The objective of this study was to determine the effect of tylosin and prebiotics (β-glucans and mannanooligosaccharides) on fermentation processes, rumen microorganisms and production yield in calves. The study was performed on clinically healthy, Black and White Lowland breed calves, 36 aged 6-8 weeks and 120 aged 10-14 weeks, respectively. The calves were randomly divided into three equal groups. The calves in group I were fed with feedingstuff supplemented by the tylosin. The second group of calves received prebiotics and the control (group III) was fed the same feedingstuff without the additives. The rumen fluid samples were collected at one week intervals for seven weeks. The following parameters of the samples were determined: protozoa and bacteria count, as well as selected basic rumen metabolism parameters (pH, volatile fatty acids, fermentation of glucose, digestion of cellulose, reduction of nitrates). In the field trials on the older animals, production parameters such as the body weight gains, growth (GR) and feed conversion rates (FCR) were investigated. The significant changes in the rumen functions with different characteristics were noted in both experimental groups. The increase in the total number of bacteria and decrease in protozoa were observed in calves treated with prebiotics (Group II). In contrast, in calves that received tylosin (Group I) the parameters behaved in a reverse manner. The positive changes were also observed in the rumen metabolism during the prebiotic applications. A significant improvement in glucose fermentation, cellulose digestion and nitrite reduction was recorded. Moreover, a significant decrease of pH and increase of volatile fatty acid concentration in rumen fluid were observed. The opposite results were noted in the calves receiving tylosin. Additionally, the production parameters were higher in the calves than in the remaining animals; however, in all experimental calves more profitable values of growth rate (GR) and body weight gain were noted than in the controls. Overall, it appears that prebiotics can be a promising alternative for withdrawn antibiotic growth promoters.
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