The aim of the study was to determine the effect of adding an antibiotic or zinc oxide together with the feed on the histological picture as well as on the apoptotic and proliferation activity of enterocytes in the mucus of the small intestine of fatteners. The investigations were carried out on 32 crossbred fatteners. The animals were fed in a two-stage system, with the addition of feed antibiotic (control group - C) or with the 0.1-percent addition of zinc oxide (the first stage of fattening; experimental group - E). Samples of small intestine segments (duodenum, jejunum and ileum) were collected post mortem and secured from 16 randomly chosen animals (8 animals from group E and 8 from C) fr histological, histochemical and immuno-histochemical analysis. Staining was conducted using the review method (H-E) and paS-Alcjan. For evaluation of apoptosis and proliferation, the antibodies bax, bcl-x bcl-2 and Ki-67 and PCNA were used. The histological, histochemical and immuno-histochemical evaluation of the mucus of the small intestine of the animals, receiving feed antibiotic or ZnO, showed a comparable influence of the used additives on the morphological traits as well as differentiated the apoptosis and proliferation abilities of the crypt epithelium (cells Ki-67 positive - duodenum and jejunum: P ≤ 0.05 K vs D; PCNA positive duodenum: P ≤ 0.01 K vs D). No negative influence of the zinc oxide additive on the mucus of the small intestine in fatteners was found, which indicates the potential possibility of employing it in the first stage of the fattening period.