Effect Of Dietary Phosphorus Amount On Milk Production And Phosphorus Excretion Of Dairy Cows In China

Two experiments were conducted to study the effect of dietary phosphorus amount on milk production, health and reproductive performance. An investigation of dietary phosphorus amount of dairy cows in East China was conducted (Expt.1). Experiment 2 was conducted to study the effect of dietary phosphorus amount on milk production and phosphorus excretion.In Expt.1, The objective of Expt.1 was to provide gist for revaluation of dietary phosphorus amount of dairy cows in East China. This investigation based on 4 dairy farms in East China. The amounts range of phosphorus of 4 farms were 0.44-0.56% (average 0.51%±0.048%). These amounts were in excess of NRC recommendation and Chinese recommendation. This investigation demonstrated that milk production was not affected by phosphorus amount. The concentrations of serum phosphorus of different farms were not statistically significant. Reproductive performance of farm with 0.56% phosphorus was worse than the others, and the difference in-phosphorus amount did not alter incidence of metabolic disease caused by calcium and phosphorus. It is indicated that, milk production, health and reproductive performance is not affected by the amount of phosphorus, when the amount is in a range of 0.44%-0.56%.In Expt 2, the effect of reducing dietary phosphorus on milk production of dairy cows in China was determined using 45 multiparous Holsteins over a full lactation period. Animals were blocked into 15 groups according to milk production of previous lactation and parity, and allocated to treatments randomly within each group. Diets contained 0.37,0.47, or 0.57% P (DM basis), based on NRC guidelines, the level recommended by the Chinese feeding standard, and the amount currently fed by most producers, respectively. Milk yield was recorded and milk composition analyzed monthly. Blood samples were collected on d-6,-3,0,3,6 relative to calving and then monthly throughout the experiment. Feces and urine were analyzed in week 12,24, and 36. All data were analyzed using the MIXED procedure of SAS software system with cow as the repeated subject using the covariance type AR (1). The model included phosphorus level, time, and interaction of phosphorus level×time. Neither DMI nor milk yield was affected by dietary P content (see Table 1). Milk fat was slightly higher for 0.37% P than for the other two dietary P concentrations. Serum P did not reflect dietary P amount, and there was no influence of dietary P on serum Ca concentration. Fecal P excretion was reduced by 25% when 0.37% P was fed compared to 0.57% P. Urinary P reached a maximum concentration for all groups during peak lactation. Reducing dietary P from 0.57 to 0.37% did not negatively affect milk production, while P excretion was significantly decreased.In summary, the dietary phosphorus amount of dairy cows in East China is obviously high. Milk production, health and reproductive performance were not affected by the amount of phosphorus, when the amount was in a range of 0.37%-0.57%. Reducing of practical amount of phosphorus is feasible, and will reduce phosphorus excretion to the environment.