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


METHODS
Prospective study.


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


METHODS
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 x 10(4) L min(-1) mU(-1) in LP ponies, compared with 0.64 x 10(4) 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 (5.5-fold) 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
Nonobese ponies predisposed to develop laminitis had compensated insulin resistance, and this phenotype was revealed by feeding plant fructan carbohydrate or by dexamethasone administration.
Bailey
Simon R
SR
Department of Veterinary Basic Sciences, Royal Veterinary College, London, NW1 0TU, England.
Menzies-Gow
Nicola J
NJ
Harris
Patricia A
PA
Habershon-Butcher
Jocelyn L
JL
Crawford
Carol
C
Berhane
Yoel
Y
Boston
Raymond C
RC
Elliott
Jonathan
J
D000821:Animal Feed / Q000009:adverse effects*; D000822:Animal Husbandry / Q000379:methods; D000824:Animal Nutritional Physiological Phenomena / Q000502:physiology; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D003907:Dexamethasone / Q000008:administration & dosage; D005260:Female; D005534:Foot Diseases / Q000097:blood / Q000662:veterinary; D005630:Fructans / Q000008:administration & dosage* / Q000378:metabolism; D005951:Glucose Tolerance Test / Q000662:veterinary; D006724:Hoof and Claw / Q000473:pathology; D006734:Horse Diseases / Q000097:blood* / Q000209:etiology / Q000517:prevention & control; D006736:Horses; D007249:Inflammation / Q000097:blood / Q000209:etiology / Q000662:veterinary; D007328:Insulin / Q000097:blood*; D007333:Insulin Resistance; D007444:Inulin / Q000008:administration & dosage / Q000378:metabolism; D007794:Lameness, Animal / Q000097:blood / Q000209:etiology / Q000517:prevention & control; D008297:Male; D006109:Poaceae; D011446:Prospective Studies
D001786:Blood Glucose; D005630:Fructans; D007328:Insulin; D003907:Dexamethasone; D007444:Inulin