Sow performance in an endemically porcine reproductive and respiratory syndrome (PRRS)-infected farm after sow vaccination with an attenuated PRRS vaccine

An assessment of enhanced biosecurity interventions and their impact on porcine reproductive and respiratory syndrome virus outbreaks within a managed group of farrow-to-wean farms, 2020-2021

Introduction

Porcine reproductive and respiratory syndrome virus (PRRSV) has been a challenge for the U.S. swine industry for over 30 years, costing producers more than $600 million annually through reproductive disease in sows and respiratory disease in growing pigs. In this study, the impact of enhanced biosecurity practices of site location, air filtration, and feed mitigation was assessed on farrow-to-wean sites managed by a large swine production management company in the Midwest United States. Those three factors varied in the system that otherwise had implemented a stringent biosecurity protocol on farrow-to-wean sites. The routine biosecurity followed commonplace activities for farrow-to-wean sites that included but were not limited to visitor registration, transport disinfection, shower-in/shower-out procedures, and decontamination and disinfection of delivered items and were audited.

Methods

Logistic regression was used to evaluate PRRSV infection by site based on the state where the site is located and air filtration use while controlling for other variables such as vaccine status, herd size, and pen vs. stall. A descriptive analysis was used to evaluate the impact of feed mitigation stratified by air filtration use.

Results

Sites that used feed mitigates as additives in the diets, air filtration of barns, and that were in less swine-dense areas appeared to experience fewer outbreaks associated with PRRSV infection. Specifically, 23.1% of farms that utilized a feed mitigation program experienced PRRSV outbreaks, in contrast to 100% of those that did not. Sites that did not use air filtration had 20 times greater odds of having a PRRSV outbreak. The strongest protective effect was found when both air filtration and feed mitigation were used. Locations outside of Minnesota and Iowa had 98.5-99% lesser odds of infection as well.

Discussion

Enhanced biosecurity practices may yield significant protective effects and should be considered for producers in swine-dense areas or when the site contains valuable genetics or many pigs.

Impacts of Quarterly Sow Mass Vaccination with a Porcine Reproductive and Respiratory Syndrome Virus Type 1 (PRRSV-1) Modified Live Vaccine in Two Herds

In recent years, there has been a considerable increase in the use of Modified Live PRRSV Vaccines (MLV) for mass vaccination in Denmark. The potential risks and negative impact of this strategy have been sparsely studied. The aim of this study was to investigate the impact of quarterly sow mass vaccination in two Danish sow herds. The study was performed as an observational prospective cohort of 120 sows in each of two commercial breeding herds in a paired design. Blood samples were taken from sows and oral fluid samples from nursery pigs (four to ten weeks old) before and after vaccination. The presence of PRRSV-1 RNA was measured by real time quantitative reverse transcription-polymerase chain reaction (RT-qPCR), and the level of PRRSV-1 specific antibodies was measured by two different serological assays. PRRS virus was not detected in the sow herds two days before and two weeks after vaccination, but the vaccine strain virus was detected in the nursery pigs. The prevalence of sows without antibodies towards PRRSV-1 went from 6-15% before vaccination to 1-4% after vaccination depending on the serological assay used, despite the fact that they had previously been repeatedly vaccinated. Four sows tested negative for antibodies in both assays after vaccination.

Generation of a cold-adapted PRRSV with a nucleotide substitution in the ORF5 and numerous mutations in the hypervariable region of NSP2

A cold-adapted porcine reproductive and respiratory syndrome virus (CA-VR2332) was generated from the modified live virus strain VR2332. CA-VR2332 showed impaired growth when cultured at 37°C with numerous mutations (^S731^F, ^E819^D, ^G975^E, and ^D1014^N) in the hypervariable region of the NSP2, in which the mutation ^S731^F might play a vital role in viral replication at 30°C. Conserved amino acid sequences of the GP5 protein suggests that CA-VR2332 is a promising candidate for producing an effective vaccine against PRRSV infection. Further studies on replication and immunogenicity in vivo are required to evaluate the properties of CA-VR2332.

Commercial PRRS Modified-Live Virus Vaccines

Porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) presents one of the challenging viral pathogens in the global pork industry. PRRS is characterized by two distinct clinical presentations; reproductive failure in breeding animals (gilts, sows, and boars), and respiratory disease in growing pigs. PRRSV is further divided into two species: PRRSV-1 (formerly known as the European genotype 1) and PRRSV-2 (formerly known as the North American genotype 2). A PRRSV-2 modified-live virus (MLV) vaccine was first introduced in North America in 1994, and, six years later, a PRRSV-1 MLV vaccine was also introduced in Europe. Since then, MLV vaccination is the principal strategy used to control PRRSV infection. Despite the fact that MLV vaccines have shown some efficacy, they were problematic as the efficacy of vaccine was often unpredictable and depended highly on the field virus. This paper focused on the efficacy of commercially available MLV vaccines at a global level based on respiratory disease in growing pigs, and maternal and paternal reproductive failure in breeding animals.

Management and Feeding Strategies in Early Life to Increase Piglet Performance and Welfare around Weaning: A Review

The performance of piglets in nurseries may vary depending on body weight, age at weaning, management, and pathogenic load in the pig facilities. The early events in a pig's life are very important and may have long lasting consequences, since growth lag involves a significant cost to the system due to reduced market weights and increased barn occupancy. The present review evidences that there are several strategies that can be used to improve the performance and welfare of pigs at weaning. A complex set of early management and dietary strategies have been explored in sows and suckling piglets for achieving optimum and efficient growth of piglets after weaning. The management strategies studied to improve development and animal welfare include: (1) improving sow housing during gestation, (2) reducing pain during farrowing, (3) facilitating an early and sufficient colostrum intake, (4) promoting an early social interaction between litters, and (5) providing complementary feed during lactation. Dietary strategies for sows and suckling piglets aim to: (1) enhance fetal growth (arginine, folate, betaine, vitamin B12, carnitine, chromium, and zinc), (2) increase colostrum and milk production (DL-methionine, DL-2-hydroxy-4-methylthiobutanoic acid, arginine, L-carnitine, tryptophan, valine, vitamin E, and phytogenic actives), (3) modulate sows' oxidative and inflammation status (polyunsaturated fatty acids, vitamin E, selenium, phytogenic actives, and spray dried plasma), (4) allow early microbial colonization (probiotics), or (5) supply conditionally essential nutrients (nucleotides, glutamate, glutamine, threonine, and tryptophan).

Gilt Vaccination with a Mixed Administration of a PRRS MLV and a PPV1 Subunit Vaccine Protects against Heterologous PRRSV1 Infection and Prevents Detrimental Effects on Piglet Performance

The efficacy of the combined administration of a porcine reproductive and respiratory syndrome (PRRS) modified live virus (MLV) vaccine and a porcine parvovirus 1 (PPV1) subunit vaccine in gilts was addressed in two experiments. Experiment A aimed to establish a 4-week onset of immunity (OOI). Gilts were randomly distributed in three treatment groups: non-vaccinated control animals (group 1), animals vaccinated with the combined vaccine (group 2), and a third group that consisted of animals vaccinated with the PRRS MLV vaccine alone (group 3). Four weeks after the first vaccination, gilts were challenged with a heterologous PRRS virus 1 (PRRSV1) and euthanized three weeks after. Besides this, experiment B pursued a 17-week duration of immunity (DOI). In this case, gilts were distributed in the same treatment groups, but for the third group, which consisted of non-vaccinated, non-challenged animals were used instead. For the DOI assessment, gilts were artificially inseminated 4 weeks after the first vaccination, challenged at day 90 of gestation, and followed up, together with their offspring, until day 20 post-farrowing. Serology and viremia post-challenge were determined in gilts from both experiments, while farrowing and piglet performance were only evaluated in experiment B. Overall, the combined vaccine helped to protect gilts from viremia post-challenge and, consequently, to prevent PRRS clinical symptoms and diminish the proportion of piglets infected congenitally or early in life. The combined vaccine also elicited a significant improvement in piglet survival rate and growth performance until weaning. The present results reveal efficacy and lack of interference of the mixed use of the tested vaccines against PRRSV1 infection, with at least 4-week OOI and 17-week DOI.

Field evaluation of the safety and compatibility of a combined vaccine against porcine parvovirus 1 and porcine reproductive and respiratory syndrome virus in breeding animals

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) and porcine parvovirus 1 (PPV1) are two common causes of reproductive failure. ReproCyc® ParvoFLEX is a novel subunit vaccine based on the protective viral protein (VP) 2 of PPV1 that has been recently licensed in the European (EU) market, whereas ReproCyc® PRRS EU is a porcine reproductive and respiratory syndrome (PRRS) modified live virus (MLV) vaccine authorized in 2015. The present work sought to evaluate the safety and compatibility of the combined administration of the abovementioned vaccines in target animals under the context of a field PRRSV (experiment A) and PPV1 (experiment B) infection. To achieve this objective, safety and lack of vaccines' antigen interference were established according to the absence of significant differences between the combined vaccinated animals (PPRSV+PPV1) and the single vaccinated animals against PRRSV or PPV1. In both experiments, gilts and sows were evaluated for local and systemic reactions after vaccination as well as for reproductive and productive performance. In addition, tissues from abortions, mummified fetuses and stillborn piglets were analyzed for the presence of PRRSV and PPV1. Lastly, serology and viremia were determined in experiment B.

RESULTS

No relevant differences in terms of safety, reproductive and productive performance between the single vaccinated and the combined vaccinated animals in either experiment were observed.

CONCLUSIONS

ReproCyc® PRRS EU mixed with ReproCyc® ParvoFLEX can be used as a safe method of protection against the detrimental effects of PRRSV and PPV1 infections in breeding female pigs in one single injection. The present results also open up opportunities to tackle reproductive problems as a whole by combining control programs against swine reproductive pathogens.

Maternally-derived neutralizing antibodies reduce vaccine efficacy against porcine reproductive and respiratory syndrome virus infection

•

Maternally-derived neutralizing antibodies impair PRRS vaccination immune responses in piglets.

•

Maternally-derived neutralizing antibodies reduce PRRS vaccine efficacy in piglets.

•

IFNa may also interfere with PRRS vaccination.

Modified live virus (MLV) vaccines are commonly used to reduce the impact of porcine reproductive and respiratory syndrome (PRRS) but limited efficacy is achieved in field conditions. Here, we evaluated the impact of maternally-derived neutralizing antibodies (MDNAs) on vaccine efficacy after PRRS virus (PRRSV) challenge. Piglets with low (A−) or high (A+) MDNA levels derived from a commercial pig herd were moved to experimental facilities to be vaccinated (V+) or not (V−) with a PRRSV-1 MLV vaccine at 3 weeks of age (woa). Because of unexpectedly low vaccine detection in A−V+ piglets post-vaccination (pv), all V+ piglets received a second vaccination at 4 woa. Five weeks (W5) pv, piglets were inoculated with a PRRSV-1 field strain to evaluate vaccine protection, and were mingled 24 h later with non-inoculated piglets of similar immune status to assess viral transmission. Vaccine strain was detected at W2 pv in 69% and 6% of A−V+ and A+V+ piglets, and at W5 pv in 50% and 25% of A−V+ and A+V+ piglets, respectively. At W5 pv, 94% of A−V+ and 44% of A+V+ piglets seroconverted, with a significant IFNg response induction in the A−V+ group only. After challenge, compared to the V− inoculated group, viremia was 100-fold lower at 10 days post-infection in A−V+ whereas viremia was not significantly reduced in A+V+ piglets. A lower transmission rate was estimated for the A−V+ group: 0.15 [0.07–0.29] versus 0.44 [0.18–1.76] and 0.32 [0.14–0.68] for the A+V+ and V− groups, respectively. Investigations about the low vaccine strain detection after the first vaccination suggested a relationship between IFNa levels and vaccine strain detection in A−V+ piglets. We showed that MDNAs impair vaccine efficacy against PRRSV both in inoculated and contact piglets, probably by reducing vaccine replication. IFNa may also interfere with PRRSV vaccination. These new data could help improving vaccination protocols.

Safety and immune responses after intradermal application of Porcilis PRRS in either the neck or the perianal region

The objective of the present study was to assess safety and immune responses in gilts after intradermal application of Porcilis® PRRS in two different application sites under field conditions. Forty-four gilts were allocated to one of three groups: Gilts of group 1 (n = 10) served as non-vaccinated controls, gilts of group 2 (n = 17) were vaccinated intradermally in the neck and gilts of group 3 (n = 17) received an intradermal vaccination in the perianal region. Clinical observations, local injection site reactions and histopathologic examination of the injection site were used for safety assessments. Frequency and degree of clinical signs were not significantly different between all three groups. Minor local reactions for both vaccination groups were observed; however, at 6, 7, 8, 9 and 15 days post-vaccination (dpv), the mean injection site reaction score was significantly lower in pigs vaccinated in the perianal region. In histopathologic examination, an extended inflammatory dimension was observed more frequently in pigs vaccinated in the neck. Blood samples were analyzed to quantify the post-vaccination humoral (ELISA and virus neutralization test) and cellular (IFN-γ ELISPOT) immune responses. PRRSV-specific antibodies were present in the serum of all vaccinated animals from 14 dpv onwards, whereas all control pigs remained negative throughout the study. Neutralizing antibody titers were significantly higher in pigs vaccinated in the perianal region at 28 dpv. At 14, 21 and 28 dpv, PRRSV-specific IFN-γ secreting cells were significantly increased in both vaccination groups compared to non-vaccinated gilts. Analysis of mean numbers of PRRSV-specific IFN-γ secreting cells did not result in statistically significant differences between both vaccination groups. The results of this study indicate that the perianal region is a safe alternative application site for intradermal vaccination of gilts with Porcilis PRRS. Furthermore, the intradermal application of Porcilis PRRS induced humoral and cellular immune responses independent of the administration site.

Modelling the economic efficiency of using different strategies to control Porcine Reproductive & Respiratory Syndrome at herd level

PRRS is among the diseases with the highest economic impact in pig production worldwide. Different strategies have been developed and applied to combat PRRS at farm level. The broad variety of available intervention strategies makes it difficult to decide on the most cost-efficient strategy for a given farm situation, as it depends on many farm-individual factors like disease severity, prices or farm structure. Aim of this study was to create a simulation tool to estimate the cost-efficiency of different control strategies at individual farm level. Baseline is a model that estimates the costs of PRRS, based on changes in health and productivity, in a specific farm setting (e.g. farm type, herd size, type of batch farrowing). The model evaluates different intervention scenarios: depopulation/repopulation (D/R), close & roll-over (C&R), mass vaccination of sows (MS), mass vaccination of sows and vaccination of piglets (MS + piglets), improvements in internal biosecurity (BSM), and combinations of vaccinations with BSM. Data on improvement in health and productivity parameters for each intervention were obtained through literature review and from expert opinions. The economic efficiency of the different strategies was assessed over 5 years through investment appraisals: the resulting expected value (EV) indicated the most cost-effective strategy. Calculations were performed for 5 example scenarios with varying farm type (farrow-to-finish - breeding herd), disease severity (slightly - moderately - severely affected) and PRRSV detection (yes - no). The assumed herd size was 1000 sows with farm and price structure as commonly found in Germany. In a moderately affected (moderate deviations in health and productivity parameters from what could be expected in an average negative herd), unstable farrow-to-finish herd, the most cost-efficient strategies according to their median EV were C&R (€1'126'807) and MS + piglets (€ 1'114'649). In a slightly affected farrow-to-finish herd, no virus detected, the highest median EV was for MS + piglets (€ 721'745) and MS (€ 664'111). Results indicate that the expected benefits of interventions and the most efficient strategy depend on the individual farm situation, e.g. disease severity. The model provides new insights regarding the cost-efficiency of various PRRSV intervention strategies at farm level. It is a valuable tool for farmers and veterinarians to estimate expected economic consequences of an intervention for a specific farm setting and thus enables a better informed decision.

Oral fluid samples used for PRRSV acclimatization program and sow performance monitoring in endemic PRRS-positive farms

An effective gilt acclimatization program is one of the most important management strategies for controlling porcine reproductive and respiratory syndrome virus (PRRSV) infection. Recently, oral fluid samples have been used as alternative diagnostic samples for various swine diseases. This study utilized oral fluids for PRRSV monitoring during the gilt acclimatization period in PRRSV endemic farms. The study was performed in two selected commercial breeding herds (farm A and farm B). PRRSV RNA and PRRSV-specific antibodies were monitored using oral fluid and serum samples. Sow performance parameters related to PRRSV infection were recorded and assessed. After PRRSV exposure during acclimatization, viral RNA was demonstrated in oral fluids from 1 to 10 weeks post-exposure (WPE). PRRSV RNA was detected in serum at 1 and 4 WPE in farm A and at 1, 4, 8, and 12 WPE in farm B. Prolonged viremia of gilts from farm B was possibly due to re-infection (within the herd) and later, reproductive problems were found in the breeding herd. The correlation of PRRSV RNA concentration in oral fluids and serum was evident. The S/P ratio values of PRRSV antibodies in oral fluid samples were higher and had similar patterns of antibody responses to the serum samples. The results suggest that the use of oral fluid samples for PRRSV monitoring during gilt acclimatization in endemic farms is effective, convenient, practical, and economical and would be most beneficial when used with other parameters.

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

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 114days 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.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): porcine reproductive and respiratory syndrome (PRRS)

Porcine reproductive and respiratory syndrome (PRRS) has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of PRRS to be listed, Article 9 for the categorisation of PRRS according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to PRRS. The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, PRRS can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL. The disease would comply with the criteria as in Sections 4 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (d) and (e) of Article 9(1). The animal species to be listed for PRRS according to Article 8(3) criteria are domestic pigs and wild boar.

Efficacy evaluation of three modified-live virus vaccines against a strain of porcine reproductive and respiratory syndrome virus NADC30-like

Porcine reproductive and respiratory syndrome reproductive virus is a devastating pathogen causing tremendous economic losses to swine production worldwide. Emergence of novel and variant PRRSV strains always leads to variable protection efficacy of modified-live virus (MLV) vaccines. Prevalence of PRRSV NADC30-like recently emerging in China has brought about clinical outbreaks of the disease. In the present study, the pathogenicity of a NADC30-like strain CHsx1401 for piglets was analyzed, and the potential cross-protective efficacy of three MLV vaccines including two commercial MLV vaccines and an attenuated low pathogenic PRRSV against this virus was further evaluated in piglets. The NADC30-like CHsx1401 was shown to cause fever, respiratory clinical signs, and lung gross and microscopic lesions of the inoculated piglets, suggesting that this virus is moderate virulent for piglets. Vaccination of piglets with the MLV vaccines could not reduce the clinical signs and lung lesions, and was partially efficacious in the reduction of viral loads in sera upon NADC30-like CHsx1401 challenge, indicating that these three MLV vaccines provide extremely limited cross-protection efficacy against the NADC30-like virus infection. Additionally, Ingelvac PRRS MLV appeared to exert some beneficial efficiency in shortening the period of clinical fever and in improving the growth performance of the challenged pigs. Our findings give valuable guidance for the choice and use of PRRSV MLV vaccines to control NADC30-like virus infection in the field.

Pathogenesis and control of the Chinese highly pathogenic porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) has remained a major threat to the worldwide swine industry ever since its first discovery in the early 1990s. Under the selective pressures in the field, this positive-stranded RNA virus undergoes rapid genetic evolution that eventually leads to emergence in 2006 of the devastating Chinese highly pathogenic PRRSV (HP-PRRSV). The atypical nature of HP-PRRSV has caused colossal economic losses to the swine producers in China and the surrounding countries. In this review, we summarize the recent advances in our understanding of the pathogenesis, evolution and ongoing field practices on the control of this troubling virus in China.

Assessment of safety and reproductive performance after vaccination with a modified live-virus PRRS genotype 1 vaccine in pregnant sows at various stages of gestation

The objective of the present study was to assess safety and efficacy of a new modified live-virus porcine reproductive and respiratory syndrome (PRRS) genotype 1 vaccine in pregnant sows at various stages of gestation under field conditions. A total of 505 sows and gilts were allocated to two treatment groups and maintained in separate facilities. Animals of group 1 were vaccinated with a commercial modified live genotype 1 PRRSV vaccine (control product, CP), while animals of group 2 were immunized with a new modified live genotype 1 PRRSV vaccine (investigational veterinary product, IVP) (ReproCyc® PRRS EU, Boehringer Ingelheim Vetmedica GmbH). Injection site reactions were noted to be significantly less frequent in the IVP group compared to the CP group for pain (p=0.039), redness (p=0.030), heat (p=0.016) and swelling (p=0.002). The mean total number of piglets alive at weaning did not differ significantly between both study groups (10.6 vs. 11.0, p=0.375). However, pre-weaning mortality was significantly higher (p=0.005) in piglets from the CP group (14.1% vs. 10.9%). Analyses of reproductive performance data for both groups did not result in statistically significant differences between CP group and IVP group for number of piglets alive (12.7 and 12.6, respectively), healthy live (11.9 and 11.8), weak (0.7 and 0.5), stillborn (1.0 and 0.8) and mummified piglets (0.3 and 0.2) per litter. No differences were detected between both groups for piglet birth weights, while body weights at weaning (7.2kg vs. 6.6kg, p=0.026) and average daily gain (0.2445kg vs. 0.2211kg, p=0.037) were significantly higher in piglets from the IVP group. In conclusion, the administration of a single dose of ReproCyc® PRRS EU to sows and gilts at various stages of gestation confirmed non-inferiority to a commercial PRRS vaccine regarding safety and efficacy parameters under field conditions.

Pathological evaluation of reproductive system of porcine reproductive and respiratory syndrome virus-vaccinated and nonvaccinated anestrus sows and gilts

The purpose of the study was to evaluate pathologically the reproductive system of nonvaccinated and porcine reproductive and respiratory syndrome virus (PRRSV)-vaccinated sows/gilts, as well as the assessment of vaccination impact on their endometrium/myometrium and ovaries. In a farrow-to-finish farm, all sows and gilts were systematically vaccinated with a PRRSV-inactivated vaccine for a period of 18 months. During the last semester before the beginning of the trial, the genital organs (uterus and ovaries) from 50 females (nonvaccinated primiparous and multiparous sows that did not exhibit signs of estrus until 10 days post-weaning) were collected at the slaughterhouse for gross and microscopic examination (parity 1 to >6). Respectively, during the following three semesters after the implementation of the experimental PRRSV vaccination scheme, the genital organs from 75 vaccinated sows-25 samples taken along the period of each semester-were also collected. Gross examinations included measurements of uterine horn (thickness and diameter) and ovaries (diameter). Microscopic examination focused on histopathological examination of ovarian cysts or other cystic formations and evaluation of the endometrium and myometrium. Measurements of uterine horn's thickness/diameter and ovaries' diameter were at normal levels, and no significant differences were found on gross examination between vaccinated and nonvaccinated females. The results of histopathological examinations did not show lesions of endometritis or myometritis, but revealed ovarian cystic formations with a diameter of >2 cm that were luteinizing cysts. The presence of these luteinizing cysts was significantly lower in PRRSV-vaccinated animals, compared to nonvaccinated, three semesters (p=0.017) after the start of vaccinations and for the total trial period (p=0.009).

Reproductive performance of sows with and without PRRS modified live virus vaccination in PRRS-virus-seropositive herds

Porcine reproductive and respiratory syndrome (PRRS) virus infection causes reproductive failures including return to oestrus, abortion, mummified foetuses, stillborn, and weak-born piglets. The objective of the present study was to investigate reproductive performance of sows in PRRS-virus-seropositive herds with and without PRRS modified live virus (PRRS-MLV) vaccination. The study was conducted in 20 PRRS-virus-seropositive commercial swine herds in Thailand. The data included 211,009 mating and 180,935 farrowing records. The analysed variables included farrowing rate (FR), return rate (RR), abortion rate (AR), total number of piglets born per litter (TB), number of piglets born alive per litter (BA), percentage of stillborn (SB), percentage of mummified foetuses (MM), and number of piglets weaned per litter (WP). The results revealed that FR in non-vaccinated sows was lower than that in vaccinated sows (85.0 vs 89.7%, respectively, P < 0.001), and RR in non-vaccinated sows was higher than that in vaccinated sows (6.9 vs 3.7%, respectively, P < 0.001). AR did not differ significantly between non-vaccinated and vaccinated sows (1.6 and 2.0%, respectively, P = 0.964). TB (11.2 and 11.5, respectively, P < 0.001), BA (10.0 and 10.6, respectively, P < 0.001), and WP (9.2 and 9.6, respectively, P < 0.001) in non-vaccinated sows were lower than those in vaccinated sows. SB (6.9 and 5.1%, respectively, P < 0.001) and MM (3.2 and 2.2%, respectively, P < 0.001) in PRRS-MLV-vaccinated sows were higher than those in non-vaccinated sows. The improvement in sow reproductive performance in PRRS-MLV-vaccinated herds was most pronounced in gilts and primiparous sows.

Characterization of a serologic marker candidate for development of a live-attenuated DIVA vaccine against porcine reproductive and respiratory syndrome virus

DIVA (differentiating infected from vaccinated animals) vaccines have proven extremely useful for control and eradication of infectious diseases in livestock. We describe here the characterization of a serologic marker epitope, so-called epitope-M201, which can be a potential target for development of a live-attenuated DIVA vaccine against porcine reproductive and respiratory syndrome virus (PRRSV). Epitope-M201 is located at the carboxyl terminus (residues 161-174) of the viral M protein. The epitope is highly immunodominant and well-conserved among type-II PRRSV isolates. Rabbit polyclonal antibodies prepared against this epitope are non-neutralizing; thus, the epitope does not seem to contribute to the protective immunity against PRRSV infection. Importantly, the immunogenicity of epitope-M201 can be disrupted through the introduction of a single amino acid mutation which does not adversely affect the viral replication. All together, our results provide an important starting point for the development of a live-attenuated DIVA vaccine against type-II PRRSV.

Porcine reproductive and respiratory syndrome virus detection in Thailand during 2005-2010 in relation to clinical problems, pig types, regions, and seasons

The objectives of the present study were to determine the prevalence of porcine reproductive and respiratory syndrome virus (PRRSV) in Thailand between 2005 and 2010. The study was conducted by retrospectively investigating the detection of PRRSV from different pig types including boars, sows, piglets, nursery pigs, and fattening pigs from six regions of Thailand, i.e., the northern, eastern, northeastern, central, western, and southern parts. The data were obtained from cases submitted to the Chulalongkorn University Veterinary Diagnostic Laboratory for PRRSV detection between 2005 and 2010. Frequency analyses and generalized linear models were used to evaluate the prevalence of PRRSV in relation to various factors. In total, 2,273 tissues (n = 636), semen (n = 210) and serum (n = 1,427) samples were included. PRRSV was detected in 32.6 % (740/2,273) of the pigs. The virus was found in 43.1 %, 15.7 %, and 30.3 % in the tissues, semen, and serum samples, respectively (P < 0.001). The prevalence of PRRSV was highest in 2005 (43.6 %) and lowest in 2009 (23.6 %) (P < 0.001). The prevalence of PRRSV was highest in nursery pigs (43.7 %) and lowest in boars (15.4 %) (P < 0.001). The prevalence of PRRSV in the hot season (34.9 %) was higher than that found in the cool season (28.1 %, P = 0.018) but did not differ significantly compared to rainy season (34.0 %, P = 0.486). The strain of PRRSV isolated in the present study was genotype 2 (54.5 %), genotype 1 (31.0 %), and mixed genotypes (14.5 %). It can be concluded that PRRSV was detected in the tissue samples more frequently than the semen and serum samples. The prevalence of PRRSV was high in the nursery pigs. A high prevalence of PRRSV was found in the hot season, indicating that climatic factors may also contribute to the prevalence of PRRSV in Thailand. Of all the PRRSV detected, 31.0 %, 54.5 %, and 14.5 % belonged to genotype 1, genotype 2, and mixed genotypes, respectively.

Pig production in subtropical agriculture

Pig production plays an important role in farming systems worldwide, especially in subtropical areas. The past few decades have seen significant changes in swine production in such regions. However, there are regional differences in pig production, and some of these are associated with serious problems which impact production systems, the environment and human health. This review introduces the pig breeds, crops and challenge of pig production that faces subtropical areas. A detailed analysis focuses on the control of production problems that are affected by limitations in management and nutritional strategies. Then, factors that drive the major changes in the pig industry in this area are examined in detail, and some insight into pig production directions is provided.

Porcine reproductive and respiratory syndrome virus vaccines: Immunogenicity, efficacy and safety aspects

Porcine reproductive and respiratory syndrome virus (PRRSV) infection is the leading cause of economic casualty in swine industry worldwide. The virus can cause reproductive failure, respiratory disease, and growth retardation in the pigs. This review deals with current status of commercial PRRS vaccines presently used to control PRRS. The review focuses on the immunogenicity, protective efficacy and safety aspects of the vaccines. Commercial PRRS modified-live virus (MLV) vaccine elicits delayed humoral and cell-mediated immune responses following vaccination. The vaccine confers late but effective protection against genetically homologous PRRSV, and partial protection against genetically heterologous virus. The MLV vaccine is of concern for its safety as the vaccine virus can revert to virulence and cause diseases. PRRS killed virus (KV) vaccine, on the other hand, is safe but confers limited protection against either homologous or heterologous virus. The KV vaccine yet helps reduce disease severity when administered to the PRRSV-infected pigs. Although efforts have been made to improve the immunogenicity, efficacy and safety of PRRS vaccines, a better vaccine is still needed in order to protect against PRRSV.

Seroprevalence of porcine reproductive and respiratory syndrome, Aujeszky's disease, and porcine parvovirus in replacement gilts in Thailand

The present study investigated the seroprevalence of porcine reproductive and respiratory syndrome virus, Aujeszky's disease virus (ADV), and porcine parvovirus (PPV) in replacement gilts from selected five swine herds in Thailand. The study consisted of three parts. First, a retrospective data analysis on the seroprevalence of porcine reproductive and respiratory syndrome virus (PRRSV) and ADV glycoprotein I (gI) in gilts, sows, boars, nursery, and fattening pigs in five herds (n = 7,030). Second, a cross-sectional study on seroprevalence of PRRSV, ADV, and PPV (n = 200) in replacement gilts. Last, the seroprevalence of PRRSV, ADV, and PPV in gilts culled due to reproductive failure (n = 166). Across the herds, the seroprevalence of PRRSV and ADV was 79.3% and 5.3%, respectively. The cross-sectional study revealed that 87.5%, 4.0%, and 99.0% of the replacement gilts were infected with PRRSV, ADV, and PPV, respectively. In the gilts culled due to reproductive failure, the seroprevalence of PRRSV, ADV, and PPV was 73.5%, 28.3%, and 86.0%, respectively. Of these culled gilts, 75.5% had been infected with at least two viruses and 18.9% had been infected with all three viruses. It could be concluded that most of the replacement gilts were exposed to PRRSV (84%), PPV (97%), and ADV (4%) before entering the breeding house. PPV was an enzootic disease among the selected herds. The prevalence of ADV was higher in gilts culled due to reproductive disturbance than in the healthy gilts.

Microbial ecology of swine farms and PRRS vaccine vaccination strategies

The present study investigated the microbial ecology and vaccination strategies against porcine reproductive and respiratory syndrome (PRRS) in field condition. Four representative farms with a history of PRRS were included in this study. Over the almost 3-year period, the average detection rate was 68.9%, making PRRSV the first most frequently detected virus, followed by porcine circovirus type 2 (PCV2) (64.2%), pseudorabies virus (PRV) (11.03%) and classical swine fever virus (CSFV) (4.41%). Streptococcus suis (77.92%), Haemophilus parasuis (51.25%) and Escherichia coli (52.39%), Pasteurella multocida (26.77%) were isolated most frequently in association with PRRSV. Under the present microbial ecology, production performances of sows their offspring after mass vaccination with a PRRS attenuated vaccine were evaluated. In addition, large scale PRRS vaccines usage and efficacy were further performed. The results indicated that mass vaccination following our immunization program can improve health status and production performances of both sows (2ml/i.m. booster after 4 weeks, and then immunized quarterly) and their offsprings (1ml/i.m. on 14-18 days of age).

Control and elimination of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSv) can have a significant economic impact on swine herds due to reproductive failure, preweaning mortality and reduced performance in growing pigs. Control at the farm level is pursued through different management procedures (e.g. pig flow, gilt acclimation, vaccination). PRRSv is commonly eliminated from sow herds by a procedure called herd closure whereby the herd is closed to new introductions for a period of time during which resident virus dies out. However, despite thorough application of biosecurity procedures, many herds become re-infected from virus that is present in the area. Consequently, some producers and veterinarians are considering a voluntary regional program to involve all herds present within an area. Such a program was initiated in Stevens County in west central Minnesota in 2004. PRRSv has been eliminated from most sites within the region and the area involved has expanded to include adjacent counties. The program has been relatively successful and reflects local leadership, a cooperative spirit, and a will to eliminate virus from the region.

An evaluation of the impact of increased lactation length on the reproductive efficiency of sows in commercial herds

The objective of this study was to evaluate the impact of increased lactation length (LL) on the reproductive efficiency of sows in herds that were performing differently. The present study used 69,314 parity records for 38,532 sows in 114 herds. Two herd groups, high-performing herds and other herds, were formed on the basis of the upper 25th percentile of pigs weaned per mated female per year. Reproductive efficiency was measured as the estimated number of pigs born alive per farrowed sow per year (PBASY) and was calculated as actual subsequent pigs born alive (PBA) multiplied by estimated litters per farrowed sow per year (LSY) for each farrowed sow. The estimated LSY was calculated as 365 days divided by the actual farrowing interval. Multilevel linear mixed-effects models were used. In our evaluation, an interaction between LL and the herd groups was found for the estimated PBASY (P<0.05). The estimated PBASY of high-performing herds did not decrease as LL increased (P>0.10), although the estimated PBASY of the other herds decreased by 0.04 pigs as LL increased by 1 day (P<0.05). As LL increased from 14 to 28 days, the estimated LSY decreased by 0.19 in the two herd groups (P<0.05). Furthermore, as LL increased by 1 day, subsequent PBA increased by 0.08 pigs in high-performing herds and increased by 0.04 pigs in the other herds (P<0.05). Increased LL may not decrease the performance of sows in high-performing herds, but it may decrease the performance in other herds.

Performance of fattening pigs in a farm infected with both porcine reproductive and respiratory syndrome (PRRS) virus and porcine circovirus type 2 following sow and piglet vaccination with an attenuated PRRS vaccine

The purpose of the study was to investigate whether, on farms with both post-weaning multisystemic wasting syndrome (PMWS) and porcine reproductive and respiratory syndrome (PRRS), the PRRS vaccination of sows and their fattening pigs protects against these syndromes. In a farrow-to-finish pig farm with a history of PRRS and PMWS, 200 gilts and sows were allocated to one of two groups of equal size. The first group (C-sow group) was used as untreated controls, while the animals of the second group (V-sow group) were vaccinated with live Porcilis PRRS vaccine. At the next weaning, all piglets of half the sows of the C sow group were vaccinated once at 35 days of age with the vaccine (CV group), while the offspring of the other half of the unvaccinated sows were left unvaccinated (CC group). Similarly, the offspring of half the sows of the V sow group were vaccinated (VV group), while those of the other half of the vaccinated sows were left unvaccinated (VC group). No significant differences in morbidity were observed between the groups during the nursery and finishing phases, while morbidity in the growers was significantly reduced in the CV- and VV-groups (P < 0.05). Growers' mortality was significantly reduced after piglet vaccination when compared with unvaccinated pigs of unvaccinated dams (P < 0.05). Average daily gain and feed conversion ratio were significantly improved in vaccinated piglets compared with those in the unvaccinated groups (P < 0.05).