Effects Of Dietary Phosphorus Level On Performance And Phosphorus Excretion Of Mid-lactation Dairy Cows

The experiment was conducted to study the effects of the dietary phosphorus (P) levels on the performance,metabolic parameters,excretion of nitrogen and phosphorus, and the optimal dose for Holstein cows during mid-lactation period.Thirty primiparous healthly Holstein cows in mid-lactatation with similar milk yield and parturition date were selected in a single factor design,and assigned randomly into 3 groups each with 10 replicates.Total P contents in the experimental ration were dividedly 0.32%,0.44%,0.56% of the dietary(DM based). The experiment lasted 75 days.The results showed that: (1) Dry matter intakes (DMI),milk yields and feed efficiencies of nutrients were not affected by dietary P level (P>0.05);(2)Dietary P level tended to increase milk protein percentage (P>0.05).The milk protein percentage of cows fed diet with P content at 0.44%, 0.56% were higher 0.63%(P>0.05),0.95%( P>0.05) than that fed diet with 0.32%P; The milk Lactose percentage of the cows fed diet with P content at 0.44%, 0.56% were higher 0.56%(P>0.05) and 0.75%(P>0.05) than that of the 0.32%P group; Comparied with the group fed diet with 0.32%P , dietary P content at 0.44% or 0.56% improved the MUN about 0.40and 0.57mg/dl (P>0.05); (3)The apparent digestibility of crude protein, NDF ,ADF and Ca was similar (P>0.05) among groups ; (4)The apparent digestibility of phosphorus of diet containing 0.32%P was significantly higher 11.19%(P<0.01) and 27.19%(P<0.01) than the diets containing 0.44% or 0.56% P. (5) Serum Ca content was unaffected by diet (P>0.05). Compared to the 0.32% P group,the serum P concentration of the 0.32% and 0.56%P group were separately increased 0.26mmol/l (P<0.01) and 0.53mmol/l(P<0.01),the saliva P concentration were separately increased 0.56mmol/l (P<0.05)and 1.74mmol/l(P<0.01). But different dietary P level had no effects on serum AKP and HYP concentrations (P>0.05); (6) The higher dietary phosphorus level could increase the P intake, and led to higher P excretion in feces.The P intake (P supplement at 0.44%, 0.56%) were higher 25.46g/d and 49.22g/d (P<0.01) than that of the 0.32%P group. Decreasing the excess dietary P not only lowered the total P excretion in manure, but also reduced water-soluble P excretion. Feeding 0.32% P diet group decreased total feces P 18.79g( P < 0.01)和41.02g(P<0.01) and water-soluble P 15.24g (P<0.01)和45.61g (P<0.01) than the diet with 0.44% or 0.56% P.(7) Comparing with the 0.32% P group, the income of feeding a cow were separately increased 0.30 RMB/d and 0.58RMB/d with the 0.44% and 0.56% P group。In summary, dry matter intake (DMI) and the performance was unaffected by dietary P level (P>0.05). Decreasing dietary phosphorus concentration to 0.32% not only could decrease phosphorus excretion, but also could improve the economic profit of feeding. As all were concerned,the optimal dose of phosphorus was 0.32% for dairy cows during the mid-lactation period.