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Studies in other species indicate high protein diets increase urinary
calcium (Ca ) excretion and may lead to negative calcium balance and reduced
bone density . As overfeeding of protein is commonplace in the horse industry ,
this study was undertaken to determine the effects of excess dietary protein on
growth , physiologic response , mineral balance , bone density , and bone
geometry in immature horses . Sixteen 10 -month -old American Quarter Horses
were blocked by age and sex into two dietary treatments . The control diet was
formulated to provide the NRC (1989 ) recommended concentration of crude
protein , while the high protein diet provided 130 % of NRC (1989 )
recommendations . All other nutrients were formulated at or slightly above NRC
(1989 ) recommendations . Blood samples , feces , and urine were collected
during the 116 -day study to determine any diet effect on pH and mineral
balance . Radiographs were made of the left third metacarpal (MCIII ) to
determine bone density via radiographic bone aluminum equivalence (RBAE ) ,
and bone geometry was determined metrically from the radiographs . Urine pH decreased over time (p < 0 .001 ) , but there were no diet effects
on blood pH or urine pH . Conversely , when normalized to day 0 values , fecal
pH was reduced by feeding the high protein treatment (p < 0 .02 ) . Density of
dorsal and palmar cortices increased over time (p < 0 .001 ) , but no differences
were observed between diets . But , normalized total medial -lateral (ML ) width of
the MCIII was higher in the control diet (p < 0 .05 ) . Fecal Ca loss was greater in
horses fed the high protein diet (p < 0 .005 ) , while Ca absorption and retention
were lower for horses on the high protein treatment (p < 0 .02 ) . Phosphorus (P )
balance was not different between diets , although feeding the high protein diet
resulted in higher P intake overall (p < 0 .001 ) .
While excess dietary protein may decrease fecal pH , increase fecal Ca
excretion , and decrease Ca absorption and retention , there was no consistent
effect of the high protein diet on bone density over the course of this study .
Further research is necessary to determine if feeding high -protein diets is
detrimental to bone quality in the growing horse . |
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