Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2025 May-Jun;39(3):e70089.
doi: 10.1111/jvim.70089.

The Seasonality of Serum Insulin Concentrations in Equids and the Association With Breed, Age, and Sex

Ana Lopes  1 , Laura Huber  2 , Andy E Durham  1
Affiliations

The Seasonality of Serum Insulin Concentrations in Equids and the Association With Breed, Age, and Sex

Ana Lopes et al. J Vet Intern Med. 2025 May-Jun.

Abstract

Background: Current laboratory reference values for serum insulin concentrations do not account for seasonal fluctuations and differences associated with breed, sex, and age.

Hypothesis: We hypothesized that serum insulin concentrations would differ with the season, breed, sex, and age.

Animals: Laboratory records from 21 236 cases.

Methods: Cases were included where basal serum insulin concentration (INS) or serum insulin concentration after administration of Karo light syrup (INSpk) was measured, along with plasma glucose, breed, age, and sex. Multivariate analysis was used to investigate a seasonal effect on serum insulin concentrations, alongside the effect of breed, age, and sex.

Results: Basal serum insulin concentration in winter was significantly higher than in the other seasons (p < 0.001). Serum insulin concentration following administration of Karo light syrup in winter was significantly higher than in summer and fall (p < 0.001). The breed effect was assessed in the 9 most prevalent breeds and the donkey. Shetland ponies had significantly higher INS and INSpk than all breeds except Welsh ponies(p < 0.01). Welsh ponies had significantly higher INS than all other breeds except Shetland ponies (p < 0.01). Welsh ponies had significantly higher INSpk than all breeds (all p < 0.001), except Arabians, New Forest ponies, and Shetland ponies. Females had significantly higher INS than males (p < 0.001) and there was a positive and significant association between age and INS (est = 0.02; SE = 0.002, p < 0.001).

Conclusions: Insulin concentrations are influenced by season, breed, age, and sex. This information is essential for better understanding and management of insulin dysregulation.

Keywords: endocrine; equine; laboratory samples; season.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflicts of interest.

Figures

FIGURE 1
FIGURE 1
Effect of season on INS (left panel) and INSpk (right panel). The central dot represents the estimated marginal mean, and error bars show the 95% confidence intervals. Seasons with different letters are significantly different (p < 0.05) according to Tukey's multiple pairwise comparisons, with Bonferroni corrections for multiple testing. INS: Serum insulin concentration; INSpk: Serum insulin concentration after administration of Karo light syrup.
FIGURE 2
FIGURE 2
Effect of breed on INS (left panel) and INSpk (right panel). The central dot represents the estimated marginal mean, and error bars show the 95% confidence intervals. Breeds with different letters are significantly different (p < 0.05) according to Tukey's multiple pairwise comparisons, with Bonferroni corrections for multiple testing. INS: Serum insulin concentration; INSpk: Serum insulin concentration following administration of Karo light syrup. Breed codes: 1. Arabians, 2. Cob, 3. Connemara, 4. Donkey, 5. Irish Sport Horse, 6. New Forest pony, 7. Shetland pony, 8. Thoroughbred, 9. Warmblood, 10. Welsh pony, 11. All other breeds. These figures represent all insulin concentrations without regard to seasons.
FIGURE 3
FIGURE 3
Effect of sex on INS. The central dot represents the estimated marginal mean, and error bars show the 95% confidence intervals. Sex with different letters is significantly different (p < 0.05) according to Tukey's posthoc comparison test. Females have significantly higher INS than males (p < 0.001). INS: Serum insulin concentration. This figure represents all insulin concentrations without regard to seasons.
FIGURE 4
FIGURE 4
Predicted effect of age on INS derived from a linear mixed effects regression model. The plot shows the predicted values of INS (y‐axis) across the range of age (x‐axis), with shaded regions representing 95% confidence intervals. Age is positively and statistically significantly associated with INS (est per year = 0.02; SE = 0.002, p < 0.001). INS: Serum insulin concentration. This figure represent all insulin concentrations without regard to seasons.
FIGURE 5
FIGURE 5
Predicted effect of GLU on INS derived from a linear mixed‐effects regression model. The plot shows the predicted values of INS (y‐axis) across the range of GLU (x‐axis), with shaded regions representing 95% confidence intervals. GLU is positively and statistically significantly associated with INS (est = 0.205; SE = 0.006, p < 0.001). INS: Serum insulin concentration; GLU: Blood glucose concentration.
See this image and copyright information in PMC

Similar articles

See all similar articles

References

    1. Frank N. and Tadros E. M., “Insulin Dysregulation,” Equine Veterinary Journal 46, no. 1 (2014): 103–112, 10.1111/evj.12169. - DOI - PubMed
    1. Asplin K. E., Sillence M. N., Pollitt C. C., and McGowan C. M., “Induction of Laminitis by Prolonged Hyperinsulinaemia in Clinically Normal Ponies,” Veterinary Journal 174, no. 3 (2007): 530–535, 10.1016/j.tvjl.2007.07.003. - DOI - PubMed
    1. de Laat M. A., McGowan C. M., Sillence M. N., and Pollitt C. C., “Equine Laminitis: Induced by 48 h Hyperinsulinaemia in Standardbred Horses,” Equine Veterinary Journal 42, no. 2 (2010): 129–135, 10.2746/042516409X475779. - DOI - PubMed
    1. Frank N., Bailey S., and Bertin F., Recommendations for the Diagnosis and Management of Equine Metabolic Syndrome (EMS) (Equine Endocrinology Group, 2022), https://equineendocrinologygroup.org/.
    1. Beythien E., Wulf M., Ille N., Aurich J., and Aurich C., “Effects of Sex, Pregnancy and Season on Insulin Secretion and Carbohydrate Metabolism in Horses,” Animal Reproduction Science 184 (2017): 86–93, 10.1016/j.anireprosci.2017.07.002. - DOI - PubMed

LinkOut - more resources