Editor's Note: This article is part of TheHorse.com's ongoing coverage of topics presented at the British Equine Veterinary Association's 51st annual Congress, held Sept. 12-15 in Birmingham, U.K.
Joint disease is well-recognized as one of the main causes of wastage in performance horses. This is mainly due to the fact that joint cartilage, once damaged, has an extremely low healing capacity, particularly in mature horses. In his study presented at the British Equine Veterinary Association's 51st annual Congress, held Sept. 12-15 in Birmingham, U.K., René van Weeren, DVM, PhD, Dipl. ECVS, from the University of Utrecht's Faculty of Veterinary Medicine, in the Netherlands, hypothesized that early exercise in young horses can help condition articular cartilage and prevent or delay future joint disorders.
His first explained that joint cartilage's low healing ability is in part due to collagen type II's (which forms the backbone of the cartilage's extracellular matrix) extremely long turnover time of 120-350 years. "These turnover times apply to mature individuals but obviously not to young, growing individuals in which there is an active process of continuous remodeling," van Weeren explained. "Therefore, one could suppose that if cartilage is to be conditioned (like muscular tissue or bone), this can only be achieved at a young age."
In van Weeren's study, he and colleagues evaluated 43 foals (starting at one week of age) that were separated into three groups: 24-hour stall rest; 24-hour pasture; and stalled with thirty minutes of gallop sprints per day. He noted that the pastured foals on average galloped at will for three and a half minutes a day, trotted for 30 seconds, and walked and slept the remainder of the time. The researchers then evaluated 24 foals' joint tissue upon euthanasia at five months, and the remaining 19 at 11 months.
Upon comparing tissue samples, van Weeren said the pastured horses and those in the stalled/sprinted group showed similar cartilage development and bone mineral density, whereas cartilage appeared not to have matured in the stalled foals. These changes were most evident between birth and five months, prompting van Weeren to suggest, "for collagen, there seems to be a limited window in time when the process of functional adaptation can take place."
Thus, said van Weeren, cartilage development appears to be partly exercise-driven, and a lack of exercise delays tissue maturation. "A well-balanced exercise program at a young age might improve tissue quality and injury resistance," he said. This raises the question of whether a combination of pasture exercise and additional exercise would result in even better conditioned cartilage.
To that end, van Weeren described a similar study described in 2008 by Rogers, et al., involving 32 Thoroughbred foals placed into one of two groups: 16 turned out on pasture without additional training and 16 on pasture with additional training (daily cantering several times round a 500-meter track, equal to a 30% increased workload). Twenty went on to have racing careers with no difference in injury rate between the groups or compared to other racehorses, and 12 were euthanized to evaluate their tissue. The researchers discovered a significant difference in the pastured and exercised foals' cartilage matrix, in that they were consistently more advanced in their development than the pasture-only foals.
"Specific training at a young age will advance normal maturation," van Weeren said. "There is increased evidence that this prevents joint disease later in life. Too little exercise might cause an irreparable delay in tissue maturation.
"Articular cartilage is responsive to biomechanical loading, and responsiveness is highest in the youngest individuals," he concluded. "The early juvenile period is the only opportunity to manipulate the collagen network."
Based on this information, he encouraged breeders and owners of young horses to consider not only housing their foals on full-time pasture, but also incorporating a controlled, mild exercise program into their daily routine to condition their joint cartilage and help prevent future injury.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.