Journal of animal science2003; 81(9); 2333-2342; doi: 10.2527/2003.8192333x

Obesity and diet affect glucose dynamics and insulin sensitivity in Thoroughbred geldings.

Abstract: Insulin resistance is considered a risk factor in obesity, laminitis, exertional rhabdomyolysis, and osteochondrosis. The objective was to use the minimal model to estimate glucose effectiveness (Sg) and insulin sensitivity (Si) in nonobese to obese horses initially adapted to forage only, then adapted to forage plus supplements rich in starch and sugar (SS) or fiber and fat (FF). Ten Thoroughbred geldings, with BCS of 5 (nonobese), 6 (moderately obese), and 7 to 8 (obese), were adapted to pasture and hay, allocated to two groups, and fed SS or FF in a switch-back design with 8 wk of adaptation. Modified frequent-sampling i.v. glucose tolerance tests were applied after adaptation to forage, SS, and FF. For the tolerance tests, horses were kept in stalls overnight and provided hay, and venous catheters were placed the next morning. Baseline samples were collected, 0.3 g of glucose/kg of BW was given i.v., and blood was sampled at 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16, and 19 min. At 20 min, 30 mU of insulin/kg of BW was given, followed by sampling at 22, 23, 24, 25, 27, 30, 35, 40, 50, 60, 70, 80, 90, 100, 120, 150, and 180 min. Plasma was analyzed for glucose and insulin, and Si, Sg, acute insulin response to glucose, and the disposition index were calculated. Normality was tested using the Shapiro-Wilk statistic. Body condition effects were analyzed using a mixed model with repeated measures. Diet effects were analyzed using a Wilcoxon signed rank test. The Sg was higher in obese than nonobese (P = 0.003) and moderately obese (P = 0.007) horses; Si was lower in obese than nonobese (P = 0.008) horses, and acute insulin response to glucose was higher in obese than nonobese (P = 0.039) horses. Effects of diet were likely confounded by body condition, but horses had lower Si (P = 0.066) when fed SS compared with FF, especially when nonobese. In conclusion, the minimal model effectively estimated Sg, Si, acute insulin response to glucose, and disposition index in horses. Obese geldings were insulin-resistant and seemed to rely primarily on Sg for glucose disposal. Feeding a diet rich in sugar and starch decreased insulin sensitivity of horses. Maintenance of body condition and avoidance of grain-based meals rich in sugar and starch would be beneficial to decrease the risk of developing insulin resistance and associated metabolic syndromes in horses, especially for horses at risk for these syndromes.
Publication Date: 2003-09-13 PubMed ID: 12968709DOI: 10.2527/2003.8192333xGoogle Scholar: Lookup
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  • Journal Article
  • Research Support
  • Non-U.S. Gov't


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The research article explores how obesity and diet, specifically those rich in starch and sugar or fiber and fat, influence glucose dynamics and insulin sensitivity in Thoroughbred geldings. It posits that obese geldings are insulin-resistant and a diet rich in sugar and starch lowers their insulin sensitivity while maintaining body condition and avoiding grain-based meals can decrease the risk of developing insulin resistance.

Objective and Design of the Study

  • The study aimed to use the minimal model to investigate the effect of diet and obesity on glucose effectiveness (Sg) and insulin sensitivity (Si) in horses.
  • Ten Thoroughbred geldings in non-obese to obese body conditions were put on a diet of either starch and sugar (SS) or fiber and fat (FF).
  • The study was carried out in a switch-back design with 8 weeks of adaptation to each diet.
  • Throughout the study, the horses underwent frequent sampling glucose tolerance tests.

Procedure and Analysis

  • The horses were kept in stalls overnight, provided with hay, and venous catheters were placed the next morning.
  • After collecting baseline samples, the horses were given a dose of glucose. Samples were taken frequently for the next few hours.
  • 20 minutes in, the horses were given a dose of insulin and subsequent samples were collected.
  • The collected plasma was analyzed for glucose and insulin concentration, and data was gathered for Si, Sg, acute insulin response, and the disposition index.
  • Different statistical tests including the Shapiro-Wilk test and a Wilcoxon signed rank test were used to analyze the data and identify any trends.

Results and Conclusion

  • The study found that Sg was higher in obese horses than in their non-obese counterparts, while Si was lower in the obese group.
  • Obese horses also showed a higher acute insulin response to glucose.
  • When it came to diet, the horses fed SS showed a lower Si compared to those fed FF, especially when the horses were non-obese.
  • Overall, the study concluded that obese geldings are insulin-resistant and their glucose disposal primarily relies on Sg.
  • Consuming a diet rich in sugar and starch worsened insulin sensitivity in the horses, suggesting that a steady body condition and avoiding such diets could decrease the risk of horses developing insulin resistance and related metabolic syndromes.

Cite This Article

Hoffman RM, Boston RC, Stefanovski D, Kronfeld DS, Harris PA. (2003). Obesity and diet affect glucose dynamics and insulin sensitivity in Thoroughbred geldings. J Anim Sci, 81(9), 2333-2342.


ISSN: 0021-8812
NlmUniqueID: 8003002
Country: United States
Language: English
Volume: 81
Issue: 9
Pages: 2333-2342

Researcher Affiliations

Hoffman, R M
  • Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061-0306, USA.
Boston, R C
    Stefanovski, D
      Kronfeld, D S
        Harris, P A

          MeSH Terms

          • Animal Feed
          • Animal Nutritional Physiological Phenomena
          • Animals
          • Blood Glucose / metabolism
          • Cross-Over Studies
          • Glucose / pharmacokinetics
          • Horse Diseases / blood
          • Horse Diseases / metabolism
          • Horses
          • Insulin / metabolism
          • Insulin Resistance
          • Male
          • Obesity / blood
          • Obesity / metabolism
          • Obesity / veterinary
          • Random Allocation
          • Statistics, Nonparametric


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