Objective—To determine whether specific treadmill
exercise regimens would accelerate age-related
changes in collagen fibril diameter distributions in the
common digital extensor tendon (CDET) of the forelimbs
of young Thoroughbreds.
Animals—24 female Thoroughbreds.
Procedure—Horses were trained for 18 weeks (6
horses; short term) or 18 months (5 horses; long
term) on a high-speed treadmill; 2 age-matched control
groups (6 horses/group) performed walking exercise
only. Horses were (mean ± SD) 24 ± 1 months
and 39 ± 1 months old at termination of the shortterm
and long-term regimens, respectively.
Midmetacarpal CDET specimens were obtained and
processed for transmission electron microscopy.
Diameter and area of at least 1,000 collagen
fibrils/specimen were measured by use of computerized
image analysis. Mass-average diameter (MAD) of
collagen fibrils and collagen fibril index were calculated
for each horse.
Results—Collagen fibril MAD for the older horses
was significantly less than that for the younger horses.
Exercise did not significantly affect fibril diameter
or distributions in either age group, and collagen
fibril index did not differ significantly between
Conclusions and Clinical Relevance—Age-related
reduction in collagen fibril MAD agreed with findings
for other tendons and species. Training did not accelerate
age-related change in the CDET, in contrast to a
reported decrease in collagen fibril MAD in the superficial
digital flexor tendon of horses trained long term.
Our results support the concept that the functionally
distinct nature of the CDET and superficial digital flexor
tendon in horses results in fundamentally different
responses to high-speed exercise regimens. (Am J Vet Res 2005;66:564–568)
Objective—To determine cellular changes associated with secondary epidermal laminae (SEL) in forefeet and hind feet of ponies with insulin-induced laminitis.
Procedures—Laminitis was induced in 4 ponies by IV administration of insulin and glucose; 4 control ponies received saline (0.9% NaCl) solution IV. Laminar tissue samples obtained from the dorsal aspects of the hooves were histologically evaluated. Primary epidermal lamina (PEL) length and width and SEL length, width, and angle were determined. Numbers of epidermal cell nuclei per micrometer and per total length of SEL and numbers of apoptotic and proliferative cells in axial, middle, and abaxial laminar regions were determined.
Results—SEL in treatment group ponies were significantly longer, were significantly narrower, and had a smaller angle relative to PEL in all laminar regions versus control ponies. In treatment group ponies, the number of epidermal cell nuclei per SEL was typically higher and the number of cells per micrometer of SEL was lower in laminar regions, apoptotic cell numbers were higher in abaxial and middle regions in forefeet and hind feet, and proliferating cell numbers were higher in axial laminar regions in forefeet and all laminar regions in hind feet, versus control ponies.
Conclusions and Clinical Relevance—Results indicated SEL elongation, narrowing, and alteration in orientation developed in all feet of ponies with insulin-induced laminitis. This was primarily attributable to cell stretching that developed at the same time as an accelerated cell death–proliferation cycle; differences in cell cycle responses among laminar regions between forefeet and hind feet may have been attributable to differences in load bearing.