Experience with a planned exposure program for the control of enzootic transmissible gastroenteritis in swine

Oral inoculation of pregnant sows and gilts with a homogenate of pig intestines containing live, virulent transmissible gastroenteritis (TGE) virus was associated with significant (P < 0.01) reduction of mortality in nursery pigs in a herd affected with enzootic TGE. The mortality of weaned pigs from April through June 1981, when sows were not vaccinated or inoculated, was 9.3%. Mortality of weanling pigs from July through December 1981 was 5.7% (P < 0.01), and stayed consistently between 2.6 and 4.8% from 1982 through 1990. After beginning the exposure program, there were no clinical signs attributable to TGE in the farrowing house or nursery until 1986, when recrudescence of TGE was evident in the nursery. Although the source of the virus could not be substantiated, recrudescence suggested that TGE virus would not be eradicated as long as exposure was continued. The most plausible explanation for the decrease in the incidence of diarrhea and mortality in the nursery pigs after initiation of the planned exposure program is that a higher, longer lasting amount of lactogenic immunity was provided to suckling pigs. Presumably over time, this resulted in less TGE virus carryover into the nursery by weanling pigs, thereby reducing and confining the environmental challenge to the nursery. Strict all-in, all-out pig movement in the nursery with thorough cleaning and disinfecting presumably further reduced the environmental challenge.