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Herd Health/Management

Transport Sanitation Reduces PRRS Risk Pig transport systems have become a major risk for the spread of porcine reproductive and respiratory syndrome

Transport Sanitation Reduces PRRS Risk

Pig transport systems have become a major risk for the spread of porcine reproductive and respiratory syndrome (PRRS) virus, and three sanitation systems tested all worked equally well in reducing that risk.

University of Minnesota PRRS researcher Scott Dee, DVM, assessed the infectivity of the livestock trailer in a Pork Checkoff-funded study. Four, 55-lb. pigs were housed in a pen within a full-size, double-deck trailer for a four-hour contamination period on days 3-7 post-contamination.

In the first phase of the study, experimentally infected pigs provided the source of trailer contamination. Infected pigs were removed and five naïve pigs were placed in the trailer pen (without pen sanitation) for four hours, then tested seven days post-exposure to determine the presence of the PRRS virus by polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA).

The second phase evaluated the ability of several intervention strategies to sanitize PRRS virus-contaminated trailers. The double-decked livestock trailer was contaminated in 15 selected sites using a modified-live-virus PRRS vaccine. Inoculated sites on both levels of the trailer included the center of the floor, front and rear corners, ceiling braces, light fixtures and gate hinges, plus the loading ramp to move pigs from level one to level two.

Following contamination, trailers were treated with a sanitation protocol, and swabbed two hours later. Samples were tested for PRRS virus by polymerase chain reaction.

Methods of sanitation used were disinfection, the thermo-assisted drying and decontamination (TADD) system and trailer baking. Disinfection was by two systems: Synergize (Preserve International) and Virkon (DuPont). TADD uses a 1.2-million btu/hour heater or a 800,000-btu/hour heater to deliver high-velocity air. A trailer baker provides 160°F- air at high velocity.

When assessing the infectivity of the trailer, results indicated that three of five naïve sentinels became infected following contact with contaminated trailer surfaces. These results support the need for proper sanitation of trailers after delivering infected animals.

All three sanitation methods proved equally effective at eliminating infectious PRRS virus from the interior of livestock trailers. The trailers that were contaminated and not sanitized were shown to contain evidence of infectious PRRS virus.

“These results indicate that contaminated transport is a risk factor for the transmission of PRRS virus from infected to naïve swine, and that multiple methods are available for significantly reducing this risk if the protocols tested are followed,” says Dee.

Researcher: Scott Dee, DVM, University of Minnesota. Contact Dee by phone (612) 625-4786, fax (612) 625-1210 or e-mail

Tonsil Test Fixes Time Of PRRS Persistence

One of the key impediments to elimination of the virus that causes porcine reproductive and respiratory syndrome (PRRS) in pigs is persistence.

Following an outbreak of PRRS, some pigs achieve full recovery from the disease — but become persistently infected with the virus and don't exhibit outward signs of disease.

These “carrier pigs” will continue to harbor a low-level viral infection for an extended period of time. Persistently infected pigs may shed the PRRS virus continuously or intermittently, posing a threat of infection to naïve pigs through either direct or indirect contact.

University of Missouri swine veterinarian Thomas Fangman and associates devised a tonsil scraping method to obtain known tonsilar crypt exudate, which can be utilized to determine the level of persistence of the virus following experimental challenge.

In the Pork Checkoff-funded study, two completely isolated groups of 44 weaned pigs were inoculated with either a commercially available modified-live-virus (MLV) PRRS vaccine or a farm-specific, live virus inoculation (LVI), or serum therapy.

Following exposure to the two methods of PRRS inoculation, tonsilar scrapings were taken at regular intervals over 160 days to determine the duration of persistence in tonsilar crypts or depressions.

The study revealed no difference in the ability of pigs vaccinated with the MLV product or LVI to produce an antibody response and clear the virus from their tonsils.

The study also demonstrated that tonsilar scrapings obtained from live animals provide a good source of viral particles and are useful in quantifying the level of virus infection in this tissue.

Researchers concluded the time necessary to eliminate the risk of PRRS transmission is at least 130 days, but a potential for risk may still exist in a population of pigs for up to 160 days.

Based on this study, the Missouri researchers advised pig isolation after exposure to PRRS virus should be at least 160 days. Likewise, the period of herd closure to introductions of gilts after a PRRS outbreak must be at least 160 days after the last animal was exposed to the virus.

Researchers: Thomas Fangman, DVM, University of Missouri; Steve Kleiboeker, DVM, Viracor, Kansas City, MO; and Melinda Coleman, DVM, Albany Veterinary Services, Albany, MO. Contact Fangman by phone (573) 882-7848, fax (573) 884-9139 or e-mail

Crowding, Not Pen Integrity, Reduces Finishing Output

Maintaining pen integrity from the nursery to the finisher barn had no effect on finishing pig performance, according to a collaborative study by researchers from the North Central Committee on Swine Management. However, crowding (providing only 6 sq. ft. of space/pig) during grow-finish had the greatest effect on growth and feed intake of pigs.

The joint effort was to determine if maintaining nursery to grow-finish pen integrity might reduce the space requirements of finishing pigs.

Collaborators concluded that crowding produced expected reductions in growth and feed intake of pigs restricted to 6 sq. ft./pig, although the reductions were fairly small.

Unlike earlier studies, this research also found that maintaining pen integrity when moving pigs from nursery to finishing units had no positive effect on pig performance.

In this study, nursery-age pigs weighing approximately 55 lb. were assigned to one of several treatment groups evaluating pen integrity, 6 or 8 sq. ft./pig. For mixed treatments, nursery pigs were also placed into pens with either 6 or 8 sq. ft./pig at finishing.

Space configurations are spelled out in Figure 1. Table 1 provides an outline of the various treatment options studied and the impact of space allowance and pen integrity on performance parameters.

For the study, the same dietary sequence was formulated for corn-soybean meal diets used by all research collaborators. Diets were formulated to 1.20, 1.00, 0.85 and 0.75% total lysine for pigs weighing 50-80 lb., 80-150 lb., 150-200 lb. and 200-250 lb., respectively.

From Day 0 to 118 of the trial, from 55 to 250 lb., no treatment effects were observed for average daily gain (ADG) or average daily feed intake (ADFI), regardless of whether pigs were mixed or not mixed (Table 1).

This suggests that keeping pigs in the same group when moving from nursery to finishing pens did not improve performance compared with pigs that were randomly mixed.

However, for the overall trial, pigs allocated 6 sq. ft. had decreased ADG and tended to have decreased ADFI, compared with pigs provided 8 sq. ft.

There was a tendency for a space allocation by mixing interaction observed for final ADG and F/G. This interaction occurred because when pigs were allocated 6 sq. ft./pig and mixed, they showed increased ADG and F/G vs. unmixed pigs at 6 sq. ft./pig. In contrast, unmixed pigs had better ADG and F/G when housed at 8 sq. ft./pig.

Despite the interactions between pen integrity and crowding, the actual performance differences for all of the treatment groups were relatively small.

The overriding conclusion of the study, consistent with other reports evaluating stocking density and space allocation, is that pigs require greater than 6 sq. ft./pig in the finishing phase for maximum growth performance.

Researchers: R.D. Goodband, Kansas State University; M.C. Brumm, University of Nebraska; L.J. Johnston, University of Minnesota; and K. Stalder, Iowa State University. Contact Goodband by phone (785) 532-1228, fax (785) 532-7059 or e-mail Goodband at

Pig Removal Strategy Offers Marketing Options

The ideal marketing strategy optimizes returns while maximizing pounds marketed and reducing the variation in live weight at slaughter.

To that end, University of Illinois animal science professor Mike Ellis and graduate student Jake DeDecker directed several studies aimed at determining the best strategy for sending pigs to market while maximizing total facility output and profitability.

Thirteen experiments were carried out on four different commercial hog farms in Illinois and Indiana. The goal was to determine the optimal marketing strategy, but also to learn how different strategies affect performance of pigs remaining in the finishing pens.

The first experiments evaluated the impact of the number of pigs removed from a pen on the growth of the remaining pigs. Results showed linear increases in growth performance as the proportion of pigs removed increased from 10 to 45%.

When the heaviest pigs were removed from a pen at around 20 days before slaughter, growth rates for the remaining pigs improved by about 11%. Both feed intake and feed efficiency increased by about 6% for those pigs, compared to pigs of similar weight in intact pens.

Variation in live weight and the total amount of feed consumed for the entire pen was reduced by pig removal in the trial. But the total amount of live weight produced per marketing group decreased as the proportion of pigs removed from the group increased.

By removing the heaviest pigs about three weeks prior to marketing the whole pens, the variation in weight at market was reduced for all of the pigs marketed.

Of interest, growth responses to pig removal were similar in single-gender pens of either barrows or gilts, and in mixed-gender pens.

There was no effect in any of the studies of pig removal on carcass measurements, morbidity or mortality.

In studying the effect of frequency of pig removal on subsequent performance, the same number of pigs was pulled from pens twice vs. once. Growth performance of the remaining pigs in the pen was similar for both removal frequencies, and exceeded the growth rates of pigs in pens left intact.

However, removing pigs from pens twice compared to only once reduced total feed consumption by 11% and decreased the proportion of lightweight pigs by 55%.

Studies also found that the increase in floor space was the main contributor to an increase in growth rates, after accounting for pigs removed from the pen. Increases in feeder space and changes in group dynamics had much smaller and inconsistent effects.

The group size pigs were reared in, 26 vs. 78 pigs/pen, had no impact on pig growth rates after pig removal.

The best marketing strategy is the one that maximizes profit; it must obviously be tailored to each situation.

These studies suggest that the economic tradeoff for marketing lies between the increased returns from the extra pigs that fall within the required weight window for marketing — and the reduction in feed costs on one hand, set against the reduction in the total weight of pigs produced on the other.

Researchers: Mike Ellis and Jake DeDecker, University of Illinois. Contact Ellis by phone (217) 333-6455, fax (217) 333-7088 or e-mail

Cull Sows Can Be Worth Feeding

Thin cull sows can be worth feeding to restore bodyweight, provided feed costs and fixed costs are in line, according to a study at Iowa State University (ISU).

ISU scientists concluded that weight could be profitably added to cull sows as long as feed prices were below $0.07/lb., and fixed costs were below $0.50/sow/day.

For the study, 29 sows were purchased from an integrated hog operation and placed into pens and gestation crates. The sows were evaluated and categorized into one of five body condition scores (BCS). Data represented the incremental performance of moving BCS up one or more from the initial score.

Jowl, heart and flank girth measurements, along with 10th-rib and last-rib backfat, loin muscle area and loin depth were collected about every 14 days.

As determined by last-rib backfat scores, 8, 17 and 4 sows were initially classified into body condition scores of 1, 2 and 3, respectively. A BCS of 1 represents an extremely thin animal, while a BCS of 5 represents a well-proportioned animal.

Feed/gain was the most efficient for cull sows that began the trial as BCS 1 (2.27 lb./lb. of gain) and increased one score. That compares to sows with an initial BCS of 2 (3.57 lb./lb. of gain) or 3 (4.76 lb./lb. of gain).

The average daily gain (ADG) when adding a single BCS to sows with an initial BCS of 1, 2 or 3 was 4.5, 3.6 and 2 lb./day, respectively.

As sows increased BCS, the efficiency of adding weight to those sows declined, the researchers determined.

After sows added their first BCS, sows decreased in feed/gain and ADG from 15 to 50%, regardless of the BCS designation of sows at the start of the trial.

Breakeven and daily fixed cost calculations supported the objective of the study, providing evidence that weight could be profitably added to cull sows.

Researchers cautioned that producers must be able to physically house cull sows. In this study, only cheap or depreciated facilities were estimated to achieve a reasonable breakeven price.

Producers should also take into account current market conditions when planning to feed cull sows.

Finally, each producer should evaluate their sow operation and determine (based on sow health and feed prices) if weight can be profitably added to cull sows.

Researchers: R.F. Fitzgerald, K.J. Stalder, L. Karriker, C.J. Johnson, L. Layman, T.J. Baas and J.W. Mabry, Iowa State University. Contact Stalder by phone (515) 294-4683, fax (515) 294-5698 or e-mail

Differences Exist in Aspirin Solubility, Absorption Levels

The differences that exist in aspirin and sodium salicylate solubility and absorption may affect the dose received by the pig and treatment effectiveness, according to a study co-authored by researchers at Iowa State and Kansas State universities.

These products are widely used in food animal production due to the current lack of antiviral drugs, low cost and over-the-counter availability. But information is lacking on recommended dose levels and concentrations achieved in plasma, and whether there are negative effects on the gastric systems of pigs.

The Pork Checkoff-funded trial was conducted in two phases.

The first phase compared the solubility of two common liquid products, an acetylsalicylic acid and a sodium salicylate product, in a typical stock solution and nursery environment. The goal was to find out how much of the active ingredient would survive for 24 hours under commercial conditions.

A stock solution containing each of the aspirin products was prepared and placed in the nursery environment and sampled at 0, 8, 16 and 24 hours.

Results indicated the sodium salicylate product was more soluble and stable under these conditions.

This product was then used in phase two of the study, which delivered the product to pigs and measured levels in the plasma. Four treatment groups of 10, 40-lb. pigs were tested at varying stock solutions. Pigs were tested and random blood samples were taken at 0, 24, 60 and 72 hours after the treatment began.

When given orally through a water medication system, the sodium salicylate product was absorbed and reached measurable concentrations in the blood. Serum concentration levels of sodium salicylate shown in Table 1 illustrate treatment levels and time of administration.

During the trials, aspirin products were only remixed once daily to simulate normal production temperatures, pressures and mixing conditions. Water readings were taken twice daily.

Water quality was tested and found to be within normal limits for the potential contaminants tested. Water quality may have a large impact on solubility, but a range of water types was not tested in this trial.

The sodium salicylate product has been shown in other species to be less ulcerogenic than acetylsalicylic acid, but this has not been tested in swine.

The researchers stressed that co-variables such as water quality, equipment types and management styles (including vaccination and treatment protocols), must be taken into consideration when extrapolating these findings to other production settings.

But results suggest the data can be used to develop dosage recommendations for future applications.

Researchers: Locke Karriker, DVM; Abby Patterson and Paula Imerman, Iowa State University; and Michael Apley, DVM, Kansas State University. Contact Karriker by phone (515) 294-2283, fax (515) 294-1072 or e-mail

Injection Devices Compared for Treatment Efficacy

Two routes of administration were evaluated for absorption, distribution and elimination (pharmacokinetics) of penicillin G in swine. The study involved nine pigs from 32 to 64 lb., and was conducted at Iowa State University.

Intravenous administration of potassium penicillin G was used to establish a baseline serum concentration curve. The area under this curve could then be evaluated to establish how available penicillin G would be by other injection methods.

Intramuscular injection of procaine penicillin G by a hypodermic needle resulted in virtually 100% of the drug being available to the animal.

Injection of the same dose of procaine penicillin G by a needleless air injection system resulted in about 73% of the drug being available to the animal.

The pharmacokinetic data derived from this Pork Checkoff-funded study will prove valuable in supporting development of dosing recommendations for procaine penicillin G in swine by the Veterinary Antimicrobial Decision Support System. That system is being developed by industry groups to assist veterinarians in making antimicrobial use decisions in food-producing animals.

Because needleless air injection systems may differ in the amount of drug that becomes available to the animal, dose adjustment may be required.

Still, the relative availability of product with the air injection system warrants further study of the process to reduce needle use in swine.

A larger study is necessary to confirm and more accurately characterize the differences in pharmacokinetics and to gauge possible changes in dosing regimens and withdrawal times.

Researcher: Brad Thacker, DVM, Intervet, Inc., formerly of Iowa State University. Contact Thacker by phone (515) 231-7851, fax (515) 597-3466 or e-mail

Needleless Injection System Promising For Swine Production

Studies at Iowa State University's (ISU) Meat Laboratory demonstrate that transdermal, needleless injection systems for use in swine hold promise for delivery of animal health products and reduction of pork carcass defects.

Pork Checkoff-funded study results demonstrate that the needle-free injection system is effective for delivery of Mycoplasmal pneumonia and pseudorabies (PRV) vaccines.

In the trial, 96 pigs were vaccinated for PRV and for mycoplasma. Pigs were divided into three groups: unvaccinated controls, vaccinated with conventional hypodermic needles and vaccinated with a needle-free, air-powered injection device.

Pigs were tattooed on the neck to mark injection sites. Blood samples were drawn at 11-13 days and 23-25 days following injection, and the serological response was measured. Injection sites were collected at slaughter and dissected to evaluate tissue damage.

The results showed that both injection methods produced similar serological response in the vaccinated pigs. Both injection methods provided significantly greater response than the controls. Injection site examinations showed no signs of lesions in any of the pigs.

But this result was not expected under the controlled conditions of this experiment. In pork carcasses, defects from hypodermic needle injections are well documented.

“It is clear that the needle-free injection system will eliminate all residual needles and needle fragments from pork carcasses, and it seems likely to reduce injection site lesions resulting from contaminated needles as well,” reports Joe Sebranek, ISU meat scientist.

“The needle-free transdermal injection system for delivery of vaccines in swine has excellent potential for use in swine production systems,” he concludes.

Researchers: Joseph Sebranek, Terry Houser and Tom Baas, Iowa State University; and Brad Thacker, DVM, Intervet, Inc. Contact Sebranek by phone (515) 294-1091, fax (515) 294-5066 or e-mail

Table 1. Effects of Mixing Pigs or Maintaining Pen Integrity and Space Allowance on Pig Performancea
Space Allowance × Pen Integrity Main Effects
Crowded (6 sq. ft.) Uncrowded (8 sq. ft.) Space Allowance Pen Integrity
Item Mixed Unmixed Mixed Unmixed Interaction 6 sq. ft. 8 sq. ft. Mixed Unmixed
Day 0-14
ADG, lb. 1.79 1.73 1.77 1.72 0.92 1.76 1.74 1.78 1.72
ADFI, lb. 3.45 3.37 3.52 3.26 0.46 3.41 3.39 3.49 3.32
F/G 1.91 1.94 1.99 1.89 0.16 1.93 1.94 1.95 1.92
Day 0-118
ADG, lb. 1.92bc 1.88b 1.93c 1.97c 0.05 1.90 1.95 1.93 1.92
ADFI, lb. 5.17 5.14 5.24 5.26 0.61 5.16 5.25 5.20 5.20
F/G 2.69bc 2.73b 2.71bc 2.67c 0.04 2.71 2.69 2.70 2.70
aData was analyzed as a 2 × 2 factorial design as a means over block approach (the combined values for the three mixed pens within a space allocation were used as a single observation). Fixed-model effects included space allowance, pen integrity and their interaction, and random effects included experimental station, replication and their interaction. The Kenward-Roger adjustment was used for the degrees of freedom. Pigs were moved from nursery to finishing facilities at approximately 54.9 lb. when they were mixed or not, and moved to pens with either 6 or 8 sq. ft.
bcMeans in the same row with different superscripts differ (P<0.05).>
Table 1. Mean Serum Concentration (µg/ml)* (Standard Deviation in Parenthesis) of Sodium Salicylate by Treatment and Time
Sample time (hrs.) T1 T2 T3 T4 T5
0 0 0 0 0 0
24 0.41 (0.31) 1.28 (1.03) 1.41 (0.64) 7.22 (2.31) 0
60 0.17 (0.15) 0.82 (0.77) 0.44 (0.50) 2.66 (2.41) 0
72 0.27 (0.20) 0.03 (0.07) 1.24 (0.79) 0.62 (0.48) 0
T1 = stock solution concentration of 19.4 ppm, T2 = 38.9 ppm, T3 = 77.6 ppm, T4 = 155.3 ppm, T5 = 0 ppm. *Levels represent micrograms/milliliter.