EFFECTS OF 2 LEVELS OF PHOSPHORUS INTAKE ON PERFORMANCE AND FECAL PHOSPHORUS EXCRETION OF DAIRY-COWS

Two groups of 26 dairy cows were fed a basal ration of grass and maize silages plus dairy concentrates according to yield. Cows in one group received 6 g P per cow and day as mineral supplement and dairy concentrates containing 4.3 g P/kg DM. In rations of the other group, addition of phosphates was omitted from mineral supplements and dairy concentrates which, therefore, contained only 3.6 g P/kg DM. Average P intakes were 68 and 60 g per cow and day, respectively. No differences in performance were found during the two years of the trial, average annual milk yield being 7500 kg milk per cow. Close to peak lactation, faecal excretion was determined in 10 cows per group indirectly by use of chromium oxide as a marker. The difference in P intake of 13 g daily was clearly reflected in a similar difference in faecal P excretion with no indication of impaired P balance at the lower P intake. It is concluded that supplementing phosphates is not required for cows producing 7500 kg/year as long as the mean dietary P concentration does not fall below 3.3. g/kg total dry matter.