Retrospective study of serological dynamics of Lawsonia intracellularis in intensive swine production systems in Chile

Objective: This study aimed to analyze the serological dynamics of Lawsonia intracellularis under field conditions in intensive swine production systems in Chile. Materials and methods: Between 2013 and 2018, 80 serological profiles were collected from 23 intensive central-Chilean swine farms, containing 3257 serum samples from different animals. A crosssectional study design with multiple sampling points was used and samples were classified into commercial pigs, growing gilts, or breeding sows. Herds were classified as single or multisite. Samples were collected after weaning in a 3- to 4-week interval. Samples were analyzed for the presence of anti-L intracellularis antibodies using a commercial enzymelinked immunosorbent assay. Results: Of the 3257 serum samples analyzed, 56.62% were positive and 15.94% were suspect for L intracellularis. Higher seropositivity was observed in breeding sows and commercial pigs, with the lowest seropositivity in growing gilts (P < .05). In commercial pigs, the highest seropositivity was observed in ages closer to market with statistical differences between production systems at specific age ranges. For growing gilts, we observed a constant increase in seropositivity without evidence of maternal immunity decline. Breeding sows had the highest seropositivity, with parity 6 or more having the highest percentage of inhibition, even though there were differences among parity groups. Implications: All farms in this study had at least one L intracellularis-positive serum sample, indicating widespread presence in intensive Chilean swine farms where vaccination was not implemented. Maternal immunity decreased between 6 and 8 weeks of age, with seroconversion increasing at 12 to 14 weeks.