Insulin and Glucose Responses to Feeding Glucose, Fructose and Inulin to Normal and Previously Laminitic Ponies
ACVIM 2010
K.E. Borer1; S.R. Bailey2; N.J. Menzies-Gow1; Y. Berhane1; P.A. Harris3; J. Elliott1
1Royal Veterinary College, London, UK; 2University of Melbourne, Australia; 3WALTHAM Centre for Pet Nutrition, Leics, UK
20099554
Ponies prone to laminitis (PLP) may be insulin resistant. Differences in serum [insulin] between PLP and normal ponies (NP) have been shown after inclusion of inulin in the diet at 3g/kg/day.1 The aim of this study was to assess the effect of feeding glucose, fructose and inulin on serum [glucose] and [insulin] in NP and PLP during the summer.
Six NP and 6 PLP randomly received glucose, fructose and inulin each at 1 g/kg/day once daily for 3 consecutive days, mixed with a commercial chaff-based feed whilst housed and fed ad-lib Timothy hay. Each carbohydrate was fed under 2 management conditions: after the ponies had been eating only grass for at least 7 days and again after eating only Timothy hay for at least 7 days. A wash-out period of at least 7 days was allowed between each carbohydrate feeding. Blood was collected over a 12 hour period following feeding on each day. Glucose was analysed by a commercial laboratory and insulin using a radioimmunoassay (Coat-A-Count, Siemens) previously validated in the authors’ laboratory. Responses of NP and PLP to each carbohydrate were compared using a 2-way ANOVA and changes over time using a 1-way ANOVA. Results are reported as mean ± SD and significance was set at p<0.05.
Following either of the preliminary basal diets (grass or hay), plasma [glucose] increased significantly to peak 2 hours after feeding glucose or fructose in both NP and PLP. Peak [glucose] after feeding glucose was 1.8-fold higher than baseline in PLP and 1.6-fold higher in NP. After feeding fructose, peak [glucose] was 1.2-1.3-fold higher than baseline in both NP and PLP. Minimal increases in plasma [glucose] occurred after feeding inulin at this dose.
After becoming accustomed to either grass or hay diets, serum [insulin] increased significantly above baseline after feeding glucose or fructose in both NP and PLP. Serum insulin responses after glucose feeding were significantly greater in PLP compared with NP, from 2 to 4 hours after feeding (days 2 and 3). Peak [insulin] after feeding glucose (2 hours after feeding; day 3) was 2.5 times higher in PLP compared to NP (425 ± 194µIU/ml vs. 167 ± 89µIU/ml). This represented an increase over baseline [insulin] of 33-fold and 15-fold in PLP and NP, respectively. The AUC for [insulin] was significantly greater in PLP vs. NP when feeding glucose after ponies had eaten only hay for 7 days previously (8616 ± 5230 vs. 3983 ± 3005). Serum [insulin] increased after feeding fructose, and was significantly higher in PLP vs. NP 2 hours after feeding. Peak [insulin] after feeding fructose (2 hours after feeding; day 3) was 1.7 times higher in PLP compared to NP (208 ± 151µIU/ml vs. 124 ± 110µIU/ml). This represented an increase over baseline [insulin] of 10-fold and 5-fold in PLP and NP, respectively. Minimal increases in serum [insulin] occurred after feeding inulin at this dose.
In conclusion, an insulin response after feeding glucose or fructose occurs in both NP and PLP, with exaggerated responses occurring in PLP. Differences in serum [insulin] after feeding 1g/kg/day glucose or fructose may distinguish between NP and PLP. Inulin fed at a low dose in this study had no significant effect on serum [insulin].
References
- Bailey et al.(2007) J Am Vet Med Assoc 231: 1365-1373.