PERSISTENCE OF PASSIVELY ACQUIRED ANTIBODIES TO MYCOPLASMA-HYOPNEUMONIAE IN A SWINE HERD

A cohort of 95 piglets born to 12 sows seropositive for Mycoplasma hyo pneumoniae (MH) was followed from birth until passively acquired MH an tibodies, detected with an ELISA, reached their lowest concentration. The objectives of the study were to determine the half-life of materna lly derived MH antibodies in the newborn piglet, and the relationship between maternal MH antibodies in the serum or colostrum and the initi al concentration and persistence of MH antibodies in the neonatal pigs . Blood samples were initially collected from newborn piglets at 4 day s of age, and subsequently at 14-day intervals. Sows were blood-sample d 1 month prior to farrowing, and colostrum was collected 2-6 h after the first piglet was born. Antibody concentrations were expressed as t he ELISA ratio between mean optical densities of the sample and the po sitive 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 expla ined 75% and 73%, respectively, of the variation in S/P ratios for 4-d ay-old piglets. The median half-life of MH antibodies was 15.8 days. T he persistence of passively acquired MH antibodies was related to the initial antibody concentration in the piglet. Kaplan-Meier product-lim it estimates of the time at which passive antibodies waned were 30, 45 , and 63 days, for piglets with initial antibody concentration classif ied as low (less than or equal to 0.30), medium (0.31-0.65), or high ( > 0.65), respectively. Accelerated failure time models were also fitte d to the data with C-RATIO or S-RATIO as predictors for duration of pa ssive 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.