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 gilts with an attenuated strain of porcine reproductive and respiratory syndrome virus (PRRSV).

ANIMALS: 16 pregnant gilts.

PROCEDURE: Pregnant gilts free of antibodies for PRRSV were assigned (4 gilts/group) to the following groups: group I, untreated controls; group II, vaccinated on day 60 of gestation; group III, vaccinated on day 60 of gestation and exposed to virulent PRRSV on day 90 of gestation; and group IV, exposed to virulent PRRSV on day 90 of gestation. Safety and efficacy of vaccination was evaluated by group comparisons of prenatal and postnatal survival of fetuses and pigs, respectively, and by the condition 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%) and II (7/44, 16.9%) but were greater for group III (18/49, 36.7%) and were greater still for group IV (23/37, 62.2%). Mean body weight 15 days after farrowing was greatest for pigs in litters of group I (4.46 kg) and progressively 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 midgestation 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 throughout gestation.