Commercial Swine Herds Research Articles

Technical note: High-performing swine herds improved their reproductive performance differently from ordinary herds for five years1

The objectives of this study were to determine changes in herd productivity and the performance of female pigs over time in commercial swine herds. Annual measurement data from 1999 to 2003 were obtained from the record files of 113 herds in Japan. Two groups were formed according to the 25th percentile of pigs weaned/mated females per year (PWMFY) in 2003; the 2 groups were high-performing herds (those constituting the top 25%) and the remaining ordinary herds. The effects of group based on PWMFY in 2003, year, and the group x year interaction on repeated measures between 1999 and 2003 were analyzed by using mixed-effects models. A regression analysis was also used to compare key measurements in productivity between the 2 groups, with years as a continuous variable. Variance components were obtained to determine herd repeatability of PWMFY for the 2 herd groups. The average female inventory increased from 290 +/- 31 to 355 +/- 42 females for these 5 yr. The PWMFY also changed from 20.9 +/- 0.21 to 21.2 +/- 0.30 pigs. An interaction between year and group was detected (P < 0.05) for PWMFY. In the regression comparison, high-performing herds increased their PWMFY by 0.31 +/- 0.09 pigs each year, whereas the ordinary herds did not increase. The number of pigs weaned per sow increased by 0.07 +/- 0.02 pigs each year in high-performing herds and increased by 0.03 +/- 0.01 pigs each year in ordinary herds. In high-performing herds, for each year, the percentage of sows mated by 7 d after weaning increased by 0.92 +/- 0.25%, the percentage of reserviced females decreased by 0.63 +/- 0.26%, and culling rate increased by 1.53 +/- 0.50%. Repeatability of PWMFY for high-performing herds and ordinary herds was 28.8 and 54.0%, respectively. This study shows that productivity in high-performing herds was improved compared with that of ordinary herds.

Effects of pcv2 vaccine on the growth performance of pigs and mortality rate in a pcv2-positive commercial swine herd (2007)

A total of 1,470 pigs were used to study a commercial sow herd with a history of Porcine Circovirus Disease (PCVD). The objective was to evaluate the effect of two commercially available Porcine Circovirus Type 2 (PCV2) vaccines on growth and mortality rates. The first vaccine was administered one week after weaning (1-dose) while the second was administered at weaning and repeated three weeks later (2-dose). A third group of unvaccinated pigs served as a control group. Pigs were individually weighed at weaning (d 0), d 113, 143, and just prior to market. On d 113, pigs on the 2-dose treatment were heavier (P<0.05) than the control group, and the 1dose treatment pigs were intermediate. At d 143, just prior to when the first pigs were marketed, both the 1-dose and the 2-dose pigs were heavier than the control pigs by 7.6 and 10.2 lb (P<0.05), respectively, and there were no significant differences in weights between the two vaccinated groups. However, differences in weights between the vaccinated and the control pigs were smaller at off-test compared to differences at d 143 due to a wider variability in on-test days as a result of multiple marketing days prior to end of the trial. Although there were no significant differences between the two vaccinated groups, ADG was greater (P<0.05) in all vaccinated pigs compared to non-vaccinated control pigs from d 0 to d 113, d 143, and at off-test. From d 113 to 143 and until the day they were taken off test, there were no differences in ADG, regardless of treatment. This suggests that the increase in growth rate in vaccinated pigs occurred during the period d 0 to 113. Barrows consistently exhibited greater ADG and heavier weights (P<0.05) than gilts throughout the trial. No significant differences in mortality rate between treatments were observed but both vaccinated groups had mortality rates that were 3% lower than the non-vaccinated control pigs. Based on these results, both commercial vaccines were effective in mitigating the effects of PCV2 virus and improving the growth performance of pigs in a PCV2 positive herd.

Regulatory considerations for marker vaccines and diagnostic tests in the U.S.

Marker vaccines and diagnostic tests can prove to be invaluable in disease eradication and control programs, as was found in the pseudorabies (Aujeszky's Disease) virus eradication program in the U.S. During that campaign, numerous gene-deleted vaccines and companion diagnostic test kits were used to differentiate infected animals from vaccinated animals, in a strategy that ultimately led to eradication of the disease in commercial swine herds. The United States Department of Agriculture played a key role in delivery of that success by developing biologics policy, evaluating each product, and ensuring that the conditions of licensure were met. What was most critical in the overall eradication effort, however, was the detailed and dedicated interaction among key players: the biologics regulators, manufacturers, Federal, State, and local regulatory partners, veterinary researchers, industry associations, and animal owners. A good disease control program has to include all of these. The regulatory requirements for licensure of marker vaccines and diagnostic test kits are not different from that for other products. There are several mechanisms for vaccine approval, some more rapid than others, but only a few that could apply to these products. Generally, the platforms that might support marker vaccines and companion diagnostic kits are those based on genetic engineering or protein manipulation. If the product is derived from the application of biotechnology, then additional regulatory considerations are applicable. Most important of these are the considerations found in the National Environmental Policy Act (NEPA), wherein deliberate release of any organism containing recombinant DNA into the environment is subject to review and approval by appropriate federal agencies. Environmental release and NEPA compliance are discussed.

Occurrence of Salmonella serotype Typhimurium DT104 on a commercial swine farm before, during, and after depopulation and repopulation

To determine whether depopulation-repopulation could be used to eradicate Salmonella serotype Typhimurium DT104 from a commercial swine farm in the midwestern United States. Observational study A commercial swine farm undergoing depopulation-repopulation to eliminate porcine reproductive and respiratory syndrome virus and Mycoplasma hyopneumoniae. Pooled fecal samples, tissue samples, and serum samples were collected from pigs on the farm before and after depopulation-repopulation. When there were no pigs on the farm, environmental swab specimens were collected for bacterial culture. Serum was analyzed for anti-Salmonella antibodies with an indirect ELISA. Salmonella isolates obtained by bacterial culture of fecal, tissue, and environmental samples were characterized by means of serotyping, phage typing, pulsed-field gel electrophoresis (PFGE), and antimicrobial susceptibility testing. 167 Salmonella isolates representing 9 serotypes were recovered from the farm. Results of PFGE and antimicrobial susceptibility testing suggested that S. Typhimurium DT104 strain was not eradicated from the farm. However, seroprevalence of anti-Salmonella antibodies and the percentage of pooled fecal samples positive for Salmonella spp were significantly decreased following repopulation. Results suggested that depopulation-repopulation in conjunction with stringent cleaning and disinfection, attention to biosecurity procedures, control of other diseases, and changes in feed management may reduce the occurrence of, but likely will not eliminate, Salmonella spp in commercial swine herds.

Muco-cutaneous candidiasis in two pigs with postweaning multisystemic wasting syndrome

In two distinct commercial swine herds, poor weight gain and an increased number of animals showing wasting were observed among nursery and growing pigs. Cases of postweaning multisystemic wasting syndrome (PMWS) and infection with Haemophilus parasuis had been previously diagnosed in these herds. One growing wasted pig from each herd was necropsied and showed enlarged lymph nodes. Pseudomembranous material adhered to the dorsum of the tongue, soft and hard palate in case 1, and in case 2, fibrinous material was seen as whitish plaques on the oesophageal surface with hyperkeratosis of the non-glandular stomach. The main histological lesions in both cases were found in lymphoid tissues with a multifocal accentuated lymphohistiocytic infiltrate, areas of lymphoid depletion and intracytoplasmic inclusions in histiocytic cells in lymph nodes and Payer’s patches. Focally, extensive ulceration was found in the stratified pavement epithelium of the tongue with necrosis and necrosuppurative infiltrate in case 1; in case 2, there was ulceration in the stomach with lymphohistiocytic infiltrate in the submucosa and ulceration in the mucosa of the oesophagus associated with yeast cells and pseudo-hyphae. Candida albicans was isolated from the oral cavity lesions. Immunohistochemistry of the lymph nodes was positive for porcine circovirus 2 (PCV2). The association between PMWS and mucocutaneous candidiasis reported here supports the potential immunosuppressive state of PMWS infected pigs.

Within-farm variability in age structure of breeding-female pigs and reproductive performance on commercial swine breeding farms

This study investigated relationships between herd age structure and herd productivity in breeding herds; it also investigated a pattern in parity proportions of females over 2 years and its relationship with herd productivity in commercial swine herds. This study was based on data from 148 commercial farms in North America stored in the swine database program at the University of Minnesota. The primary selection criterion was fluctuations in breeding-female pig (female) inventories over a 2-year interval. Productivity measurements and parity proportions of females were extracted from the database. A 24-month time-plot in proportions of Parity 0 and Parities 3–5 females (mid-parity) was charted for each farm. Using these charts, a change in proportions of Parity 0 and mid-parity for each farm was categorized into patterns: FLUCTUATE (Parity 0 and mid-parity proportion lines crossed) or STABLE (the two proportion lines never crossed). Higher proportions of mid-parity sows were correlated with greater pigs weaned per female per year (PWFY; P < 0.01). Farms with a FLUCTUATE (73% of the 148 farms) pattern had lower PWFY than those with a STABLE pattern ( P < 0.01). The STABLE farms had higher proportions of mid-parity sows, higher parity at culling, higher frequency of gilt deliveries per year, and lower replacement rate than the FLUCTUATE farms ( P < 0.01). In conclusion, maintaining stable subpopulations with mid-parity and Parity 0 are recommended to optimize herd productivity.

Erratum to ?Farrowing rates and litter size following transfer of vitrified porcine embryos into a commercial swine herd? 6Therio. 61 (2004) 1533?15439

Erratum to ?Farrowing rates and litter size following transfer of vitrified porcine embryos into a commercial swine herd? 6Therio. 61 (2004) 1533?15439

Farrowing rates and litter size following transfer of vitrified porcine embryos into a commercial swine herd

The objective was to determine farrowing rates and litter sizes that could be achieved in a typical farm-to-farm porcine embryo transfer program using vitrified blastocysts that were zona pellucida intact when cryopreserved. The embryos were transferred surgically on-farm into recipient sows that were managed throughout gestation and farrowing under the same conditions as other sows in the herd. Twenty recipient sows (mean parity 2.1) received a total of 568 embryos; seven received 203 embryos derived from donor sows, five received 139 embryos from gilts and eight received a mixture of 161 embryos from sows and 65 from gilts. Sixteen sows (80%) were confirmed pregnant at approximately 35 days gestation, 15 farrowed at full term (farrowing rate 75%). One sow died during gestation (with a total of 18 fetuses in utero). A total of 123 piglets were born (mean, 8.2), of which 115 were born alive (mean, 7.7). Of the 568 embryos transferred to all 20 sows, 21.6% resulted in piglets born and 29.0% survived to produce piglets in sows that farrowed. There were no significant differences in embryo survival among sow, gilt or mixed sow and gilt embryos. The ratio of males to females was 71/52 and the mean birth weight was 1.6 kg (range 0.6-2.6 kg). In conclusion, vitrified zona pellucida intact embryos can be used to transfer genetic material from farm-to-farm with acceptable reproductive performance.

Further evaluation of a novel polymeric antimicrobial for the control of porcine postweaning colibacillosis

Objectives: To evaluate a new polymeric antimicrobial for the control of porcine postweaning colibacillosis (PWC). Materials and methods: In an experimental infection study, three groups of 12 weaner pigs received either Chemeq polymeric antimicrobial in the food, a therapeutic dosage of apramycin orally, or no treatment. Three days after weaning, the pigs were challenged orally with cultures of [beta]-hemolytic Escherichia coli O8:K87:K88, then monitored daily and euthanized 11 days after weaning. In a field trial, 148 weaned pigs in a commercial swine herd were divided into five groups, receiving polymeric antimicrobial either in their water or food, apramycin in their water, a commercial E coli PWC bacterin, or no treatment. Postweaning performance was monitored. Results: In the infection study, pigs receiving polymeric antimicrobial had less diarrhea than the apramycin-treated group (P &lt;.01) but not the untreated control group, and had fewer hemolytic E coli in their large intestines than the control pigs (P &lt;.05). In the field trial, pigs receiving polymeric antimicrobial had less diarrhea than pigs in the other groups (P &lt;.05), and fewer were removed from the study because of severe PWC (P &lt;.05). Discussion: Antimicrobial resistance is increasing amongst PWC strains of E coli, and new antimicrobials and strategies are needed to maintain postweaning health and production. Chemeq polymeric antimicrobial reduced diarrhea after weaning, and was a useful adjunct to the control of PWC. Implications: Chemeq polymeric antimicrobial has therapeutic advantage in the treatment and control of PWC.

Observations of piglet-directed behavior patterns and skin lesions in eleven commercial swine herds

Objectives: To determine the frequencies of piglet-directed behavior performed by weaned piglets in 11 commercial herds during relatively short videotaped observations, and to test the relationships among frequency of observed behavior, injury scores, and biosecurity scores. Materials and methods: Behavior and skin lesion scores (Mild, Moderate, or Severe) were sampled during a single visit to each of 11 commercial swine herds. The frequencies of belly nosing, nosing or chewing on ears and tails, and aggression were sampled from 2-hour video recordings of the pigs. For each herd, a biosecurity score was compiled from information regarding isolation from other herds as well as general on-farm hygiene practices according to the Ontario Swine Health Improvement Plan. Results: All three recorded behavior patterns were observed in each herd, but frequencies varied across herds. Belly nosing was observed most often, and its frequency was negatively correlated with average weaning age. Aggression had the lowest frequency among the three behaviors, but was positively correlated with nosing or chewing on the ears or tails of other pigs. Skin scores were not significantly correlated with frequencies of behavior or weaning age. However, the proportion of pigs with Moderate and Severe lesions on the ears and abdomen decreased as the biosecurity score for the herd improved. Implications: Frequencies of belly nosing in commercial herds were negatively correlated with weaning age. However, belly nosing was also observed at a relatively high frequency in one herd with later weaned piglets, suggesting that other factors may influence this behavior.

Detection of porcine circovirus type 2 in feces of pigs with or without enteric disease by polymerase chain reaction.

To establish the sensitive polymerase chain reaction(PCR) method and detect porcine circovirus type 2 (PCV2) from intestines and feces of commercial swine herds with or without enteric disease, intestinal samples from 68 pigs and 29 fecal samples from commercial swine farms were collected. A primer set, forward primer 5'-GAAGAATGGAAGAAGCGG-3' and reverse primer 5'-CTCACAGCAGTAGACAGGT-3', could detect the virus at a concentration as low as 2 infectious virions per milliliter under controlled conditions using PK-15 cell-adapted PCV2. The genomic nucleotide sequences of open reading frame 1 (ORF1) PCR products from fecal samples were found to have complete homology with other PCV2s deposited in the GenBank database. Transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) as the other enteric pathogens were also investigated by performing duplex reverse transcription-PCR (RT-PCR). Among 63 pigs with clinical enteric disease, 18 PCV2s (14 from intestines and 4 from feces), 7 TGEVs from intestines, and 18 PEDVs (14 from intestines and 4 from feces) were detected by PCR and the duplex RT-PCR. In 34 pigs (14 from intestines and 20 from feces) without clinical enteric disease, only PCV2 was detected in 19 pigs (3 from intestines and 16 from feces). Both PEDV and PCV2 were found in 6 pigs with clinical enteric disease. Among 15 PCV2 samples that were PCR-positive, 4 were culture-positive at passage level 3 in PK-15 cells. These results reveal that PCV2 is shed through the feces of pigs without clinical enteric disease, which suggests the potentiality of the fecal-oral transmission of PCV2 in feces.

A prolonged outbreak of polioencephalomyelitis due to infection with a group I porcine enterovirus.

A commercial swineherd in Indiana experienced high death loss of nursery pigs with neurologic disorders for a prolonged period. Polioencephalomyelitis was the consistent histopathological lesion in affected animals. A porcine enterovirus (PEV) classified to group I was isolated from spinal cords and brains collected from the affected animals. The isolate (ISUVDL 200103183) was determined to belong to either serogroup 5 or 6 at the National Veterinary Services Laboratories, Ames, IA. No other significant viral or bacterial agents were isolated from or detected in the animals. A prospective longitudinal serological monitoring of pigs in the index herd for the PEV isolate revealed that colostrum-derived neutralizing antibodies to the virus rapidly declined, and by the age of 21 days the majority of piglets had no or minimal neutralizing antibody against the virus. Seroconversion to the virus then coincided with increased mortality in the herd. Results of diagnostic and cohort observations supported a diagnosis of PEV infection as the cause of the prolonged outbreak of "polio." Investigation into factors that may be contributing to the prolonged problem is currently in progress.

Impacts on conceptus survival in a commercial swine herd.

An estimated 30 to 40% of potential piglets are lost before farrowing in U.S. or European pig breeds. Because these studies were conducted in limited numbers of university research herds, we decided to characterize the timing, pattern, and extent of conceptus loss in a commercial swine herd in Iowa (Pig Improvement Company; Camborough Line). Sows (parities 2 to 14) were slaughtered on d 25 (n = 83), 36 (n = 78), or 44 (n = 83) of gestation. These days coincide with periods before, during, and after uterine capacity becomes limiting to conceptus survival. At slaughter, numbers of corpora lutea (CL) and uterine horn length were determined, and conceptuses were removed and evaluated. Uterine horn length and CL number did not differ among these days of gestation, averaging 217 cm and 26.6 CL, respectively. In contrast, numbers of conceptuses decreased (P < 0.05) from 15.8 on d 25 to 12.9 on d 36, then remained relatively constant through d 44 (12.1). Thus, conceptus survival averaged 60.2% on d 25, 50.1% on d 36, and 46.3% on d 44, based on numbers of CL present. There was a positive correlation (P < 0.001; r = 0.50) between numbers of viable conceptuses on d 25 and ovulation rate, but this association was completely lost by d 36 (P > 0.10) when uterine capacity becomes limiting. In agreement with this premise, uterine horn length and conceptus number were not associated on d 25 but exhibited positive correlations (P < 0.05) on d 36 (r = 0.36) and d 44 (r = 0.40). On all 3 d examined, the numbers of viable conceptuses were not associated with fetal weight but were negatively correlated (P < 0.05) with placental weight. Compared with the commonly reported values for ovulation rate and percentage conceptus loss in university research herds, values from these production animals were extremely high. Data suggest that throughout this period, larger litters were associated with conceptuses exhibiting small placentae. These data lend support to the concept that increased placental efficiency (fetal weight/placental weight) may contribute to increased litter size in the pig.

Factors associated with death due to hemorrhagic bowel syndrome in two large commercial swine farms

Objective: To investigate the roles of season, gender, animal density, concurrent disease, and antibiotic feeding regimen on the occurrence of hemorrhagic bowel syndrome (HBS). Methods: Retrospective analysis of finishing records from two large commercial swine herds. Results: Gender, animal density, and concurrentdisease were not associated with death due to HBS. Rates of death due to HBS were higher for pigs finished during the summer than for those finished in the winter. Rates of death due to HBS were lower in pigs fed rations containing bacitracin methylene disalicylate or chlortetracycline than in pigs on rations containing virginiamycin or no antibiotic. Implications: A definitive cause of HBS is still lacking; however, these results lend support to a non-infectious etiology involving intestinal volvulus. To further investigate whether HBS and volvulus are two separate syndromes, veterinarians and farm personnel trained to perform necropsies should palpate the mesenteric root before opening the abdomen.

Defined competitive exclusion cultures in the prevention of enteropathogen colonisation in poultry and swine.

A competitive exclusion culture (CE) containing a mixture of 29 different bacterial isolates obtained from the cecae of broiler chickens was developed utilizing continuous-flow culture techniques. This culture (CF3) has been efficacious in controlling gut colonization by enteropathogens in both experimentally infected broilers and under commercial field conditions. In day-old broiler chicks provided CF3, and challenged with 10,000 CFU Salmonella typhimurium greater than a 99% reduction in Salmonella cecal colonization levels was observed compared to control chicks. Similarly, CF3 has also been shown to protect experimentally infected broiler chicks from cecal colonization by S. enteritidis (Phage types 4 and 13), S. gallinarum, Listeria Monocytogenes, and Escherichia coli O157:H7. A commercial product was developed from CF3 and is sold under the tradename PREEMPT. In a Food and Drug Administration approved, double blinded, pivotal field trial, chicks treated with PREEMPTT' had significantly fewer salmonellae than untreated chicks at end-of-growout. This product is the first of its kind available to the U.S. poultry industry. Using similar technology a product has also been developed that decreases shedding of salmonellae in neonate and weaned pigs, and also has been shown to reduce mortality associated with enteropathogens in young pigs both in the laboratory and in a commercial swine herd.

Lifetime reproductive and financial performance of female swine.

To evaluate reproductive and financial performance for commercial swine herds grouped on the basis of pattern of removal of female swine. Cohort study. 25 swine herds. Lifetime reproductive productivity was summarized as number of pigs weaned per herd day per mated female and as number of herd days per pig weaned per mated female. Factors associated with these 2 measures were determined by use of linear regression. Financial data from a commercial database were used to estimate maximum number of parities at removal associated with profitability. Sensitivity analysis was used to simulate how variations in daily maintenance cost and value per weaned pig would influence profitability. Mean number of pigs weaned per herd day per mated female was 0.054; mean number of herd days per pig weaned per mated female was 20.2. Both these measures were associated with proportion of nonproductive days during herd life, preweaning mortality rate per litter weaned, mean lifetime number of pigs born alive per litter weaned, and mean lifetime lactation duration. Maximum parity at time of removal associated with profitability ranged from 5 to 8. Daily maintenance costs per female had a greater impact on lifetime profitability than did value per weaned pig. Results suggest that lifetime reproductive and financial performance is optimized among swine herds that have higher proportions of high-parity females.

Diagnostic performance of a reverse transcription-polymerase chain reaction test for porcine reproductive and respiratory syndrome virus.

Porcine reproductive and respiratory syndrome (PRRS) virus first appeared in swine in Canada in the late 1970s, in the United States in the mid 1980s, and in Europe in 1990.23 Since that time, PRRS virus infection has become endemic in most pork-producing areas of the world. Although infection is frequently subclinical, PRRS virus plays a significant role in swine health, as reflected in the number of cases submitted to veterinary diagnostic laboratories located in swine-dense areas. For instance, in 1998 the Iowa State University Veterinary Diagnostic Laboratory (ISU-VDL) performed 90,608 serologic tests for the detection of PRRS virus antibody (J. Zimmerman, personal communication), and among diagnostic cases involving swine, 83% of samples (5,026/6,023) submitted for virus isolation included a request for isolation of PRRS virus (K.-J. Yoon, personal communication). Economically, PRRS is generally perceived to be the most significant infectious disease of swine in North America. Over the last several years, the economic impact of PRRS virus on swine production has stimulated a substantial investment of research resources into the search for effective disease control strategies. The development of accurate and rapid diagnostic assays has been an essential part of this effort. Numerous procedures have been developed and implemented for the diagnosis of PRRS, including serum antibody assays, virus isolation techniques, and antigen detection and visualization in tissues by immunohistochemistry or immunofluorescence microscopy.24 In addition, a number of polymerase chain reaction (PCR) assays and in situ hybridization techniques have been developed for the detection of PRRS virus RNA in clinical specimens, including serum, semen, and tissues.4,9–12,16,17 The transfer of PCR technology into the diagnostic setting has been of particular interest to diagnosticians and swine practitioners. Generally, PCR is considered to offer distinct advantages over other techniques, including faster availability of results, higher diagnostic sensitivity, and higher diagnostic specificity. At the present time, however, documentation of the specific diagnostic performance characteristics of PCR assays is sparse. Here, we report observations on the diagnostic performance of a PCR assay for the detection of PRRS virus. The original intent of this research was to use a reverse transcription-nested PCR (RT-nPCR) to detect PRRS virus genomic material in field samples collected from 20 commercial swine herds. Field samples (n 5 756) were submit-

Spatial and temporal epidemiology of pseudorabies virus infection

Abstract Objective To examine the pattern of pseudorabies virus (PRV) infection in Pennsylvania and identify the area factors associated with herd quarantine status. Sample Population 123 PRV-quarantined commercial swine herds identified between 1986 and 1993 were selected as cases, and 162 uninfected herds were selected as controls. Procedure Herd location, demographics, and temporal vaccination and quarantine data for a case-control study were obtained from producer questionnaires and state records, using a database of swine herds from 2 Pennsylvania counties. Any herd that was on quarantine as of Jan 1, 1991, or quarantined subsequent to this date, was defined as a case. A herd was defined as a control if it had never been quarantined for PRV. Controls were group matched to cases by year. Study herds were centered in a circle, or buffer zone, with a 1.61-km (1-mile), 3.22-km (2-mile), or 6.44-km (4-mile) radius, and densities of operation types, quarantined herds, nonquarantined herds, and vaccinated herds in the buffer zone were compared. The analytical outcome was the probability of a herd being quarantined, conditional on the buffer zone density of herds quarantined, herds not quarantined, and herds in which a PRV vaccine was used. These density variables were categorized into high, medium, and low, or just high and low categories. Confounding by year was assessed in the analysis. Analysis was performed, using unconditional logistic regression. Results Decreased density of PRV-quarantined herds in the study region was associated with reduced risk of a herd becoming quarantined, whereas increased density of nonquarantined, presumably uninfected herds was associated with decreased probability of a herd becoming quarantined. Decreased density of vaccinated herds was associated with increased probability of a herd becoming quarantined. In addition, being a farrow-to-finish study herd was associated with increased probability of becoming quarantined, compared with being a feeder pig producer study herd. Conclusions Associations with quarantine status and area densities of vaccinated, nonquarantined, and quarantined herds indicate the importance of area spread in PRV control. These effects are seen most strongly at a 3.22-km (2-mile) radius, but also are seen at a 6.44-km (4-mile) radius. (Am J Vet Res 1996;57:1563–1568)

Characterization of feed intake patterns during lactation in commercial swine herds.

This study created and used a data-base containing 25,719 farrowing and 19,393 subsequent litter records abstracted from the PigCHAMP records of 30 commercial farms and daily feed intake records of 25,040 of these lactating sows. Each lactation feed record was categorized into one of six patterns: RAPID, rapid increase in feed intake following farrowing; MAJOR, major drop in feed intake during lactation; MINOR, minor drop; LLL, low feed intake throughout lactation; LHH, low feed intake during the first week then increasing for the remainder of lactation; and GRADUAL, gradual increase in feed intake throughout lactation. At the herd level, patterns RAPID, MAJOR, MINOR, LLL, LHH, and GRADUAL were observed in 22.8%, 32.9%, 27.8%, 1.0%, 8%, and 14.7% of sows, respectively. On a sow basis, across all feed intake records of all farms, patterns RAPID, MAJOR, MINOR, LLL, LHH, and GRADUAL were observed at frequencies of 17.8%, 38.3%, 25.8%, 1.2%, 1.5%, and 15.4%, respectively. Using logistic regression, the risk factors affecting the occurrence of MAJOR and MINOR patterns were lower parity, thicker backfat, higher room temperature, and greater feed intake during early lactation. Average daily feed intake and the day of peak intake were 5.2 (1.4 SD) kg/sow and 12.6 (4.6 SD) d after farrowing. Regression coefficients of factors affecting ADFI derived from multiple regression analyses were 247 g for parity, 9 g for weaning litter weight (kg), -13 g for room temperature (degree C), 62 g for lactation length (d), and -.4 g for energy density (kcal/kg). This study demonstrated substantial individual sow and farm variation in overall feed intake and pattern of feed intake during lactation. It also identified key risk factors (i.e., parity, lactation length, room temperature, weaning litter weights, energy density) for ADFI and pattern of feed intake on commercial farms.

Multiple manifestations of season on reproductive performance of commercial swine

Summary Seasonal variation oj reproductive performance of female swine was analyzed by use of a data base that included farrowing records from 42 commercial swine herds. Farrowing rates of sows bred during December or January were higher (P &lt; 0.001) than those bred in July or August (79.2 vs 74.1%). The percentage of sows with irregular (prolonged) return-toestrus intervals after mating in December or January (2.63%) was lower (P &lt; 0.01) than those mated in July or August (4.65%). Sows mated in November through January had greater total number of pigs born per litter (11.66 vs 11.19 pigs per litter), more pigs born alive per litter (10.39 vs 9.84 pigs per litter), and greater litter birth weights (15.20 vs 14.28 kg) than sows mated in June through August (P &lt; 0.001). Adjusted 21-day litter weights were lower (P &lt; 0.001) for litters from sows farrowing in July or August (52.04 kg) than sows farrowing in all other months (55.13 kg) except June and September. Sows that had their litters weaned in June through August had longer (P &lt; 0.001) weaning-to-estrus intervals (7.95 days) than sows that had their litters weaned in November through January (6.84 days). The effects of season varied across parities. Primiparous sows had the greatest seasonal variability in weaning-to-estrus interval, whereas multiparous sows had the greatest seasonal variability in total number of pigs born per litter and pigs born alive per litter.