Published online by Cambridge University Press: 09 March 2007
The effects of dietary P restriction to half the recommended minimum level on growth, bone and renal mineralization and urinary composition were studied in female kittens. In two separate experiments, 8-week-old 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 there was an additional low-P diet in which the Ca concentration was reduced from 9·5 to 4·8 mmol/MJ (7·5 v. 3.8 g Ca/kg diet). P restriction slightly but systematically reduced weight gain (to a maximum of 16%) and growth of the tibia (by 1–4%); the former effect was statistically significant (P < 0·05) between the ages of 15 and 20 weeks in Expt 1 only, and the latter did not reach statistical significance at any time point (P g 0·13). No adverse effect of P restriction was found on mineralization of femur at the age of 39 weeks. Kidney Ca concentrations were significantly lowered (Expt 1, 6 v. 20/μmol/g dry weight, P < 0-001; Expt 2, 7 v. 16/μmol/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 depressed (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 39 weeks of age.