Management and demographic factors associated with seropositivity to transmissible gastroenteritis virus in US swine herds, 1989-1990

Serum neutralization testing was used to determine transmissible gastroenteritis (TGE) titres of up to 10 sows per herd for 392 herds that participated in the 3 month monitoring of sows and litters in the National Swine Survey. Of the sampled herds, 101 (25.8%) had sow seroprevalences of at least 80%, 79 (20.1%) had seroprevalences between 10 and 79%, and 212 (54.1%) were seronegative. Herds with less than 5 samples tested were excluded from analysis. In the logistic regression analysis, a herd was considered seropositive if at least 20% of sampled females had titres of 1:8 or higher (160 herds) and a herd was seronegative if all sows had titres of under 1:8 (178 herds). Factors considered for inclusion in logistic regression models included breeding herd size, bio-security measures, pig introductions and movements, and access of possible non-porcine reservoirs to the facilities with pigs. After controlling for the effects of season, number of samples tested and TGE vaccination history, large female breeding herd size (at least 500 sows compared with the reference category of 100-199 sows) and purchase of more than 25 pigs from non-specific pathogen free herds were associated with higher odds of herd seropositivity. There was some evidence of an increased risk of seropositivity when there were more than two swine herds within a 3 mile radius of the study herd.