Serum insulin-like growth factor 1 in the aging horse

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.