The additive is a preparation containing viable spores of a strain of Bacillus subtilis which has never been authorised in the EU. It is intended to be used in feeds for chickens for fattening at the recommended dose of 1 × 109 colony-forming unit (CFU)/kg complete feedingstuffs. The bacterial species B. subtilis is considered by EFSA to be suitable for the qualified presumption of safety approach to safety assessment. As the identity of the active agent has been established and the susceptibility to antibiotics and lack of toxigenic potential have been demonstrated, the use of Bacillus subtilis DSM 28343 can be presumed safe for the target species, consumers of products derived from animals fed the additive and the environment. Bacillus subtilis DSM 28343 is not an eye/skin irritant but should be considered as a potential respiratory sensitiser. In the absence of data, no conclusion can be drawn on the skin sensitisation potential. Bacillus subtilis DSM 28343 at the proposed dose has the potential to be efficacious in improving growth of chickens for fattening. B. subtilis DSM 28343 is compatible with the coccidiostats lasalocid A sodium, diclazuril, monensin sodium, maduramicin ammonium, decoquinate, nicarbazin, robenidine hydrochloride and halofuginone hydrobromide.