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Relationship between activity
and bone formation in immature animals
K.M. Hiney, B.D. Nielsen
and A.J. Zanella
Michigan State University,
East Lansing, USA
While confinement housing negatively impacts bone mass, high intensity exercise of short duration, as well as free-choice exercise, may prove beneficial. This study investigates this theory in two domestic species.
First, 18 calves (eight wk old) were assigned to one of three treatments: group housed (GR), confined without exercise (CF), or confined with exercise (EX). CF and EX were housed in tie stalls (0.65 m x 1.55 m) and EX calves were sprinted 50 m/d, five d/wk. GR were housed with other calves in a 62 m2 pen with free access to exercise. On d 0, 21, and 42, behavior was video-recorded and duration of standing, lying, walking, and trotting were recorded on 4 randomly selected hours. After 42 d, calves were euthanized and metacarpal bones were scanned using computed tomography to determine bone mineral density (BMD).
Also, 18 Quarter Horse weanlings (5 mo old) were studied for 56 d, with three similar treatments. CF and EX were housed in 3.7 m x 3.7 m stalls. EX was sprinted 82 m/d, 5 d/wk. GR horses were housed together in a 992 m2 drylot with free access to exercise. On d 0, 28 and 56, radiographs of the third metacarpus were taken to estimate changes in bone mineral content (BMC), and behavior was video-recorded and analyzed as above.
EX groups had greater BMD (calves) or gained more BMC (weanlings) compared to CF and GR. Surprisingly, BMD and BMC did not differ between CF and GR. GR calves did not differ from CF in time spent lying down or standing. With horses, time walking did not differ between treatments. There was no difference between GR and CF in lying or standing, while EX horses spent more time lying than either CF or GR. Therefore, despite being allowed opportunity for exercise, neither GR calves or horses exercised much more than CF, explaining the lack of differences in bone mass. Perhaps if the group enclosure had been larger or more enriched, or if social stability of the group were altered, animals may have been more active stimulating greater bone formation.