Obesity in horses increases risk of disease

Obesity in horses increases risk of disease Obesity in horses and ponies is becoming a widespread. It is associated with increased risk of disease - in particular insulin resistance and laminitis. It is helpful to evaluate the amount of fat in the body ("adiposity"), both to assess the extent of the problem and to monitor the response to dietary and management changes. In humans, accumulation of fat in the abdomen is associated with a higher risk of diabetes and cardiovascular disease. If the fat is more widely distributed it tends to cause fewer problems. Similarly in horses and ponies, it is the accumulation of fat depots in the abdomen and crest that is of more concern than a generalised obesity.

Morphometrics such as Body Mass Index (BMI) are used in humans as a measure of overall adiposity. Central or abdominal fat deposition is assessed by the ratio of waist to hip measurements.

What measures are available for assessing the amount of fat in the horse's body?

Body condition score (BCS) is well established as a means of assessing the overall adiposity in horses and ponies. But what about regional adiposity? How can we measure the accumulation of fat that is seen in horses with cresty necks?

Rebecca Carter and fellow workers at Virginia Tech and the Middleburg Agricultural Research and Extension Center have developed a system for assessing accumulation of fat in the crest.

Their "Cresty Neck Score" (CNS) assigns a score on a scale from 0 to 5. Grade 0 indicates that no crest is palpable or visible. Grade 5 indicates that the crest is so large that it permanently falls to one side.

They also identified morphometric measurements that were closely correlated to body condition score and cresty neck score. Such measurements provide a more objective approach, and have the advantage of being easier for people without specialist training to determine.

They found that the ratio of girth : height was strongly correlated with body condition score.

Crest height (measured midway down the neck from the dorsal midline of the neck to the junction of the crest and the neck muscle) or the ratio of neck circumference at mid-neck (NC): height were suitable morphometrics for assessing neck adiposity. Both showed a strong correlation with CNS.

The researchers found that the relationship of the various morphometrics with the BCS, CNS and blood parameters differed between horses and ponies. So values for horses and ponies need to be interpreted differently.

For example, a horse with a body condition score of 7/9 or more was no more likely to have raised blood insulin levels than a horse of moderate BCS. A pony with BCS or 7/9 or more was nearly 10 times more likely to be hyperinsulinemic than a pony of moderate BCS.

A pony with a cresty neck was 19 times more likely to be hyperinsulinemic than a pony with a moderate neck. Horses with cresty necks were not significantly more likely to have raised insulin levels.

But that doesn't mean that if you have a horse, you don't need to worry about it getting hyperinsulinemia from being overweight, explains Dr Carter. "There was a higher percentage of hyperinsulinemic horses when they were overweight or cresty compared to normal, but for some reason the statistics didn't work out to be significant for the odds ratios."

She suggests that different girth:height or NC:height cutoff values need to be used to indicate overweight/cresty in horses compared with ponies.

She concludes that the CNS allows a more standardised assessment of neck adiposity, as does BCS for overall adiposity. Objective alternatives are provided by the ratio of girth : height for overall adiposity, and NC : height for regional (crest) adiposity.

For more details see:

Apparent adiposity assessed by standardised scoring systems and morphometric measurements in horses and ponies.
RA Carter, RJ Geor, WB Staniar, TA Cubitt, PA Harris.
Vet J (2009) 204 - 210

Reproduced with kind permission of Mark Andrews BVM&S CertEP MRCVS
© Copyright Mark Andrews  - Equine Science Update 2009

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