Proposal for the assessment of phosphorus requirements of dairy cows

One measure to contribute to reducing environmental pollution with phosphorus (P) is to decrease P intake of dairy cows and thus decreasing P excretion with faeces. The current P recommendations are mainly based on data obtained with sheep and goats. We have attempted to the factorial method, i.e., using the net P requirement for maintenance and milk production and the true absorption coefficient. However, inevitable fecal P losses and the true absorption of P are not known for cows. Thus, we have calculated the inevitable P losses, and the true absorption coefficient using data on saliva production, saliva-P content and the efficiency of P re-absorption. The data were either directly or indirectly derived from literature values and experimental results. We propose the following P requirement for dairy cows: P requirement (g/day/600-kg cow)=19+1.43×kg milk. The present recommendation is up to 22% lower than the current recommendations for high-yielding dairy cows used in the UK