Safety and efficacy of vaccination of pregnant gilts against porcine reproductive and respiratory syndrome

Objective-To determine the safety and efficacy of vaccination of pregnant g ills with an attenuated strain of porcine reproductive and respiratory synd rome virus (PRRSV). Animals-16 pregnant gilts. Procedure-Pregnant gilts free of antibodies for PRRSV were assigned 14 gilts/group) to the following groups: group I, untre ated controls; group ii, vaccinated on day 60 of gestation; group ill, vacc inated on day 60 of gestation and exposed to virulent PRRSV on day 90 of ge station; and group IV, exposed to virulent PRRSV on day 90 of gestation. Sa fely and efficacy of vaccination was evaluated by group comparisons of pren atal and postnatal survival of fetuses and pigs, respectively, and by the c ondition and rate of weight gain of liveborn pigs. Results-Collective (prenatal and postnatal) death losses up to day 15 after farrowing (conclusion of study) were similar for groups I (7/47, 14.9%) an d II (7/44, 16.9%) but were greater for group III (18/49, 36.7%) and were g reater still for group IV (23/37, 62.2%). Mean body weight 15 days after fa rrowing was greatest for pigs in litters of group I (4.46 kg) and progressi vely less for the other groups (3.87, 3.76, and 2.18 kg for groups ii, iii, and IV, respectively). Conclusions-Using these conditions, vaccination of gilts during midgestatio n appeared to be safe. However, it provided only partial protection against subsequent exposure to virulent virus. Clinical Relevance-Attenuated-PRRSV vaccines may have to be administered to naive gilts > 30 days before conception to provide maximum protection thro ughout gestation.