Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/26/2008
Publication Date: 6/24/2008
Citation: Esser, N.M., Hoffman, P.C., Coblentz, W.K., Orth, M.W., Weigel, K.A. 2008. Bone development in dairy heifers fed diets with and without supplemental phosphorus. Journal of Dairy Science. 91:481. Interpretive Summary:
Technical Abstract: The NRC 2001 P requirements for heifers (0.20-0.35 %) and endogenous levels (0.20-35 %) of P in feeds are similar suggesting supplemental P in heifer diets may be minimally required. Because long term studies are unavailable 183 Holstein heifers and 182 crossbred heifers were fed diets with (0.38 %) and without (0.28 %) supplemental P from 4-22 m of age in a replicated pen design. Two sub-populations of heifers were selected at trial mid-point for measurement of bone development and metabolism. Thirty-two heifers at 21 m of age, balanced by breed and dietary treatment were evaluated for bone development. External frame measurements included hip height, length, heart girth, hip width, cannon bone circumference, pelvic length, pelvic height, and pelvic width. Heifers were given a spinal block, tails docked with the 13 and 14th coccygeal vertebrae retained. Tissue was removed from vertebrae, defatted and evaluated for ash and mineral content. The 13th coccygeal vertebrae were scanned using peripheral quantitative computed tomography. Cortical, trabecular and total bone densities were determined. A second sub-population (n=64) of heifers 12 m, balanced for breed and dietary treatment, were evaluated for pyridinoline and osteocalcin levels to assess bone metabolism. Data were analyzed as a completely randomized design using PROC GLM of SAS with breed, treatment and their interaction. External frame measurements revealed significant differences (P < 0.07) in frame size between Holstein and crossbred heifers. Supplementing P had no effect (P > 0.10) on external frame measurements, bone density, or bone metabolism markers. Bone P and Mg contents were lower (P < 0.08) and bone K content higher (P < 0.05) in heifers fed no supplemental P. Data suggest supplementing P to heifers modestly increased bone P content but increased bone P was not reflective of frame development, bone density or bone metabolism.