Indagini in vitelli da carne vaccinati con mutanti termosensibili dei virus parainfluenza-3 (PI-3), rinotracheite infettiva (IBR) e adenovirus (BAV-3)

The results of a field experiment carried out in imported beef-calves to test the efficacy of intar-nasal vaccination with temperature-sensitive mutants of PI-3, IBR and BAV-3 are reported. The study was carried out on a total of 146 vaccinated and 159 control animals distributed in 3 different farms during 5 production cycles. On the basis of the observation of the occurrence of respiratory clinical signs, serological conversions, weights at slaughter, the use of the vaccine tested did not seem to have increased either the antibody levels or the resistance against respiratory diseases of vaccinated animals compared to controls. No apparent economic benefit was obtained by the use of the vaccine. Hypotheses are formulated about the possible reasons of the discrepancies between the results obtained in experiments carried out in seropositive animals under field conditions such as those of the present experiment and those obtained in seronegative animals under controlled conditions, reported by other Authors.