Because of these benefits it is no surprise the use of probiotics has rapidly increased, and with it the availability of commercial products. However, choosing the right probiotic in this abundance of products is not an easy task.
One of the major distinctions in the current probiotic market is the difference between single- and multi-strain products. The idea behind multi-strain products is mainly that by combining multiple probiotics in the same product, each strain brings its own benefits and as a result, the final product can list multiple advantages.
Although this may sound logical at first, there are some important considerations to this reasoning that should not be neglected. In what follows, only spore-forming probiotics will be kept in mind: spores offer superior stability during storage, feed processing and within the animal. As such, comparing a single-strain product containing spores with a multi-strain product without spores would not be fair either way.
If multiple probiotics are used in one product, an aspect of inherent competition might be introduced, depending on the characteristics of the strains used. This is especially the case if they are part of the same genus (Bacillus for example). Due to their similarities, the strains are expected to compete for similar requirements, including nutrients and space. This could potentially diminish the intended beneficial effect, as the probiotics might challenge each other. Strains of the same genus are often also active at the same location within the gastrointestinal tract, adding to the logic that they could compete with one another.
Omnipotent products do not exist
The reasoning behind combining multiple probiotics into one product, resulting in multiple benefits for said product, leads to the question how many strains can be combined. If that number increases, the list of benefits should become much more substantial as well. As such, in theory this logic could lead to a product containing an unlimited number of strains, and thus with a very long list of benefits. Some commercial probiotic products do follow this reasoning, but as is evident from the market, they are far from dominating compared to single- or limited multi-strain products.
In vivo trials do not support a clear multi-strain superiority
A recent field study evaluated three Bacillus strains (two B. subtilis and one B. amyloliquefaciens; Sandvang et al., 2021) in supporting broilers during a Clostridium perfringens-based necrotic enteritis (NE) challenge. The trial included the three strains on their own, as well as all three in the same treatment, and was set up to examine the potential synergy between the strains.
From the data, it was clear that all probiotic treatments showed significant benefits compared to the control. When the data was examined per growing phase, at least two of the three single-strain treatments consistently performed to the same level of the multi-strain combination, for all individual measured technical parameters.
Regarding multi-strain superiority, the combination only outperformed all single-strains when body weight and the adjusted feed conversion ratio were considered simultaneously, and only when the data was aggregated for the overall period.
All probiotic treatments had a positive effect on health indicators such as lesion scores and mortality, and also here the multi-strain treatment consistently scored to the same level of at least two of the three single-strain treatments.
Despite the goal of creating synergies in multi-strain probiotic products, there are multiple logical arguments to keep in mind when probiotic strains are combined. The commercial market seems to agree with this reasoning, as multi-strain probiotic products do not outcompete single-strain products. Finally, recent peer-reviewed research confirmed once again that probiotics work, but also that there is room to debate the idea of multi-strain superiority.