The sight of a foal frolicking in his pasture is likely to delight any horse owner, but it’s not just about having fun, according to researchers.
The importance of providing foals with the opportunity to play in order to ensure healthy bone development is highlighted in a just-published New Zealand scientific review.
Massey University researchers Chris Rogers and Keren Dittmer, writing in the open-access journal Animals, conclude that play behaviour in foals not only maps the immediate response of bone but provides the developmental framework for future response.
Bone is a dynamic tissue known to change both its shape and properties in response to strain or load.
“The increasing vigour and complexity of play as the foal matures reinforces the concept of cumulative adaptation and the necessity to provide appropriate stimuli early in life to capitalize on this cumulative compounding effect,” they say.
Modern foal-rearing systems need to provide appropriate opportunities for foals to spontaneously play to optimise bone development and reduce the risk of musculoskeletal injuries later in life, they suggest.
Scientific literature describing play under commercial equine rearing systems is relatively sparse, the pair note.
The need to play
Physical play is common in a wide range of species and appears innate in mammals.
Foals are capable of locomotor activity soon after birth, with spontaneous play seen early in life.
It has an obvious role in the development of locomotor skills in these fast-growing youngsters, capable of putting on more than 1.5 kilograms a day until weaning at around six months.
Even then, they are likely to continue to grow at about 0.7 kilograms a day until 14 months, when they will have achieved around 90% of their mature height.
According to Rogers and Dittmer, these progressive cumulative loading cycles seen in foals – bouts of locomotor play – in both the timing and magnitude, reflect the microstrain required to stimulate bone development.
The pair set out in their paper to explore the interaction between play and bone development in horses, from a molecular through to a whole-animal level.
They examined it through the mechanostat theorem, which assumes that, at a tissue level, bone attempts to keep localised strain within a certain physiological range.
Loads above this range result in bone changes to reduce the strain, while strain below this threshold results in remodelling to maintain the localised physiological range.
Indeed, other researchers, applying the mechanostat theorem, propose that horses used for competitive events that include movements outside the natural range on a frequent basis should be introduced to such exercise at an early age, when skeletal architecture could be influenced to adapt to the load.
“Based on published literature describing locomotor play in foals and the microstrain at different gaits in the horse, it was proposed that locomotor play in foals aligns with the mechanostat theorem in both the magnitude and frequency of load cycles applied,” Rogers and Dittmer write.
“The cumulative increases in the complexity and intensity of locomotor play as the foal develops, in turn, ensure the strain rates associated with play remain above the local physiological range and promote material and architectural changes in the distal (lower) limb bones.”
On this basis, spontaneous locomotor play may be vital to ensure optimal bone development in the horse.
The researchers, who cite 66 papers in their review, say there are hints within the existing literature that support the hypothesis that early exercise/play primes the musculoskeletal system.
For example, early work by a team at Utrecht University showed that restricted exercise – confinement to a stall – resulted in poorer cartilage development in the lower limbs than foals kept at pasture who were able to exercise freely.
“This ability to express natural play behaviour was not associated with gross changes in bone morphology but did reduce the prevalence of osteochondrosis lesions, demonstrating the subtle interaction of early exercise and tissue development.”
They conclude that available bone data, in conjunction with published material on other tissues – most notably cartilage – point toward play behaviour not only mapping the immediate response of bone in foals, but providing the developmental framework for future response.
“The increasing vigour and complexity of play as the foal matures reinforces the concept of cumulative adaptation and the necessity to provide appropriate stimuli early in life to capitalize on this cumulative compounding effect.”
Does Juvenile Play Programme the Equine Musculoskeletal System?
Chris W. Rogers and Keren E. Dittmer
Animals 2019, 9(9), 646; https://doi.org/10.3390/ani9090646