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

Effects of varying monosodium phosphate intake on phosphorus excretion in dairy cows

Phosphorus excretion in faeces was measured by total collection using dairy cows fed five amounts of P in a 5 × 5 Latin square design with three week periods. Milk production was 23 ± 4 kg per day at the onset of the trial (DIM 185 ± 11). Different quantities of monosodium phosphate (MSP) were added to a basal diet to obtain daily P intake levels of 44, 67, 92, 117 and 142 g (2.4, 3.7, 5.1, 6.4 and 7.8 g P kg¿ 1of DM, respectively). Faecal P excretion increased linearly (r2 = 0.97) as dietary P intake increased and the apparent digestibility of P was calculated to be 0.37, 0.28, 0.22, 0.21 and 0.22, respectively. The relatively low apparent digestibility is explained by excess P intake in relation to the requirements. The concentration of P in faeces ranged from 4 to 23 g kg¿ 1 of DM corresponding to the lowest and highest level of P intake, respectively. Variation of P in faecal output was substantial among days, though total DM and P intake was constant throughout the collection periods. Results indicate a requirement for sampling over at least 5 consecutive days, even when using total faecal collectio