Evaluation of the effect of a porcine reproductive and respiratory syndrome (PRRS) modified-live virus vaccine on sow reproductive performance in endemic PRRS farms

Highlights

• The PRRSV MLV reduced numbers of stillborn piglets.

• The PRRSV MLV increased number of weaned piglets.

• No adverse effects relative to vaccination were observed during the entire gestation.

Abstract

The efficacy of a porcine reproductive and respiratory syndrome (PRRS) modified-live virus vaccine in reproductive performance was evaluated under field conditions. Three PRRS endemic farms were selected based on their history of PRRS-associated reproductive failures. On each farm, a total of 40 sows were randomly allocated to either vaccinated (n = 20) or unvaccinated (n = 20) groups. Sows were vaccinated six weeks prior to breeding. Clinical data showed a significant improvement in reproductive performance in vaccinated sows. Sows in the vaccinated groups had a significantly (P < 0.05) reduced number of stillborn piglets in all 3 farms. Sows in the vaccinated groups also had a significantly (P < 0.05) higher number of live-born piglets in one of the farms. Sows in the vaccinated groups had a significantly (P < 0.05) higher number of weaned piglets in two of the farms. Premature farrowing, one of the late gestation symptoms of PRRS, was also reduced due to vaccination as suggested by the increase in gestation length and the reduction in the number of stillborn piglets. No adverse systemic or local side effects relative to vaccination were observed during the entire gestation. No vaccine strain was detected in the vaccinated sows from all three farms at 70 and 114 days post vaccination and in live-born piglets at the time of farrowing. Vaccination of sows with this PRRS vaccine was effective in improving reproductive performance in endemic PRRS farms.

Introduction

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically important swine infectious diseases affecting the swine industry worldwide. The causative agent is PRRS virus (PRRSV) which belongs to the order Nidovirales, family Arteriviridae, and genus Arterivirus. Antigenic and genetic analyses have established two major PRRSV genotypes, type 1 PRRSV (European genotype) and type 2 PRRSV (North American genotype), which share approximately 60% nucleotide identity genome-wide (Allende et al., 1999, Snijder et al., 2013, Dea et al., 1996, Murtaugh et al., 1995, Nelsen et al., 1999). Infection with PRRSV is associated with reproductive failure in sows and respiratory distress in growing pigs (Zimmerman et al., 2012).

PRRSV infection can be epidemic and endemic. Epidemic infection occurs when immunologically naïve hosts are infected regardless of the individual’s age. Endemic infection occurs in susceptible subpopulations that have either declining or no immunity. To date, PRRS remains endemic in most Korean swine farms despite wide use of commercial vaccines against it. Instead of eradication, PRRSV control may be a more efficient and realistic strategy based on the common use of continuous production systems with high pig densities and high PRRSV prevalence. One of the most common control strategies for endemic PRRSV in Korean farms is vaccination. In the field, in PRRSV-positive pig farms, 89% of sows typically receive a PRRS vaccine (http://www.kahpa.or.kr).

A commercially available PRRS modified-live virus (MLV) vaccine (Fostera™PRRS, Zoetis, Parsippany, NJ, USA), based on a virulent US PRRSV isolate (P129 strain, type 2 PRRSV) and attenuated using CD163-expressing cell lines, was licensed for protection against respiratory diseases in 2012 and reproductive failure in 2015. Vaccination with this PRRS MLV vaccine led to improved growth performance and decreased mortality in growing pigs when evaluated under field conditions (Park et al., 2014a). However, no field studies evaluating the efficacy in reproductive performance of vaccinated sows have been performed to date. The objective of this field study was to evaluate the effect of this vaccine on the reproductive performance of sows from endemic farms.