Depopulation and repopulation (depop-repop) have long been recognized as a successful and reliable means to eradicate disease. The cost of downtime in depop/repop, however, has been a limitation to its use in disease eradication programs.

Making the decision to depopulate and repopulate a herd is a difficult one that must be well thought out to understand both the cost and potential benefits.

It may be a relatively quick decision, such as if a new disease breaks in the herd — porcine reproductive and respiratory syndrome (PRRS), pseudorabies (PRV), Actinobacillus pleuropneumonia (APP), swine dysentery — or after long-term frustration with chronic diseases.

Reasons to Depopulate

Disease eradication is the primary reason for herd depopulation. Besides eradication, depopulation is expected to decrease mortality and medication costs and improve average daily gain and feed efficiency.

Depopulation has been successful for many different diseases, and can be used to rid an operation of multiple diseases simultaneously.

Depopulation and repopulation are the fastest, most reliable ways to return the herd to high-health status. This can be particularly vital in multiplication herds or any farm that needs to quickly reestablish its health status.

Herd location is a key factor in the decision, because it will determine the odds of the project being a long-term financial success. If the herd is in a good, fairly isolated location, the decision to depopulate is easier vs. a farm located in a very pig-dense area, which is likely to become reinfected with the disease.

Swine Vet Center staff has developed state maps from aerial photos identifying all the local hog farms to help evaluate area risk, identify where to do off-site breeding projects and for routing pigs (Figure 1).

Parity distribution of the herd can be another reason to consider depopulation. There can be a number of reasons for parity distribution becoming heavily weighted with older-parity females. If the goal is to eradicate a disease from the herd, and if herd parity distribution is older, then the decision to depopulate makes more sense.

Genetics is another argument for depopulation. This is a good opportunity for rapid genetic improvement, and can help offset some cost of upgrading herd health with better performance in the offspring.

The U.S. swine industry has changed to predominantly Isowean production units, easing the process of depopulation. Downtime is dramatically reduced because pig age variation is less on sites.

As D.L. (Hank) Harris, DVM, described in the first Blueprint article (Multi-Site Systems Broaden Protection, p. 6), the purpose of Isowean production was to eliminate the need for herd depopulations. But it has actually made depopulation easier and less expensive due to the separation of production sites.

For a depop-repop to be successful, gilts of the proper health status and in adequate numbers must be on hand. Health status and genetic quality must match up well enough for production and in products sold at market.

Whether to depopulate in a high or low market is a long-standing debate. If cull sow price is high, more of the cost of replacement gilts can be offset, even though the cost of replacement gilts will likely go up as well. The timing and effect of downtime must also be considered in relationship to the market price.

There is always risk in depopulation, so financial impact must be considered. Each producer must evaluate the financial impact if the depopulation fails and the herd rebreaks during the depopulation or soon after. This can be a financially devastating blow.

Planning is Critical

Once the decision is made to depopulate a herd, the hard work of developing a good plan begins. Adequate time devoted to the planning phase can really help to ensure success. It's best to plan a year ahead, but 4-6 months is the minimum to make sure everything is organized.

Evaluate the overall production flow and assess project breakdown into manageable parts. This is easier to do in multiple-site systems and minimizes downtime.

For multiple sow farms, decide if all farms will be depopulated at once or if they should be done in phases.

If done in phases, the best place to start is at the multiplication level, so that internal replacements can be made as soon as possible.

If the system has multiple farrowing sites, and the project will be done in phases, use existing inventory in farms that have yet to be depopulated. This reduces the cost of gilts on farms yet to be sold off. This also allows the system to make better use of the younger parity animals in the herd to be depopulated, rather than just sending them to slaughter. Mixing these herds is always a risk, but generally, if gilt introduction stops, the herds stabilize and herd health may even improve before depopulation.

Breeding of the new herd can be done on-site or off-site. On-site projects require more downtime (20 weeks average). Off-site projects will allow minimal downtime for production (30 days for the sow farm).

Off-Site Breeding Project

There are several factors to consider when developing an off-site breeding project.

Isowean farms are not a big concern since they don't impact the downstream sites at the same time.

Nursery and grow-finish run all-in, all-out by site, and are relatively easy once you get past the sow farm site.

To be able to accomplish this minimal downtime goal, there will have to be an off-site gilt-breeding project. This requires a site that can hold the sow herd inventory. Using 15 sq. ft. stocking density, this will generally require two times the normal finishing capacity. For example, a 2,400-sow farm will need 5,000 head of finishing capacity.

Site location for biosecurity must be as good as the sow farm to reduce project risk during this phase. The mapping software (Figure 1) can help identify sites at risk. Be sure to:

  • Provide people access to the site.

  • Ensure there are shower-in, shower-out facilities.

  • Allow space to breed animals in the barns.

  • Provide some temporary housing for boars, and put some crates in a pen to house boars separately. The best success has been to heat-check and group gilts that are in heat into a pen. Breed gilts 21-42 days after they have been regrouped. This has resulted in the best conception rates for breeding and gestating in pens.



Financial Impact of Depop-Repop

Using a partial budget is a good way to evaluate the impact of a depopulation-repopulation program.

It's important to make sure that as many costs as possible are accounted for, because many unforeseen costs can creep into the system.

Building a spreadsheet model is a very good way to run different scenarios throughout the model. Running an optimistic and pessimistic model will satisfy everyone on the production team as well as the lender. Important items in the partial budget include:

  • Cost of replacement stock (including freight, royalties and all other charges).

  • Cost of the off-site breeding project.

  • Finishing space costs. Include cost of space, cost of lost opportunity of finishers sold, cost of additional space if rented, and cost of deciding if finishers will be marketed at a lighter weight because of space limitations.

  • Unit staffing. Are there employees available to work on the project, or will there need to be more training of new employees?

  • Important biosecurity measures. Be sure to consider downtime of employees between sites, separate transport and clean and/or dirty stock.

  • Cost of repairs and maintenance of facilities while empty.



Benefits

There are many benefits to the depop/repop cleanup process. It can benefit sow herd performance, but has a negative effect on production during the startup phase, including gilt performance and the effect of using off-site facilities.

Long-term production benefits include increased pigs produced and better herd efficiency.

Grow-finish performance is improved by lower mortality, improved average daily gain, feed conversion and space requirements.

Once the model is developed, it can be refined to meet the unique features of the project to more accurately predict the outcome from depopulation-repopulation.

Remember it is just a model, and is designed to give an overview of the project. Don't spend too much time modeling the project; spend more time planning.

Observations of Herd Depopulations

The most common observation after depop-repop is: “I didn't remember raising pigs could be this easy and fun again.” Improvements can be expected throughout production, from farrowing through finishing. The magnitude of the change depends on the herd's status before the depopulation.

One disappointing point has been in herds depopulated for PRRS. A number of them have broken back with the disease over time. From sequencing information, it's clear that none of the herds have broken back with the original herd strain. The survival time chart (Figure 2) shows the rate of breakback in herds.

Summary

Making the decision to depopulate and repopulate is never easy. Once the decision is made, planning the depopulation/repopulation becomes a very important task. If things are done well, the odds of the project being successful are high. This takes time and organization as well as good communication with all members of the production team.

It requires everyone thinking of as many details as possible, taking the time to come up with the best solutions to problems.

Keep the project document as a living document. Updating it as the process goes along is essential to the success of the program.

Maintaining good communication with all team members, and keeping them informed and updated regularly, will help make sure that small details are not missed or forgotten.

If planning and execution of the plan are done properly, the project will be successful and the goals achieved.

Developing Plans for Cleanup, Restocking

Outlined below are steps for cleanup, developing a written plan, identifying replacements and restocking the farm.

The site will need to be cleaned, disinfected and fumigated just like the main herd, but before the project begins.

The site will also need downtime before population, but that will depend on the history of the site.

Pest Control

Set up the pest control program for the farm so numbers can be reduced as much as possible at depopulation. Use professional exterminators for the best results.

Written Plan

  • Develop a detailed, written plan.

  • Outline every project that needs to be done in both the new and old herds.

  • Note dates that projects must be done.

  • Color-code or use a marking system to clarify which system has responsibility.

  • Build the schedule around the delivery date to keep the rest of the project dates in line.

  • Provide time in the schedule to evaluate and repair all equipment, and order all parts and materials ahead of time to prevent delays.

  • Keep the project as a living document that is updated as changes occur.

  • Develop a detailed plan for the depop-repop (Table 1).



Source for Replacements

Identifying a source for replacements should be one of the first steps in the planning process, since this may determine the timetable of the depopulation.

Make sure there are plenty of gilts available (equal to 20 weeks' worth of inventory). Have at least 5-6 weeks worth of the breeding target so there is enough inventory of the proper age to cycle, and meet breeding targets without having to dip into younger gilts, which will decrease herd performance.

Make arrangements to take all the various ages of gilts in staged population so that the entire population is in place when the project begins, to avoid any changes in the health status of the source farm during the project.

Once you've found a source of suitable replacements that meet genetic and inventory needs:

  • Do a vet-to-vet communication (your herd veterinarian contacting the source herd's veterinarian).

  • Conduct serologic monitoring to make sure there are no subclinical diseases in the herd. Monitor both finishing herds and sow herds for differences between the populations. Testing a statistical sample of both (usually 30 sows and 30 finishers) will give a good picture of the farm. A standard set of diseases to monitor would include PRRS, Mycoplasmal pneumonia, swine influenza virus, TGE/PRCV and APP.

  • If possible, arrange a visit to the source farm.

  • Audit the biosecurity practices at the source farm. Explain the project to the source farm staff so they can understand what you are trying to accomplish and can help the farm meet its goals.

  • Meet with staff in charge of transportation so they understand the importance of the project and their role in its success.

  • Audit transport procedures and truck washing to make sure they are not putting the project at risk.

  • Plan a route to ship pigs that minimizes the risk of contact with gilts being transported to the off-site breeding farm. The mapping program can be useful here.

  • Design the delivery schedule to get the herd in place as soon as possible so the isolation period can begin.



Old Herd Cleanup Plan

Work ahead, because old herd cleanup is a bigger job than anyone realizes. As soon as areas are empty, clean them up. Other steps include:

  • Understand that one cleaning won't be good enough.

  • Remove all organic matter.

  • Inspect washing after the barn is dry.

  • Have someone else inspect the area each person has cleaned.

  • Use a flashlight to check quality of cleanup after it has dried.

  • Use sidewalk chalk to mark problem areas; it marks well but washes off easily.

  • Carry a screwdriver and putty knife to check the hard-to-get-at areas, and make sure they are clean.



Problem areas include beams that slats sit on, joints in between the slats, tops of feed lines, and electrical conduit and plumbing lines.

The most important thing is to plan enough time for everything to get dried out completely.

Site Repairs

Depopulation is an excellent time to do site repairs. Plan this activity well in advance of the actual depopulation so work can be scheduled and repairs ordered to avoid delays once the site is emptied. Larger projects may start before depopulation. Advantages to repairs during depop are that workmen don't have to work around the pigs, and biosecurity is easier before the cleanup is complete.

Disinfection

Disinfection of the site is a crucial job prior to herd repopulation.

Downtime is one of the best things we can do, plus having everything clean and dry. Summer months prove best due to less cost to dry things out, and less heating cost while leaving the facilities sitting empty.

The most common downtime is four weeks, but some projects have been done in as little as one week. This is a herd-by-herd decision based on pathogens to clean up and the level of risk the producer is willing to accept.

The site should be disinfected once it is washed and has passed inspection.

Getting everything dry is probably the best disinfectant.

Remove any standing water left after washing (i.e. water troughs, etc.). A leaf blower can be helpful for this job.

Most projects have been double-disinfected followed by fumigation.

Make sure disinfectants used are different classes of compounds so the widest range of coverage can be achieved (i.e. disinfect with Tektrol and Synergize, then fumigate with formaldehyde.).

The site should completely dry between applications of disinfectants.

Fumigation should be scheduled just prior to the animals returning to the site, leaving just enough time for the facility to air out thoroughly and be rinsed down before refilling.

Fumigation will also help to kill any other pests (rodents, insects, etc.).

Restocking Plan for the Farm

Transportation is important to make sure the project isn't put at risk.

If using farm trucks, be sure vehicles are cleaned using the same guidelines as the farm. Trucks must be separated into new herd and old herd to avoid cross-contamination; use separate truck washes.

Map out the route to deliver the new inventory to the farm from the off-site breeding project. Check the route for farms to decide if changes need to be made.

Review farm biosecurity protocol and make the necessary upgrades to keep the disease eradicated.

Table 1. Detailed Plan for Depopulation-Repopulation

Red denotes activities with the herd and site being depopulated. Black denotes activities with the new herd.
Date Week Month Activity
2/8/2002 6 2 Breed last group to farrow at home farm (2/11/2002).
2/15/2002 7 2 Clean and disinfect off-site project. Fumigate the off-site project (2/25/02).
3/1/2002 9 3 Populate off-site project with new gilts.
3/8/2002 10 3 Begin vaccination of select weight gilts.
Empty out isolation (3/11/02), clean up as soon as possible and double-disinfect.
3/15/2002 11 3 Begin breeding the new gilts (3/19/2002).
3/22/2002 12 3 Begin booster vaccination of select weight gilts.
3/29/2002 13 3 Heat check the first new herd heat checks, and then continue the heat checking on a weekly basis. Give booster vaccines to gilts that have been vaccinated. Receive the last shipment of gilts from Canada (3/27/02).
4/19/2002 16 4 Breed last group in the old herd (4/20/02). Fumigate at the Isowean barn (4/18/02). Conduct first preg-check of new herd breeding, then check the following week.
4/26/2002 17 4 Cull sows that are bred and will not farrow before the depopulation date (sows bred after 2/11/2002). Then cull the wean sows after they have had a chance to dry up. Take new gilts to the isolation barn (550 head) (4/22/02).
5/3/2002 18 5 Consolidate sows to the breeding barn. Begin cleaning the gestation barn.
5/17/2002 20 5 Get gestation barn ready for disinfection. Test isolation barn and take necessary gilts to the breeding site.
5/24/2002 21 5 Reload isolation to hold 550 head.
5/31/2002 22 5 Breeding barn cleaned and ready for disinfection. Farrow the last sows in the old herd (5/29/02).
6/7/2002 23 6 Depopulated all animals, and clean and disinfect the last two farrowing rooms. Wean the last pigs from the site (6/6/02). Totally depopulate the site by 6/7/02. Prefarrow vaccination for new herd, then continue on a weekly basis.
6/21/2002 25 6 Give second prefarrow vaccinations for the new herd, then continue on a weekly basis.
6/28/2002 26 6 Fumigate home farm (7/1/02).
7/5/2002 27 7 Repopulate home farm (7/5/02). Close up females and gilts from isolation barn loaded first.
7/12/2002 28 7 Begin farrowing new gilts (7/11/2002). Reload the isolation barn (550 head).
7/26/2002 30 7 Wean the first group to the nursery or wean-to-finish barn.