Inside look: Secrets of internal fat in horses revealed

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A pony showing generalised obesity.
A pony showing generalised obesity.

Researchers have developed an internal fat scoring system for horses, which will ultimately help improve understanding of the link between internal fat and conditions such as laminitis, insulin dysregulation and colic.

The “Equifat” system’s aim is to unlock the mysteries of equine internal fat stores and determine whether there is a link between Body Condition Score (BCS) and specific internal fat stores.

Post mortem image of the ventral abdominal wall of an obese pony (not the above pony).
Post mortem image of the ventral abdominal wall of an obese pony (not the above pony).

Fat tissue is the body’s largest endocrine (hormonal) organ and secretes numerous chemical messages to communicate with other organs in the body. In people CT imaging can be used to identify regional fat storage. Its distribution is known as ‘fat patterning’ and abdominal fat is now recognised as a risk factor for metabolic and cardiovascular disease. However, little is currently known about any health risks associated with specific areas of regional fat in horses. Previous work has shown that BCS is correlated with the total amount of body fat but until now it has not been possible to identify whether specific regional fat stores drive this correlation or whether all fat stores may be implicated.

While equine external fat is commonly assessed using body condition scoring, there isn’t a practical way to check for fat on the inside because the horse’s large size makes full body MRI or CT scans impractical. The new Equifat System aims to address this problem; the research project developed and used a five-point score to assess internal fat deposits in post mortem horses and to establish any links between Body Condition Score (BCS) and internal fat.

The study initially involved photographing the internal fat deposits in 38 horses and ponies at post mortem. All horses were euthanized for reasons unrelated to the study and not for research purposes. The photographs were ranked in order of least to most visual fat and then used to develop the five-point Equifat scoring system. To verify the reliability of the system the scores were checked twice by a group of observers.

To determine whether there is a link between BCS and internal abdominal fat stores a further 207 horses were body condition scored. The same horses were then scored using Equifat immediately after euthanasia.

The Equifat scoring system was developed from the ranking of anatomically defined depot-specific photographic images in order of increasing visually apparent adiposity.
The Equifat scoring system was developed from the ranking of anatomically defined depot-specific photographic images in order of increasing visually apparent adiposity. More detail on this is here.

The study demonstrated that Equifat was a reliable method for quantifying internal fat and showed a strong association between external regional fat deposits assessed via body condition scoring and internal abdominal (retroperitoneal) fat stores. It is hoped that future studies may discover more about the link between internal abdominal fat and disease risk through using this new method during surgical and post mortem evaluations.

Equine nutritionist Clare Barfoot, the research and development manager at Spillers, said the Equifat system had been shown to be a robust and reliable method of scoring internal fat.

“There was a strong positive association between BCS and the Equifat retroperitoneal (the fat that sits behind the membrane that surrounds various abdominal organs) fat score and a lesser association between BCS and omental fat (which is found under the muscles of the belly),” she said.

Rhia is classified as obese. Photo: World Horse Welfare
Rhia is classified as obese. © World Horse Welfare

“It is an exciting and important step that can be utilised in future studies to help us further understand the links between external and internal fat stores and their role in conditions such as colic, laminitis and insulin dysregulation and ultimately help to prevent them.”

The Equifat system is the result of a research collaboration between the University of Liverpool and equine feed company Spillers, and was developed and evaluated in collaboration with the Waltham Equine Studies Group, which Spillers uses to develop its feeds.

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