title: Influence of calcium and phosphorus feeding on markers of bone metabolism in transition cows.
abstract: A study was carried out to verify the effect of Ca and P levels on production, digestibility, and serum bone metabolism biomarkers in dairy cows. Fifty-two nonlactating multiparous cows (>or=3 lactations) were confined in a free-stall barn approximately 20 d before calving. A standard close-up diet was fed to cows once daily until d 2 postpartum. Cows were randomly assigned to 1 of 4 dietary treatments arranged in a 2 x 2 factorial approach averaging 0.64% Ca for high Ca (HCa), 0.46% Ca for low Ca (LCa), 0.47% P for high P (HP), and 0.38% P for low P (LP) on a dry matter basis. Experimental diets were fed twice daily from 3 d in milk (DIM) until 31 DIM. Intake and milk yield were recorded daily. Milk samples were collected on d 28, 29, and 30 postpartum for components analyses. Blood samples were drawn 10 d before expected calving, at calving, and at 15 and 30 DIM for serum analyses of osteocalcin, a biomarker of bone accretion, and pyridinoline, a biomarker of bone resorption. Total fecal collection was conducted when cows in a block averaged 20 DIM. Intake and production traits were not significantly affected by any of the dietary treatments. Cows averaged nearly 21 kg/d dry matter intake and 44 kg/d milk yield from 6 to 31 DIM. There were no significant differences across treatments in body weight or body condition score loss. Phosphorus intake, P fecal output, P digestibility, and P apparent absorption were affected by dietary P content. Calcium intake was higher with HCa, but Ca fecal output, digestibility, and apparent absorption showed an interaction between dietary Ca and dietary P. Calcium fecal output was 100.6 g/d for cows fed HCaHP, intermediate for cows on the HCaLP diet (89 g/d), and similar among cows fed the 2 LCa diets (70 g/d with LCaHP and 75 with LCaLP). There was no significant effect of Ca or P on osteocalcin measurements. Pyridinoline concentrations were affected by dietary Ca levels and tended to have a significant dietary Ca x dietary P interaction. Phosphorus apparent digestibility occurred independently of dietary Ca levels. Results of this study suggest that more bone was mobilized in cows fed LCa diets, but excess dietary P caused greater and prolonged bone mobilization regardless of dietary Ca content.
authors.affiliation: Louisiana State University AgCenter Southeast Research Station, Franklinton 70438, USA. vmoreira@agcenter.lsu.edu
authors.forename: V R
authors.initials: VR
authors.lastname: Moreira
authors.forename: L K
authors.initials: LK
authors.lastname: Zeringue
authors.forename: C C
authors.initials: CC
authors.lastname: Williams
authors.forename: C
authors.initials: C
authors.lastname: Leonardi
authors.forename: M E
authors.initials: ME
authors.lastname: McCormick
mesh_terms: D000042:Absorption; D000596:Amino Acids / Q000097:blood; D000818:Animals; D015415:Biomarkers / Q000097:blood*; D001842:Bone and Bones / Q000378:metabolism*; D002118:Calcium / Q000032:analysis; D002136:Calcium, Dietary / Q000008:administration & dosage* / Q000493:pharmacokinetics; D002417:Cattle / Q000502:physiology*; D004032:Diet; D004063:Digestion; D005243:Feces / Q000737:chemistry; D005260:Female; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000737:chemistry; D015675:Osteocalcin / Q000097:blood; D010758:Phosphorus / Q000032:analysis; D016226:Phosphorus, Dietary / Q000008:administration & dosage* / Q000493:pharmacokinetics; D049590:Postpartum Period; D011247:Pregnancy
chemical_list: D000596:Amino Acids; D015415:Biomarkers; D002136:Calcium, Dietary; D016226:Phosphorus, Dietary; D015675:Osteocalcin; D010758:Phosphorus; C015484:pyridinoline; D002118:Calcium