Use of diagnostic assays in aggressive management of commingled swine production systems

Matt S. Anderson, DVM

Suidae Health and Production, 2200 Hwy 18 East, Box 591, Algona, IA 50511; Tel: 515-295-8777; Fax: 515-295-4954; Cell: 515-341-8777; E-mail: matt_Anderson@suidaehp.com.

Anderson MS. Use of diagnostic assays in aggressive management of commingled swine production systems. J Swine Health Prod. 2003;11(4):193.

It is difficult to imagine life as a swine veterinarian without cell phones, hand-held personal digital assistants, laptops, spreadsheets, and record-keeping systems. Advancing technology often seems to lead us more into the conference or board room and farther away from actual pig farms. However, the value in knowing what is happening in the populations of animals that are our patients is unmistakable, and the timely acquisition of this knowledge is more critical than ever. Serological and polymerase chain reaction (PCR) tests are excellent means of acquiring the necessary information. Aggressively using these diagnostic tools may have the added benefit of getting us on farms more often, creating the opportunity for us to interact with farm personnel and diagnose and resolve little problems before they become big problems.

We all have had multiple opportunities to witness the suboptimal performance that we have come to expect when animals of divergent health status are commingled, especially in continuous flow production systems. This has driven the evolution of the swine industry toward single-sourcing pigs into all in-all out facilities, which usually improves mortality rate and total removal, and optimizes performance. The economic downside of this strategy is that facilities are often managed inefficiently during stocking and marketing: facilities cost (on a per head basis) increases, and throughput for the system decreases. There may be the additional disadvantage of higher transport costs when partial loads of pigs are moved over long distances. This has become very significant in many production systems as the distance between sow farm and nursery-grow-finish facilities has increased. Weaning once a week overcomes the difficulty, but this of course creates efficiency problems in our sow units.

Logistical considerations often make commingling pigs appealing. Economic pressures dictate that, if we are to be successful, we must manage these facilities very carefully. Diagnostic assays may be used in numerous ways to benefit producers (and pigs) in commingled pig flows. Several specific examples are described below.

When managing the commingled pig flow from multiple sow units naive for porcine respiratory and reproductive syndrome (PRRS), knowing as soon as possible when a unit becomes infected with PRRS virus allows the pig flow from the unit to be redirected such that most of the pigs remain healthy. In my experience, it is possible for a previously naive sow farm to be serologically PRRS-positive for as long as 4 to 6 weeks before clinical signs are observed. Analyzing sow serum by PRRS ELISA (Herdchek ELISA; Idexx Laboratories, Westbrook, Maine) or by PCR or both may give us a time advantage to redirect the pigs from an infected unit away from the commingled, PRRS-negative pig flow. The tests may also be done in weaned pigs.

It is sometimes equally beneficial to get a PRRS-stable (non-shedding) sow farm's pigs out of a commingled PRRS-positive flow. Prior to redirecting these pigs back into a PRRS-negative flow, it is important to test by PRRS PCR several times in successive weeks to be sure that the sow farm is truly stable. When PCR testing is used in this manner, reducing the number of samples in a PCR pool may help to avoid a problem with false negative results.

Swine influenza may be a considerable problem in commingled pig flows. Many veterinarians use swine influenza virus (SIV) titers to analyze vaccination protocol compliance, testing either weaned pigs or sows.

In pig flows where mycoplasma is expected to have a detrimental effect on performance, longitudinal serology profiles for PRRS, SIV, or both may be used to determine the timing of vaccine or medication administration.

There are many other examples where aggressive use of serologic assays may be of great benefit to producers. Statistical charts may be used to derive sampling numbers appropriate to given situations. Bleeding pigs isn't glamorous, but as a means of acquiring timely epidemiologic information, it is critical to serving our clients.