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Effect of dietary fructans and dexamethasone administration on the insulin response of ponies predisposed to laminitis

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  • 1 Departments of Veterinary Basic Sciences
  • | 2 Veterinary Clinical Sciences
  • | 3 Royal Veterinary College, London, NW1 0TU, England; Equine Studies Group, WALTHAM Centre for Pet Nutrition, Melton Mowbray, Leicestershire, LE14 4RT, England
  • | 4 Veterinary Clinical Sciences
  • | 5 Departments of Veterinary Basic Sciences
  • | 6 Departments of Veterinary Basic Sciences
  • | 7 Department of Clinical Studies, New Bolton Center, University of Pennsylvania, Kennett Square, PA 19348
  • | 8 Departments of Veterinary Basic Sciences

Abstract

Objective—To determine whether pasture, and specifically the addition of fructan carbohydrate to the diet, induces exaggerated changes in serum insulin concentration in laminitispredisposed (LP) ponies, compared with ponies with no history of the condition, and also to determine insulin responses to the dexamethasone suppression test.

Design—Prospective study.

Animals—10 LP and 11 control adult nonobese mixed-breed ponies.

Procedures—Insulin-modified IV glucose tolerance tests were performed (5 ponies/group). In diet studies, ponies were kept on pasture and then changed to a hay diet (10 ponies/group). Second, ponies were maintained on a basal hay diet (4 weeks) before being fed a hay diet supplemented with inulin (3 g/kg/d [1.4 g/lb/d]). Serum insulin and plasma glucose concentrations were analyzed before and after dietary changes. Serum cortisol and insulin concentrations were also measured in a standard dexamethasone suppression test.

Results—The LP ponies were insulin resistant (median insulin sensitivity of 0.27 × 104 L•min−1•mU−1 in LP ponies, compared with 0.64 × 104 L•min−1•mU−1 in control ponies). Median insulin concentration in LP ponies was significantly greater than that in control ponies at pasture, decreased in response to feeding hay, and was markedly increased (5.5fold) following the feeding of inulin with hay. The LP ponies had a greater increase in serum insulin concentration at 19 hours after dexamethasone administration (median, 222.9 mU/L), compared with control ponies (45.6 mU/L).

Conclusions and Clinical Relevance—Nonobese ponies predisposed to develop laminitis had compensated insulin resistance, and this phenotype was revealed by feeding plant fructan carbohydrate or by dexamethasone administration.

Abstract

Objective—To determine whether pasture, and specifically the addition of fructan carbohydrate to the diet, induces exaggerated changes in serum insulin concentration in laminitispredisposed (LP) ponies, compared with ponies with no history of the condition, and also to determine insulin responses to the dexamethasone suppression test.

Design—Prospective study.

Animals—10 LP and 11 control adult nonobese mixed-breed ponies.

Procedures—Insulin-modified IV glucose tolerance tests were performed (5 ponies/group). In diet studies, ponies were kept on pasture and then changed to a hay diet (10 ponies/group). Second, ponies were maintained on a basal hay diet (4 weeks) before being fed a hay diet supplemented with inulin (3 g/kg/d [1.4 g/lb/d]). Serum insulin and plasma glucose concentrations were analyzed before and after dietary changes. Serum cortisol and insulin concentrations were also measured in a standard dexamethasone suppression test.

Results—The LP ponies were insulin resistant (median insulin sensitivity of 0.27 × 104 L•min−1•mU−1 in LP ponies, compared with 0.64 × 104 L•min−1•mU−1 in control ponies). Median insulin concentration in LP ponies was significantly greater than that in control ponies at pasture, decreased in response to feeding hay, and was markedly increased (5.5fold) following the feeding of inulin with hay. The LP ponies had a greater increase in serum insulin concentration at 19 hours after dexamethasone administration (median, 222.9 mU/L), compared with control ponies (45.6 mU/L).

Conclusions and Clinical Relevance—Nonobese ponies predisposed to develop laminitis had compensated insulin resistance, and this phenotype was revealed by feeding plant fructan carbohydrate or by dexamethasone administration.

Contributor Notes

Dr. Bailey's present address is Faculty of Veterinary Science, University of Melbourne, Parkville, VIC 3010, Australia.

Supported by the WALTHAM Centre for Pet Nutrition.

Presented in part at the American College of Veterinary Internal Medicine Annual Congress, Louisville, June 2006.

Address correspondence to Dr. Bailey.