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Two long-term individual feeding experiments (336 and 307 days) were carried out with 52 (experiment I; Black and White dairy cattle) and 22 (experiment II; Yellow cattle) growing bulls. Rations varied in P-content. In experiment I straw: concentrate-mixture (1:2.5) were fed, phosphorus content of rations amounted to 2, 3 or 4 g/kg DM. In experiment II maize silage was fed ad lib. supplemented with 2.4 kg concentrate per animal per day. P-content of rations amounted to 3 and 4 g/kg DM. Apparent digestibility of rations was determined during experiments. Blood samples were taken to analyse selected parameters of metabolism. Various P-supply did not significantly influence apparent digestibility of organic matter and crude nutrients in both experiments. Bulls fed 2 g P/kg DM decreased DMI in experiment I already after 50 days of experiment. After 168 experimental days daily weight gain of bulls fed with 2 g P/kg DM was 124 or 132 g lower than that of bulls fed with 3 or 4 g P/kg DM respectively. P-concentration of inorganic P in serum decreased to < 2 mmol/l, bone mineralisation was reduced. There exist no significant differences in feed intake, weight gain and metabolic parameters of bulls fed with 3 or 4 g P/kg DM. Increase of P-supply from 2 to 3 or 4 g/kg DM compensated partially the lower weight gain. Application of 3 or 4 g P/kg DM in experiment II effected daily weight gains of > 1200 g and did not significantly influence all investigated criterions.

Five smaller (body weight: 227.9 +/- 23.7 kg) and large growing bulls (435.2 +/- 14.3 kg per animal) each were fed with rations rich (chopped wheat straw:concentrate = 1:1) or poor in roughage (straw: concentrate = 1:4). Animals were kept in balance cages; 20 days adaptation period were followed by 10 days collection period. Body weight of bulls did not significantly influence apparent digestibility of rations. digestibility of organic matter of fibre rich ration was significantly lower (66.8%) than those of concentrate rich ration (74.4%). Feeding and body weight did not significantly influence metabolic parameters of mineral status. The fecal P-excretion amounted to 0.94 and 1.08 g per kg DMI in bulls fed with rations rich and poor in roughage. No influence of body weight was measured. Feeding and body weight did not significantly influence fecal P-excretion per kg DOMI (between 1.44 and 1.58 g P/kg DOM). For calculation of P-requirements for growing cattle fecal P-excretion amounted to 1.0 or 1.5 g P/kg DM and DOMI, respectively.