Acid-binding capacity (ABC) of a feed is the amount of acid required to reduce the pH of feed to a special level such as 3. All poultry feed ingredients used in this study were collected from feed mills in Iran. The pH and ABC were determined using the standard methods in deionized and magnetized water at room and body temperatures. The pH of most feed ingredients was raised in magnetized water as compared to deionized (untreated water). The pH of most feed ingredients especially organic acids was decreased in warm water. Energy sources accompanied by synthetic amino acids and common salt and some additives such as prebiotic and zeolite had the lowest values of ABC (less that 400 mEq/kg). Protein sources and some supplements and additives had average ABC of about 400-1000 mEq/kg, and some vitamins and minerals had high level of ABC (more than 1000 mEq/kg) among all ingredients. Calcium carbonate and sodium bicarbonate, along with ammonium formate and calcium propionate had the highest ABC values among all ingredients. Pelleting did not show any pronounced impact on pH or ABC of whole diet; while extruding did not alter ABC of soybean but significantly increased ABC of flaxseed. These results give indication that the type of feed ingredient, or processing and solution used for ABC evaluation, especially magnetizing treatment and ambient temperature, are determining factors for ABC of feedstuffs. تفاصيل المقالة