Effects of age and diet on glucose and insulin dynamics in the horse.

The study explores how age and diet influences the insulin sensitivity and glucose response in horses. The findings show that older horses have lower insulin sensitivity compared to the younger ones, regardless of their diet. Furthermore, diet types also have an impact on these responses, with diets rich in starch and sugar provoking greater insulin response and insulin sensitivity in older horses.

Objective of the Research

The purpose of the research was to understand how age and diet influence insulin sensitivity (SI) in horses. Traditionally, these factors haven’t been extensively studied in this context. Researchers wanted to measure the parameters during an insulin-modified frequently sampled intravenous glucose tolerance test (FSIGTT) after adapting the horses to different types of diets. This included a hay-only diet (HAY), a diet supplemented either with starch and sugar (SS), or a diet fortified with oil and fiber (FF). They also aimed to study the glucose and insulin responses after a standardised meal challenge (SMC) in both adult and aged mares.

Research Methodology

• A Latin square research design was used and involved eight adult mares (5-12 years) and nine aged mares (>19 years) which were all healthy.
• The different diets were provided for a duration of 6 weeks, with the FSIGTT and SMC tests carried out after 31-32 days and 41 days on each individual diet respectively.
• The collected data was analysed with a mixed ANOVA for repeated measures.

Research Findings

• The acute insulin response to glucose (AIRg) was found to be greater in aged horses, while SI was lesser, regardless of the diet.
• Both AIRg and SI increased in aged horses after adapting to a starch/sugar-rich diet compared to the hay diet.
• In adult horses, the same trends were observed after adapting to SS, although these weren’t statistically significant.
• The peak insulin concentration and area under the insulin vs. time curve during the SMC were greater in aged mares compared to adult mares, irrespective of the diet.
• The area under the glucose vs. time curve was lower after adapting to SS, compared to other diets, in both adult and aged horses.

Conclusion and Limitations

• During the initial stages of the study, there was transient weight loss and only female horses were included in the study.
• Incomplete ingestion of the Standardised Meal Challenge by four horses was considered a limitation.
• Despite the limitations, the study concluded that insulin responses to both intravenous and enteral nonstructural carbohydrate challenge increase with age in healthy horses, irrespective of the diet.