At weaning piglets are exposed to physiological and environmental stress, which often result in reduced feed intake and little or no weight gain (Ravindran and Kornegay, 1993). During the last few decades, diets for weaning piglets have been boosted with various antibiotics in prophylactic doses against gastrointestinal disorders in order to obtain economic benefits due to improved growth rates (4 to 15%) and feed efficiency (2 to 6%; Mroz, 2003). However, growing public concern about the use of antibiotics in animal agriculture and the risk of developing cross-resistance of pathogens to antibiotics used in human therapy has prompted the pig industry to look for alternatives to antibiotic growth promoters that will give similar pig performance. The objective of this study was to evaluate the potential of inorganic acids (phosphoric acid) for nursery pig diets in order to determine their effects on weight gain, diarrhoea and resistance to illness.