127 How to Best Calculate Acid Binding Capacity at pH 4 in Feed Ingredients for Weanling Pigs

Abstract

Abstract The value of acid binding capacity at pH 4 (ABC-4) of feed ingredients can be used to formulate weanling pig diets for improved feed efficiency and free of ZnO. In practice, it is expensive and time consuming to analyze all ingredients used in pig diet formulation. Therefore, the objective of this study was to determine the most efficient and cost-effective method to accurately predict ABC-4 in feed ingredients used in weanling pig diets. Variation of the ABC-4 value is low in most feed ingredients, and the average value of ABC-4 is accurate enough for use in feed formulation [Lawlor et al. (2005)]. However, limestone and soybean meal (SBM) were studied because of their contribution to dietary ABC-4, and their inherit variability in ABC-4. Results showed that when ABC-4 of limestone and SBM is analyzed, the error in ABC-4 of final feed decreases by 58%. Therefore, if SBM and limestone are analyzed for ABC-4, and fixed values are used for all other ingredients, the value of ABC-4 in the final diet will be +/-20 mEq/kg of the target ABC-4 (P < 0.05). When ingredients are not analyzed for ABC-4, the variability increases and value in final feed will vary between +/- 48 mEq ABC-4/kg (P < 0.05). Next, 39 samples of SBM were collected from the US, Brazil, and Argentina to develop a prediction equation of ABC-4 for SBM from its macro-nutrient composition. Values of ABC-4 of SBM ranged between 773 and 878 mEq/kg, with an average of 824 mEq/kg and STD of 28 mEq ABC-4/kg. No significant relationships between the analyzed macro-nutrients and ABC-4 of SBM were observed (R2 = 0.01, with cross-validation). Therefore, the accuracy and precision of predicting ABC-4 of SBM were not improved by developing a derivative formula to estimate ABC-4 in SBM from its macro-nutrients. Next, 24 samples of limestone were collected from Canada to develop methods to predict ABC-4 accurately and quickly. The value of ABC-4 ranged between 20,823 and 23,412 mEq/kg, with an average of 22,117 mEq/kg and STD of 431 mEq/kg. A good correlation was obtained between ABC-4 and near infrared spectroscopy calibration (NIR) lines (R2 = 0.79, unground, with cross-validation). We conclude that for accurate and rapid determination of ABC-4, and ease of application in nursery diet formulation, ABC-4 can be analyzed in limestone using NIR, in SBM using wet chemistry, and for all other ingredients fixed values can be used. Additionally, for accurate formulation of nursery diets, a safety margin of 20 mEq/kg can be applied to the target ABC-4 value in the final diet.