Weight gain and obesity in horses should be avoided to prevent insulin resistance, increased insulin and leptin blood levels, and laminitis, and to maintain a healthy metabolic state.

To date, "it is unknown whether obesity is the primary cause of or contributes to metabolic abnormalities or whether these abnormalities are inherent characteristics of the animal," wrote a group of researchers from the Virginia-Maryland Regional College of Veterinary Medicine. The research team, which included authorities in the fields of equine nutrition and metabolic disorders, hypothesized that diet-induced weight gain in horses would decrease insulin sensitivity and increase blood levels of various hormones and fatty acids.

To test this hypothesis, they fed 13 Arabian or Arabian-cross geldings, ranging in age from 8 to 20 years, 200% of their maintenance energy requirements for 16 weeks. Horses gained an average of 86 kg and body condition scores increased from 6 to 8 (out of 9)