Pig Health Featured Articles
Depopulation: The importance of doing it properly
By DuPont Animal Health Solutions - There are now a number of programmes for eliminating diseases from pig units but they are doomed to failure unless the pathogens are eliminated from the unit as well as the animals.
Work by the MLC shows the cost of disease on a typical UK pig farm runs at approximately £200 per sow per year, or £9.81 per pig produced. It is not surprising that the elimination of diseases from a pig farm has become a major part of the producer and veterinarian's armoury. Many programmes have been devised, but in recent years the most successful include the elimination of PRRS, Enzootic Pneumonia, Actinobacillus pleuropneumonia, Aujeszky's disease (Pseudorabies), Swine Dysentery and Mange. In each of these biosecurity has an integral role to play, and failure of the biosecurity part of the programme will inevitably mean failure of the whole programme.
The target of any disease elimination programme is to eliminate economically important diseases from the pig unit. Often we are trying to eliminate one disease but can also eliminate others - e.g. in a partial depopulation and medication programme using Tilmicosin (Pulmotil™ - Elanco) to eliminate Enzootic pneumonia and APP we might easily eliminate PRRS (especially if we vaccinate at the same time), Mange (via appropriate treatment) and we are likely to reduce the impact of PMWS, Salmonella and Ileitis.
These are extremely powerful techniques and are ones we will use increasingly in the future. First we seek to eliminate the pathogens from the animal (by depopulation, by management changes, by strategic medication / vaccination or most commonly by a combination of these).
At the same time we must eliminate the pathogens from the unit by terminal cleaning and disinfection. If we fail to do this well enough the animals will become re-infected. Finally by continuous biosecurity, we must prevent the unit from becoming re-infected.
Elimination of Pathogens from the Animal
Elimination of the target pathogens from the animal can be achieved by various means. First we can depopulate and replace the pigs with ones known to have come from a free source. Prior to repopulating it is necessary to apply a thorough terminal disinfection programme to remove any pathogens that may be left in the unit. This is the most broad-spectrum disease elimination, only limited by our ability to thoroughly clean up and disinfect the unit and our ability to prevent re-infection through continuous biosecurity.
Secondly we can partially depopulate the unit. The aim is to remove actively infected and/or shedding animals and retain stabilised immune animals that will not shed the relevant pathogens. Biosecurity becomes important in removing the remaining pathogens from the depopulated area. The most common partial depopulations at present are combined with strategic medication to remove the specific bacterial pathogens from the retained animals. (e.g. The Tilmicosin procedure mentioned above, or Valemulin programme to eliminate Serpulina hyodysenteriae).
We can eliminate pathogens by medication/vaccination programmes without depopulation. An extreme example would be the swine dysentery programme mentioned above, which can be carried out successfully without depopulation but with some movement of pigs and very high levels of internal biosecurity. A variation of this approach would be the elimination of a pathogen by a combination of testing and removal of affected stock, usually combined with a vaccination programme (e.g. programmes for Aujeszky's Disease / Pseudorabies).
Next we can eliminate pathogens by management changes aimed at stopping re-cycling of pathogens. The best example of this would be a change from continuous population of a building/farm with finishing pigs to an All-in, All-out system. Again terminal disinfection would be an essential part in preventing the carry-over of pathogens from one batch to the next.
Terminal Disinfection
Terminal disinfection can be divided into stages.
Dry Cleaning:
Remove all movable equipment and dry clean the inside of the building/housing using mechanical scrapers, brushes shovels and forks and dispose of all soiled bedding and refuse in accordance with local authority or governmental guidelines.
All equipment removed from the building must be thoroughly cleaned (DAHS Biosolve™ at 1:100 leave 20-30 min), rinsed with clean water and then disinfected (DAHS Virkon® S at 1:100).
Building Pre-cleaning and Sanitising:
Apply a heavy duty cleaner (DAHS Biosolve™ at 1:100) to all internal surfaces at low pressure and leave for 20-30 minutes to penetrate and loosen dirt and muck before washing down at high pressure with clean water. Allow to dry thoroughly. In most programmes the slurry system will need emptying and treating in the same way.
Water System Sanitisation. Clean gross deposits out of tanks etc., then apply a suitable disinfectant such as DAHS Virkon® S. Allow it to run through the system, leave for up to 1 hour then drain through all drinkers. Ensure that drinkers do not become blocked.
Cleaning and Disinfection of moveable equipment. Soak and then spray with DAHS Biosolve. Then pressure wash clean, paying special attention to inaccessible areas, e.g. food hoppers, and caked on deposits. Move to a clean area and disinfect.
Disinfection. This is necessary because even with the best cleaning, the level of pathogens remaining will pose a risk to the next batch of pigs. Use a broad-spectrum disinfectant such as DAHS Virkon® S active against viruses, bacteria, fungi and other pathogen organisms. Ensure the disinfectant is thoroughly applied to all surfaces at the advised levels. Allow to dry.
Continuous Biosecurity
The aim of continuous biosecurity in disease eradications is three-fold. Firstly we want to prevent pathogens entering the unit during a programme. Secondly in programmes which involve a period where there are clean and dirty areas of the unit we need to prevent spread of infection from one area to the other. Finally we want to prevent re-infection of the unit after the programme is completed.
The perimeter of the site must be secure. If there are clean and dirty areas they must be clearly defined and the boundary secured. Access of visitors, vehicles and animals must be totally controlled. Staff and visitors need to change overalls and boots on entry (possibly after showering). Footdips must be used at the farm entrance, the entrance to all buildings and between areas. Boots must be clean before dipping. Vehicles must be clean prior to arrival and must pass through a disinfectant wheel dip or spray. Loading bays with correct operating protocols are needed.
Moving of equipment around the unit should be minimised. If movement is essential thoroughly clean and disinfect. Water systems need sanitising. Aerial disinfection can reduce cross-infection especially where animals of different statuses are present. Sows can be washed prior to entry into farrowing. Rodent control is especially important as rodents can carry many diseases. A thorough rodent elimination programme is needed before starting any disease elimination programme.
| Activity of DAHS Virkon® S against pathogens mentioned in this article | ||
| Agent | Virkon-S Activity | Test Country |
| PCV2 | 1:100 | USA |
| Aujeszky's Disease (Pseudorabies) Virus | 1:100 | USA |
| PRRS | 1:700 | UK |
| Lawsonia intracellularis (Ileitis) | 1:100 | Scotland |
| Serpulina hyodysenteriae | 1:400 | Scotland |
| Salmonella spp. | 1:100 | USA |
| Mycoplasma hyopneumoniae | 1:800 | UK |
| Actinobacillus pleuropneumonia | 1:200 | UK |
To ensure regulatory compliance in your country please read the label carefully.
For more information about vehicle disinfection programmes using world-leading products, such as DAHS Virkon® S, visit the DuPont Animal Health Solutions website, the largest biosecurity website resource in the world at www.ahs.dupont.com
Source: DuPont Animal Health Solutions - February 2005
