Gut flora stabilisers
Gut flora stabilisers are functional group 4b of zootechnical additives: micro-organisms or other chemically defined substances which, when fed to animals, have a positive effect on the gut flora (Regulation (EC) No 1831/2003, Annex I). Each one needs an EU authorisation for specific species.
Are they "probiotics"?
That is the casual name, but in feed law they are zootechnical additives, each with a specific strain name, an identification number and an authorisation limited to particular animal species.
What does a number like 4b1841 tell you?
"4" is the zootechnical additives category and "b" the gut flora stabilisers group; the rest identifies the specific additive. Example: in Implementing Regulation (EU) 2019/1315, 4b1841 is a preparation of Enterococcus faecium DSM 7134 authorised for sows.
Why does the species matter most?
The authorisation covers only the species and categories of animals listed in the regulation. The number alone is not enough: check the species column.
Sources
Guide: The EU feed additives register: how to check an additive number on a pet food label
Educational information about the rules, not veterinary advice.