In industrial poultry production, especially in broiler chickens, coccidiosis, caused by Eimeria protozoa parasites in the digestive tract, continues to be a serious health and economic problem. In economic terms, the losses are mainly caused by the costs of prevention and treatment, as well as the reduced weight gain and reduced condition of the birds. Currently, the prophylactic program of this disease unit is mainly based on the use of chemotherapeutics. Another way to control coccidiosis is active immunoprophylaxis, based on the vaccination of chickens for fattening, and passive immunoprophylaxis, based on vaccination of the parent flock. An alternative, effective way to reduce the negative effects of protozoan infestation by Eimeria may be the use of herbs and their extracts, pre- and probiotics and betaine.

The withdrawal of antibiotic growth stimulators as of 1 January 2006 in the European Union countries has forced the search for alternative solutions to improve the health and productivity of poultry. The poultry industry also faces the challenge of developing alternative feeding systems with the restriction or exclusion of coccidiostats. One of them is the use of probiotic strains as feed additives. This study aimed to determine the effect of the use in compound feed of a probiotic containing Bacillus licheniformis on rearing rates and postmortem performance of broiler chickens. The experiment was performed on 8012 unsexed broiler chickens of the Ross 308 line divided into four equal groups. The experimental factors were the addition of a probiotic containing Bacillus licheniformis bacteria and the addition of a coccidiostat. The introduction of probiotic bacteria into compound feed did not increase the body weight of birds, in particular, control weights, and at the end of rearing, but it decreased the feed conversion rate (FCR) and mortality. Addition of probiotic in compound feed did not have a significant effect on bird muscle. The mean weight of pectoral muscle between control (C+, C–) and study (C–BL, C+C–BL) groups did not show statistically significant differences; however, the highest mean weight of the evaluated parameter was visible in the C+ group (0. 665) and the lowest in the C–BL group (0. 623). Similarly to the mean weight of the carcass, also in the mean weight of thigh muscles, the lowest statistically significant values were observed in chickens belonging to the C+C–BL group (vs. C–; P <0.05). Based on the obtained results, it can be acknowledged that the probiotic bacteria Bacillus licheniformis in broiler feed can be a good feed additive to replace antibiotics/coccidiostats. This probiotic has a positive effect on the overall health of birds, contributes to better use of nutrients and stimulates growth and development of broiler chickens.