Mycoplasma bovis (M. bovis) is an important pathogen affecting cattle, causing various diseases including pneumonia which mainly occurring in calves. Control of M. bovis infections is difficult due to the lack of commercial vaccines in most parts of the world and increasing trends of antimicrobial resistance in field isolates of the pathogen; therefore, it seems reasonable to look for new solutions for the prevention of the infection. Pegbovigrastim is a pegylated form of naturally occurring circulating cytokine in cattle that affects bovine leukocytes and some cell functions. Most studies on pegbovigrastim have focused on reducing the occurrence of mastitis and other diseases occurring during the periparturient period in cows, while this study attempts to use pegbovigrastim in the prevention of respiratory diseases in calves, which are largely caused by M. bovis. Based on previous observations on the immunostimulatory properties of pegbovigrastim in cattle, for the first time, the effect of its injection on the number and phagocytic and oxidative burst activities of peripheral blood granulocytes and monocytes in calves experimentally infected with M. bovis was investigated. Pegbovigrastim administration in the calves significantly stimulated an increase in peripheral blood granulocyte and monocyte counts and phagocytic activity of the cells, especially granulocytes, which was also generally expressed in the course of M. bovis infection. In response to pegbovigrastim administration, a general increase in the oxygen burst activity of the cells was observed. This effect was also shown despite ongoing infection with M. bovis which, taken together, may indicate a beneficial effect of pegbovigrastim injection on the immunity of the affected animals.