Abstract
BackgroundDietary 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.ResultsUrinary 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).ConclusionsIn 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.
Highlights
Calcium (Ca) homeostasis in cats is hormonally regulated by calcitriol, parathyroid hormone (PTH) and calcitonin [1]
The increase in faecal Ca excretion indicates that Ca homeostasis of cats is mainly regulated in the intestine and not by the kidneys
Calcium and Vitamin D in Cats physiological relevance of the acidifying effect observed when feeding diets high in Ca and P
Summary
Calcium (Ca) homeostasis in cats is hormonally regulated by calcitriol, parathyroid hormone (PTH) and calcitonin [1]. Calcitriol further enhances intestinal Ca and phosphate absorption, while calcitonin lowers blood Ca concentration by Ca accretion in bones [1]. In addition to these hormones, fibroblast growth factor 23 (FGF23) has been recognized to affect Ca and phosphorus (P) metabolism [2]. FGF23 increases renal P excretion, decreases gastrointestinal P absorption, downregulates PTH and decreases plasma calcitriol concentrations [2]. In this way, calcitriol, and plasma P concentrations are reduced by FGF23 [2]. On the last day of each feeding period, blood samples were taken
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