It is well recognised that human obesity is linked with systemic inflammation and predisposes the individual to multiple diseases. However, it is unproven if obese equines also produce more inflammatory mediators and if there are breed specific differences. Researchers in Germany have therefore investigated if diet-induced obesity is associated with increased inflammatory signatures in adipose tissue (fat) of equines and if a breed predisposition exists between ponies and horses.
Nineteen healthy, non-overweight and metabolically healthy equines received a hypercaloric diet (200% of their recommended energy intake) for 2 years. Ten Shetland pony geldings (mean age ± SD 6 ± 3 years) and nine Warmblood horse geldings (mean age ± SD 10 ± 3 years) were included. All equines had a moderate body condition score (BCS ≤ 3 out of 5) without an increased cresty neck score (CNS ≤ 3 out of 5) at the start of the study. Equines with a previous history of metabolic disease were excluded. Body weight, body condition score and cresty neck score were assessed weekly throughout the study. At three time points, insulin sensitivity was determined by a combined glucose-insulin test. Adipose tissue samples were collected from two intra-abdominal and two subcutaneous depots under general anaesthesia at each time point after administering an inflammation trigger (endotoxin). Markers of inflammation were determined in the adipose tissue using the molecular technique quantitative PCR. The bodyweight and body condition score of all of the equids increased during the study. The expression of CD68 (a marker of macrophage infiltration) in adipose tissue increased with bodyweight gain. Expression of the pro-inflammatory cytokine mediators interleukin (IL)-6, IL-1β and tumour necrosis factor-α also increased after bodyweight gain and was higher in subcutaneous adipose tissue than abdominal adipose tissue. No breed related differences were found. The expression levels of markers of fat metabolism were higher in the adipose tissue of horses than in that of ponies.
The authors conclude that obesity in equids is associated with some signs of inflammation. The observed increased migration of macrophages into intra-abdominal adipose tissue as equids gain weight might predispose them to obesity-related conditions. The higher expression of markers of fat metabolism in horses may indicate a higher fat storage capacity than in ponies. These differences in fat storage might be associated with a higher susceptibility to obesity-related comorbidities in ponies in comparison to horses.
References
Blaue, D., Schedlbauer, C., Starzonek, J. et al. The influence of equine body weight gain on inflammatory cytokine expressions of adipose tissue in response to endotoxin challenge. Acta Vet Scand 62, 17 (2020).Available HERE