Objective: To evaluate the correlation between plasma alpha-melanocyte-stimulating hormone (alpha-MSH) concentration and body mass index (BMI) in healthy horses.
Animals: 82 healthy horses.
Procedure: Plasma alpha-MSH concentration was determined by radioimmunoassay. At the time blood samples were collected, body condition scores (BCS) were determined and measurements of girth circumference, body length, and height were obtained. Weight was estimated by use of the following formula: estimated weight (kg) = [girth (cm)2 x length (cm)]/11,877. Body mass index was calculated as estimated weight (kg)/height (m)2.
Results: A correlation was found between BMI and BCS (rs = 0.60 [95% confidence interval (CI), 0.44 to 0.731). A weak correlation was found between plasma alpha-MSH concentration and BMI (rs = 0.25 [95% CI, 0.03 to 0.45]) and BCS (rs = 0.26 [95% CI, 0.04 to 0.46]). A correlation was found between plasma alpha-MSH concentration and BMI in horses > or = 10 years old (rs = 0.49 [95% CI, 0.20 to 0.69]) but not in horses < 10 years old (rs = -0.04). Horses in the upper quartile of BMI had significantly greater plasma alpha-MSH concentration (median, 9.1 pmol/L; range, 2.0 to 95.3 pmol/L) than horses in the lowest quartile of BMI (median, 70 pmol/L; range, 3.6 to 15.7 pmol/L).
Conclusions and clinical relevance: A correlation exists between plasma alpha-MSH concentration and BMI in horses. Further study is required to determine whether melanocortin receptor defects underlie this correlation or, alternately, whether plasma alpha-MSH concentration is simply a correlate of adiposity.