work is needed to evaluate the effects of various nutraceutical supplements marketed for the management of EMS or PPID. Nonetheless, owners should be encouraged to focus on caloric restriction, forage NSC, and so forth rather than the feeding of supplements with unproven efficacy in the management of IR.


References


1. Brosnahan MM, Paradis MR. Demographic and clinical characteristics of geriatric horses: 467 cases (1989–1999). J Am Vet Med Assoc 2003;223:93–98.


2. Brosnahan MM, Paradis MR. Assessment of clinical char- acteristics, management practices and activities of geriatric horses. J Am Vet Med Assoc 2003;223:99–103.


3. National Animal Health Monitoring System. 2006. Equine 2005, Part II: Changes in the US Equine industry, 1998– 2005. USDA-APHIS-VS, Fort Collins, Colorado.


4. Ireland JL, Clegg PD, McGowan CM, et al. A cross sectional study of geriatric horses in the United Kingdom, part 1: demographics and management practices. Equine Vet J 2011;43:30–36.


5. Hotchkiss JW, Reid SWJ, Christley RM. A survey of horse owners in Great Britain regarding horses in their care, part 1: horse demographic characteristics and manage- ment. Equine Vet J 2007;39:294–300.


6. McFarlane D. Equine pituitary pars intermedia dysfunc- tion. Vet Clin North Am Equine Pract 2011;27:93–113.


7. Frank N, Geor RJ, Bailey SR, et al. Equine metabolic syn- drome. J Vet Int Med 2010;24:467–475.


8. Johnson PJ, Slight SH, Ganjam VK, et al. Glucocorticoids and laminitis in the horse. Vet Clin North Am Equine Pract 2002;18:219–236.


9. Donaldson MT, Jorgensen AJ, Beech J. Evaluation of sus- pected pituitary pars intermedia dysfunction in horses with laminitis. J Am Vet Med Assoc 2004;224:129–135.


10. McGowan CM, Frist R, Pfeiffer DU, et al. Serum insulin concentrations in horses with equine Cushing’s syndrome: response to a cortisol inhibitor and prognostic value. Equine Vet J 2004;36:295–298.


11. Ralston SL, Squires EL, Nockels CF. Digestion in the aged horse. J Equine Vet Sci 1989;9:203–205.


12. Ralston SL, Malinowski K, Christensen R. Digestion in aged horses: revisited. J Equine Vet Sci 2001;21:310– 311.


13. Anon. National Research Council Nutrient Requirements of Horses. 6th edition. Washington, DC: National Academy Press; 2007.


14. Ireland JL, Clegg PD, McGowan CM, et al. A cross sectional study of geriatric horses in the United Kingdom, part 2: health care and disease. Equine Vet J 2011;43:37–44.


15. Ralston SL, Nockels CF, Squires EL. Differences in diag- nostic test results and haematological data between young and aged horses. Am J Vet Res 1988;49:1387–1392.


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