There are many products on the market sold as probiotics with label claims to enhance growth and production. Regulations governing the licensure, sale, and addition of these products to animal feeds require only that the product be safe, without regard to product usefulness. How probiotics act to modulate the ecology of the gastrointestinal tract is poorly understood. The addition of some probiotics, especially lactic acid-producing bacteria such as the ones included in this probiotic mixture have been shown to provide benefical effects such as enhanced weigh gain and feed conversion and protection from infection in pigs and other animals 5-8. One the other hand, other researchers have tried to identify beneficial effects of other probiotic bacteria without success9-12. In fact, in one study in dogs, animals actually excreted more Salmonella and Campylobacter following treatment with probiotics13. Importantly, most studies that fail to find beneficial effects of probiotic feed rarely end up in the scientifically peer-reviewed literature, thus the balance of readily available literature tends to support widespread effectiveness of probiotic feeding. Presently, since we do not know how these products work, it is a hit-or-miss approach to achieving favourable food safety, animal health and production effects by incorporating them in the ration.
It is been previously hypothesized that the effects of LAB are modulated primarily through the production of short-chain or volatile fatty acids that have a detrimental effect on Gram-negative bacterial flora (primarily coliforms and E. coli). Data from this study and other recently published literature however suggest that this mechanistic view is oversimplified . LAB are known to produce VFAs14. Although probiotic fed pigs in the experimental challenge had higher total VFA concentrations, no correlation were found between VFAs and E. coli or coliforms concentrations in this study . This is in accord with another recently published study conducted in piglets with a different probiotic preparation 15. Coliform and E. coli concentrations generally increased as the animals aged. This may account for the differences in counts observed in the experimental and field studies. The experimental studies, the pigs were followed only for 3 weeks post weaning whereas in the field study pigs were tested until they left the nursery. It is of interest to note that the E. coli and coliform concentrations were significantly (negatively) correlated with feed consumption (i.e. pigs that ate more had less E. coli). From this study it is not possible to determine if high concentrations of these organisms are a direct result of less feed consumption and an unhealthy balance of microorganisms in the intestine or whether high E. coli concentrations actually contribute to the cause of decreased appetite and feed conversion.
Since the gastrointestinal microbiology of piglets may vary significantly depending upon environment, health, and other management factors it is presently not possible to guarantee or predict the effectiveness of a particular probiotic treatment on individual farm even it has been previously assayed under different management conditions. In order to consistently select and predict the potential beneficial effects of a particular probiotic treatment, the mechanism of action must first be established.
