title: Impact of Increasing Dietary Calcium Levels on Calcium Excretion and Vitamin D Metabolites in the Blood of Healthy Adult Cats.
abstract: BACKGROUND
  Dietary calcium (Ca) concentrations might affect regulatory pathways within the Ca and vitamin D metabolism and consequently excretory mechanisms. Considering large variations in Ca concentrations of feline diets, the physiological impact on Ca homeostasis has not been evaluated to date. In the present study, diets with increasing concentrations of dicalcium phosphate were offered to ten healthy adult cats (Ca/phosphorus (P): 6.23/6.02, 7.77/7.56, 15.0/12.7, 19.0/17.3, 22.2/19.9, 24.3/21.6 g/kg dry matter). Each feeding period was divided into a 10-day adaptation and an 8-day sampling period in order to collect urine and faeces. On the last day of each feeding period, blood samples were taken.
  
  
  RESULTS
  Urinary Ca concentrations remained unaffected, but faecal Ca concentrations increased (P < 0.001) with increasing dietary Ca levels. No effect on whole and intact parathyroid hormone levels, fibroblast growth factor 23 and calcitriol concentrations in the blood of the cats were observed. However, the calcitriol precursors 25(OH)D2 and 25(OH)D3, which are considered the most useful indicators for the vitamin D status, decreased with higher dietary Ca levels (P = 0.013 and P = 0.033). Increasing dietary levels of dicalcium phosphate revealed an acidifying effect on urinary fasting pH (6.02) and postprandial pH (6.01) (P < 0.001), possibly mediated by an increase of urinary phosphorus (P) concentrations (P < 0.001).
  
  
  CONCLUSIONS
  In conclusion, calcitriol precursors were linearly affected by increasing dietary Ca concentrations. The increase in faecal Ca excretion indicates that Ca homeostasis of cats is mainly regulated in the intestine and not by the kidneys. Long-term studies should investigate the physiological relevance of the acidifying effect observed when feeding diets high in Ca and P.
authors: Institute of Animal Nutrition, Department of Veterinary Medicine, Freie Universität Berlin, Königin-Luise-Str. 49, 14195, Berlin, Germany.
authors: Nadine
authors: N
authors: Paßlack
authors: Institute of Nutritional Science, University of Potsdam, Arthur-Scheunert-Allee 114-116, 14558, Bergholz-Rehbrücke, Germany.
authors: Bettina
authors: B
authors: Schmiedchen
authors: Institute of Nutritional Science, University of Potsdam, Arthur-Scheunert-Allee 114-116, 14558, Bergholz-Rehbrücke, Germany.
authors: Jens
authors: J
authors: Raila
authors: Institute of Nutritional Science, University of Potsdam, Arthur-Scheunert-Allee 114-116, 14558, Bergholz-Rehbrücke, Germany.
authors: Florian J
authors: FJ
authors: Schweigert
authors: Institute of Veterinary Physiology, Department of Veterinary Medicine, Freie Universität Berlin, Oertzenweg 19b, 14163, Berlin, Germany.
authors: Friederike
authors: F
authors: Stumpff
authors: Clinic of Small Animals, Department of Veterinary Medicine, Freie Universität Berlin, Oertzenweg 19b, 14163, Berlin, Germany.
authors: Barbara
authors: B
authors: Kohn
authors: Institute of Biometry and Clinical Epidemiology, Charité -Universitätsmedizin Berlin, Hindenburgdamm 30, 12203, Berlin, Germany.
authors: Konrad
authors: K
authors: Neumann
authors: Institute of Animal Nutrition, Department of Veterinary Medicine, Freie Universität Berlin, Königin-Luise-Str. 49, 14195, Berlin, Germany.
authors: Jürgen
authors: J
authors: Zentek
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000818:Animals; D002118:Calcium / Q000032:analysis / Q000097:blood / Q000378:metabolism* / Q000652:urine; D002130:Calcium Phosphates / Q000032:analysis / Q000097:blood / Q000378:metabolism* / Q000652:urine; D002136:Calcium, Dietary / Q000032:analysis / Q000097:blood / Q000378:metabolism* / Q000652:urine; D002415:Cats / Q000097:blood / Q000502:physiology* / Q000652:urine; D004032:Diet; D004435:Eating; D005243:Feces / Q000737:chemistry; D005260:Female; D008297:Male; D014807:Vitamin D / Q000032:analysis / Q000097:blood / Q000378:metabolism*
chemical_list: D002130:Calcium Phosphates; D002136:Calcium, Dietary; D014807:Vitamin D; C485829:calcium phosphate, dibasic, anhydrous; D002118:Calcium