Any successful weight loss program starts with reducing the number of calories consumed. And for an obese horse at high risk of laminitis, a regimen may involve not only a reduction in feed but stall confinement as well.

When food intake is restricted, ‘inedible’ bedding materials such as wood shavings are often recommended for stabled horses. The goal is to prevent them from ingesting straw—a risk factor for impaction colic. A study investigating weight loss (and weight loss resistance) in horses, yielded some interesting and unexpected results relating to whether and when horses eat bedding.

Led by Caroline McGregor-Argo, BVSc BSc(Hons) PhD DipECAR MRCVS, the team from Liverpool Veterinary School and Mars Horsecare monitored 12 healthy but overweight horses confined to stalls and bedded on pine wood shavings for 16 weeks. The horses were turned out for 30 minutes a day but not allowed to graze. The horses’ feed intake was also restricted. They received 1.25 percent of their body weight as dry matter in forage—significantly less than the 1.5 to 2 percent of body weight recommended for horses not needing weight management. Changes in their body weight and body condition were monitored throughout the study. In week 15 the time spent feeding was evaluated, and in the final week a 72-hour digestibility study was undertaken.

None of the horses developed major health problems during the study, nor did they display stereotypic behaviors. But an analysis of their manure yielded a surprise. Some of the horses were excreting significantly more energy and acid detergent fiber (ADF) than they were being fed.

A head-scratching result

To understand this head-scratching result, the researchers took a closer look at how the horses were managed. They found only one other potential source of energy and ADF: the wood shavings used to bed the stalls. Sure enough, a review of 24-hour recordings of the horses made during the study period confirmed that over half of the horses had “supplemented” their restricted diets by eating their bedding. In fact, three of the horses had consumed significant amounts of bedding. One had consumed as much as 1 kilogram (2.2 pounds) of wood shavings daily.  

Had these horses developed a taste for wood? Not likely. Instead, Argo attributes their bedding consumption to natural equine feeding patterns. Horses are “trickle feeders,” she says, normally spending as much as 60 percent of their time grazing during the day. By comparison, when the study horses were fed twice a day, they spent only about 29 percent of their day eating. Thus, their natural grazing instinct led them to consume the wood shavings.

How to discourage the behavior

Argo notes that none of the study horses became ill from ingesting wood shavings. But that doesn’t mean the behavior is without consequence. Over the long term, she says, the effects of ingesting bedding are unknown, so it’s wise to discourage the behavior. She advises using rubber mats to reduce the amount of bedding needed or eliminate it entirely.

In addition, the researchers advise considering other methods of safely increasing dietary forage while still reducing calorie intake.

References: Curtis GC, Barfoot CF, Dugdale AHA, Harris PA, Argo CMcG (2011) Voluntary ingestion of wood shavings by obese horses under dietary restriction. Br J Nutrition 106, S178–S182

Argo CMcG, Curtis GC , Grove-White D, Dugdale A, Barfoot CF, Harris PA (2012) Weight loss resistance; a further consideration for the nutritional management of obese Equidae. The Veterinary Journal 194 179–188