Seasonal changes in the combined glucose-insulin tolerance test in normal aged horses.

This study explored seasonal variations in the blood glucose and insulin response as observed in elderly horses, using a combined glucose-insulin tolerance test. The research found no significant seasonal impact on the test’s results.

Objective of the Study

• The primary aim of this research was to investigate any potential seasonal changes in the test results of the combined glucose-insulin tolerance test (a diagnostic procedure for Equine Metabolic Syndrome). This annual variation is important as horses with EMS are often more prone to laminitis – a painful and potentially crippling disease affecting horses’ hooves – during the spring and summer seasons, when endogenous insulin concentrations have been reported to increase.

Research Methodology

• The research involved nine healthy, aged horses with no prior history of laminitis or visible signs of EMS.
• Each horse was intravenously fed with dextrose (150 mg/kg) and insulin (0.1 U/kg). Following the administration, plasma glucose and serum insulin concentrations were repeatedly measured at specific time intervals.
• The test was performed repeatedly in different months: February, May, June, August, September, and November.
• The readings of glucose and insulin concentrations were compared across different months, with the help of a statistical technique called Repeated Measures ANOVA. This analysis aimed to identify any significant shifts in glucose and insulin levels brought about by seasonal variations.

Findings of the Study

• The findings revealed that the levels of glucose and insulin among the subjects remained significantly stable throughout the year, indicating no clear signs of insulin resistance.
• Coefficient variables such as mean area under the glucose concentration curve registered a significant dip in August and November in comparison to readings from February. In November, this was also observed as a reduction in comparison to June’s readings.
• The lowest glucose level (nadir) was found to be much lower in November as compared to February.

Conclusions

• The overall results presented no substantial seasonal variations in glucose-insulin tolerance, indicating that the effect of the seasons on this clinical test’s results is minimal.
• This finding suggested the combined glucose-insulin tolerance testing is reliable for year-round diagnosis of EMS in older horses, at least in the southeastern part of the United States, where this study was based.