Prevalence of Mycoplasma hyopneumoniae in piglets at weaning as a predictor of the severity of the disease in growing pigs

摘要

Mycoplasma hyopneumoniae remains a significant pathogen in the pig industry, despite a very important trend towards high health production. 1>2 In offsite weaning herds, there appears to be considerable variation between groups as regards severity ofthis disease, with a number of groups reaching slaughter without obvious evidence of disease, while others may show clinical signs and lesions in varying degrees. We have postulated that these differences are a reflection of the prevalence of infected piglets at weaning, since these animals presumably constitute the main infection source for the group. This hypothesis is based in the apparent slow spread of this organism, particularly when the microbial pressure is low, as well as the apparent need to have a significant population within the group infected before clinical signs become evident and characteristic lesions can be detected.3 It has been suggested that vertical transmission of the agent is influenced by sow parity distribution and the infection pressure in the sow herd.2 The manifestation of these two factors can be different in every farrowing group, resulting in fluctuation of the vertical transmission rates and prevalence at weaning. Our group has shown that sow interventions (both vaccination and antibiotic feed treatment) significantly reduced the prevalence of infected pigs at weaning; suggesting that vertical transmission during lactation is the main risk factor for developing disease in the group. However, there are no studies supporting this hypothesis and there are no estimates of which prevalence levels determine the severity of disease for the group. Therefore, we need information that supports that sow interventions constitute an adequate means of controlling the problem in growing populations.