Date of Award
Doctor of Philosophy
Veterinary Microbiology and Preventive Medicine
George W. Beran
First litter gilts (N = 210) in 15 herds were monitored through their first gestation. Prevalence of 6 infectious agents associated with reproductive failure was estimated in the sow and finisher populations in each herd. The association between reproductive failure and infection, as determined by a ≥4-fold increase in antibody titer, was determined. Farrowing ≥3 stillborn pigs, farrowing ≥3 mummified fetuses, and farrowing ≤6 live pigs were statistically associated with seroconversion to infectious agents;The sensitivity, specificity, and diagnostic titer of the microtiter serum neutralization test (SN) for the diagnosis of encephalomycarditis virus was determined. Antibody titers up to 1:8 were observed in uninfected animals and ranged from 1:5.7 to 1:1024 in infected animals. SN antibody titers of 1:8 were highly suggestive of infection, with an estimated 97.8 % sensitivity and 95.7 % specificity at this dilution. Antibody titers of 1:16 or greater were conclusive for EMCV infection, based on a test specificity of 100% at these dilutions;A total of 2614 animals from 104 herds located throughout the state of Iowa were tested for antibodies against EMCV. A difference (P < 0.002) was observed between the prevalence in sows and gilts (17.2%) vs. finishing animals (12.2%). Breeding swine in total confinement (20.5%) showed a higher prevalence (P = 0.04) than breeders in other types of housing (12.1%), while the prevalence in finishing animals raised in total confinement (6.4%) was lower (P = 0.02) than finishers not raised in total confinement (13.6%). No association was detected between prevalence and herd size, or prevalence and season of the year. The true prevalence of EMCV in Iowa swine was estimated to be 13.8% in breeding stock and 8.5% in finishing animals. On a herd basis, 89.4% (93/104) of the herds had one or more EMCV-positive animals. These animals were also tested against for antibodies against Toxoplasma gondii by ELISA. The true prevalence of toxoplasmosis was estimated as 5.4% among finishing swine and 11.4% among sows and gilts. Herds with fewer than 100 breeders were more likely to be infected than herds with 100 or more breeders (P < 0.05). Seropositivity in breeding stock was approximately the same in infected herds, regardless of herd size. Herds with finishers in total confinement were as likely to become infected as herds with other types of facilities, but infected herds with finishers in confinement appeared to have a lower in-herd prevalence than herds with other types of facilities (P = 0.09). No seasonal effects were observed and prevalence remained relatively constant throughout the year.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Jeffrey J. Zimmerman
Zimmerman, Jeffrey J., "Epidemiologic aspects of infectious agents involved in reproductive inefficiency in swine " (1990). Retrospective Theses and Dissertations. 9913.