Sow mortality in a pig production system in the midwestern USA: Reasons for removal and factors associated with increased mortality

BACKGROUND

Sow mortality has become a growing concern in the pig production industry over the past decade. Therefore, we aimed to describe sow mortality and associated factors in a production system in the midwestern USA.

METHODS

Mortality records from 2009 to 2018 for four farrow-to-wean farms were described. Environmental, farm- and individual-level factors associated with weekly mortality and individual risk of dying throughout a sow's lifetime were assessed.

RESULTS

Deaths occurred at a median of 116 days from last service, or 26 days postpartum. The median parity upon death was two. Overall, the main reasons for death were locomotion (27%) and reproduction (24%). A higher weekly number of deaths was associated with spring (incidence rate ratio [IRR] 1.27, compared to winter). Sows had a higher mortality when they were exposed to at least one porcine reproductive and respiratory syndrome (PRRS) outbreak during their lifetime (IRR 1.55) and when housed in groups (pens) during gestation (IRR 1.32). Conversely, they had  a lower mortality when housed in filtered farms (IRR 0.76), accounting for an interaction term between parity at removal and PRRS outbreak exposure.

LIMITATIONS

Issues with data completion and information accuracy were present, and prospective data collection throughout sows' lifetimes is still needed.

CONCLUSION

Efforts to reduce infectious diseases within the herd and manage environmental stressors should help reduce mortality.

The Application of 3D Landmark-Based Geometric Morphometrics towards Refinement of the Piglet Grimace Scale

Proper methods of assessment to objectively identify pain are essential for welfare improvements of piglets undergoing surgical castration on commercial farms. The Piglet Grimace Scale (PGS) is used to identify changes in facial expressions caused by acute pain in piglets undergoing tail docking and castration. However, subjective scoring methods are a concern for the validation of the PGS. The objectives of this study were to evaluate and refine the PGS through 3D landmark geometric morphometrics. Male piglets (n = 88) were randomly allocated to one of two treatments: castration and sham-castration. Piglet facial images were taken at four time points (before treatment, immediately post-treatment, 1 h post-treatment, and 4 h post-treatment) using a photogrammetry rig. Images were scored by four raters using five facial action units (FAUs): orbital tightening, ear position, temporal tension, lip contraction, and nose bulge/cheek tension. Three-dimensional facial models were generated and landmarked denoting 3 FAUs (orbital tightening, lip contraction, and nose bulge/cheek tension). Results suggest that orbital tightening and ear position may be reliable FAUs for the PGS. However, neither the PGS nor 3D landmark-based geometric morphometrics were able (both p > 0.10) to reliably identify facial indicators of pain in piglets undergoing castration.

History and best practices of captive bolt euthanasia for swine

The definition of animal welfare includes how an animal dies. As such, euthanasia is intrinsically linked to animal welfare and ensuring a good death through effective, safe, and validated practices is a critical piece of promoting positive animal welfare. The objective of this review is to provide a better understanding of the literature on the euthanasia of swine via penetrating captive bolt (PCB) and nonpenetrating captive bolt (NPCB), as well as a history of captive bolt use, and indicators of sensibility and insensibility. To do this, we performed a systematic review that included 30 peer-reviewed articles and 17 other publications. Nonpenetrating captive bolt devices have been validated as an effective single-step euthanasia method for neonatal and pre-weaning swine, as well as a two-step euthanasia method for nursery swine. Penetrating captive bolt devices have been validated as an effective euthanasia method for nursery and market swine up to 120 kg, but further investigation is required for the use of captive bolt devices on mature breeding sows and boars.

Surgical Castration Changes Struggle Behavior and Vocalizations in Male Piglets

This study assessed acute pain in piglets during castration through behavioral indicators. Piglets (n=88) were randomly allocated to one of two treatments: surgical castration and sham-castration. Within 24 hours after birth, identical castration procedures were followed for both treatment groups, except sham piglets were not castrated. Struggle behavior (curl ups, leg kicks, and body flailing) and vocalization (duration and peak frequency) were analyzed during the castration procedure. Castrated piglets kicked more frequently than sham piglets (28.8 vs. 21.3 kicks/min, SE = 0.09; P = 0.02). Additionally, 51.2% of castrated piglets displayed body flailing, whereas only 4.4% of sham piglets displayed the same behavior (P = 0.03). Castrated piglets responded with more high frequency (≥1,000 Hz) calls than sham piglets (23.6 vs. 18.6 calls/min, SE = 0.26; P = 0.04) and high frequency calls tended to be of longer duration for castrated piglets (0.45 vs. 0.27 sec/call, SE = 0.04; P = 0.08). Results indicate that surgical castration increased the frequency of leg kicks, body flailing, and high frequency calls compared to sham-castration, suggesting these may be useful behavioral indicators of acute pain in piglets.

Animal movement in a pastoralist population in the Maasai Mara Ecosystem in Kenya and implications for pathogen spread and control

Livestock movements are important drivers for infectious disease transmission. However, paucity of such data in pastoralist communities in rangeland ecosystems limits our understanding of their dynamics and hampers disease surveillance and control. The aim of this study was to investigate animal movement networks in a pastoralist community in Kenya, and assess network-based strategies for disease control. We used network analysis to characterize five types of between-village animal movement networks. We then evaluated implications of these networks for disease spread and control by quantifying topological changes in the network associated with targeted and random removal of nodes. To construct these networks, data were collected using standardized questionnaires (N = 165 households) from communities living within the Maasai Mara Ecosystem in southwestern Kenya. Our analyses show that the Maasai Mara National Reserve (MMNR), a protected wildlife area, was critical for maintaining village connectivity in the agistment network (dry season grazing), with MMNR-adjacent villages being highly utilized during the dry season. In terms of disease dynamics, the network-based basic reproduction number, R₀, was sufficient to allow disease invasion in all the five networks, and removal of villages based on degree or betweenness was not efficient in reducing R₀. However, we show that villages with high degree or betweenness may play an important role in maintaining network connectivity, which may not be captured by assessment of R₀ alone. Such villages may function as potential "firebreaks." For example, targeted removal of highly connected village nodes was more effective at fragmenting each network than random removal of nodes, indicating that network-based targeting of interventions such as vaccination could potentially disrupt transmission pathways in the ecosystem. In conclusion, this work shows that animal movements have the potential to shape patterns of disease transmission in this ecosystem, with targeted interventions being a practical and efficient measure for disease control.

Focus on PoCUS or hocus pocus? Integrating point-of-care ultrasound into residency and clinical practice

Point-of care ultrasound (PoCUS) is a new clinical diagnostic paradigm that plays an instrumental role in the ongoing anesthesiologist’s evolving role towards a perioperative physician. Currently, there are few approved curricula that incorporate a PoCUS program into anesthesia residency. This article examines relevant PoCUS applications for anesthesiologists, presents an overview of existing international guidelines for education and training, and reflects on the need for specialty-wide standards. We present a possible framework, that could offer a first move towards a structured PoCUS pathway for Belgian anesthesia residents and facilitate its incorporation into national anesthesia practice.

Behavioral indicators of slow growth in nursery pigs

The objective of this study was to determine how feeder-space allowance affects behaviors of slow- and fast-growing pigs during the nursery period. Nursery pigs (n = 192; initial weight = 7.4 ± 1.6 kg) were housed in 24 pens of 8 pigs, with 12 pens provided with either a two-space feeder or a five-space feeder. Pigs were categorized as slow growers (SG) and fast growers (FG) based on adjusted market weight (SG < 105 kg; FG ≥ 105 kg). Behaviors of pigs were video-recorded during the first four days after entering the nursery and on Day 21. Eating speed was measured on 96 focal pigs when they were nine weeks old. SG spent more time at the drinker than did FG (p < .05). SG spent less time in the standing/walking posture (p < .05) in pens with five-space feeders compared with SG in pens with two-space feeders. These results suggest that providing more feeder space may benefit SG in terms of improving the welfare of these pigs.

Identifying factors contributing to slow growth in pigs

Pigs that grow slower than their contemporaries can cause complications for animal welfare and profitability. This study was conducted to investigate factors that may contribute to slow growth of pigs. Pigs ( = 440) farrowed by 65 sows were monitored from birth to market. Pigs were categorized as slow, average, and fast growers based on market weight adjusted to 170 d of age (slow growers were <105 kg, average growers were between 105 and 125 kg, and fast growers were >125 kg). Blood samples were collected from 48 focal pigs at 9 and 21 wk of age and analyzed for hormone and free AA concentrations. Data were analyzed using the Mixed and Logistic procedures of SAS. Slow-growing pigs accounted for 10% of pigs marketed, average growers accounted for 49% of pigs marketed, and fast growers accounted for 41% of pigs marketed. Compared with fast growers, slow growers were lighter at birth ( < 0.01), at weaning ( < 0.01), and at nursery exit ( < 0.01) and had less backfat ( < 0.01) and smaller loin muscle area ( < 0.01) at marketing at 21 wk of age. Slow growers had lower plasma concentrations of IGF-1 ( = 0.03) and insulin ( < 0.001) during the nursery period and lower concentrations of leptin ( < 0.001) and insulin ( < 0.001) during the finishing period compared with average and fast growers. Serum concentrations of several essential, nonessential, and total free AA were less for slow growers during both the nursery and finishing periods compared with average and fast growers. Gilts were more likely to become slow growers than barrows (odds ratio = 2.17, 95% confidence interval = 1.19 to 3.96, = 0.01). Litter size and parity of the pigs' dam were not associated with slow growth. These results suggest that low concentrations of IGF-1, insulin, leptin, and AA may contribute to or be associated with slow growth in pigs.

Honey bee surveillance: a tool for understanding and improving honey bee health

Honey bee surveillance systems are increasingly used to characterize honey bee health and disease burdens of bees in different regions and/or over time. In addition to quantifying disease prevalence, surveillance systems can identify risk factors associated with colony morbidity and mortality. Surveillance systems are often observational, and prove particularly useful when searching for risk factors in real world complex systems. We review recent examples of surveillance systems with particular emphasis on how these efforts have helped increase our understanding of honey bee health.

Molecular characterization of high-level-cholera-toxin-producing El Tor variant Vibrio cholerae strains in the Zanzibar Archipelago of Tanzania

Analysis of 1,180 diarrheal stool samples in Zanzibar detected 247 Vibrio cholerae O1, Ogawa strains in 2009. Phenotypic traits and PCR-based detection of rstR, rtxC, and tcpA alleles showed that they belonged to the El Tor biotype. Genetic analysis of ctxB of these strains revealed that they were classical type, and production of classical cholera toxin B (CTB) was confirmed by Western blotting. These strains produced more CT than the prototype El Tor and formed a separate cluster by pulsed-field gel electrophoresis (PFGE) analysis.

Longitudinal assessment of two Mycoplasma hyopneumoniae enzyme-linked immunosorbent assays in challenged and contact-exposed pigs

The objective of the current study was to compare the sensitivity of 2 Mycoplasma hyopneumoniae enzyme-linked immunosorbent assays (ELISAs) in experimentally challenged and contact-exposed pigs in a long-term longitudinal assessment. On day 0 of the assessment, twelve 2-month-old M. hyopneumoniae-negative pigs were inoculated with M. hyopneumoniae strain 232 (group A). Twelve negative pigs were placed alongside the inoculated pigs, allowing direct contact exposure (group B). A third group of 12 pigs was allocated into 2 independent pens; no direct contact was allowed (group C). A longitudinal serologic profile was performed; samples were collected on days 0, 28, 35, 42, 49, 63, 91, 119, 154, and 170 of the study. Serum samples were tested using a blocking ELISA and an indirect ELISA. Results of the study demonstrated higher sensitivity of the blocking ELISA during early infection (clinical signs). Both ELISAs were 100% sensitive in challenged and naturally infected groups at several testing points during late infection (63, 91, 119, 154, and 170 days of the study) and showed a long antibody detection period. Both tests worked equally well during the chronic phase of infection but the blocking ELISA was more sensitive during acute stages of infection.

Vaccination of influenza a virus decreases transmission rates in pigs

Limited information is available on the transmission and spread of influenza virus in pig populations with differing immune statuses. In this study we assessed differences in transmission patterns and quantified the spread of a triple reassortant H1N1 influenza virus in naïve and vaccinated pig populations by estimating the reproduction ratio (R) of infection (i.e. the number of secondary infections caused by an infectious individual) using a deterministic Susceptible-Infectious-Recovered (SIR) model, fitted on experimental data. One hundred and ten pigs were distributed in ten isolated rooms as follows: (i) non-vaccinated (NV), (ii) vaccinated with a heterologous vaccine (HE), and (iii) vaccinated with a homologous inactivated vaccine (HO). The study was run with multiple replicates and for each replicate, an infected non-vaccinated pig was placed with 10 contact pigs for two weeks and transmission of influenza evaluated daily by analyzing individual nasal swabs by RT-PCR. A statistically significant difference between R estimates was observed between vaccinated and non-vaccinated pigs (p < 0.05). A statistically significant reduction in transmission was observed in the vaccinated groups where R (95%CI) was 1 (0.39-2.09) and 0 for the HE and the HO groups respectively, compared to an R_o value of 10.66 (6.57-16.46) in NV pigs (p < 0.05). Transmission in the HE group was delayed and variable when compared to the NV group and transmission could not be detected in the HO group. Results from this study indicate that influenza vaccines can be used to decrease susceptibility to influenza infection and decrease influenza transmission.

Use of a production region model to assess the efficacy of various air filtration systems for preventing airborne transmission of porcine reproductive and respiratory syndrome virus and Mycoplasma hyopneumoniae: results from a 2-year study

Porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae (M hyo) are economically significant pathogens of pigs that can be spread between herds via the airborne route. As area/regional control and eradication programs for these pathogens move forward, it becomes critical to understand conditions associated with airborne transport and to develop strategies to reduce this risk. While MERV 16-based air filtration is a potential intervention, it is costly and has only been evaluated against PRRSV. Therefore, it is important to test current and alternative filtration strategies against multiple pathogens to enhance their application in the field. To address this issue, we used a production region model to evaluate meteorological risk factors associated with the presence of each pathogen in air as well as the ability of mechanical and antimicrobial filters to protect susceptible populations against PRRSV and M hyo. In summary, conditions common to both pathogens included cool temperatures, the presence of PRRSV or M hyo in source population air and wind direction. PRRSV-positive air days were also characterized by low sunlight levels, winds of low velocity in conjunction with gusts and rising humidity and pressure. In regards to filter efficacy, while all types tested successfully prevented airborne transmission of PRRSV and M hyo, differences were observed in their ability to prevent airborne transport. These data provide a better understanding of the aerobiology of two important diseases of pigs and validate several air filtration technologies for protecting susceptible populations against the airborne challenge of PRRSV and M hyo.

Long-distance airborne transport of infectious PRRSV and Mycoplasma hyopneumoniae from a swine population infected with multiple viral variants

Airborne transport of porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae (M hyo) has been reported out to 4.7 km. This study attempted to determine whether this event could occur over longer distances and across multiple viral variants. To accomplish this goal, a mixed infection of 3 PRRSV variants (1-8-4, 1-18-2 and 1-26-2) and M hyo 232 was established in a source population of growing pigs. Over 21-day period, air samples were collected from the source population and at designated distances from the herd. Samples were tested for PRRSV RNA and M hyo DNA by PCR and if positive, further characterized. In exhaust air from the source population, PRRSV and M hyo were detected in 21 of 21 and 8 of 21 air samples, respectively. Five of 114 (4.4%) long-distance air samples were positive for PRRSV and 6 of 114 (5.2%) were positive for M hyo. The 5 PRRSV-positive samples were collected at 2.3, 4.6, 6.6 and 9.1 km from the herd. All contained infectious virus and were >99.2% homologous to PRRSV 1-8-4. No evidence of PRRSV 1-18-2 or 1-26-2 was detected in long-distance samples. All 6 M hyo-positive samples were 99.9% homologous to M hyo 232 and 3 samples (collected at 3.5, 6.8 and 9.2km from the herd) were infectious. These results indicate that airborne transport of PRRSV 1-8-4 and M hyo 232 occurs over longer distances than previously reported and that both pathogens remained infectious.

Effect of lameness on sow longevity

OBJECTIVE

To analyze the association of lameness and performance variables on sow longevity by use of time-to-event analysis.

DESIGN

Cohort study.

ANIMALS

674 sows from a commercial breeding herd.

PROCEDURES

A lameness assessment was performed on each sow. Data on farrowing performance and longevity were collected for the sows during 3 or fewer parities from the database of the herd during 2005 and 2006. The association of risk factors with sow longevity within 350 days after lameness assessment was analyzed via Cox regression analysis. Pigs per day, total production days, and survival at 350 days after lameness evaluation were compared between lame and nonlame sows.

RESULTS

Numbers of preweaning baby pig deaths, stillborn pigs, and mummified pigs were negatively associated with sow longevity within 350 days after lameness assessment. A higher number of pigs born alive and younger parity of sows were protective. Lame sows had a higher risk (1.710 times as high) of removal from the herd within 350 days after lameness assessment. The number of pigs born alive per day, survival of sows at 350 days, and total number of days in the herd were lower in lame sows.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of this study indicated significant differences in the survivability of lame and nonlame sows in a commercial herd. Parity and farrowing performance variables were factors influencing sow longevity in this herd. Producers need to minimize sow lameness and remove lame sows from a herd early (when treatment is not an option) to minimize economic loss.

Further assessment of fomites and personnel as vehicles for the mechanical transport and transmission of porcine reproductive and respiratory syndrome virus

This study re-evaluated the role of fomites and personnel in the mechanical transport and transmission of porcine reproductive and respiratory syndrome virus (PRRSV) between pig populations. Swabs were collected from hands, boots, coveralls, and other fomites following contact with infected pigs and compared with identical samples collected in the absence of PRRSV exposure. Naïve pigs were provided contact with contaminated fomites/personnel and blood tested periodically post-exposure [positive exposure population (PEP)] and compared with populations that did not gain exposure via these routes [negative exposure population (NEP)]. The majority of swab samples from hands, coveralls, and boots from personnel and fomite samples (cable snare and bleeding equipment) following contact with the PRRSV-infected Source Population. Transmission of PRRSV to the PEP was observed (7/7) cases but not in the NEP. In conclusion, under the proper conditions, transport and transmission of PRRSV by fomites and personnel may occur between swine populations in the absence of intervention.

Evidence of long distance airborne transport of porcine reproductive and respiratory syndrome virus and Mycoplasma hyopneumoniae

The ability of porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae to be transported over long distances via the airborne route was evaluated. A source population of 300 grow-finish pigs was experimentally inoculated with PRRSV MN-184 and M. hyopneumoniae 232 and over a 50-day period, air samples were collected at designated distances from the source herd using a liquid cyclonic collector. Samples were tested for the presence of PRRSV RNA and M. hyopneumoniae DNA by PCR and if positive, further characterized. Of the 306 samples collected, 4 (1.3%) were positive for PRRSV RNA and 6 (1.9%) were positive for M. hyopneumoniae DNA. The PRRSV-positive samples were recovered 4.7 km to the northwest (NW) of the source population. Four of the M. hyopneumoniae-positive samples were obtained at the NW sampling point; 2 samples at approximately 2.3 km and the other 2 samples approximately 4.7 km from the source population. Of the remaining 2 samples, one sample was obtained at the southeast sampling point and the other at the southwest sampling point, with both locations being approximately 4.7 km from the source. The four PRRSV-positive samples contained infectious virus and were ≥ 98.8% homologous to the MN-184 isolate used to inoculate the source population. All 6 of the M. hyopneumoniae-positive samples were 99.9% homologous to M. hyopneumoniae 232. These results support the hypothesis that long distance airborne transport of these important swine pathogens can occur.

Further assessment of houseflies (Musca domestica) as vectors for the mechanical transport and transmission of porcine reproductive and respiratory syndrome virus under field conditions

The purpose of this study was to evaluate the potential for houseflies (Musca domestica) to mechanically transport and transmit porcine reproductive and respiratory syndrome virus (PRRSV) between pig populations under controlled field conditions. The study employed swine housed in commercial livestock facilities and a release-recapture protocol involving marked (ochre-eyed) houseflies. To assess whether transport of PRRSV by insects occurred, ochre-eyed houseflies were released and collected from a facility housing an experimentally PRRSV-inoculated population of pigs (facility A) and collected from a neighboring facility located 120 m to the northwest that housed a naïve pig population (facility B). All samples were tested for PRRSV RNA by polymerase chain reaction (PCR). To assess transmission between the 2 populations, blood samples were collected from naïve pigs in facility B at designated intervals and tested by PCR. A total of 7 replicates were conducted. During 2 of 7 replicates (1 and 5), PCR-positive ochre-eyed houseflies were recovered in facility B and pigs in this facility became infected with PRRSV. Chi-squared analysis indicated that the presence of PRRSV in an insect sample was significantly (P = 0.0004) associated with infection of facility B pigs. Porcine reproductive and respiratory syndrome virus was not recovered from other reported routes of transmission during the study period, including air, fomites, and personnel. In conclusion, while an insufficient number of replicates were conducted to predict the frequency of the event, houseflies may pose some level of risk for the transport and transmission of PRRSV between pig populations under field conditions.

Evaluation of alternative strategies to MERV 16-based air filtration systems for reduction of the risk of airborne spread of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) is a re-emerging disease of pigs and a growing threat to the global swine industry. For sustainable disease control it is critical to prevent the airborne spread of the etiologic agent, PRRS virus, between pig populations. The application of MERV 16-based air filtration systems to swine facilities in an effort to reduce this risk has been proposed; however, due to the cost and air flow restrictions of such systems the need for alternative strategies has arisen. Therefore, the objective of this study was to evaluate 3 groups of alternative biosecurity strategies for reducing the risk of the airborne spread of PRRSV. Strategies evaluated included mechanical filters, antimicrobial filters and a disinfectant-EVAP (evaporative cooling) system. Results from this study indicate that while alternatives to MERV 16-based biosecurity protocols for protecting farms from the airborne spread of PRRSV are available, further information on their efficacy in the field is needed before conclusions can be drawn.

Outcome of performance-based removal and replacement decisions in commercial swine herds

OBJECTIVE

To evaluate the success of removal and replacement decisions in commercial swine herds when sow removal was attributed to problems with fertility, fecundity, or old age.

DESIGN

Retrospective case-control study.

ANIMALS

3,000 sows removed from 3 commercial swine herds (case sows), 3,000 matched control sows retained in the herds, and 3,000 replacement gilts.

PROCEDURES

Control sows were included to generate an estimate of reproductive performance that could have been expected had case sows been retained in the herds. Control sows and replacement gilts were followed up until the next farrowing or until removed from the herd, and reproductive performance, calculated as number of pigs born alive per mated female per year, was compared between groups.

RESULTS

In 2 of the 3 herds, reproductive performance was significantly higher for replacement gilts than for control sows matched with case sows removed for reasons of fertility, and in all 3 herds, reproductive performance was significantly higher for replacement gilts than for control sows matched with case sows removed for reasons of fecundity. In the 2 herds with case sows removed because of age, reproductive performance did not differ significantly between replacement gilts and control sows. The odds of greater performance among replacement gilts relative to control sows ranged from 1.305 to 1.955 for removals attributed to fertility, 1.305 to 1.955 for removals attributed to fecundity, and 1.000 to 3.999 for removals attributed to age.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that performance-based removal and replacement programs in commercial swine herds may not yield the anticipated results.

An investigation of the success of production-based sow removal and replacement in the context of herd performance

Production-based removal and replacement has been used as a method to improve sow herd performance. Limited data are available as to the reliability of this approach. The purpose of this investigation was to use a retrospective case-control study to assess the success of replacement events when herd productivity was greater or less than the mean for removal events attributed to problems with fertility, fecundity, or old age. For each of 3 herds, 1,000 consecutive sows removed between parities 1 and 6 for reasons of fertility, fecundity, or old age were matched to sows with similar histories that were retained in the herd (controls) and to gilts that were first bred into the herd around the time of the case removal events. Controls and gilts were followed until their next parity or removal event, and the outcome was measured as a standardized calculation of born alive per mated female per year. Herd performance at the time of the case removal events was categorized according to greater or less than the mean for fertility or fecundity on monthly farrowing rates and average piglets born alive per litter. Success of removal/replacement events were evaluated according to removal reason and contemporary herd performance. A model was developed to estimate production and financial implications of changes to productivity-based culling, using a Monte Carlo simulation with a 1,000-iteration run. Born alive per mated female per year from gilts was greater (P = 0.0001) than from controls in 1 of 3 herds when herd fertility was greater than the mean, 1 of 3 herds when herd fertility was less than the mean (P = 0.0065), 3 of 3 herds when herd fecundity was greater than the mean (P < 0.030), and 2 of 3 herds when herd fecundity was less than the mean (P < 0.020). The financial model sensitivity analysis indicated greater likelihood of economic advantage for a scenario without production-based removals in parities 1 to 6.

Analysis of periparturient risk factors affecting sow longevity in breeding herds

The association of periparturient risk factors with sow longevity and the validity of sow removal decisions made during the periparturient period were analyzed. Data pertaining to 2066 sows from a commercial breeding herd from the US Midwest were used in this study. The likelihood of removal from the herd within 35 d post-farrowing decreased with a younger parity, the absence of lameness or other health problems, a higher lactation feed intake (LFI) and a greater number of live-born piglets (P < 0.05 for all). A greater number of piglets born alive, the absence of lameness and a younger parity lowered (P < 0.05 for all) the likelihood of removal of sows from the herd before the next parity. The number of piglets born alive was higher (P < 0.05) among sows without any health problems during the previous periparturient period. A greater (P < 0.05) number of sows that were retained without any health problems during the periparturient period farrowed. More sows (P < 0.05) retained with health problems during the periparturient period were culled compared with sows retained without health problems during the periparturient period. In summary, periparturient factors such as LFI, the incidence of lameness or health problems, as well as sow-level characteristics such as higher parity and fewer piglets born alive predicted the removal of a sow from the breeding herd. Sows retained with periparturient health problems had reduced longevity and fewer live-born piglets, and fewer such sows had another farrowing. Key words: Longevity, sow, risk factor, feed intake

Development and validation of an enzyme-linked immunosorbent assay for the diagnosis of porcine proliferative enteropathy

The objective of this study was to develop an indirect enzyme-linked immunosorbent assay (ELISA) using a sonicated pure culture of Lawsonia intracellularis as the antigen (So-ELISA). A total of 332 serum samples, consisting of 232 experimentally infected animals and 100 animals naturally infected with L. intracellularis, were used to assess the diagnostic sensitivity. Three hundred and fifty-five sera from uninfected animals were used to determine the diagnostic specificity. The receiver operating characteristic and mean +3 standard deviation of optical density (OD) values from uninfected animals were used for selecting cut-off points. The diagnostic accuracy of So-ELISA was considered to be high as the area under the curve index was 0.991 with 0.0029 standard error. The optimal cut-off for So-ELISA was set at 0.45 OD with 89.8% sensitivity and 99.4% specificity based on a combination of good sensitivity and high specificity. No cross-reactivity was found in sera from pigs exposed to Brachyspira pilosicoli, B. hyodysenteriae, Campylobacter mucosalis, C. jejuni, or C. coli. Inter- and intracoefficient of variation of all control sera tested with So-ELISA was less than 10%. The observed agreements between So-ELISA and the immunoperoxidase monolayer assay tested with experimental challenge animals and field samples were 95.08% with 0.88 kappa and 90.65% with 0.74 kappa value, respectively. So-ELISA was able to detect the seroconversion of infected animals at 2 to 4 weeks after exposure to L. intracellularis. Based on the validation results, So-ELISA could be used as an alternative serology for proliferative enteropathy diagnosis.

Effect of Mycoplasma hyopneumoniae colonization at weaning on disease severity in growing pigs

To determine whether Mycoplasma hyopneumoniae colonization at weaning in off-site weaning systems is associated with the severity of respiratory disease due to this agent in growing pigs, we studied 20 groups, each group representing a different week in production, in sow herds at 3 farms of 3000 sows each that had a prevalence of M. hyopneumoniae colonization at weaning higher than 5%. The calculated sample size for assessment at weaning was 39 piglets for each group under study; 39 litters were randomly selected, and 1 piglet was randomly selected from each litter for testing and ear-tagged. In total, 780 piglets were tested. The presence of M. hyopneumoniae in nasal swabs at weaning was established by nested polymerase chain reaction (PCR). All groups were followed until slaughter, at which time blood samples were collected from each ear-tagged pig to test for M. hyopneumoniae antibodies, bronchial swabs were collected for detection of M. hyopneumoniae DNA by nested PCR, and the lung lesion score and percentage of affected lungs in the same animals were calculated. Correlation analyses showed a positive correlation between colonization at weaning and all 4 dependent variables indicating infection at slaughter: average lung lesion score, percentage of affected lungs, presence of M. hyopneumoniae on the bronchial epithelium, and seroconversion. This study provides evidence that severity of the disease can be predicted by the prevalence at weaning in segregated systems. Therefore, strategies focused on reducing colonization at weaning seem to be important elements in the global control of M. hyopneumoniae in segregated production systems.

Effects of allometric space allowance and weight group composition on grower-finisher pigs

The average daily gain (ADG; kg d-1), pen efficiency (PE; kg ADG m-2 floor space) and welfare indicators (injury levels, salivary cortisol concentrations and behaviour) of grower-finisher pigs were evaluated in groups of 19 barrows, at four levels of floor space allowances calculated mathematically (area = k × BW0.667) using a constant k, (with values 0.027, 0.031, 0.034, and 0.037) for a mean final market weight of 116 kg and in two levels of group weight composition (uniform and varying weights – based on uniformity and variation of body weights of pigs within a pen at the beginning of the experiment). The corresponding space allowances (m2 pig-1) at the market weight of 116 kg were 0.64 (SA0.64), 0.74 (SA0.74), 0.81 (SA0.81), and 0.88 (SA0.88). The data were analyzed using repeated measure ANOVAs and independent sample T tests. The pigs in SA0.64 had a lower ADG (0.859 ± 0.017), spent a lower proportion of time lying in preferred areas (55.22 ± 1.644) and had higher total injury scores (4.581 ± 0.139) and higher number of aggressions (1.94 ± 0.286) (P < 0.05 for all) than those in SA0.88 (0.936 ± 0.020; 61.02 ± 1.203; 3.858 ± 0.208; 1.08 ± 0.212, respectively) and SA0.81 (0.916 ± 0.019; 59.77 ± 1.417; 3.855 ± 0.112; 1.24 ± 0.238, respectively). Pigs in SA0.64 had higher (P < 0.05) overall PE (1.344 kg ADG m-2 floor space) than those in SA0.88 (1.063 ± 0.023) SA0.81 (1.131 ± 0.024) and SA0.74 (1.224 ± 0.029) allowance treatments. Pigs in the varying weight group spent a higher (P < 0.05) proportion of time lying in preferred areas (59.73 ± 0.942) than the uniform weight group (57.08 ± 1.078). Pigs in SA0.74 and SA0.64 spent lower proportion of time (P < 0.05) lying isolated (2.76 ± 0.441 and 2.18 ± 0.372, respectively) than pigs in SA0.81 (4.52 ± 0.467). The uniform weight group exhibited more (P < 0.05) exploratory behaviour (8.83 ± 0.448) than the varying weight group (7.25 ± 0.356). On fully slatted floors, space allotted considering the final market weight of barrows corresponding to k values of 0.037 and 0.034 were better (P < 0.05) than 0.027 in terms of growth rate and welfare indicators. Key words: Space allowances, welfare, daily gain, grower-finisher, pig

Influence of isolate pathogenicity on the aerosol transmission of Porcine reproductive and respiratory syndrome virus

The objectives of this study were to evaluate the role of isolate pathogenicity in the aerosol transmission of Porcine reproductive and respiratory syndrome virus (PRRSV) and to determine whether PRRSV could be detected in air samples. To assess transmission, we exposed naive recipient pigs to aerosols from pigs inoculated with PRRSV MN-30100, an isolate of low pathogenicity, or MN-184, a highly pathogenic isolate. Blood samples and nasal-swab samples were collected from the inoculated pigs during the exposure period and tested for the presence of PRRSV RNA by quantitative (real-time) reverse-transcriptase polymerase chain reaction (RT-PCR); the amount of RNA was expressed as the median tissue culture dose per milliliter (TCID50/mL). The recipient pigs were clinically evaluated for 14 d after exposure and tested on days 7 and 14 by qualitative RT-PCR and enzyme-linked immunosorbent assay (ELISA). To prove the presence of PRRSV in aerosols, air samples were collected from each recipient-pig chamber by means of an air sampler. The PRRSV RNA concentrations were significantly higher (P = 0.01) in the blood samples from the pigs infected with PRRSV MN-184 than in the blood samples from those infected with PRRSV MN-30100; however, the concentrations in the nasal-swab samples were not significantly different (P = 0.26). Recipient pigs exposed to aerosols from pigs infected with PRRSV MN-184 became infected, whereas those exposed to aerosols from pigs infected with PRRSV MN-30100 did not; the difference in transmission rate was significant at P = 0.04. We detected PRRSV MN-184 RNA but not PRRSV MN-30100 RNA in air samples by PCR. Under the conditions of this study, PRRSV isolate pathogenicity may influence aerosol transmission of the virus.

The impact of animal age, bacterial coinfection, and isolate pathogenicity on the shedding of porcine reproductive and respiratory syndrome virus in aerosols from experimentally infected pigs

The objective of this study was to evaluate the role of different variables (animal age, bacterial coinfection, and isolate pathogenicity) on the shedding of Porcine reproductive and respiratory syndrome virus (PRRSV) in aerosols. Animals were grouped according to age (2 versus 6 mo) and inoculated with a PRRSV isolate of either low (MN-30100) or high (MN-184) pathogenicity. Selected animals in each group were also inoculated with Mycoplasma hyopneumoniae. The pigs were anesthetized and aerosol samples (1000 breaths/sample) collected on alternating days from 1 to 21 after PRRSV inoculation. The results indicated that animal age (P = 0.09), M. hyopneumoniae coinfection (P = 0.09), and PRRSV isolate pathogenicity (P = 0.15) did not significantly influence the concentration of PRRSV in aerosols. However, inoculation with the PRRSV MN-184 isolate significantly increased the probability of aerosol shedding (P = 0.00005; odds ratio = 3.22). Therefore, the shedding of PRRSV in aerosols may be isolate-dependent.

Further evaluation of alternative air-filtration systems for reducing the transmission of Porcine reproductive and respiratory syndrome virus by aerosol

The purpose of this study was to compare 4 methods for the reduction of aerosol transmission of Porcine reproductive and respiratory syndrome virus (PRRSV): high-efficiency particulate air (HEPA) filtration, 2x-low-cost filtration, bag filtration, and use of a filter tested against particles derived from dioctylphthalate (DOP). The HEPA-filtration system used a prefilter screen, a bag filter (Eurovent [EU] 8 rating), and a HEPA filter (EU13 rating). The low-cost-filtration system contained mosquito netting (prefilter), 2 fiberglass furnace filters, and 2 electrostatic furnace filters. Bag filtration involved the use of a filter rated EU8 and a minimum efficiency reporting value (MERV) of 14. The 95%-DOP, 0.3-microm-filtration system involved a pleat-in-pleat V-bank disposable filter with a 95% efficiency rating for particles 0.3 microm or greater in diameter and ratings of EU9 and MERV 15. No form of intervention was used in the control group. The experimental facilities consisted of 2 chambers connected by a 1.3-m-long duct containing the treatments. Recipient pigs, housed in chamber 2, were exposed to artificial aerosols created by a mechanically operated mister containing modified live PRRSV vaccine located in chamber 1. Aerosol transmission of PRRSV occurred in 0 of the 10 HEPA-filtration replicates, 2 of the 10 bag-filtration replicates, 4 of the 10 low-cost-filtration replicates, 0 of the 10 95%-DOP, 0.3-microm-filtration replicates, and all 10 of the control replicates. Using a similar approach, we further evaluated the HEPA- and 95%-DOP, 0.3-microm-filtration systems. Infection was not observed in any of the 76 HEPA-filtration replicates but was observed in 2 of the 76 95%-DOP, 0.3-microm replicates and 42 of the 50 control replicates. Although the difference between the 95%-DOP, 0.3-microm and control replicates was significant (P < 0.0005), so was the level of failure of the 95%-DOP, 0.3-microm system (P = 0.02). In conclusion, under the conditions of this study, some methods of air filtration were significantly better than others in reducing aerosol transmission of PRRSV, and HEPA filtration was the only system that completely prevented transmission.

Pig characteristics associated with mortality and light exit weight for the nursery phase

One thousand and ten weaned pigs that were reared in 1 nursery in Iowa from weaning (17 +/- 2 days ) until 10 weeks of age were evaluated. A weaning weight threshold of 3.6 kg maximized the sensitivity and specificity to correctly predict the likelihood of dying or being light in weight at exit from the nursery (< or = 14.5 kg). Weaning weight < or = 3.6 kg (OR = 2.92), barrow (OR = 1.75), and sow unit (A versus B, OR = 2.14) were significant predictors of mortality in the nursery. Birth weight < or = 1.0 kg (OR = 2.66), weaning weight < or = 3.6 kg (OR = 8.75), gilt (OR = 1.4), sow unit (OR = 2.38), and gilt as nursing sow at weaning (OR = 1.66) were significant predictors of being lightweight at nursery exit. Eighteen per cent of the nursery deaths and almost half of lightweight nursery pigs could be prevented if there were no lightweight pigs at weaning.

Evaluation of the effects of animal age, concurrent bacterial infection, and pathogenicity of porcine reproductive and respiratory syndrome virus on virus concentration in pigs

OBJECTIVE

To evaluate the influences of animal age, bacterial coinfection, and porcine reproductive and respiratory syndrome virus (PRRSV) isolate pathogenicity on virus concentration in pigs.

ANIMALS

Twenty-one 2-month-old pigs and eighteen 6-month-old pigs.

PROCEDURE

Pigs were grouped according to age and infected with mildly virulent or virulent isolates of PRRSV. The role of concurrent bacterial infection was assessed by infecting selected pigs with Mycoplasma hyopneumoniae 21 days prior to inoculation with PRRSV. On alternating days, blood and swab specimens of nasal secretions and oropharyngeal secretions were collected. On day 21 after inoculation with PRRSV, selected tissues were harvested. Concentrations of PRRSV were determined by use of quantitative real-time PCR and expressed in units of TCID(50) per milliliter (sera and swab specimens) or TCID(50) per gram (tissue specimens).

RESULTS

Concentrations of virus were higher in blood and tonsils of pigs infected with virulent PRRSV. Pigs infected with virulent PRRSV and M hyopneumoniae had significantly higher concentrations of viral RNA in lymphoid and tonsillar tissue. Coinfection with M hyopneumoniae resulted in a higher viral load in oropharyngeal swab specimens and blood samples, independent of virulence of the PRRSV isolate. Two-month-old pigs had significantly higher viral loads in lymph nodes, lungs, and tracheal swab specimens than did 6-month-old pigs, independent of virulence of the PRRSV isolate.

CONCLUSIONS AND CLINICAL RELEVANCE

Multiple factors affect PRRSV concentration in pigs, including pathogenicity of the PRRSV isolate, age, and concurrent infection with M hyopneumoniae.

Retention of ingested porcine reproductive and respiratory syndrome virus in houseflies

OBJECTIVE

To evaluate retention of porcine reproductive and respiratory syndrome virus (PRRSV) in houseflies for various time frames and temperatures.

SAMPLE POPULATION

Fifteen 2-week-old pigs, two 10-week-old pigs, and laboratory-cultivated houseflies.

PROCEDURE

In an initial experiment, houseflies were exposed to PRRSV; housed at 15 degrees, 20 degrees, 25 degrees, and 30 degrees C; and tested at various time points. In a second experiment to determine dynamics of virus retention, houseflies were exposed to PRRSV and housed under controlled field conditions for 48 hours. Changes in the percentage of PRRSV-positive flies and virus load per fly were assessed over time, and detection of infective virus at 48 hours after exposure was measured. Finally, in a third experiment, virus loads were measured in houseflies allowed to feed on blood, oropharyngeal washings, and nasal washings obtained from experimentally infected pigs.

RESULTS

In experiment 1, PRRSV retention in houseflies was proportional to temperature. In the second experiment, the percentage of PRRSV-positive houseflies and virus load per fly decreased over time; however, infective PRRSV was found in houseflies 48 hours after exposure. In experiment 3, PRRSV was detected in houseflies allowed to feed on all 3 porcine body fluids.

CONCLUSIONS AND CLINICAL RELEVANCE

For the conditions of this study, houseflies did not support PRRSV replication. Therefore, retention of PRRSV in houseflies appears to be a function of initial virus load after ingestion and environmental temperature. These factors may impact the risk of insect-borne spread of PRRSV among farms.

Effect of group size and structure on the welfare and performance of pregnant sows in pens with electronic sow feeders

Pregnant sows were housed in dynamic, twice-mixed, and static groups of different sizes in pens with electronic sow feeders (ESFs) to study the effect of group size and structure on sow welfare and performance. The total injury score (TIS) was significantly higher (P < 0.05) in the dynamic group than in the other groups in general and 2 wk after mixing. The salivary cortisol concentrations were similar in the 3 groups. The frequency of queuing was significantly higher (P < 0.05) in the twice-mixed group and the frequency of nonagonistic social interactions significantly lower (P < 0.05) in the dynamic group. The total number of aggressive acts was positively and significantly correlated (P < 0.05) with the frequency and duration of queuing in all the groups. Farrowing performance and longevity did not differ between the groups. The higher TIS and lower number of nonagonistic social interactions indicated that welfare was compromised in the dynamic group as compared with the other groups.