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 deexx004@umn.edu.

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 fangmant@Missouri.edu.

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 goodband@ksu.edu.

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 Mellis7@uiuc.edu.