Persistence of passively acquired antibodies to Mycoplasma hyopneumoniae in a swine herd

A cohort of 95 piglets born to 12 sows seropositive for Mycoplasma hyopneumoniae (MH) was followed from birth until passively acquired MH antibodies, detected with an ELISA, reached their lowest concentration. The objectives of the study were to determine the half-life of maternally derived MH antibodies in the newborn piglet, and the relationship between maternal MH antibodies in the serum or colostrum and the initial concentration and persistence of MH antibodies in the neonatal pigs. Blood samples were initially collected from newborn piglets at 4 days of age, and subsequently at 14-day intervals. Sows were blood-sampled 1 month prior to farrowing, and colostrum was collected 2-6 h after the first piglet was born. Antibody concentrations were expressed as the ELISA ratio between mean optical densities of the sample and the positive control (S/P ratio). Multiple linear regression models with sow pre-farrowing blood sample ratio (S-RATIO) or sow colostrum ratio (C-RATIO) and other covariates as predictors for initial S/P ratios explained 78% and 73%, respectively, of the variation in S/P ratios for 4-day old piglets. The median half-life of MH antibodies was 15.8 days. The persistence of passively acquired MH antibodies was related to the initial antibody concentration in the piglet. Kaplan-Meier product-limit estimates of the time at which passive antibodies waned were 30, 45, and 63 days, for piglets with initial antibody concentration classified as low (≤ 0.30), medium (0.31-0.65), or high (> 0.65), respectively. Accelerated failure time models were also fitted to the data with C-RATIO or S-RATIO as predictors for duration of passive antibodies in the piglet. Both models, which also included total piglet serum protein, sow parity, and breed of piglet, provided time estimates of antibody persistence that were consistent with the range detected in the study.