Ahmadreza Mirzaei1* , Seyed Amin Razavi 2 , Daryoush Babazadeh2 , Richard Laven3 , and Muhammad Saeed4
1 Post-Doctoral fellow at College of Veterinary Medicine, University of Florida, Florida, USA
2 Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran
3 School of Veterinary Science, Massey University, Private Bag, Palmerston North, New Zealand
4 Department of Animal Nutrition, College of Animal Sciences and Technology, Northwest A&F University, Yangling, China * Corresponding author: Ahmadreza Mirzaei, College of Veterinary Medicine, University of Florida, Florida, USA. Email: ahmadrez.mirzaei@ufl.edu
Abstract:
There are many reports of the positive effects of probiotics on gastrointestinal tract (GIT) microorganisms and the immunological systems of their hosts. Probiotics have prophylactic and metaphylactic properties. The two main mechanisms of action of probiotics seem to be the release of compounds with beneficial effects and direct interaction with the cells of the host. The aim of this review was to evaluate the benefits of probiotic use in farm animals and to identify how they influence farm animal performance. The published data suggest that dietary supplementation of probiotics can improve the growth performance, nutrient digestibility, and immune response of farm animals, including cows, sheep, goats, pigs, aquacultures, and poultry. In ruminants, studies have shown that probiotics can significantly enhance the immune response, milk yield, food digestibility, and weight gain, particularly in ruminants exposed to stressful conditions. This is also the case in aquaculture as probiotics have been shown to enhance growth and reproduction traits, provide protection against pathogens, have positive effects on immunity, optimize digestion, and increase water quality. In horses, there is still controversy about the advantages of probiotic supplementation. In addition, some studies showed valuable effects of using probiotics on treatments of GIT diseases, and some studies showed adverse effects of supplementation of probiotics in horses. In poultry, balancing the intestinal microflora is not achievable but controlling the population of microflora is possible and studies showed that supplementation of probiotics could influence some aspects such as improving performance and health parameters. So, probiotics are used by almost all farmers who are trying to reduce antibiotic resistance. In conclusion, dietary supplementation of probiotics to farm animals has many notable influences on their performance, immune system, and diet digestion.
- Introduction:
Probiotics have attracted great attention due to their positive effects on gut microbiota and immunological systems in humans and livestock1,2. Probiotics are used as prophylaxis and for therapeutic purposes in both humans and farm animals3,4, with probiotics being a safe and viable alternative to the use of antibiotics growth promotors which can result in antibiotic resistance in microbial population5. When used in farm animals instead of antibiotics dietary supplementation of probiotics can improve growth performance, nutrient digestibility, and immune response and reduce the incidence of diseases 1,5. In addition, probiotics increase the oxygen concentration in the gastrointestinal tract (GIT) in a multiplicity of ways including through depleting oxygen-scavenging compounds, such as nitrates. Moreover, probiotics secrete hydrolytic enzymes that can hydrolyze bacterial toxins and inactivate toxin receptors, leading to a decrease in toxin-mediated infections in farm animals6.
Probiotics decrease pathogenic microorganisms in the GIT and establish a better microbial population in the GIT7. Probiotics can also activate an immunologic response and assemble a series of immunoregulatory molecules8. Some probiotics produce metabolites that can modulate metabolic pathways in the cell, such as bacteriocins, amines, and hydrogen peroxide. These metabolites can adjust cell apoptosis, proliferation, inflammation, and differentiation9. Microorganisms used as probiotics should be nonpathogenic, optimize host health, and improve GIT function. The microorganisms commonly used as probiotics in animal diets are principally bacteria, usually Gram-positive bacteria. Lactobacillus and Enterococcus are natural flora in the alimentary tract of most animals and are usually present in amounts of 107-108 and 105-106 CFU/g, respectively10. Lactobacillus acidophilus (L. acidophilus), L. lactis, L. plantarum, L. bulgaricus, L. casei, L. helveticus, L. salivarius, Bifidobacterium spp., Enterococcus faecium (Ent. faecium), Ent. faecalis, Streptococcus thermophilus, Escherichia coli are the most commonly used probiotic bacteria in farm animals and probiotic fungi such as Saccharomyces cerevisiae (Sacc. cerevisiae) and Sacc. boulardii are the most commonly used probiotic fungi 11-15. Of note, no other substances should be supplemented during the administration of probiotics such as antibiotics, disinfectants, and materials that interrupt with the mechanism of action of probiotics. In addition, water used for dilution should not contain chlorine or disinfectants10. Factors, such as the optimal selection of microbial strains, host species, and age are critical in the selection of probiotics15. Given the positive effects of dietary supplementation of probiotics on farm animals’ immune response and growth performance, the current study aimed to review the benefits of probiotics and their mechanism of action in farm animals.
