DIETARY PHOSPHORUS RESTRICTION TO HALF THE MINIMUM REQUIRED AMOUNT SLIGHTLY REDUCES WEIGHT-GAIN AND LENGTH OF TIBIA, BUT SUSTAINS FEMUR MINERALIZATION AND PREVENTS NEPHROCALCINOSIS IN FEMALE KITTENS

The effects of dietary P restriction to half the recommended minimum l evel on growth, bone and renal mineralization and urinary composition were studied in female kittens. In two separate experiments, 8-week-ol d weanling kittens were fed on purified diets containing either 4.6 or 9.2 mmol P/MJ (2.8 or 5.6 g P/kg diet). In the second experiment ther e was an additional low-P diet in which the Ca concentration was reduc ed from 9.5 to 4.8 mmol/MJ (7.5 v. 3.8 g Ca/kg diet). P restriction sl ightly but systematically reduced weight gain (to a maximum of 16%) an d growth of the tibia (by 1-4%); the former effect was statistically s ignificant (P < 0.05) between the ages of 15 and 20 weeks in Expt 1 on ly, and the latter did not reach statistical significance at any time point (P greater than or equal to 0.13). No adverse effect of P restri ction was found on mineralization of femur at the age of 39 weeks. Kid ney Ca concentrations were significantly lowered (Expt 1, 6 v. 20 mu m ol/g dry weight, P < 0.001; Expt 2, 7 v. 16 mu mol/g dry weight, P < 0 .01) in cats fed on the low-P diets, this effect not being affected by the dietary Ca:P ratio. Urinary P concentration was significantly dep ressed (by 50-96%) after feeding the low-P diets (P < 0.001). P intake did not influence P, Ca and Mg retention during the period of 15 to 3 9 weeks of age.