outdoor grazing (michael nefdt)Outdoor grazing at Summerhill Stud
(Photo : Michael Nefdt)

Many people involved in the thoroughbred industry believe that it is better to stable a horse rather than to put a horse to pasture. Guests to Summerhill are often taken by surprise when we share with them the fact that, barring any medical problems, our mares and foals live outdoors 24/7. Our 2 year olds and horses in training also spend more time outdoors than do most in trainers’ yards.

Stacey Oak DVM, MSc writes for The Horse that if you think you are pampering and protecting your horse in his cushy, comfortable stall instead of turning him out on pasture, think again. Michigan State University researchers have found that stabled horses are exposed to eight times as much endotoxin in the air than their pastured counterparts. The result? These high endotoxin concentrations can play a role in airway inflammation in stabled horses, particularly those with Recurrent Airway Obstruction (RAO).

“In Northern climates, horses are often stabled and fed hay instead of being turned out on pasture. This common practice can actually be detrimental as it may impair the horse’s welfare and exercise performance due to a high exposure to airborne pathogenic-disease causing-and inflammatory materials,” explained study co-author Frederik Derksen, DVM , PhD, from Michigan State’s Pulmonary Laboratory in the Department of Large Animal Clinical Sciences.

Inflammation of a horse’s airway is known to be a risk factor for poor racing performance. Swiss investigators have shown that in show jumpers and dressage horses, inflamed airways are associated with lackluster performance. In horses diagnosed with Recurrent Airway Obstruction RAO, exposure to organic substances in stables and hay dust, such as endotoxin (likely from concentrated point sources such as manure) and fungal products, can be particularly concerning as they trigger an inflammatory response and airway obstruction.

To determine the difference in endotoxin concentrations in the breathing zone of stabled versus pastured horses, Frederik Derksen and colleagues selected six horses to participate in the study. Each horse was fashioned with a personal sampler and endotoxin concentrations in collected air samples were measured.

Endotoxin concentrations for stabled horses were 7.08 x 103 endotoxin units (EU)/m3 which were significantly higher than the 0.85 x 103 ERU/m3 measured for pastured horses. No correlation between endotoxin concentrations and ambient temperature or relative humidity was observed.

“These endotoxin concentrations are sufficiently high that horses exposed to these levels, particularly those with RAO, are likely to suffer from airway inflammation,” summarized Frederik Derksen. “Horses with airway inflammation likely don’t feel well and perform poorly. Therefore, airway health of horses matters to horses and their owners!”

The study, “Endotoxin concentrations within the breathing zone of horses are higher in stables than on pasture,” will be published in a forthcoming edition of The Veterinary Journal.