|Weinberg, Zwi -|
Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: March 29, 2013
Publication Date: July 22, 2013
Citation: Weinberg, Z.G., Muck, R.E. 2013. Potential probiotic effects of lactic acid bacteria on ruminant performance. In: Daniel, J. L. P.,Santos, M. C., and Nussio, L. G., editors. Proceedings of the III International Symposium on Forage Quality and Conservation, FEALQ, Piracicaba, SP, Brazil. pp. 47-68. Technical Abstract: Probiotics are microbial feed supplements that benefit animals by improving the microbial community of the digestive tract. In humans, probiotics are species that can survive the stomach and influence the intestinal microflora. The mode of action of human probiotics is not as yet proven. However, there are various hypotheses: competitive exclusion, modulation and enhancement of the immune system against pathogens, production of antimicrobial substances such as bacteriocins, changes in the intestinal environment by fermentation of carbohydrates by the probiotic microorganisms, and shifts in the metabolism of intestinal bacteria from being proteolytic to saccharolytic. In cattle, active dry yeasts are the dominant probiotics. There are various assumptions regarding the ways by which yeasts exert beneficial effects on the host animal: aiding in the establishment of the microbial population in the rumens of calves, stabilizing rumen pH, stimulating cellulolytic rumen bacteria by supplying vitamins and other growth factors, scavenging oxygen to maintain anaerobic conditions in the rumen, and inhibition of potential pathogens. Lactic acid bacteria (LAB) are the other group of microorganisms that have been shown to have a positive effect on ruminant performance. Some have been fed directly to ruminants, but more interesting is the effect of some LAB silage inoculants on animal performance – milk production, gain, feed efficiency. While the shifts in the products of silage fermentation from using a LAB silage inoculant are beneficial to cattle, the increases in milk production, for example, from some inoculants are several times greater than that expected from the changes in silage fermentation. Recent research has focused on various aspects of why that may be happening. For a true probiotic effect, the LAB strain must be able to survive in the rumen. Inoculant strains that have been tested have survived for at least 72 h in rumen fluid and increased pH, which should have a positive effect on digestion of structural carbohydrates in the rumen. Inoculant strains have been tested for antibacterial activity, and 9 of 10 strains showed antibacterial activity. When silages with and without inoculant treatment were analyzed for in vitro digestibility with and without starch added, silages inoculated with certain LAB strains exhibited less inhibitory effect of starch on fiber digestibility. In separate in vitro analyses, silages treated with certain LAB strains have produced more ruminal microbial biomass than untreated silages. Both improvements in digestibility and increases in ruminal microbial biomass can explain the observed increases in milk production. However, the exact mechanisms for these improvements in rumen microbial activity are still to be discovered.