Influence of feeding various phosphorus sources on apparent digestibility of phosphorus in dairy cows

The present investigated differences in the apparent digestibility of phosphorus (ADP) in lactating cows fed various feed materials containing organic forms of phosphorus (P) or a highly available inorganic phosphorus source. Cows milking an average of 36 kg energy corrected milk (ECM) were used in a 4×4 Latin square design with 4-week periods to measure the P excretion in faeces. Four different concentrates with monosodium phosphate (MSP), rapeseed (RS), sunflower seed/palm kernel (SSP) and wheat middlings/bran (WMB) as the main P source (0.56–0.67 of P in the total diet) were offered, together with grass silage. The dietary supply of P was 82–93 g per day, corresponding on average to 4.0 g per kg DM intake. Daily faecal P excretion was determined by total collection for 5 days and the P ranged from 39.7 to 45.8 g per day. ADP were 0.498, 0.519, 0.474 and 0.522 for MSP, RS, SSP and WMB, respectively. There were no significant differences between the diets in terms of ADP, milk production or milk composition. The retention of P was 9–17 g per day, the highest values being associated with the highest P intake. Under normal feeding conditions for dairy cows, there seems to be no need to use different absorption coefficients for different concentrate ingredients.