Acid-binding capacity of feed in swine nutrition

Young pigs have an immature gut and do not provide adequate gastric acidity to digest nutrients and inhibit bacteria growth in the gut. Diets have intrinsic ability to alter gastric acidity. Acid-binding capacity (ABC) and buffering capacity (BC) are often used to describe the ability of feedstuffs to influence pH changes, but methods to measure and units to express ABC and BC values vary among studies and need standardisation. Some feed ingredients, noticeably minerals have high ABC values, thus could neutralise gastric acidity in pigs. The ABC values are related to initial pH but vary among and within feedstuffs, thus, more research is required to depict the full picture. Diets with high ABC values are detrimental to young pigs. Diet ABC values can be reduced by lowering protein content, alternative use of minerals, coarse grinding, and inclusion of organic acids (OA). Most OA have negative but varied ABC values and are effective and practical in lowering pH and ABC values of diets. However, their ability to alter gastric acidity has been inconsistent. Whether dietary OA inhibits hydrochloric acid secretion in the stomach of pigs requires elucidation. Lowering ABC values may increase ileal digestibility of protein and improve growth performance of pigs. However, the dose response of OA to lower ABC values of diets on growth performance of pigs is inconsistent. Other dietary factors, e.g., mineral and fibre content or the ABC value of the basal diet may affect efficacy of OA. Lowering diet ABC values via dietary OA and OA salts may increase microbiota diversity and reduce E. coli counts in the gut, reduce diarrhoea incidence and Salmonella prevalence, and reduce ammonia emission, thus has the potential to replace antibiotics and zinc oxide used in pig feed currently. However, lowering diet ABC values via certain dietary OA may affect feed palatability and preference, cause metabolic acidosis and affect bone health of pigs. In conclusion, diet composition determines its ABC value that affects diet nutrient digestion, growth performance and gut health of pigs. Incorporating the concept of lowering ABC values of feed is an important factor to manage growth performance and gut health of young pigs. To establish and verify a system of using ABC values to formulate pig diets, more research is warranted.