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Herd Health: Health Considerations When Introducing Gilts

There are several ways to introduce new genetic material into a breeding herd. Live animals may be purchased or produced within a system as selects, breeder weaners or weaned pigs.Or, new genes may enter a herd via semen, embryos or cesarean-derived piglets. Regardless, the goal of any introduction is to improve genetics while maintaining herd health.Creating Stability Properly managing replacement

There are several ways to introduce new genetic material into a breeding herd. Live animals may be purchased or produced within a system as selects, breeder weaners or weaned pigs.

Or, new genes may enter a herd via semen, embryos or cesarean-derived piglets. Regardless, the goal of any introduction is to improve genetics while maintaining herd health.

Creating Stability Properly managing replacement gilts forges a key link in providing homogenicity (equality) of health between incoming stock and the existing sow herd.

This homogenicity and stabilization of immunity is very critical in maintaining a balanced, sustainable production system.

To reach this goal, any animals received should go through a period of isolation, acclimation and recovery prior to being introduced into the new herd. Producers should establish a similar system for both internally and externally sourced animals. When designed and operated properly, a gilt development program should lower the cost of producing weaned pigs.

Isolation Period Isolation is defined as segregation from the main herd. It is a period of time to observe pigs for any health changes and conduct any desired profiling which may include observation of clinical signs, serology, necropsies and sentinel animal assessment.

This period also allows the genetic supplier to contact you if there has been any health change in the source herd. This health change information is available through monthly veterinary visits, production data and routine diagnostics.

Isolation has the function of protecting the receiving herd from exposure to known clinical diseases and allowing identification of incubating diseases at time of delivery. It also prevents disease challenges in the recipient herd from overwhelming incoming animals until they are prepared

Isolation should occur 21-30 days post-delivery and be completed in a separate facility from the main herd.

Ideally, this separation should be a half mile or more from the breeding herd. However, many producers have found it is consistently effective to separate incoming animals by 75 ft. from the breeding/gestation population.

The herd health risk is a function of agent, separation distance, animal population, age of the pig, biosecurity and physical location of the isolation unit with respect to the sow population. As the size of the group in isolation increases, and separation distance decreases, the risk of aerosol disease transfer increases.

The isolation unit is typically similar to a standard finishing facility but many designs are used effectively. These standard buildings are often totally slotted, natural or power ventilated, double curtain with a shallow pit. The pit should be self-contained for waste storage to coincide with the period of isolation. The buildings are sized according to the flow of animals into and out of the facility and the length of the isolation period.

Installation of a crate in every other fenceline is a very practical means of housing cull animals for natural exposure. These crates also serve as boar housing for estrus stimulation and detection.

The people flow assumes that animals in isolation are of high risk to the main herd. The building should have a separate shower and entry. Ideally, one person has the responsibility of caring for these animals. People within the main unit can manage the isolation unit as long as it is visited as the last task of the day and the personnel maintain separate boots and clothes and shower in or out.

The isolation facility must be all-in, all-out in order to maintain a period of isolation. It cannot be operated continuous flow.

Acclimation Period Acclimation is the process of incoming animals becoming accustomed to new facilities, recipient herd pathogen levels and endemic disease agents in the receiving herd.

Acclimation involves vaccination of animals to develop acquired immunity, and exposure to receiving herd pathogens to develop natural immunity. The purpose of acclimation is to stimulate individual animal and population immunity.

Achieving homogenicity or equality of immunity within a very large percentage of the population is crucial to reducing subpopulations within the herd.

Acclimation starts after isolation is complete. The time required for this stage is directly related to success of natural exposure, time required for immunity to develop to vaccine and natural exposure and the recovery period to reduce risk of disease spread.

The acclimation program should be herd and system specific, based on the health status of the incoming animals and the receiving herd.

Because of this variability, a system of disease profiling should be used to identify if natural or vaccine exposure has been successful in controlling agents such as Porcine Reproductive and Respiratory Syndrome (PRRS), parvovirus, etc., that can be readily analyzed. Placement of negative sentinels into the acclimated population with subsequent testing either with serology or necropsies can also be used in this assessment.

In short, the program for a single herd will be different than the program for multiple sow herds commingling weaned pigs. The program should be reviewed semi-annually or if a health change occurs in the sow herds.

Acclimation should occur as a controlled challenge, because some populations can be overwhelmed, resulting in disease and death in pigs.

To develop a specific program, you need to have a solid understanding of the health status of your own herd.

The vaccination program will depend on your herd health strategy. One-site, farrow-to-finish herds may have a minor vaccination program, while segregated-production herds will have a vaccination strategy to maximize protective colostral antibodies for the piglets. The latter will depend on an intensive vaccination program to stabilize health, avoid sub-populations and allow successful, segregated production.

Timing of vaccination depends on the vaccine used and time of exposure. Vaccination may begin late in the isolation period to stimulate immunity prior to natural exposure. Vaccination and/or exposure to the more common agents such as Mycoplasmal pneumonia and swine influenza virus (SIV) is a critical factor in maintaining sow herd stabilization (immunity) to prevent spread through segregated nursing pigs.

A word of caution: Let your veterinarian direct the acclimation program as there are times such as pseudorabies elimination when acclimation doesn't apply.

Natural acclimation entails contact with "seeder" animals from the recipient herd along with feedback. Exposure assumes that the seeder animals from the receiving herd are actually shedding viruses or bacteria. Cull sows often serve as the contact animals, but may be a poor source of seeders for some diseases.

Good candidates are low-parity sows, non-breeding gilts or gilts that have aborted or been rebred. Low-parity animals are the best candidates because they have just been exposed to the pathogen load within the sow herd. Those young gilts/sows haven't produced solid immunity that would reduce their ability to transmit disease organisms.

Unfortunately, our ability to identify these successful candidate animals is limited.

A more common source of seeders for PRRS is nursery pigs. Nursery pigs have longer viral activity, increasing the odds of successful exposure early in the acclimation period.

Serological profiling for agents like PRRS can identify the exact group for exposure and can tell if successful exposure has occurred.

Contact animals are introduced to the incoming group for two to four weeks and then are removed. The length of exposure depends on the disease agent and the transmissibility between the two groups. Sampling either by serology, polymerase chain reaction (PCR) or virus isolation may help identify candidates as seeders.

The key is identifying the group that has recently been actively infected because they have a much higher risk of shedding. As a guide, one cull, parity-zero gilt or parity-one female to 20 animals has been satisfactory for exposure. The exact ratio of exposure population to incoming population is also unscientific and depends on the disease agent.

With some disease agents, such as transmissible gastroenteritis (TGE), one clinically affected animal is effective. In other cases, several animals must be used to increase the chance of exposure and the rapidity of exposure.

It's vital that these seeder animals be dispersed throughout the acclimation population. This can be done either by housing them within all the populations or by moving them daily between the various groups. Seeder pigs or pens should be rotated once or twice daily during the early acclimation period to increase exposure.

Naive groups being acclimated will generally transmit the agents readily amongst themselves, but slow transmission increases the length of the acclimation period or the number of contact animals needed. This contact should be completed aggressively the first few days of the acclimation phase.

Acclimation is also frequently done by oral feedback of mummies, viscera (lungs and intestines) of stillborns, weak newborns from recently farrowed litters and feces of recently farrowed sows. The exact feedback protocol is also unscientific but the general guidelines are:

* Collect viscera from one stillborn and one newborn, weak pig per 10 head of gilts to be fed back. Use stillborns and weak pigs from as many litters as possible, with no more than four pigs from any one litter.

* Collect all the mummies in one day.

* Collect 11/42 cup of manure per gilt to be fed back.

* Collect parts of five placentas per 20 animals. Collect the day of farrowing.

Once this material is collected, homogenize it using a grinder or garbage disposal. Mix with equal parts of cold water. Scatter this material into troughs, at least two cups per gilt, twice for two weeks. Or, more frequent feedback is useful as long as it is done appropriately. Assign someone to this task and make them accountable.

Most recently, acclimation has focused on PRRS. But this procedure is also extremely valuable for parvovirus, enterovirus, SIV, mycoplasma, rotavirus and E. coli.

Historically, producers have realized the benefit of acclimation because it controls viruses causing reproductive losses.

Recovery The last phase of health management for incoming animals is recovery. This period begins after isolation and acclimation. The recovery period allows stabilization of individual and group immunity, reducing risk of disease spread to the receiving sow herd.

It is commonly accepted that a recovery of 60 days or longer is necessary for the entire group to be at low risk of transmission, before adding them to the existing herd. The importance of this recovery period has been seen with PRRS. Most animals stopped shedding PRRS virus 21-30 days post-exposure.

Certain incoming groups may need a recovery time of 90 days or longer to limit transmission risk. Profiling for PRRS can give you guidelines as to the stability of the immunity and the length of recovery time.

The exciting point here is that recovery time from PRRS seems to work for other agents including parvovirus, SIV and the enteroviruses.

To provide a 60-day recovery period, design the isolation, acclimation and recovery (I/A/R) process to have the animals available for servicing. If your target breeding age is 210 days, and you need at least a 60-day I/A/R period, replacement animals need to be received at 140-150 days of age.

If you have just one gilt developer facility, you can't receive animals at less than nine-week intervals to avoid continuous flow. In this situation, you will need to receive staggered-age gilts in a batch program.

More practically, two or more gilt developer units are required. This allows you to alternate the flow between the two units. Each gilt developer unit needs to be designed based on the inventory of animals, length of occupation and exit age and weight of the gilts. Maintaining a separate period of isolation followed by acclimation and recovery works out to a period of delivery through introduction into the breeding herd of 90 days.

Gilt developer models and operational processes need to be discussed in depth with your veterinarian. Figures 1-4 illustrate various models.

The combined health management program covering I/A/R may make it more practical to receive staggered age and weight gilts as breeder/weaners or weaned pigs.

Breeder/weaners are typically 50-60 lb. If you do not receive or enter them at staggered ages and weights, you need multiple isolation or developer buildings.

Accepting younger pigs allows for a longer period of exposure and monitoring to improve the success of the acclimation.

It also provides an extended recovery time for those groups of animals requiring it, while still keeping the flow of gilts available to meet weekly service targets.

Receiving weaned pigs or breeder/ weaners makes several groups available to the production system and provides breeding flexibility in case of problems.

The same processes/procedures must be followed for animals in an internal, closed-herd multiplier as from an outside source. Don't assume herd health of those sources is similar to that of your herd. Profiling has proven that internally produced replacement animals aren't consistently healthy. They need to go through the same acclimation and recovery period as externally produced replacements.

Groups will vary from PRRS negative to PRRS positive within the same building or system, especially if there is room separation or building separation of groups.

In a successful, segregated production system (two-site, three-site, multi-site) the segregated groups will have a different health status than the sow groups.

Boars should be brought in using the same system as gilts unless they are going to a separate, off-farm stud.

Table 2 illustrates a timeline for a typical gilt development system.

There are costs in constructing and operating gilt developer facilities for successful I/A/R. The data in Table 1 was derived from implementing gilt development plans in a commercial system.

Summary The benefits of properly conducted I/A/R have been identified by numerous researchers. The gilt developer system needs to incorporate all aspects of this program. The design and sizing of these facilities depends on the capacity for the gilt pool within the breeding herd facility, the age and weight of service, the age and weight of the incoming animals and the length of I/A/R.

Success depends on following detailed procedures and designating a person accountable for implementation.

Isolation - a population that is separated from other pigs for a period of time.

Acclimation - the process of becoming accustomed to a new level of health and farm conditions.

Quarantine - a period of detention or isolation of incoming animals from the receiving herd with restrictions placed on entrance to, and exit from, any facility where a communicable disease may exist.