Antibody responses of guinea-pigs, rabbits and pigs to inactivated porcine parvovirus vaccines.

Antibody responses were compared in guinea-pigs, rabbits and pigs following vaccination with inactivated porcine parvovirus (PPV) vaccines. Mean PPV hemagglutination inhibition (HI) antibody titers of 52, 56 and 36 at 1 week after first vaccination and 896, 640 and 512 at 2 weeks after second vaccination were detected in guinea-pigs, rabbits and pigs, respectively. PPV vaccines prepared with greater concentrations of virus, as determined by hemagglutination (HA) units, and of aluminum hydroxide gel adjuvant, induced higher HI antibody titers in guinea-pigs. Optimal concentrations for inducing consistently high antibody titers consisted of vaccine virus with a HA titer of 256/0.1 ml and gel adjuvant at a final concentration of 50%. A second vaccination at 4 weeks compared to 2 or 3 weeks after first vaccination resulted in higher mean HI titers. These data provide preliminary information on the use of guinea-pigs or rabbits as laboratory animal models for testing the potency of PPV vaccines.

The seasonal breeding pattern of sows in seven confinement herds.

The breeding herd records from 7 confinement herds were analyzed to determine the association of season with the frequency of estrus within 1 week after weaning and the farrowing rate following mating during this estrus. All herds utilized the cooling of sows during lactation and water fogging during the postweaning, breeding and early gestation periods. During July, August and September, the frequency of estrus within 7 days after weaning was lower (P < 0.05) than the frequency of estrus during October, November and December. The farrowing rate for matings during September and October was lower (P < 0.05) than the farrowing rate for sows mated from February through May. These data suggest that reduced postweaning estrous activity and fertility may occur in confinement herds, despite the use of cooling systems used to minimize heat stress of sows during hot weather.

Use of PMSG in the prevention of seasonal post-weaning anestrus in sows.

PMSG (500 I.U.; administered I.M.) prevented post-weaning anestrus when given to sows weaned during the months of August, September and October compared to untreated controls during the same months. During winter and spring months, there was no difference in the post-weaning return to estrous rate for treated and control sows. Control sows had a greater degree of estrous synchrony following weaning during winter and spring months compared to summer months. PMSG-treated sows were in estrus earlier (frequently Day 3) than controls. Results indicate that PMSG, given at weaning, is effective in preventing summer-early fall post-weaning anestrus.

Angiomicrographic investigation of the vessels associated with physes in young pigs.

There is little information available relating to the vasculature of physes of pigs, hence the object of the present study was to establish the distribution of blood vessels in normal physes of pigs at one and 15 days old. By the use of an angiomicrographic technique it was possible to demonstrate that vessels were in two main categories; first, those which entered the physis from the epiphysis and terminated, or branched and then terminated half to two thirds of the distance into the depth of the physis; second, vessels which crossed the full depth of the physis. Since vessels that cross the physis from epiphysis to metaphysis were a frequent feature of normal physes they do not seem to be a congenital defect which predisposes to the development of dyschondroplasias in young pigs.

Pig weaning weight and changes in hematology and blood chemistry of sows injected with recombinant porcine somatotropin during lactation.

Weaning weight of pigs on d 18 to 21 of age was used to determine the effects of recombinant porcine somatotropin (rpST) on lactational performance of their dams. Crossbred Landrace x Yorkshire sows (n = 180, 202 to 270 kg BW) were assigned to receive daily i.m. injections of either 0, 8, or 16 mg of rpST on lactation d 7 to 20. Initially, injections of 16 mg of rpST/d caused 100% mortality (four sows); thus, a dose of 4 mg of rpST/d replaced 16 mg. Subsequently, 5 of 19 and 1 of 17 sows died in response to daily injections of 8 and 4 mg of rpST, respectively, resulting in termination of the experiment. Before termination, 48 sows (16 from each of the 0-, 4-, and 8-mg treatment groups) completed a lactation of 18 to 21 d in duration. Analysis of these data indicated that daily injection of lactating sows with rpST increased (P less than .05) weaning weight of pigs only if they were from litters that averaged greater than or equal to 2.6 kg/pig on lactation d 7. The BW of sows was decreased by rpST (P = .07). Subsequent experiments revealed 1) that rpST-induced death of lactating sows was caused from hemorrhaging of ulcers that developed at the pars esophagea, 2) that there was vacuolation of the liver and kidney of dead sows, and 3) that daily injection of 16 mg of rpST into nonlactating growing pigs (50 to 100 kg BW) for 28 d did not cause death or any observable illness in spite of 100% mortality of lactating sows after two to nine injections.

Culling patterns in selected Minnesota swine breeding herds.

This investigation was conducted to study culling patterns in swine breeding herds. Data were obtained from 89 Minnesota swine breeding herds and included 5918 sows and 1324 gilts for a total of 7242 culled femaled. Each producer was involved for 12 consecutive months. They were asked to record every female that was removed from the herd, the reason for its culling and its parity. The annual culling rate for the sample averaged 50%, but varied considerably between herds ranging from 15% to 85%. Culled females had produced an average of 3.77 litters. Half of the females culled did not produce more than three litters. Reproductive failure accounted for 32% of all removals. The average parity of the females culled in that category was only 2.37: almost 33% were gilts. Failure to conceive represented 75% of all females culled for reproductive failure. Proportionally, culling as a result of anestrus was higher in gilts. It accounted for 33% of all gilts culled for reproductive failure which was twice as much as for sows. Inadequate performance accounted for 17% of all removals. These sows had produced an average of 5.11 litters. These results indicated that few animals were culled on the basis of first litter performance. Old age comprised 14% of all removals and the average parity at culling for this category was 7.11. Death accounted for 12% and the average parity for these females was 3.40. Locomotor problems and peripartum problems were the cause of 28% and 23% of all deaths, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of parasympathominetics on porcine stillbirth.

To study the effect of 2 parasympathomimetic drugs in reduction of incidence of stillborn pigs, 84 sows and gilts were randomly allotted to 3 treatment groups. Single 1-ml injections of isotonic saline solution, carbachol (2 mg/ml), or neostigmine bromide (5 mg/ml) were subcutaneously administered to pigs of groups A, B, and C, respectively. Injections were given midway through parturition in an attempt to hasten the delivery of the last pigs in the litter, where the corresponding incidence of stillbirth is greatest. The mean time of injection was after the birth of 3.5 pigs. Total stillbirths/litter for carbachol-treated (0.23) and neostigmine-treated (0.21) pies were significantly different (P greater than 0.0001) from those for control pigs (0.88). Before injection, stillbirths/litter for control pigs (0.23) were not significantly different from those for carbachol-treated (0.18) or neostigmine-treated (0.12) pigs. After treatment, stillbirths/litter for carbachol-treated (0.06) and neostigmine-treated (0.09) pigs were both significantly different (P greater than 0.0001) from those for saline solution-treated control pigs (0.65). When injected midway through parturition, carbachol and neostigmine reduced stillbirth rate by reducing stillbirths which occur late in farrowing.

Role of the rat in the transmission of porcine parvovirus.

Rats experimentally inoculated with porcine parvovirus (PPV) shed virus in excreta from 3 to 21 days. Rats inoculated subcutaneously with PPV responded serologically with hemagglutination-inhibition titers (512-1,024). The PPV antigen was readily detected in lung and spleen 2 and 3 days after rats were inoculated and in liver and intestine, 4 days. The rats remained clinically healthy. Rats given PPV orally or in drinking water either with PPV-infected cell culture fluid or swine fetal homogenate failed to respond serologically to PPV, the exception being 2 of 4 rats exposed to swine fetal homogenate over a 5-day span. Pigs exposed to PPV-contaminated rat excreta, either by direct oral dosing or by contaminating the feed, failed to seroconvert. Pigs given (IM) PPV which had been isolated on cell culture from rat excreta did seroconvert. Results of these experiments indicated that rats became infected with PPV, but did so after systemic challenge exposure or prolonged oral exposure to highly infective swine fetal homogenate. Insufficient virus was shed by rats to cause susceptible pigs to seroconvert upon oral feeding--thus indicating that a minimal dose is necessary to ensure oral challenge. In a preliminary experiment, seronegative pigs given different doses of PPV orally showed a gradient level of serologic response and different rates of shedding.

Radial immunodiffusion enzyme assay for detection of antibodies to pseudorabies virus in swine serum.

A radial immunodiffusion enzyme assay for the detection and quantitation of antibodies to pseudorabies virus in swine sera was developed and the methods were standardized. The assay combined the principle of radial immunodiffusion with enzyme-linked immunosorbent assay. Quantitation of pseudorabies virus antibody titers was determined by measuring the diameter of a colored circular zone after overnight incubation of antibody with antigen. The specificity and sensitivity of the radial immunodiffusion enzyme assay were compared with that of the standard virus-neutralization test, and the results were determined to be correlated highly (r = 0.694, P less than 0.0001). The assay also appeared to be highly reproducible and simple to perform.

Effect of porcine parvovirus serostatus on the reproductive performance of mated gilts in an infected herd.

Gifts from 2 commercial swine operations (farm A and farm B) that were bred each week were tested for porcine parvovirus antibody. On farm A, 21.9% (weekly, 2% to 35%) of the 657 gilts tested over a 16-week period were seronegative within 1 week of mating. On farm B, 17.7% (weekly, o to 40%) of the 164 gilts tested over a 10 week period were seronegative within 1 week of mating. Eighty-one gilts from farm A which were seronegative at time of mating were retested at the end of the gestation. Of the 81 gilts, 4 1 had developed antibody titers. The litter size decreased by 1.3 live pigs/litter. The percentage of small litters (less than or equal to 6 born alive) in the group that seroconverted was 36.6% compared with 10% in the gilts that remained seronegative throughout gestation.

Survey of porcine parvovirus infection in swine fetuses and their dams at a Minnesota abattoir.

Reproductive tracts were recovered from 209 sow and 32 gilt carcasses at slaughter; animals had been pregnant not less than 27 days. Of 241 litters examined, 28 (11.6%) contained one or more porcine parvovirus (PPV)-infected fetuses, as determined by immunofluorescent microscopy. The frequencies in sow and gilt litters were 12.0% and 9.4%, respectively. The PPV antigen was detected in 219 of 334 (65.6%) dead or mummified fetuses and in 12 of 2,172 (0.5%) live fetuses examined. The 18 litters which contained only dead or mummified fetuses were infected with PPV. As the percentage of litter mummification increased, the likelihood of finding PPV increased. The PPV antibody was detected in ovarian follicular fluids of 94.3% of the sows and 78.1% of the gilts. These findings indicate that PPV is highly associated with fetal mummification and that some pregnant gilts and sows are susceptible to infection.

Clinical, virologic, and histopathologic observations of induced porcine parvovirus infection in boars.

Twelve 8- to 12-month-old crossbred boars were inoculated with a virulent strain (NADL-8) of porcine parvovirus (PPV). Hemicastrations were performed on 6 boars 3, 7, 10, 14, 21, and 28 days after an IM injection of 10(8) median cell culture infectious dose (CCID50) of PPV (n = 3) or injection of 10(7.4) CCID50 given intratesticularly (IT, n = 3). Noninfected cell culture medium (0.25 ml) was injected into each testicle of a 7th boar (IT inoculated control). Virus or viral antigen was detected in testicular and epididymal tissues up to 14 days after inoculation. Direct immunofluorescence indicated that viral antigen was mainly associated with the vasculature of the interstitium. Microscopic lesions were not evident in the testicles and epididymides of IM inoculated boars. Acute-to-chronic testicular degeneration was evident in the IT inoculated boars, as well as in the IT inoculated control boar. Six boars were inoculated IM or orally/nasally with 10(7.9) CCID50 of PPV. Semen was collected twice weekly for 8 weeks after inoculation. Virus was not detected in any ejaculates. Semen also was collected from 4 boars for 5 weeks before inoculation, and preinoculation and post-inoculation semen quality was compared. Pronounced changes in sperm output, ejaculate volume, motility, or morphologic defects were not observed. The reproductive consequences of experimental PPV infection in boars were minimal because reproductive function was unaffected and venereal transmission of PPV was not detected.

Semen changes in boars after experimental infection with pseudorabies virus.

Two groups of adult boars were inoculated with a field strain of pseudorabies virus (PRV) by intranasal droplet; one group was given 5 x 10(5) median tissue culture infective doses (TCID50), and the other, 5 x 10(6) TCID50. (A third group was maintained as controls.) Ejaculates were examined twice a week for volume, sperm numbers, sperm morphology, and presence of PRV. Severe clinical disease with fever followed administration of the larger virus dose. Death (one boar), testicular degeneration, and transient elevation in spermatozoa with proximal cytoplasmic droplets were seen in different members of this group. The smaller dose resulted in seroconversion, but did not produce signs of disease. In this group, volume, sperm numbers, and sperm morphology did not decline when compared with base-line values or data of control animals. The virus was not isolated from semen. Effects of PRV infection on semen quality in boars seem to be related to the associated clinical signs of systemic disease.

Histochemical morphologic features of growth cartilages in long bones of pigs of various ages.

Growth cartilages were obtained from humeri, femora, and ulnae of 31 pigs between 1 and 169 days old. On the basis of stain uptake and distribution, distinct layers were identified in articular-epiphyseal cartilage complexes and growth plates. The laminated appearance was dependent on stain uptake by territorial and interterritorial matrices and was more distinct in pigs greater than 15 days old. There was morphologic heterogeneity, which probably represented a functional heterogeneity, among chondrocytes in all layers and zones of both types of growth cartilage. The laminar appearance of growth cartilages and the distribution of different types of cells were similar for all pigs in each age category and for all sites.

Factors that influence litter size in swine: parity 3 through 7 females.

The influence of 7 factors on litter size for the combined parities 3 through 7 (age at conception of the first litter, parity-1 litter size, duration of lactation in the preceding parity, weaning-to-conception interval in the preceding parity, farrowing-to-conception interval in the preceding parity, number of matings per conception, and month of conception) was investigated in 11,929 litters from 5 commercial herds. Age at conception of the first litter did not influence litter size in these parities in any herd. In the 4 herds that kept such data, duration of lactation negatively influenced the weaning-to-conception interval, and duration of lactation and weaning-to-conception interval positively influenced the litter size in the next parity. Because the effects of duration of lactation and weaning-to-conception interval could not be investigated separately, their effects on litter size were simultaneously investigated, using the farrowing-to-conception interval for these combined parities. In all herds except one, the increase in live litter size was between 0.02 and 0.09 pig for each day increase in the preceding farrowing-to-conception interval less than 36 days (P less than 0.05). Duration of lactation within this farrowing-to-conception interval similarly influenced litter size. Litter size in litters of any herd was not affected by a preceding farrowing-to-conception interval greater than 35 days. In all herds except one, mean litter size of females with a farrowing-to-conception interval greater than 35 days was 0.26 to 0.96 pig greater (P less than 0.1) than for females with a farrowing-to-conception interval greater than 36 days. In 1 of 3 herds that kept such data, 2 matings per conception resulted in a larger mean live litter size than 1 or 3 matings (P less than 0.05). When these females were grouped on the basis of their conception during one of the 3-month seasonal periods, no influence of season on litter size was found. The effect of parity-1 litter size on litter size of subsequent parities 3 through 7 was significant. The regression coefficient ranged from 0.11 to 0.22 (P less than 0.01) in the farrowing-to-conception interval less than 36 days in all herds. In females with a farrowing-to-conception interval greater than 35 days, this association was significant only in one herd.(ABSTRACT TRUNCATED AT 400 WORDS)

Seasonal influence on the fertility of sows and gilts.

Seasonal fluctuations in the farrowing rates (FR( of sows and gilts were determined by analysis of breeding records from 11 herds, covering a total of 26 herd-years of data. Of 22,997 sow and gilt matings, 72.7% resulted in farrowing. For matings during July, August, and September, 60.8% of females farrowed, compared with 76.9% for matings during the remainder of the year. The FR was higher in multiparous sows than in primiparous sows and was lowest in nulliparous gilts. The FR was 65.5% for gilts bred in confinement and for gilts maintained outside. The seasonal fluctuation in FR was similar for confinement and outside-housed gilts. Water sprinkling or evaporative cooling methods did not prevent seasonal fluctuations in the FR of sows or gilts. For sows confined to crates after breeding, the FR was 13.8% higher than for sows in group-housing systems, but the seasonal fluctuation in FR was not substantially altered. It was concluded that the FR of female swine is markedly influenced by season of the year and by parity. The seasonal fluctuations in FR occurred in group- and individually housed swine and in confinement and outside-bred gilts. Water sprinkling or evaporative cooling systems, as used in the herds investigated, appeared to be of questionable value in preventing infertility during the warm months.

Factors influencing litter size in swine: parity-one females.

The influence of age at conception, number of matings per conception, season of conception, and breed of female on parity-1 litter size was investigated in 4,944 females from 5 commercial swine herds located in North America. The influence of age at conception on reproductive performance of females in subsequent parities also was investigated. As the age at conception increased from 180 to 245 days, litter size increased 0.017 and 0.012 pig per day, respectively, (P less than 0.05) in 2 of the 3 herds that recorded such data. Age at conception did not influence litter size when conception occurred after 245 days of age. Longevity (parity achieved before death or culling) of females was not influenced by age at first conception. Gilts that conceived before 220 days of age had significantly shorter weaning-to-conception intervals in one herd and shorter farrowing-to-conception intervals in another herd throughout subsequent parities. In 1 of 3 herds that recorded such data, live and total litter size increased from 9.46 to 10.46 and 10.16 to 11.50, respectively (P less than 0.05), as number of matings increased from 1 to 3 per conception. No significant influence of number of matings per conception was observed in the other 2 herds. The effect of season of conception was variable among herds. In 2 herds, there was no significant effect of season of conception on subsequent litter size.(ABSTRACT TRUNCATED AT 250 WORDS)

Seasonal influence on estrous activity in sows and gilts.

Seasonal fluctuations in the estrous activity of sows after weaning and of sows and gilts after mating were determined by analysis of breeding records from eight swine herds covering a total of 19 herd-years of data. Of 11,461 sows, 78.4% were in estrus within 7 days after weaning. From July through September, 68.6% of sows returned to estrus within 7 days after weaning, compared with 82.0% during the remaining 9 months of the year. An increase in postweaning anestrus of more than 30 days' duration also occurred during summer months. Seasonal fluctuations in the frequency of postweaning estrus were similar for sows moved from farrowing facilities to environments with or without specialized temperature control features. For sows confined to crates after weaning, the rate of postweaning return to estrus was 10.4% greater than for sows in group-housing systems, but the seasonal pattern in postweaning return to estrus was not altered. Postweaning estrous failure was more obvious in primiparous sows than in multiparous sows, especially during summer and fall. The frequency of delayed return to estrus after infertile mating was 63.7% for matings during the period July through September and 29.7% for the period January through March. It was concluded that postweaning and postservice estrous activities in swine are influenced by season of the year and by parity. Group housing of sows or individual crating of sows, and water sprinkling or evaporative cooling systems in the postweaning breeding area, as used in the herds investigated, appear to be of questionable value in preventing estrous failure during summer and fall months.

Isolation of toxigenic strains of Pasteurella multocida from lungs of pneumonic swine.

Lungs from 113 pneumonic pigs were examined for Pasteurella multocida. The lungs were smeared directly onto blood agar and homogenized in brain-heart infusion broth and then inoculated intraperitoneally in mice. Pasteurella multocida isolates were typed for serotypes A (by hyaluronidase inhibition of capsule) and D (by acriflavine autoagglutination). Strains were tested for toxin production by intradermal injection of 0.2 ml of filtered 24-hour culture supernatants into guinea pigs. Most lungs (70.8%) yielded isolations. Most isolants (87.5%) were type A and 12.5% were type D. Of the type D strains, 80% were toxigenic. Of the type A isolants, 18.2% were toxigenic.

Pneumonia and atrophic rhinitis in pigs from a test station--a follow-up study.

Pneumonia and atrophic rhinitis were studied for the second consecutive year in pigs at the same test station. Pneumonia was found to reduce mean daily gain by 3.3% for every 10% of the pig's lungs that had lesions. Atrophic rhinitis did not affect mean daily gain. There was no association between the development of atrophic rhinitis and the development of pneumonia. Pigs that were vaccinated with a Bordetella bronchiseptica bacterin did not have turbinate atrophy scores or mean daily gains different from those in pigs that were not vaccinated. Yorkshire and Hampshire pigs had higher prevalences and severity of pneumonia and atrophic rhinitis, compared with pigs of other breeds.