Introduction: Mycoplasma (M.) hyorhinis is an ubiquitous pathogen within the swine population and can be detected in both, healthy and diseased animals. It is considered as a member of the bacterial flora of the upper respiratory tract, even in healthy pigs. The relevance of this pathogen is yet discussed, but M. hyorhinis is known to cause pneumonia, polyserositis and arthritis in pigs. The objective of this survey was to investigate the effects of Tulathromycin (Draxxin®, Fa. Pfizer GmbH, Berlin, DE) on M. hyorhinis in pigs in a field trial.
Materials and Methods: This survey includes 150 pigs with an average bodyweight (bw) of 18 kg at the beginning of the study. They are randomly divided into a treatment and a control group. Pigs of the treatment group receive a single dose of 2.5 mg tulathromycin / kilogram bw intramuscularly on study day 0. From each group, 30 pigs are determined for further clinical examination. Bronchoalveolar lavage fluid samples (BALF) are collected from these 60 animals on study days 0, 5 and 15. Pigs are anaesthetized with ketamine (20 mg / kg bw) and azaperone (2 mg / kg bw) for BALF sampling and also examined during anaesthesia. The BALF is analysed for M. hyorhinis by PCR and culture. On study days 0 and 15 all pigs are weighed and on study days 0, 1, 2, 3, 5, 7, 9, 11, 13 and 15 a cough index is calculated for both groups by counting all coughing fits of pigs in one pen during ten minutes and dividing them by the number of animals in that pen.
Results and Discussion: The percentage of positive animals and the amount of M. hyorhinis detected on study day 0 does not differ significantly between the two groups. In the treatment group, the percentage of positive animals and the amount of M. hyorhinis isolated from BALF is significantly reduced from study days 0 to 5 and 5 to 15. A significant reduction for the amount of M. hyorhinis can also be detected in the control group over the study period. However, the percentage of positive animals and the amount of the pathogen are significantly higher in the control group on study day 5 and 15 when compared to the treatment group. The cough index of the treatment group falls constantly from day 1 to 9 and stays below the values of the control group over the second half of the study. The clinical score is significantly reduced from study day 0 to 5 in both groups, but from day 5 to 15 it does rise significantly in the control group while staying low for the treated animals. The mean body weight does not differ significantly between groups on day 0. During the trial period the average daily weight gain is significantly higher in treatment group when comparing to the control group. These results widely coincide with the results of PALZER et al. (2007a), who study the efficacy of tulathromycin against pathogens of the respiratory tract in a similar designed investigation. The trial data verifies the positive effect of a single treatment with tulathromycin on the health status and performance of the pigs. In particular the reduction of the amount and the detection rate of M. hyorhinis in the treatment group prove the efficacy of tulathromycin against this pathogen.