When you are involved to increase your Day Old Duck quality, many ways are possible : hatchery management, vitamins & microelements in breeders, & sometimes additives. In this huge world of additives, Probiotics have a specific target = change the microbiota to a healthy one ! Many studies in all the species proved that is possible, and, a better microbiota means a better health.
Several families of Pre/Probiotics exist on the market, one is the live microorganisms (bacterium alone or a mixture). We can speak sometimes to a “new flora”. The idea is to provide good bacteria inside the feed, the water or on the eggshell/ducklings (at the hatchery level). Those additives should decrease the health challenges, so, less use of antibiotics.
Inside feed &/or water, we want to limit the development of undesirable bacteria by many ways = competition for nutrients, place on the gut wall, less energy spend to fight against bad bacteria … This way is very efficient when birds are young, but less & less efficient with age. Why ? Because when a duck is adult, the gut is fully mature, to change is microbiota, you should provide the “new flora” all the time. Otherwise, you will come back to the previous flora in a short time (except if this new flora is coming from “Duck bacteria strain”, in this case, this flora could multiply alone by natural colonization).
On the eggshell, at the hatchery, we want to avoid development of bad bacteria from unfertile eggs or eggs with a dead embryo/duckling. The timing (at which day of incubation) & the flora used are crucial to reach a good effect (this way is more complicated than inside feed). On the ducklings, they will ingest this flora to make a good first colonization of their gut (same effect than inside feed or water but earlier).
We use and test those additives at different levels to provide the best duckling quality everywhere. Currently, they are used, even in very good conditions. By this way, they could increase the performance of growth, laying rate… Never forget that use a live good bacterium in the same time to an antibiotic treatment is useless, because you will kill it ! However, use this live bacterium just after an antibiotic treatment will be very useful to create a new & good microbiota (whatever the age). Keep in mind also that should work well in young duck, however, I think no live bacteria from duck are available on the market (mostly they come from broiler strains). In addition, like all additives, you must try in your local conditions to check if it’s working well or not for your farms !