What do horses and astronauts have
in common? Early in the space program astronauts were found to have significant
loss of musculoskeletal strength and other health issues after spending time in
space. Horses kept in confinement for extended periods have been found to have
similar problems, with losses in bone strength, joint health and reduced
function in other organ systems. Both horse and human bodies were designed for
movement, and anything that limits activity can have a negative impact on
strength and overall health.
Wild or feral horses routinely
travel 3 to 10 miles per day to graze. Herds of horses also participate in
group activities of mock fighting chasing, bucking and rolling. They spend the
majority of the day in motion. This is in stark contrast to the activities of
many stabled horses. Horses kept in stalls may stand around for 23 hours a day,
with possibly one hour of riding or turnout. Because this is not what horses were
designed to do, inactivity can have a negative effect on their physical and
mental soundness.
Bone is a living tissue that must
be “stressed” by movement and concussive forces to maintain strength. When
gravity and activity are lacking, significant losses in musculoskeletal strength
occur quickly and cannot be overcome by nutritional supplements. Researchers at
Michigan State University have conducted investigations into the effects of
confinement on bone mineralization in horses. Stalled horses, from weanlings to
mature horses, were reported to have a lower bone mineral content (BMC) than
their pastured counterparts as early as 28 days into the study. Weanlings housed in stalls had lower BMC and
smaller cannon circumference at 28 days than weanlings maintained in pasture
full time and those pastured for 12 hours and stalled for 12 hours a day. Horses
pastured 12 hours a day had similar measurements to those pastured full time. After
28 days of total confinement in stalls, weanlings began to show increased
activity, rearing, bucking and running around in small circles in their stalls.
Interestingly, that level of activity resulted in increased BMC measures by day
56 of the study.
Highly conditioned horses at
Virginia Polytechnic Institute and State University were kept stalled for 12
weeks and walked on a mechanical walker for two 30-minute sessions every day. Bone
mineral content began to decline at 3 weeks into the study, with more
significant loss by 12 weeks. An earlier
study reported that short, vigorous sprints were the most effective way to
increase bone strength. It was evident in this study that an hour a day on the
walker didn’t combat bone demineralization. In another study, horses being
conditioned experienced increased BMC when fed a higher calcium diet (0.69% vs.
0.35%). However, feeding higher calcium didn’t prevent the decline in BMC in
stalled horses in the latter study, indicating that diet supplementation cannot
overcome lack of activity.
Inactivity is detrimental to the
entire musculoskeletal system, including bones, muscles, joints, tendons and
ligaments. People confined to bed rest for a week to 9 days have been shown to
lose as much as 20% to 30% of original muscle strength. Ligaments have been
found to undergo biomechanical changes as early as 2 weeks after immobilization.
Joint cartilage, which does not have its own blood supply, relies on synovial
fluid to provide nutrients. This action requires joint movement. When horses
stand still for most of the day, nutrient delivery to joint cartilage is
diminished and may damage joints.
Along with the potential problems
confinement presents for the musculoskeletal system, the digestive system may
be affected as well. When the body doesn’t move, the motility of the digestive
system declines, which can increase the risk for impaction colic in horses. Confinement
also tends to increase the incidence of stress-related behaviors. Cribbing,
weaving, kicking and even gastric ulcers have been associated with being housed
in stalls. There is no doubt horses living predominantly in stalls potentially
have more health problems than horses kept in pasture for most of the time. The
research shows that living in a stall and walking on a walker for 2 hours a day
just doesn’t do the job.
While many horse owners cannot keep horses in herds
out on pasture, the research suggests that consistent, ample turnout and
regular exercise can contribute significantly to keeping horses happy and
healthy.
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