Growth and Development The current trend in the horse industry is to
accentuate growth in young horses; however, some fear developmental
orthopedic disease (DOD) if growth is too rapid or foals become too large.
Additional support for this theory was obtained in recent research done on a
Kentucky Thoroughbred farm in which 271 foals were evaluated over four years.
It was found that foals that developed DOD were larger at birth and grew more
rapidly than foals without DOD.
If foals are fed for rapid weight
gain, they will have an increase in bone mineral content, according to one
study. However, the study showed that there were no differences in bone
mineral quality in foals fed for rapid weight gain versus those fed for slow
weight gain. Foals that do gain weight rapidly might have an increase in
serum osteocalcin, indicating that more bone growth is taking place. However,
they observed an increased incidence of physitis in foals fed for rapid
gain.
Concerns over a connection between glucose intolerance and
insulin resistance to development of osteochondritis dissecans (OCD)
lesions prompted the development of an oral dextrose challenge test for
glucose intolerance. Research at Rutgers found that there might indeed be
an association of glucose intolerance and OCD.
Studies at Kentucky
Equine Research on the effects of feed on the incidence of OCD indicated that
providing feed with a low glycemic response could reduce the incidence of
OCD.
Owners of young horses strive to make weaning time as stress-free
as possible, and researchers wondered what the effects of weaning time are
on body weight, wither height, and bone density. It was found that weaning
had no effect; however, a decline in weight gain at one and three weeks
after weaning is normal.
If young horses enter race training, there
will be a period of bone demineralization, then a period of
re-mineralization. A study of yearling Quarter Horses showed a significant
decrease in the density of metacarpal bone believed to be caused by the
exercise-induced bone remodeling. "The research indicated the onset of speed
work often coincides with the time of greatest demineralization (50-60 days
into training), which may account for the high incidence of skeletal injuries
in 2-year-old horses in training," according to the authors of the study.
"Training methods and protocols should be designed to reflect the findings
that significant demineralization of metacarpal bone occurs in the first 60
days of training."
Further research shows that feeding higher levels of
phosphorus, calcium, and magnesium than those recommended by the NRC might
increase bone mineralization. And even for long yearlings not in training,
calcium levels might need to be increased to 115% of NRC recommendations,
according to Oklahoma researchers.
For many young horses, once
training is begun, they are then confined to stalls. However, research
suggests this might be detrimental. Michigan researchers found that confined
long yearlings and 2-year-olds had a loss of bone mineral content in
comparison with those on pasture. Rich recommended allowing young horses free
access to exercise on pasture, or if this is not an option, then training
should be modified to account for the bone loss. One product that might help
prevent bone mineral loss is exogenous somatopropin (eST).
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