Mycoplasma hyopneumoniae (Afhp) is widely recognized as an economically significant bacterial pathogen of growing pigs, is the primary pathogen or enzootic pneumonia, and an important player in Porcine Respiratory Disease Complex (PRDC).1 Prevalence of infection with Mycoplasma hyopneumoniae is very high worldwide where pigs are commercially produced and most pigs are considered infected unless specific programs were put in place to eliminate the organism. Mycoplasma hyopneumoniae infection and clinical disease in growing pigs sourced from Mhp positive breeding herds is closely tied to the shedding status of the dam and her propensity to shed Mhp and infect her offspring during lactation.2 Specifically, primiparous sows are more likely ro infect their offspring than are multiparous sows. Additionally, it is clear that replacement breeding animals can shed Mhp and infect contacts for at least 200 days after infection.3Successful attempts to eliminate Mycoplasma hyopneumoniae from breeding herds arewell documented through various protocols involving combinations of antimicrobial therapy, vaccination, herd closure, depopulation, or partial depopulation/The concept of maintaining a breeding population free of Mycoplasma hyopneumoniae and thus producing growing pigs free of enzootic pneumonia is ideal and should be accomplished wherever it is feasible. Mycoplasma hyopneumoniae naive breeding replacements are commonly available today and the utilization of these naive replacement breeding animals hasbeen both a value and a challenge. Mhp naive gilts used in established Mhp infected breeding farms has sometimes led to increased colonization of the growing pig population, poor gilt reproductive performance and poor gilt retention due to chronic respiratory disease. Aerosol transmission of Mycoplasma hyopneumoniae is well documented and proximity to infected farms is a significant risk factor for infection or reinfection.5-6 Viable Mhp has been documented out to at least 9.2km from an infected sourcefarm. Unfortunately, not all breeding herds are good candidates for elimination due to the risk of re-infection. Knowing that some breeding farms will be required to maintain a positive stable status due to infection risk, the goal for these farms must be to reduce the rate of colonization with Mhp as low as possible during lactation so the growing pig population is minimally infected. A critical component of reducing piglet colonization is proper, early gilt acclimation.
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