Unhealthy changes occur in the hearts of obese horses, fresh research has shown.
The study, reported this week in the journal Animals, showed that significant changes occur in the architecture of the heart muscle and blood vessels in obese horses.
The researchers believe their work is the first to analyze cardiovascular tissue in obese horses.
The draft horses used in the study had increased amounts of fat in and around the heart, with blood vessels showing evidence of increased thickening.
The visible structural changes were similar to those seen in overweight people, reported Natalia Siwinska and her fellow researchers in the veterinary school at the Wroclaw University of Environmental and Life Sciences.
The changes, they said, may be an indicator of subclinical dysfunction, which could lead to severe disease.
“Obesity is a global problem, not only in humans but also in companion animals, including horses,” the study team wrote.
“It is well known that obesity in horses is associated with an increased risk of laminitis, other orthopedic problems, reproductive disorders, and decreased exercise capacity.
“In humans, however, obesity is known to be of great importance in increasing the risk of cardiovascular disease and thereby increasing the death rate.”
The researchers set out to determine if microscopic changes occurred in the heart and vessels structure in obese horses.
Their findings were based on analysis of heart and artery specimens taken from 19 four-year-old draft slaughter horses. Twelve of the animals were assessed as extremely obese, while seven had normal body condition.
The study team reported that the hearts of the obese horses were surrounded by a more pronounced amount of pericardial fat, in contrast to the lean group, in which this fat was negligible.
In some obese horses, the infiltration of fat tissue into the heart muscle structure was clearly visible.
The heart tissue and great arteries showed more intense disturbances in their architecture when compared to the healthy group.
Changes seen in the diameter of arteries on the obese horses may have been due to the remodeling of the arterial walls and their gradual stiffening, as seen in obese people.
Several horses in the obese group also showed fibrosis – thickening or scarring of tissue. Its presence may indicate that normal tissue had been replaced by fibrous tissue after the death of heart cells.
The authors noted that the obesity seen in the horses, raised by two different breeders for the purpose of slaughter, was diet-related. The obese animals had been fed 14 to 18kg of cereal a day, plus a continual supply of hay. The leaner group had been fed with oats and hay at 7 to 9kg a day.
All horses had been kept in a free-range system with access to pasture.
The nature of the study meant that cardiac function was not assessed. “Extending the research to assess heart function in obese horses would be particularly interesting,” they said, noting that it might prove difficult because thick layers of fat can hinder the penetration of ultrasound waves.
The study, they said, was designed to test horses with the same body condition score – in this case, extremely obese horses with the highest index score of 9.
“It would be interesting to extend the study to less obese and also overweight animals in order to determine the exact correlation of this parameter with histological changes in cardiovascular tissue.”
In conclusion, they said the microscopic changes seen in the heart muscle and arteries were similar to those seen in overweight people.
“Microscopic changes in the heart tissue may be an indicator of subclinical cardiomyopathy, and changes in the vessels of the extremities — laminitis.”
The observed changes, they said, 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 life span.
The findings provide cause for deeper reflection on the effects of obesity on horses’ bodies and point to the need for prevention.
The direct effects of obesity on cardiovascular health and function require further exploration, they said.
The study team comprised Siwinska, Izabela Janus, Agnieszka Zak-Bochenek and Agnieszka Noszczyk-Nowak.
Siwinska, N.; Janus, I.; Zak-Bochenek, A.; Noszczyk-Nowak, A. Influence of Obesity on Histological Tissue Structure of the Cardiovascular System in Horses. Animals 2022, 12, 732. https://doi.org/10.3390/ani12060732