Study On Optimum Supply Of Calcium And Phosphorus In Dairy Cows

The apparent digestibility of Ca and P under the different physiological stages of dairy cows; effects dietary calcium level on the apparent digestibility of calcium, plasma bio-chemical traits, and relative hormone levels; and influence of inorganic phosphorus level on in vitro fermentation of mixed ruminal microorganism were studied in the present paper. The results were listed below:Experiment one: The apparent digestibilities of Ca and P in different growth and production stages of dairy cows were measured in the experiment. The results indicated that: the calcium apparent digestibility and phosphorus apparent digestibility were significantly effected by different growing period (p < 0.05). The Ca apparent digestibility of the 12 and 24 month-old were significantly higher than that of 18 month-old(p < 0.05), the P apparent digestibility of 12 and 24 month-old cows were significantly higher than that of 18 month-old(p < 0.01). The Ca apparent digestibility and P apparent digestibility were significantly effected by different lactating periods (p < 0.05).The Ca and P apparent digestibility of the first and the second lactating month were significantly higher than the 5th month and the 9th lactating month(p < 0.05). The Ca and P apparent digestibility changed significantly from dry period to around parturient period(p < 0.05), The Ca and P apparent digestibility of preparturient were significantly lower than that of dry and pastparturient period (p < 0.05).Experiment two: 4 lactating dairy cows (milk yield 20.33 ± 0.92kg ) were used, adopting 4x4 Latin square design, the dietary calcium levels were 0.50,0.68, 0.83, 0.96% (DM basis). Experimental result as follows: The different dietary calcium levels significantly influenced the Ca apparent digestibility( p < 0.05 ) .The Ca apparent digestibility declined with the increasing of the dietary Ca levels. The blood and urine pH were significantly influenced by the different dietary calcium levels(p < 0.05).When the dietary Ca levels increased, the blood and urine pH increased(p < 0.05). Milk production was significantly influenced by the different dietary Ca levels (p < 0.05). Milk production (21.97kg) of 0.68% level was significantly higher than those of other groups. Plasma ALP was significantly influenced by dietary Ca levels(p < 0.05). Plasma PTH of 0.50% level was significantly higher than those of other groups(p < 0.05). The dietary calcium levels effected Plasma CT and BGP significantly (p < 0.05),Plasma CT and BGP increased when dietary calcium levels raised.Experiment three: The effects of rumen fermentation by adding inorganic P in vitro were studied, Concentration of inorganic phosphorus were 0, 30, 60, 90,120,150,200,250,300 and 350 mg/L.The gas production, pH, VFA, dry matter and NDF degradation of 48h fermentation in vitro were measured. The results as follows: Different inorganic P levels significantly influenced the gas production and DM digestibility by 48h fermentation in vitro (p < 0.05). The gas production and DM digestibility increased and reached its maximum when inorganic P was 200mg/l and then declining. pH was significantly influenced by different inorganic phosphorus levels (p < 0.05 ). pH decreased when inorganic P levels increased (p < 0.05) and reached its minimum when inorganic P was 200mg/L. Acetate, propionate, butyrate acid and total VFA production were significantly effected by the concentration of inorganic phosphorus (p < 0.05) .Acetate, propionate, butyrate acid and total VFA production were the highest when the concentration of inorganic phosphorus was 200mg/L.