This paper reviewed issues regarding the use of probiotics (feed additive) in animal feeding. Probiotics are increasingly used in commercial animal production operations to advantageously alter gastrointestinal flora, thereby improving animal health and productivity. The major outcomes from using probiotics include improvement in growth, reduction in mortality, and improvement in feed conversion efficiency. Although it is not well defined, the mechanisms of probiotics activity to achieve their role include alteration in intestinal flora, enhancement of growth of nonpathogenic bacteria, forming lactic acid and hydrogen peroxide, suppression of growth of intestinal pathogens, and enhancement of digestion and utilization of nutrients.
Different probiotics contain different microorganisms which may behave differently, as probiotics are not single entities. It has been indicated that multi-strain preparation is highly efficient in animal feeding. Finally, the efficacy of probiotics have been found to be variable depending on survival rate and stabilities of strains, doses, frequency of administration, interactions with some medicines, health and nutritional status of the animal and the effect of age, stress and genetics of animals.