Equine veterinarians are all too familiar with the effects of obesity on the endocrine system and metabolic health. Educating clients about the hazards of obesity is a daily part of equine practice. A Polish study took a look at more specific effects on organ systems, such as how obesity might also affect the cardiovascular (c-v) system [Siwinska, N.; Janus, I.; Zak-Bochenek, A.; et al. Influence of Obesity on Histological Tissues of the Cardiovascular System in Horses, Animals 2022, 12, 732; doi.org/10.3390/ani12060732].
The study involved 19 four-year old draft horses. Seven of them with body condition scores (BCS) of 4-5 out of a Henneke scale of 9. The other 12 were extremely obese with BCS of 9 induced through excess feed over a 6-9-month period. Blood samples were collected prior to euthanasia, then the hearts with arteries were collected after euthanasia. Comprehensive measurements were made, including thickness and diameter of blood vessels. In addition, analysis was made of fiber degeneration and fiber architecture changes, fatty and fibrous infiltration in heart muscle, and thickening of blood vessel intima.
The researchers identified notable differences between lean and obese horses:
- Obese hearts were surrounded by pronounced pericardial fat compared to negligible fat in the lean horses. Excess pericardial fat secretes pro-inflammatory cytokines that can affect diastolic function.
- Obese hearts had infiltration of adipose tissue into cardiac muscle.
- Steatosis and fibrosis were observed in 9/12 obese horses and none in lean horses. Increased interstitial fibrosis might replace normal cardiac tissue following cardiomyocyte death.
- All obese horses experienced cardiomyocyte degeneration.
- The aortas of obese horses were affected by significant architectural changes. This has the potential to lead to aortic rupture.
- The intima of pulmonary, coronary and palmar arteries was thicker in obese horses. The palmar arteries provide blood to the distal limb and hoof, and so these changes might add to the risk of laminitis.
- AST and leptin were significantly higher in obese individuals. High leptin levels are associated with hypertension in humans. High AST levels are associated with fatty liver, hyper-lipidemia, insulin deregulation and reduced levels of antioxidants.
- Ghrelin, a hormone that stimulates appetite, increases food intake and promotes fat storage, was lower in obese horses. Ghrelin might be protective of the c-v system by lowering blood pressure and protecting against ischemic/reperfusion damage.
- All other blood chemistries were comparable between obese and lean horses.
While notable changes were observed in these extremely overweight equine individuals, some degree of cardiovascular changes might be observable in different levels of obesity.
The authors concluded: “Histological changes in obese equine heart muscle and arteries are similar to those observed in obese people. The observed changes may have a significant impact on the function of the cardiovascular system, causing not only a decrease in exercise capacity, but also, serious consequences that may shorten the animal’s lifespan.”