BACKGROUND: Insulin-like growth factor 1 (IGF-1) has important roles in anabolic processes in the musculoskeletal system and has been reported to decrease with age in both people and horses.

OBJECTIVES: The objective of this study was to determine serum IGF-1 levels in the aging horse from early to late adulthood (age range 5-27 years).

METHODS: Healthy horses (n = 72) were used in a cross-sectional study, while 37 paired serum samples were available for a longitudinal study. Serum IGF-1 protein was determined using an ELISA kit validated for use in equine samples.

RESULTS: No association was found between serum IGF-1 levels and age in the cross-sectional study. In the longitudinal study, a latent variable model fitted to the data revealed that horses in general experienced a 5.2% increase of serum IGF-1 levels over a 5-year period, but horses crossing a change point around 9 years of age between the 2 samples experienced an 11.0% decrease.

CONCLUSIONS: In this study, there was no evidence for aging being a factor in changes of IGF-1 levels in an adult and old horse population.