| Three experiments were conducted in this study to investigate the feasibility for predicting truly digestible phosphorus in plant feedstuffs through the contents of total phosphorus (TP). phytate phosphorus (PP) and intrinsic phytase activity (Phy). The true phosphorus digestibility values of nineteen kinds of single feed ingredients were measured based on comparison of endogenous P loss determined by Regression analysis technique (REG) and Difference technique. Meanwhile true P digestibility values were compared with P dialyzability determined by in vitro method. The equations for predicting values of truly digestible P for growing pigs were established at last with the contents of TP, PP and Phy in plant feedstuffs.Experiment one A comparison of two techniques to measure the gastrointestinal endogenous phosphorus outputs and true phosphorus digestibility with pigsThe Regression analysis technique (REG) and Difference technique were used to estimate endogenous P outputs and true P digestibility value with soybean meal (SBM) or wheat middling meal (WM) as only P source in diets for animals. Eight barrows, average initial body weight 20kg, were allotted two groups randomly, fed four diets each group according to a 4X4 Latin Square design. Four cornstarch-based diets containing four levels of P (0.15. 0.20, 0.30 and 0.35%) based on fed status each group were formulated from SBM or WM. Each experimental period comprised 8d with 4-d adaptation and 4-d collection feces. Results showed that: There were significant linear relationship (P<0.05) between fecal P outputs and dietary inputs of P when both expressed as g/kg.DM intake diet with TP level of diet from 0.15% to 0.35%. which suggests a stable amount of endogenous P lose in feces for pig. No significant differences (P>0.05) of endogenous P existed determined by REG and Difference technique with SBM and WM, implicated that the two assays are valid for estimating endogenous P outputs in pigs. The endogenous P output was 0.65-0.68g/kg.DM intake dietsunder tested TP levels and true P digestibility value of SBM and WM in growing pigs were 52.1% and 63.7% respectively.Experiment two True phosphorus digestibility values and their additivity measured in single feed ingredients and predicting models of true digestible phosphorus for growing pigsFive trails according to two of 6 X 6 and three of 4 X 4 Latin Square design were conducted to determine true P digestibility values of 17 kings of single feed ingredients and 2 compound diets for growing pigs of 25kg initial weight by substitute assay based on analyzing the contents of their TP, PP and Phy activity and their relationships among them. Meanwhile the additivity of digestibility values measured in single feed ingredients were tested. Results showed that: 1. There are great differences of contents of TP, PP and Phy activity among different species of plant feedstuffs. There are rich contents of Phy in kinds of cereal, such as wheat, barley and their by-products. 2. A significant linear relationship was found between PP and TP in tested samples. The higher PP the higher TP existed, but no significant linear relationship was found between PP and Phy. 3. True digestibility values are good additivity in diet formulation. 4. Some high-accuracy and applied prediction equations in this experiment were as follows:Apparent digestible P (g/kg) = -0.411-0.405 XTP (g/kg) - 0.227 X PP (g/kg) -r 0.00315 X Phy (FTU/kg) R: = 0.822. RSD = 0.272. PO.001.True digestible P (g/kg) = -0.0629+0.655 X TP (g/kg) - 0.412 X PP (g/kg)R2 - 0.859. RSD - 0.386, P<0.001. True digestible P (g/kg) = -0.220+0.589 X TP (g/kg) - 0.304 X PP (g/kg)+ 0.003 X Phy (FTU/kg) R2 = 0.882, RSD = 0.244. PO.OOO 1.5. The accuracy of prediction equation could be improved after feedstuffs is classified by different nutrients, especially different contents of PP and Phy activity.Experiment three In Vitro procedure for assessing phosphorus availability in feed ingredients and establishing prediction model of t... |
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