Abstract
BACKGROUND: This field efficacy study was designed to determine the efficacy of a new bivalent vaccine containing porcine circovirus type 2d (PCV2d) and Mycoplasma hyopneumoniae at three independent pig farms. METHODS: Three pig farms were selected based on their history of subclinical PCV2 infection and enzootic pneumonia. Each farm housed a total of 40, 18-day-old pigs that were randomly allocated to 1 of 2 treatment groups. Pigs were administered a 2.0 mL dose of the bivalent vaccine intramuscularly at 21 days of age in accordance with the manufacturer's recommendations, whereas unvaccinated pigs were administered a single dose of phosphate-buffered saline at the same age. RESULTS: Clinically, the average daily weight gain of vaccinated groups was significantly higher (p < 0.05) than those of unvaccinated animals during the growing (70-112 days of age), finishing (112-175 days of age) and overall (3-175 days of age) stages of production. Vaccinated animals elicited neutralizing anti-PCV2 antibodies and PCV2d-specific interferon-γ secreting cells (IFN-γ-SC), which reduced the amount of PCV2d genomic copies in blood and reduced lymphoid lesions severity when compared with unvaccinated animals. Similarly, vaccinated animals elicited M. hyopneumoniae-specific IFN-γ-SC, which reduced the amount of M. hyopneumoniae in the larynx and reduced lung lesions severity. CONCLUSIONS: The result of the field trial demonstrated that the bivalent vaccine was efficacious in the protection of swine herds suffering from subclinical PCV2d infection and enzootic pneumonia.