Production losses five months after outbreak with a recombinant of two PRRSV vaccine strains in 13 Danish sow herds
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(2020) 6:26
RESEARCH
Open Access
Production losses five months after outbreak with a recombinant of two PRRSV vaccine strains in 13 Danish sow herds C. S. Kristensen1* , M. G. Christiansen1, K. Pedersen1 and L. E. Larsen2
Abstract Background: In July 2019, a PRRSV-negative boar station was infected with a recombinant of two PRRSV vaccine strains, which subsequently spread to at least 36 herds that had received semen from the boar station. In the following months, all the infected herds reported reduced productivity. The aim of the present study was to evaluate the impact of the PRRS outbreak. Results: Production data were collected from 13 of the herds. The average levels of farrowings/week, liveborns/ litter, stillborns/litter, pre-weaning mortality and weaned pigs/litter were compared for the five-month period after infection and the preceding 7 months before infection with the new variant of PRRSV-1. Twelve herds experienced a decrease in farrowings/week (0.1–10.8% fewer farrowings/week), and all herds experienced fewer liveborns (0.8– 4.8 fewer liveborns/litter) and more stillborns (0.6–2.6 more stillborns/litter). Pre-weaning mortality nearly doubled in half of the herds. Overall, the 13 herds were missing 2.4–6.5 pigs/litter at weaning during the 5 months after infection compared to the seven preceding months before infection. Conclusion: In this study, the impact of this new PRRSV-1 variant on productivity exceeded that typically seen in Danish herds infected with PRRSV-1. Keywords: PRRSV, Production loss, Stillborn, Pre-weaning mortality
Background Since it first appeared at the beginning of the 1990s, porcine reproductive and respiratory syndrome virus (PRRS V) has been one of the major health challenges in pig production. According to figures from the Danish SPF society, approximately 35% of Danish pig herds are positive for antibodies to PRRSV, although the prevalence of serologically positive herds is declining [1]. Both PRRSV-1 and PRRSV-2 are prevalent in Danish herds, and some herds are infected with both species. In 1994, production losses due to acute infections with PRRS in 30 Danish herds were estimated to be 1.2 pigs/ * Correspondence: [email protected] 1 SEGES Danish Pig Research Centre, Copenhagen, Denmark Full list of author information is available at the end of the article
year [2]. A Danish study from 2013 found an average decrease in liveborns of 0.7 liveborns/litter, an average increase in the number of stillborns of 0.3 stillborns/litter and an average of 1.0 weaned pig less per litter [3]. Limited surveillance of the genetic diversity is practised in Denmark, but the available data indicate that, until the summer of 2019, two major clades of PRRSV-1 were co-circulating [4]. One of the clades shares a high level of genetic similarity to the Porcilis vaccine strain “DV” and probably represents a group of field viruses originating from this vaccine strain. The strains clustering in the other clade are up to 12% different from the “Porcilis-like” viruses and include the first PRRSV-1 stra
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