Transmission of influenza A virus and porcine reproductive and respiratory syndrome virus using a novel nurse sow model: a proof of concept

Selecting the optimal strategies when using nurse sows for supernumerous piglets

Hyper-prolific sows frequently do not have a sufficient number of functional teats for their piglets to nurse which has led to the use of nurse sows to manage these surplus piglets. This review discusses strategies for using nurse sows and factors that influence preweaning survival and weight gain of their litters, as well as those that affect their subsequent rebreeding performance. Rearing piglets using a nurse sow can be as successful as piglets reared with their biological mother and is thus a powerful management tool to decrease preweaning piglet mortality. Selecting a young sow as nurse sow is beneficial for piglet survival; however, piglets nursing first parity sows often have a lower daily weight gain than piglets nursing multiparous sows. A litter of uniform surplus piglets is preferably handled using the two-step nurse sow strategy. A consequence of nonuniform litters will most likely be an increased mortality and decreased weaning weight among the smallest piglets within a litter. The subsequent fertility of nurse sows is not compromised. There is an increased risk of lactational oestrus when using nurse sows leading to an increased weaning-to-oestrus interval; however, litter size in nurse sows is identical or even moderately higher in the subsequent parity compared with nonnurse sows.

Managing Reproduction in Hyperprolific Sow Herds

The rearing of large litters from hyperprolific sows is a characteristic of modern genotypes. However, these sows have body and reproductive characteristics that differentiate them from the genotypes of the past decades, making it necessary to adopt different management strategies. This review describes the main care and challenges associated with the hyperprolificity of sows during the period in which replacement gilts are selected, along with gestation, parturition, lactation, and the weaning-estrus interval. It describes the challenges that these sows' piglets will face during the lactation period and includes some strategies adopted to develop these surplus piglets. In addition, it identifies areas where more research is needed to understand the reproductive management of modern genotypes.

Farm management practices associated with influenza A virus contamination of people working in Midwestern United States swine farms

Indirect transmission of influenza A virus (IAV) contributes to virus spread in pigs. To identify farm management activities with the ability to contaminate farmworkers' hands and clothing that then could be a source of virus spread to other pigs, we conducted a within-farm, prospective IAV surveillance study. Hands and clothes from farmworkers performing the activities of piglet processing, vaccination, or weaning were sampled before and after the activities were performed. Samples were tested by IAV rRT-PCR and virus viability was assessed by cell culture. A multivariate generalized linear model was used to detect associations of the activities with IAV contamination. Of the samples collected for IAV rRT-PCR testing, there were 16% (12/76) collected immediately after processing, 96% (45/48) collected after vaccination, and 94% (29/31) collected after weaning that tested positive. Samples collected immediately after vaccination and weaning, i.e., activities that took place during the peri-weaning period when pigs were about 3 weeks of age, had almost 6 times higher risk of IAV detection and had more samples IAV positive (p-value < 0.0001) than samples collected after processing, i.e., an activity that took place in the first few days of life. Both, hands and clothes had similar contamination rates (46% and 55% respectively, p-value = 0.42) and viable virus was isolated from both. Our results indicate that activities that involve the handling of infected piglets close to weaning age represent a significant risk for IAV dissemination due to the high level of IAV contamination found in farmworkers' hands and coveralls involved in the activities. Biosecurity protocols that include hand sanitation and changing clothing after performing activities with a high-risk of influenza contamination should be recommended to farmworkers to control and limit the mechanical spread of IAV between pigs.

Evaluation of internal farm biosecurity measures combined with sow vaccination to prevent influenza A virus infection in groups of due-to-wean pigs

Background

Influenza A virus (IAV) is an important respiratory pathogen of pigs that affects pig health, well-being and productivity, has zoonotic potential, and has significant economic impact for producers. The ultimate goal is to maintain herds free from IAV. Due to the probability of IAV introduction into the herds, it is also desirable for herds to have some immunity to the virus. In this study, we evaluated a protocol that combined sow vaccination with the implementation of internal biosecurity practices during the pre-weaning period with the goal to wean IAV negative pigs.

Five IAV positive breeding herds were vaccinated twice, 3 weeks apart with a herd-specific autogenous vaccine. For the subsequent 8 weeks, a biosecurity protocol was maintained, consisting of no pig movements after 3 days of age, no use of nurse sows, workers changing disposable gloves between litters, workers not stepping into farrowing crates, and daily disinfection of tools and materials used to handle pigs.

Results

Following these interventions, four of the five treatment farms had significant reductions in IAV detection (p value < 0.05). Three of the farms tested negative at all sampling points post-intervention and one farm had a 21% reduction in IAV positivity.

Conclusions

This study indicates that a protocol that combines sow vaccination and enhanced biosecurity practices may limit IAV transmission among piglets and enable the weaning of groups of pigs free from the virus.

Evaluation of dam parity and internal biosecurity practices in influenza infections in piglets prior to weaning

Influenza is an important respiratory disease of pigs and humans. Controlling influenza in pigs is challenging due to the substantial genetic diversity of influenza A virus (IAV). In this study, we assessed the impact of internal biosecurity practices directed at limiting exposure of piglets to IAV before weaning; evaluated the association of sow parity with IAV prevalence in piglets and the levels of maternally derived antibodies (MDA), and documented the frequency of detection of IAV on farmworkers' hands and the instruments used when handling pigs. The control group included litters in rooms where no specific changes were made to standard farm procedures. The treatment group included litters in rooms where no cross-fostering or nurse sows use was allowed, and where farmworkers were required to change gloves between litters when handling pigs. Both, younger (≤ Parity 3) and older parity sows (>Parity 3) were represented in all rooms included in the study. Overall, litters in the treatment group had lower IAV prevalence (29.9 %) than litters in the control group (44.2 %) (p < 0.001), and at day 8 of age the litters from the control group had 7.5 times higher IAV prevalence than the litters from the treatment group. However, at weaning differences were not found (77.2 % vs. 81 % for treatment vs. control, respectively, p = 0.41). There were no differences in IAV detection between parity groups at any of the sampling points (p = 0.86) and incidence of detection in sows from farrowing to weaning was 29 %. Piglets that tested ELISA negative were 1.3 times more likely to test IAV positive than piglets that were ELISA positive for IAV antibody test, suggesting that effective colostrum intake may reduce the likelihood of infection. IAV was detected on 46 % of the instruments used when handling piglets and on 58 % of farmworkers' hands, indicating the potential risk for mechanical transmission of IAV in pigs. Overall, we showed that the implementation of internal biosecurity practices that limit IAV exposure to newborn piglets helped delay IAV infections but were not sufficient to reduce the prevalence of IAV infection in litters at weaning.

Impact of nurse sows on influenza A virus transmission in pigs under field conditions

Piglets prior to weaning play a central role in maintaining influenza infections in breeding herds and the use of nurse sows is a common practice to adopt piglets that fall behind and that otherwise would die. Transmission of influenza A virus (IAV) from nurse sows to adopted pigs has been reported experimentally, however, the importance of this route of transmission under field conditions has not yet been elucidated. A cohort study to assess the IAV status in nurse and control sows and their respective litters was carried out in three influenza positive breed-to-wean farms. A total of 94 control and 90 nurse sows were sampled by collecting udder skin wipes and oral swabs at enrollment (∼ 5-7 days after farrowing) and at weaning. Six piglets per litter were sampled randomly at enrollment, 2 days post-enrollment (DPE), 4 DPE, at day 14 of lactation (14DL) and at weaning. At enrollment, 76 % (69/91) of udder wipes and 3 % (3/89) of oral swabs from nurse sows were positive by rRT-PCR compared with 23 % (21/92) of udder wipes and 0 % (0/85) of oral swabs from control sows. Of the 94 control litters sampled, 11.7 %, 14.9 %, 22.9 %, 46.8 % and 63.9 % tested rRT-PCR IAV positive at enrollment, 2DPE, 4DPE, 14 DL and weaning, respectively. Corresponding prevalence for nurse sow litters were 12.2 %, 30.2 %, 37.0 %, 59.4 % and 56.4 %. The odds of IAV positivity were significantly higher (p < 0.05) for litters from nurse sows 2 DPE (odd ratio (OR) = 6.13, 95 % CI = 1.8-21.2), 4 DPE (OR = 5.5, 95 % CI = 1.7-17.8) and 14 DL (OR = 3.7, 95 % CI = 1.1-12.3). However, there were no differences in the proportion of positive samples at weaning. Moreover, approximately 18 % of the control sows and 11 % of nurse sows that tested IAV negative in oral swabs at enrollment, tested IAV positive at weaning. This study indicates that nurse sows can contribute to the transmission and perpetuation of IAV infections in pigs prior to weaning, particularly during the first week after adoption.