The effects of probiotic feed additives in animals mainly consist of (1) maintaining normal intestinal flora by competitive exclusion and antagonism, (2) increasing digestive enzyme activity and decreasing bacterial harmful enzyme activity (e.g. β-glucuronidase) and ammonia production, (3) improving feed intake and digestion and (4) stimulating the immune system .
The Bacterial antagonism And Competitive Exclusion
According to the concept of competitive exclusion, added cultures of beneficial microorganisms to the feed, compete with potentially hazardous bacteria for organic substrates like carbon and energy sources and adhesion sites. Probiotics have the potential to colonize and multiply in the gut, blocking receptor sites and inhibiting the adhesion of hazardous enteropathogenic bacteria like E. coli or Salmonella.
The presence of acid-producing microorganisms in the gastrointestinal tract has crucial antagonistic activity against pathogenic microorganisms. Probiotics can compete with different harmful microorganisms by producing and secreting some substances with bactericidal effects such as bacteriocins, hydrogen peroxide and diverse organic acids.
Immune Modulation
Regular use of probiotics significantly increases the production of natural interferons/cytokines, boosts the activity of macrophages, lymphocytes, and natural killer (NK) cells, raises levels of immunoglobulin (IgG, IgM, and IgA), and stimulates the creation of γ-interferon. Probiotics increase the number of lymphocytes and lymphoid cells in lamina propria and intra-epithelial lymphocytes (IEL) in the small intestine and are found to inhibit the growth of infective microorganisms.