**7. Final considerations**

There is still a long way to go and studies must be done to optimize probiotic formulas in order to guarantee the desired effect. Promising steps were evidenced with the administration combined with other strains of the same or different species and also with other additives such as: phenolic compounds, enzymes, prebiotics and unconventional ingredients.

Generally, the efficacy of probiotics in broilers is evaluated by parameters such as weight gain, feed conversion, and resistance to pathogens, ignoring other aspects such as commercial or natural conditions of the product used, its interaction with feed components and the environment, and their impact on the animal's response. During the use of probiotics, other mechanisms by which these live microbes can affect the host, such as the role in the maturation of the nervous and enteric systems that mediate animal behavior through the gut-brain-microbiota axis, need to be considered.

Even with validated effects of probiotics in several studies, research still shows that the different responses found suffer influences related to environmental factors, specific to the host or the strain, dosages recommended by the manufacturers of the products, types of strains used either alone or in combination, joint use of zootechnical additives, as well as different experimental conditions and greater or lesser health challenge in the broiler breeding phases.

Considering all of the aspects described above, new approaches to checking the effects of probiotics will be possible, and it would be interesting to go beyond the usual comparison that focuses on "treated animals compared to untreated animals" that is observed in most studies to assess effectiveness of probiotics. Both in research and in the application (judged by the supplier market) of probiotics, the role they play as an additive is evidenced, not exactly as a growth-promoting additive, but one that improves, restores, and or installs the optimal conditions for the obtaining the best performance in broilers.
