Prevention and control of infectious diseases in pigs: management comes first

The new pig diseases that have emerged force us to re-evaluate existing production systems. If there is no vaccine, improved management methods must be used to control the disease; even with a vaccine, control may still fail without management. This article provides some basic methods to help pig farms adopt suitable approaches to control infectious diseases according to their own situations.

Goals of disease control

It must be clear that the goal is to "control" the disease, not yet to eradicate it. Overall, control measures usually reduce the pig population in a reasonable way to cut off transmission routes and properly disinfect equipment.

Partial elimination is achieved by interrupting farrowing, which creates a "bubble" that can move through the system; complete eradication of the virus within a farm is possible only in small groups.

Transmission of disease

It occurs through direct contact between pigs, nasal secretions, saliva, feces, and urine; pens used for long-term rearing carrying disease; vertical transmission through the placenta during gestation, with newborn piglets carrying disease; movement of pathogen-carrying pigs within the farm or introduction from outside, such as mechanical transmission (vehicles, equipment, shoes, clothing), carriers (insects, rats, mice, birds), airborne transmission, wild animals, and insemination with semen from infected boars.

Principles of disease control

Whichever control method is used, strict biosecurity procedures are essential to prevent the entry of disease, such as transport (pigs, feed, bedding), protective clothing for visitors, sources of feed and bedding, water supply, food for carrier personnel, and disposal of dead animals. The principles of disease control include the following:

Adequate isolation facilities must be established: pig farm construction must be far from residential areas, major roads, and so on; there must be enough space to raise replacement breeding pigs on an all-in/all-out basis; management personnel must not work in the production area; breeding stock must be purchased from high-health units, kept isolated from disease-infected herds, with a minimum isolation period of 63 days.

The most important control method is to stop or at least limit the spread of disease within the farm. To achieve successful control, the farm's management standards must be raised. There are four "golden principles": limit contact between pigs; "stress" is a killer; good hygiene conditions; good nutrition.

Limit contact between pigs: disease can spread through contact between pigs, and limiting contact can reduce the prevalence of disease. Contact between pigs may be indirect. Injections, surgical tools, instruments and equipment, feces, personnel, and carriers (flies, rats, mice, birds).

Stress is a killer: stressed animals get sick easily; exposure to microorganisms places major pressure on the immune system, and if the immune system is overloaded, bacteria and viruses may cause disease; if a measure will cause stress to pigs, consider whether other methods that cause less stress can achieve the same purpose.

Good hygiene conditions: nothing can replace good hygiene and biosecurity measures; cleaning and disinfecting buildings will produce results; prevent needles and other tools from spreading disease.

Adequate nutrition: good nutrition is not only needed for growth, but also plays an important role in the development of the immune system; colostrum provides protective capacity and prevents piglets from being infected by diseases already present on the farm; ensure piglets receive as much colostrum as possible within 12 hours after birth; provide high-quality feed, especially providing high levels of antioxidants in weaned piglet feed, which helps strengthen the immune system.

Management methods that must be adopted

All-in/all-out system: sources of infection can spread between pigs; the all-in/all-out system prevents this risk; it can be applied to each stage of each cycle, such as farrowing, weaning, growing, and fattening; there must be no crossover between batches throughout the system; pigs that do not meet standards must not be retained and mixed into the next batch; staff must follow the flow of animals.

Batch production: due to housing limitations, the traditional weekly production model often makes it difficult to achieve the batch isolation required by the all-in/all-out system, so switch to batch farrowing so that each batch can be large enough; a system with one batch every 3 weeks has proven effective: the larger the number in each batch, the easier it is to achieve batch isolation; it conforms to the natural rule that sows have one estrous period every 3 weeks, making management easier; a 21-week production cycle, with piglets weaned 4 weeks after birth, is relatively ideal. It facilitates detailed weekly division of labor, such as: service, farrowing, weaning, cleaning, and disinfection.

Limit mixing of pigs to the greatest extent possible: mixing increases contact between pigs and puts them in a tense state; when possible, keep pigs grouped unchanged from weaning to fattening; wean piglets on the same day and keep each litter as a small group; if pigs from different litters must be mixed to form larger groups, minimize the number of litters; keep growing pigs/finishing pigs always in the same small pen; it is best to achieve the desired group size by dividing each group into small groups rather than by mixing pigs; pigs in the same group should enter the fattening period at the same time, and groups may be subdivided to adapt to housing; do not mix groups to increase group size; eliminate mixing between different batches in every part of the system.

Strictly implement cleaning and disinfection procedures: most sources of infection survive in organic waste; if pig pens are not completely disinfected, disease will be passed to the next group of pigs; clean and disinfect immediately after pigs are moved out; soak with water so that organic matter is easy to remove, then after washing, clean with detergent and rinse, and allow it to dry completely before moving in the next batch of pigs; place footbath disinfection pools at every entrance.

Manage colostrum well at farrowing: it is best for piglets to have good colostrum intake within 6 hours after birth. Some sows may not have antibodies, so consider "fostering" techniques, that is, exchanging piglets within 6 to 12 hours (newborn piglets must be fed at least once from their biological mother).

Stop fostering 24 hours after birth: antibody absorption stops after 24 hours; fostering after 24 hours may help spread viruses and should be avoided as much as possible.

Solid separation between pens: open separation makes indirect contact between pigs likely; it makes transmission of pathogens likely; change open separation between pens into solid separation.

At weaning, keep pig density in the barn low: the lower the density, the less stress on pigs; less stress is equivalent to good health. Recommended density: from weaning to 22 kg, 0.3 sq m per pig; growing to 50 kg, 0.6 sq m per pig; fattening, 0.75 sq m per pig.

Increase feeding points: if piglets fight over food, stress increases. Increasing feeding points reduces competition for food; each weaned piglet should have at least 7 cm of space, and even larger pigs must be guaranteed sufficient feeding space so that they can all eat at the same time.

Good nutrition: feed intake usually declines at weaning, increasing stress; the improvement of the immune system requires a good nutrient supply; provide high-quality feed after weaning to reduce stress caused by weaning; frequently renew feed and keep it fresh; ensure clean water is easily available at all times. If you would not drink such water, why ask pigs to drink it?

Improve temperature and ventilation control: cold causes stress and lowers immunity; reduce temperature variation in the pig's living environment; maintain the optimum temperature for pig life; ensure the appropriate temperature for newly weaned piglets. Improving ventilation in the barn helps reduce irritation of the respiratory system by harmful gases. Recommended maximum levels: ammonia 10 ppm, carbon dioxide 0.15%. Eliminate cold drafts and irritating air currents; reduce dust.

Limit the number of pigs in each group: the fewer pigs in a pen, the fewer opportunities for disease transmission between individuals; it is recommended to keep each litter as one group; if pigs from different litters must be mixed to form larger groups, keep principle 3 in mind.

Do not clip teeth at weaning: is it necessary to clip teeth? It may only serve to spread disease.

Strictly implement hygiene measures: ensure good hygiene standards during injections and tail docking, change needles between different litters, and disinfect instruments between different pigs; when using many tools, place them all in a disinfection tray for rotation; keep barns independent; use footbath disinfection pools; each barn should use its own equipment.

Establish rules for sick pigs: the longer a sick pig stays in the pen, the greater the chance other pigs will be infected; establish a policy for sick pigs and persist with it long term; move them quickly to isolation pens for treatment. How long until recovery, and when to euthanize.

Handling dead pigs: do not place them around the barns; before disposal, place them far away from the barns.

In short, to prevent new infections from being brought into the herd, strict biosecurity procedure programs are needed. Introduce breeding stock from high-health units; the better the health status of a herd, the smaller the impact of new diseases in the herd. To successfully control disease, a high-standard management system must be implemented. Keep the four principles in mind: reduce contact between pigs; stress is an important killer; good hygiene; good nutrition.