Feeding nursery pigs with low acid-binding capacity-4 diets: systematic review of growth performance, gut health, digestibility, and diarrhoea

Weaned pigs have poor gastric acidic conditions and an immature gastrointestinal tract up to 7 to 8 weeks of age, which is related to reduced growth potential and increased diarrhoea risk. To decrease the gastric pH of weaned pigs, low acid-binding capacity-4 (ABC-4) diets have been suggested; ABC-4 is defined as the amount of acid required to reduce the pH to 4.0. This systematic review aims to provide a comprehensive understanding of the effects of low ABC-4 diets, using various dietary strategies, on growth performance, gastric pH, gut microbiome composition, digestibility, and diarrhoea occurrence in weaned pigs, and their potential as an alternative to pharmacological doses of zinc oxide (ZnO). A manual literature search was completed using the online databases Web of Science and Google Scholar with combinations of the following keywords: ‘pig’ OR ‘piglet’; and ‘fumaric acid’ OR ‘formic acid’ OR ‘citric acid’ OR ‘lactic acid’ OR ‘malic acid’ OR ‘fermented soybean’ OR ‘specialty soy protein sources’ OR ‘crystalline lactose’ OR ‘calcium carbonate’; and ‘performance’ OR ‘gastric pH’ OR ‘microbiome’ OR ‘diarrhoea’ OR ‘digestibility’. The searches yielded 1,128 articles (published between 2000–2025; 30 selected). Among the strategies, supplementing free organic acids seem a simple approach to reduce the ABC-4 levels of diets without altering the other feed ingredients. Feeding low ABC-4 diets positively affects growth performance in weaned pigs, while increasing gastric acidity and microbiome diversity, reducing faecal Salmonella and Escherichia coli counts, and decreasing incidence of diarrhoea, even when low doses of ZnO are used.