Effect Of Dietary Phosphorus Levels On Ruminal Fermentation, Milk Performance And Digestion And Metabolism Of Phosphorus Of Dairy Cows

The experiment was conducted to study the effect of dietary phosphorus levels on rumen fermentation, milk performance, digestion and metabolism of phosphorus in cows through in vivo rumianl fermentation test, feeding trial and metabolism test in order to confirm the reasonable addition of phosphorus in diets and provide theoretical basis for decreasing the enviroment contamination from phosphorus during dairy farming.The experiments were divided into 5 parts. Three healthy Holstein dairy cows with similar body weight (600kg) and fitted with ruminal cannulas were chosen as experiment animals in trial 1, and this experiment was divided into 2 parts. Each part was made up of three kinds of diets in a 3×3 Latin square design. and the phosphorus levels in part one were 0.27%, 0.43%, 0.59%, and 0.35%,0.43%, 0.51% in part two.The ruminal fluid samples were collected at the time points of 2h, 4h, 8h, 12h, and 24h after feeding, in order to study the effect of dietary phosphorus levels on ruminal fermentation by determining the pH value, the concentrations of NH3-N, BCP, VFA and the inorganic phosphorus in rumen liquids.Forty Holstein dairy cows with familiar body weight (600kg), age, lactation period ( 150d) and milk production(18kg/d) were divided into 5 groups(Group A, B, C, D and E) at random , using singal factor assignment in the trial 2,3and 4, with 8 cows in each group, and the phosphorus levels in each group were 0.27%, 0.35%, 0.43%, 0.51% and 0.59% respectively. Pre-trial period was 15 d, and the experimental period was 60 d. The trials were conducted to study the effect of dietary phosphorus levels on milk performance, biochemistry indexes in serum, and the apparent digestibility of nutrients in diets.Fifteen Holstein dairy cows with familiar body weight(600kg), milk production(18kg/d) and physiological state were chosen form Group A, B, C, D and E after the feeding trial, 3 cows in each group. It was conducted to study the effect of dietary phosphorus levels on the digestion, metabolism and distribution of phosphorus in cows.The results showed as followed under the present experimental conditions:1. The inorganic phosphorus concentration in rumen was increased from 299.75 mg/L to 469.86mg/L, to a greater or lesser degree by the increasement of the levels of phosphorus in diet(0.27%～0.59,DM),and the concentrations of BCP also improve with the increasment of phosphorus in diets. But the dietary phosphorus levels had no significant effects on the concentrations of NH3-N and VFA and pH value(P>0.05).2. The dietary phosphorus levels did not have an obvious effect on the improvement of milk production and the compositions in milk, but the milk production for the group fed the diet containing low levels of phosphorus (0.27%,DM) was less than others.3. The dietary phosphorus levels could improve the phosphorus concentration in serum,but had no significant effects on the concentration of Ca and BUN in serum. The diets with high (0.59%,DM) or low(0.27%,DM) levels of phosphorus could not cause the changes in the concentration of hormone related to calcium and phosphorus significantly.4. The dietary phosphorus levels had no significant effects on the appearant digestibility of DM, NDF, ADF, CP ,Ca and DMI of dairy cows(P>0.05), but the diet with high phosphorus level could decrease the appearant digestibility of phosphorus and calcium significantly(P<0.05),and the diet with low phosphorus level tended to decrease the DMI of dairy cows .5. The increasement of phosphorus in diet could improve phosphorus intake, fecal phosphorus excretion, total phosphorus excretion and digestible phosphorus significantly(P<0.05), and the deposition of phosphorus decreased for the group with high level of phosphorus (P<0.05). The dietary phosphorus levels caused the decreasement of the appearant digestibility of phosphorus significantly(P<0.05). Phosphorus intake increased the digestible phosphorus in a quadratic dose–dependent manner (P<0.05,R2=0.9176).6. The suitable addition of phosphorus in cows'diet was 0.46% (DM) considering all kinds of experimrnt indexes and the regression analysis, and then the digestible phosphorus reached the top of 26.57 g/d, with the highest phosphorus intake (71.25 g/d), 44.67g/d and fecal phosphorus excretion respectively.