In any process, we can experience drift over time. It is the reason we have oversight — production and service managers, veterinarians, records, dashboards and metrics. The speed of drift has to do with a multitude of drivers — turnover, training and resources available, complexity of the task, ease of implementation and auditing rigor. For those engaged in pig production, a farm team's ability to consistently execute on a day-to-day basis determines the farms level of production and health.
As we think about processes we ask of our farm teams, we need to think about how individuals are engaged with the process; this will help prevent drift. You need to provide them with What? Why? How? One of the common areas that drift occurs in sow herds is gilt acclimatization. This article will focus on the what, why and how, specifically with regard to natural planned exposure.
Gilt acclimatization is a multi-step process to mitigate gilt health as she enters the herd as well as piglet health issues (in utero, suckling and post-wean). Some of these steps involve age at which gilts enter the sow herd population, vaccination, live animal exposure and infectious material exposure. Our understanding of this has helped improve sow herd health and downstream performance specifically for pathogens like porcine reproductive and respiratory syndrome, porcine epidemic diarrhea virus and mycoplasma.
There are other pathogens that we don't fully understand the best ways to acclimate gilts including porcine circovirus 2 or 3 or bacterial pathogens like Streptococcus suis and Haemophilus parasuis. This article will focus on infectious material exposure, commonly referred to as pre-breeding feedback. As we think about this practice, perhaps a more appropriate term would be 'Natural Planned Exposure.'
There are some known viruses that can cause reproductive or pig health issues if fetuses are infected during gestation. Parvovirus and atypical porcine pestivirus are subclinical to the adult animal but will clinically infect the fetuses. Porcine parvovirus is endemic in most swine populations around the world. The virus can be shed from feces and other secretions of infected pigs and is hardy in the environment, remaining infectious for months.
Maternal antibodies are excellent in protecting young pigs and blocking natural infection, with antibodies finally reaching non-detectable titers in mid finishing, around 20 weeks of age. Commercial vaccines are available but do not mitigate clinicals signs in all situations. Gilts can develop protective immunity through natural planned exposure after about 20 weeks of age and prior to 30 weeks when they may be bred.
Parvovirus infection in farms with antibody-negative pregnant animals will materialize as an increase in mummified fetuses. This is typically observed in young parity animals, Parity 1 and sometimes Parity 2 litters, depending on who has been exposed in the farm previously to parvovirus. These mummified fetuses will be varying in size as that virus moves intra-uterine, infecting fetuses at different points in gestation.
Another virus that has long been recognized but only recently named (2015) is atypical porcine pestivirus. This virus is described to be the causative agent of "shaker pig syndrome" or "congenital tremors," where young parity litters will farrow piglets with intentional tremors. This virus is relatively widespread in the industry, though not all farms display clinical signs. Similar to parvovirus, Parity 1 and some Parity 2 litters may farrow litters of pigs with varying degrees of tremors. Some are slight, some are severe enough that the individual piglets cannot suckle. The tremors are called intention tremors, observed when the pigs are trying to move or suckle. You do not observe these tremors while the pigs are sleeping or resting.
Think of the immunity and exposure similar to parvovirus. Adult animals infected do not show clinical signs but seronegative animals infected during gestation will have piglets with clinical litters. Similar to parvovirus, if we can expose gilts to this virus prior to pregnancy, we generally will not observe clinical signs in piglets. To date, there is no commercial vaccine available for APPV.
It is difficult to measure success of NPE, so you will hear varying number of protocols for how to best accomplish this. Our goal is to be successful and simple, so we don't induce drift in the process.
Materials that have high infectious levels of parvovirus:
- Feces or environment from animals that have recently been infected. Focus on recently exposed gilt groups.
- Traditionally, farms collect material from Parity 1 litters, assuming there is some shedding of virus in a stressed animal. This includes mummified fetuses, sow feces, placenta. When polymerase chain reaction testing this material, we variably will find parvovirus PCR-positive tests.
Materials that have high infectious levels of atypical porcine pestivirus:
- Shaker pigs will have the virus throughout most tissue types. It is easiest to harvest all internal organs from shaker pigs. If the farm does not have many shaker pigs, then harvesting internal organs from Parity 1 litters appears to keep these farms in check.
Monitors should continue to collect this material over time as they observe it in the farrowing house. Put that material in sleeves and throw it in the freezer for the gestation team. Grinding it can help with releasing virus from the material to improve exposure.
Most NPE is done between about 22 and 28 weeks of age, after maternal antibodies wane and prior to breeding. There are various protocols regarding the amount of material and a number of exposure events. Most commonly, gilts are exposed multiple days in a row in order to ensure exposure, such as three days in the same week. Exposure in a gilt developer can be difficult due to lack of a trough or solid flooring for spreading out the NPE material. Typical tools are utilizing sections of gestation trough and removing those from the pens when not in use, spreading material on the slat seams so you have an 8-inch solid area, utilizing rubber mats or wean-to-finish mats to feed on, or utilizing ice blocks of NPE material and exposing in the pens. We don't have to get 100% of the animals infected with NPE. If we can get some infected, it should shed and spread to the rest of the group.
NPE is a necessary process for some of the known viruses in which commercial vaccines are not available or do not provide complete protection. There are still areas the NPE process that we do not understand, as gilts are being exposed to much more than these two viruses. Improvement in diagnostics continues to let us better understand pathogens that are in NPE and the gilt's immune response. Remember to design a process that has low risk of drift — explaining the who, what and how to consistently execute NPE.