The trial objective was to compare the performance and animal health parameters of pigs raised according to one of 3 antibiotic (AB) protocols: standard AB medication consisting of mass treatment on days 4 and 21 and judicious AB therapy given therapeutically thereafter as group medication in water and feed or by individual injection (group T1, N = 702); modified AB medication identical to group T1 but with mass treatment only on day 4 and without subsequent therapeutic feed medication (group T2, N = 675); or an antibiotic-free (ABF) regimen (group T3, N = 702). All pigs were vaccinated with a modified-live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine 3 days after weaning. Using a seeder pig model to mimic endemic field infection dynamics, pigs were contact-challenged with virulent PRRSV lineage 1 strain 174 four weeks after vaccination. At finishing, average daily gain (ADG) and mean feed conversion ratio (FCR) were significantly better (p ≤ 0.05) for the T1 and T2 groups compared to the T3 group. There were no significant differences in post-weaning ADG and FCR between the T1 and T2 groups. Mortality and removals significantly favored (p ≤0.05) the T1 and T2 groups (20.94% and 24.89%, respectively) versus the T3 group (57.98%). Net revenue per pig was $105.43, $98.79, and $33.81 for the T1, T2 and T3 groups, respectively. Under the conditions of this study, these results indicate that in a PRRSV-endemic setting involving bacterial co-infections, an ABF production strategy may leave pigs at considerable risk of exposure to severe clinical disease and that judicious use of antibiotics can significantly improve animal health.

The objective of our study was to characterize the Mycoplasma hyopneumoniae genetic diversity within a swine operation comingling weaned pigs. Bronchial swabs and tracheal aspirates were collected from 3 nursery-to-finish farms. During the finishing production stages, samples were obtained from mortalities and from live coughing pigs in rooms where mortality was not observed. A total of 105 samples were examined by a M. hyopneumoniae real-time polymerase chain reaction and subjected to genetic typing using a multilocus variable number tandem repeat analysis (MLVA) assay. The MLVA was used to identify genetic variants based on the number of repeats in 2 variable number tandem repeats loci, namely P97 and P146, thought to mediate adherence of M. hyopneumoniae to swine cilia. Four distinguishable M. hyopneumoniae variants were identified: MVLA variants 9-15, 11-21, 9-21, and 7-15. Variant 9-15 was the most prevalent, observed in 79% of rooms, and detected on all 3 farms. Variant 11-21 was present in 37% of the rooms on 2 of the 3 farms. Only one 9-21 variant was identified in 1 farm, and all samples of variant 7-15 were recovered from another farm. Based on the low prevalence and limited geographic distribution of the last 2 variants, it is hypothesized that they might be the result of in-situ recombination. All variants detected in this investigation appeared to belong to 3 clusters. Overall, a limited number of variants and clusters were identified in a system that comingles pigs from different sources, suggesting limited M. hyopneumoniae genetic variation within commercial swine production environments.

Objective: To report the in vitro susceptibility to veterinary antimicrobial agents of Actinobacillus pleuropneumoniae, Bordetella bronchiseptica, Pasteurella multocida, and Streptococcus suis isolated from diseased pigs in the United States and Canada from 2016 to 2020. Materials and methods: In vitro broth microdilution susceptibility testing for minimal inhibitory concentration values were performed using ten antimicrobial agents (ampicillin, ceftiofur, danofloxacin, enrofloxacin, florfenicol, penicillin, tetracycline, tilmicosin, trimethoprim-sulfamethoxazole, and tulathromycin) with A pleuropneumoniae (n = 250), B bronchiseptica (n = 602), P multocida (n = 874), and S suis (n = 1223) following methods and susceptibility breakpoints approved by the Clinical and Laboratory Standards Institute. Results: Actinobacillus pleuropneumoniae isolates were 100% susceptible to ceftiofur, florfenicol, and tulathromycin and P multocida isolates were 100% susceptible to ceftiofur. High rates of susceptibility (95% to > 99%) were observed for A pleuropneumoniae to tilmicosin; for P multocida to ampicillin, enrofloxacin, florfenicol, penicillin, tilmicosin, and tulathromycin; for S suis to ampicillin and florfenicol; and for B bronchiseptica to tulathromycin. Tetracycline exhibited low susceptibility rates against A pleuropneumoniae (0% to 10.6%), P multocida (23.2% to 38.2%), and S suis (0.8% to 2.1%). No susceptibility of B bronchiseptica to ampicillin (0%) and low rates of susceptibility to florfenicol (3.9% to 15.2%) were also observed. Implications: Under the conditions of this study, the predominant pathogens associated with swine respiratory disease in the United States and Canada, A pleuropneumoniae, B bronchiseptica, P multocida, and S suis collected during 2016 to 2020, display high rates of susceptibility to most veterinary antimicrobial agents.

Haemophilus parasuis is an economically important swine pathogen with 15 recognized serovars. An enzyme-linked immunosorbent assay (ELISA) was developed that detects serum antibodies to the oligopeptide permease A (OppA) polypeptide membrane protein present in the reference strains for 13 of the H. parasuis serovars. Using the OppA-ELISA, H. parasuis serologic profiles were assessed on 2 swine farms, with seroconversion defined as an OppA-ELISA sample-to-positive (S/P) ratio ≥0.5. Ten gilts from each farm were vaccinated for H. parasuis using either a live avirulent culture vaccine (farm 1) or an inactivated autogenous vaccine (farm 2). Seroconversion occurred in 100% of farm 1 gilts and 90% of farm 2 gilts, with a mean S/P ratio (MSPR) of 3.36 and 1.43, respectively. The OppA-ELISA MSPRs were determined for 2 piglets, 1 male and 1 female, randomly selected from 10 first-parity (P1), 10 second-parity (P2), and 10 third-parity (P3) litters farrowed by respective vaccinated gilts on each farm. On both farms, postfarrowing MSPRs and rate of seropositivity were highest in P1 versus P2 and P3 dams. Parity 1 piglets had higher MSPRs and rates of seropositivity versus later parities, with the difference being significant ( P < 0.05) on farm 2. Polymerase chain reaction analysis of nasal swabs indicated that 100% of farm 1 piglets and 47–84%, depending on parity, of farm 2 piglets were H. parasuis–colonized at weaning. The results indicated that H. parasuis vaccination of gilts will not maintain serologic responses in the OppA-ELISA over their reproductive lifetimes, and that maternally derived antibodies do not prevent H. parasuis colonization of piglets.

Gilts immunized against gonadotropin-releasing factor (GnRF) have reported improvements in carcass characteristics including increased belly weights and thickness, and increased loin intramuscular fat (IMF) compared with controls. The objective was to determine the optimal market timing post second dose (PSD) for anti-GNRF-treated gilts for carcass characteristics. Treatments were arranged as a 2×4 factorial: control vs anti-GnRF (d7 and 77; d0 = 8 wk of age) and marketing time PSD anti-GnRF: (first cut: 10 heaviest gilts; last cut: remaining gilts): d18 and 39 PSD; d25 and 46 PSD; d32 and 53 PSD; and d39 and 60 PSD. Pen (n=120) was the experimental unit (12-18 pens per treatment; 21 gilts per pen). Carcass data were determined from 107-188 gilts per treatment per day PSD with primal data collected from 39-54 carcasses per treatment per day PSD. At 25 wks of age, 52.5±0.05% of control gilts vs. 0.92±0.01% of anti-GnRF gilts were cycling based on ovarian structures. Regardless of cut, anti-GnRF increased (P ≤0.05) HCW, backfat, and belly depth. Loin depth and belly weights were greater (P ≤0.05) in second cut anti-GnRF gilts compared with control. Calculated percent lean was decreased in both marketing events in anti-GnRF gilts compared with control. While belly yield was similar, iodine value was decreased in anti-GnRF gilts compared with control, regardless of marketing event. Trimmed loins were lighter (P = 0.02) in second cut anti-GnRF gilts, but had greater (( P < 0.01) IMF compared with control gilts. Shear force was similar between treatments. Use of anti-GnRF in gilts results in heavier carcasses and several primal weights. The time PSD to market anti-GnRF-treated gilts does not appear to impact carcass quality indicating that it is best to focus on optimal timing based on performance traits.

Postpartum metritis, or the inflammation of the uterus after parturition, is often a direct result of bacterial infection and considered to contribute to agalactia / dysgalactia in multiple species. Diagnosing metritis has included evaluation of vaginal and cervical fluid (CF) discharge for signs of infection (i.e., purulent discharge, strong odor, and discoloration). Metritis in sows results in economic losses for the swine industry due to increased numbers of sows requiring repeat inseminations to establish pregnancy, longer weaning to estrus intervals, association with increased abortions, and is also linked to agalactia. This study aimed to compare the microbial communities of the CF, the vaginal cavity, and feces from sows shortly after parturition, to identify similarities and differences in relative microorganism abundance between these body sites. Fecal and vaginal swabs were collected from 82 sows within 24-36 hours post-parturition. Additionally, CF was collected from each sow and classified based on color and consistency. Extraction of DNA was performed from all 246 samples and used for 16S rRNA gene Illumina MiSeq sequencing. Sequence analysis was conducted using MOTHUR (V1.43.0). No changes in CF microbial community composition or structure were determined related to CF color but differences (P < 0.05) were detected relative to CF consistency. Taxa were compared across body sites to identify correlated phylotypes using CoNet (V1.1.1). The abundances of several phylotypes harboring metritis-relevant pathogens were correlated with common commensal microorganisms across body sites (including Fusobacterium, Streptococcus, Escherichia, and Staphylococcus) suggesting interactions between these body sites exist. This work provides initial insights into postpartum sow CF microbial communities, and the interconnectedness with the vaginal and fecal microbiota. This project was supported by Zoetis (TI-07021).