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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/4378 |
| Date | 30 October 2006 |
| Creators | Spooner, Holly Sue |
| Contributors | Gibbs, Pete G., Potter, Gary D. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 505386 bytes, electronic, application/pdf, born digital |
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