| In order to utilize phosphorus in plant feedstuff's efficiently and explore more simple and convenient ways to determine available phosphorus to direct inorganic phosphorus addition in animal diets, three experiments as follows were conducted in this research.Experiment 1 was conducted to determine phosphorus digestibility of corn, oat, broken rice, brown rice, buckwheat, sorghum, fababean and pea, and to examine whether digestible phosphorus in different feed ingredients were additive when used in diet formulation for growing-finishing pigs. One semi-purified soybean-cornstarch basal diet ( 0.3% phosphorus content), eight single tested diets formulated with corn, oat, broken rice , brown rice ,buckwheat ,sorghum, fababean and pea partially substituting for soybean and cornstarch in the basal diet, respectively, and diet A ( soybean and cornstarch were partially substituted with corn, oat, broken rice and rough rice) and diet B (soybean and cornstarch were partially substituted with buckwheat, sorghum, fababean and pea) , and twelve Duroc X Landrace X Yorkshine pigs with initial average body weight of 27.2 + 2.3 kg, were used in the experiment according to two 6X6 Latin Square Design with the same basal diet. Experiment 2, an in-vitro study, was conducted to determine the dialyzability of phosphorus in different plant feedstuffs as experiment 1, with phytase supplementation (500 FTU/kg) and no phytase, respectively, and to research the relationship between the dialyzability with no phytase and apparent or true phosphorus digestibility. Experiment 3 was conducted to investigate the effects of sodium chloride on phosphorus and other nutrients (dry matter, crude protein and calcium) digestibility. Thirty-six Duroc X Landrace X Yorkshine pigs about 20 kg were used. All the pigs were randomly assigned to 6 groups according to a Completely Randomized Design and fed on 6 diets with different NaCl levels (0.1 % N 0.2 %, 0.3 %, 0.4%, 0.5% and 0.6%) ,respectively. The results showed that:Apparent phosphorus digestibilities of corn, oat, broken rice, brown rice, buckwheat, sorghum, fababean and pea were 17.16%, 5.98%, 31.91%, 28.61%, 30.36%, 31.02% and 26.33%, respectively. The corresponding true phosphorusdigestibilities were 40.33%, 27.45%, 44.62%, 41.89%, 49.72%, 42.34%, 50.76% and 36.56%, respectively. Apparent and true phosphorus digestibilities (%) of diet A were 15.45 + 5.11 and 40.38+2.79, 49.80% and 4.11% higher than the corresponding predicted values, respectively. While the indexes of diet B were 21.23+2.90 and 40.58 + 0.90, 40.84% and 14.09% higher than corresponding predicted values. It is suggested that apparent digestible phosphorus both in diet A and diet B are not additive, while true digestible phosphorus in the two diets are additive to some extent, but the additivity in diet A is better than that of diet B.There was significant difference on phosphorus dialyzability of the feedstuffs with or without phytase (P<0.01) . Significant quadratic effect was examined between phosphorus dialyzability (x) without phytase supplementation and apparent phosphorus digestibility (y1) (P<0.05), and significant linear relationship was existed in the dialyzability (x) and true phosphorus digestibility (y2)(P<0.05). The models are y1 =-0.0923x2+ 5.6710x-56.0221 (R2 = 0.7147 RSD=5.5995 P=0.0001 n=54)and y2 = 1.2021x +11.8370 (R2 = 0.4734 RSD=6.8005 P=0.0001, n=54), respectively.Differences of dry matter, crude protein and calcium digestibility among different groups in experiment 3 were not significant(P>0.05). But significant differences were examined in apparent and true phosphorus digestibilities (P<0.05). Apparent and true phosphorus digestibilities were highest (41.50% and 53.25%, respectively) when sodium chloride level was 0.3%. With sodium chloride level increasing, the apparent and true phosphorus digestibilities declined, but still higher than the values determined with 0.1% or 0.2% sodium chloride levels. Nearly significant quadratic effects were examined between sodium chloride (x) and apparent (y1) or t...
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