Effects of an inactivated vaccine for bovine mycoplasmosis on calves naturally affected with Mycoplasma bovis

Three autogenous vaccine trials were carried out on farms where Mycoplasma bovis had been identified as a major pathogen. The first trial was carried on a veal farm in the Lombardia region of northern Italy. Vaccine, prepared by saponising an M bovis strain taken from the farm some months before, was given as single inoculation to 24 calves on arrival while 19 were left unvaccinated. Six months later calves were sent to the abattoir where lungs were examined for gross pathological lesions. The mean weight of the vaccinated group was higher though not significantly so and mean lesion scores were similar; however the percentage of vaccinated calves with severe lung lesions and pleuritis was lower than in the non vaccinates. A second trial was carried out in northern England on a farm where monthly batches of male calves from a nearby dairy herd were reared under a feedlot system. One group of 27 calves were vaccinated with a saponised strain of M bovis isolated from the lungs of a pneumonic calf on the farm prior to the start of the trial. A second batch of 25 calves was left unvaccinated. The groups of calves were monitored for nine months prior to slaughter and records kept of antibiotic usage and mortality. The mortality rates in the vaccinated calves were about 15% compared to 28% in unvaccinated calves; however there was no difference in the number of times calves were treated for respiratory disease. A third batch of calves, treated with oxytetracycline on arrival because a number were already showing respiratory signs, had a lower mortality rate and fewer subsequent treatments. A third trial was carried out on a milk veal unit in the Veneto region of Italy. A group of 19 calves were vaccinated on arrival with a saponised isolate taken earlier from the farm; a similar number of calves of the same batch were left unvaccinated. After 6 months animals were routinely processed at the abattoir and lungs inspected. Results showed that vaccinated calves had higher mean body weights and although similar mean lung scores there was a smaller percentage of vaccinated calves with severe lung lesions and pleuritis.