A major constraint for accurate estimation of body fat and diagnosis of obesity is the lack of a simple and reliable testing method. The widely used body condition score (BCS) is subjective, and other methods are costly. These researchers showed that increased plasma leptin (a peptide hormone synthesized and secreted primarily by adipose tissue) was associated with obesity in both research dogs and clinical cases. In humans and rodents, blood leptin is known to positively correlate with body fat. For this study, canine leptin was cloned to produce recombinant canine leptin in Escherichia coli, establishing a sandwich ELISA for canine leptin. After a highly positive correlation was found between body fat and leptin concentration in 20 female beagles of various body weights, 5 young male beagles (3 years old, 11.5 to 13.3 kg) were tested before and after experimental development of obesity. In addition, 59 clinical cases involving dogs of various breeds, ages, and sexes with a high BCS were studied. Results indicated that plasma leptin clearly reflects body fat (more than body weight) and is a good biochemical index of adiposity in dogs as in other species. Plasma leptin should be useful for quantitative obesity assessment in small animal practice. It is simple, reliable, and noninvasive compared with other methods, such as ultrasonography and the D2O dilution method.

COMMENTARY: At last, a hormone that might be used to assess adiposity in dogs; to evaluate the efficacy of weight reduction programs; and to alert clients to the presence of obesity, which could affect the lifespan of their dogs. 

Experimental and clinical studies on plasma leptin in obese dogs. Ishioka K, Soliman MM, Sagawa M, et al. J Vet Med Sci 64:349-353, 2002.