Phosphorous requirements of adult cats

Six healthy adult cats were fed six different low phosphorous diets (number s in abbreviation indicate approximate intake of calcium and phosphorous pe r kg body weight: Ca50/P50, Ca100/P50, Ca200/P50, Ca25/P25, Ca50/P25, Ca100 /P25). The diets were given for 15 days followed by a 13 days repletion per iod. Phosphorous and calcium balance, plasma phosphorous and calcium, and u rine pH were determined. Apparent digestibility of phosphorous was primaril y affected by Ca/P) ratio and to a lesser extent by phosphorous intake. In both diets with a Ca/P-ratio of 1:1 it amounted to around 50%, when the Ca/ P-ratio was elevated to 2:1 it decreased to around 30%. When the Ca/P-ratio was increased to 4:1 apparent phosphorous digestibility decreased to 19% ( Ca200/P50) and 1% (Ca100/P25), respectively. There was a significant correl ation between phosphorous intake (X; mg/kg body weighs (BW) per day) and fa ecal excretion (Y; mg/kg BW per day): Y=1.94+0.61X; r=0.78*, n=35). Renal p hosphorous excretion depended on phosphorous intake as well as on Ca/P-rati o. Endogenous renal losses (4.5 mg/kg BW per day) were estimated from the m ean of trials with a phosphorous intake below 35 mg/kg BW per day. Even tho ugh the depletion periods lasted only 2 weeks and in spite of repletion per iods in between experiments clinically evident signs of phosphorous deficie ncy occurred in some cats at the end of the trial Ca100/P25 (hypophosphatae mia, hemolytic anaemia, abnormal mobility of the tarsal joint, permanent fl exion of the hind legs, apathy, metabolic acidosis). From the endogenous lo sses a recommended daily intake of 65 mg/kg BW were derived.