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Partial depopulation or segregated disease control

(88) This method applies the principles of SW but in the combined breeding/finishing herd. To start the system pigs are weaned for a period of 6-10 weeks into separate naturally ventilated straw based accommodation or outside farrowing arks. They should be far enough away from the endemically infected pigs to prevent droplet spread (>15m). The growing finishing herd of endemically infected pigs is either then totally depopulated or each house is emptied sequentially. The segregated pigs are returned in to the housing system without contact with the infected pigs if these are still on the farm.

This method can be applied to the breeding/finishing farm which cannot adopt a true SW system. If the farm has a problem with endemic respiratory disease it is first necessary to break the cycle. This is carried out by rearing the pig's into separate accommodation for a period of six to eight weeks or so, whilst the remainder of the pigs are sold off the farm. (Fig.3-44). Such pigs are weaned either within the farm perimeter or its surrounds depending on facilities, into either straw based kennels or outdoor arcs. They are not allowed droplet contact with endemically infected pigs in the existing houses and as far as possible are separated on a weekly basis. In practice the distance under natural ventilation need be as little as 15m and under fan assisted ventilation 35m.

A Dutch straw barn can make ideal temporary accommodation for housing the weaners. Each weeks weaners should be separated by walls made of straw bales (or outdoor arcs 15m apart). During the next 6 to 9 weeks as the endemically infected pigs are sold from the farm each house is depopulated washed and disinfected. Once the weaner to finisher accommodation has been emptied and cleaned (Fig.3-44 method 1) the segregated weaners re-enter the buildings.

Each building however must be split into sections, each to hold one weeks worth of pigs (or part) so that an all in, all-out management operation is established. This is important to its continuing success. The design and layout of temporary (or permanent) accommodation that can be used is shown in Fig.3-45 and Fig.3-46 and some farms with the availability of straw have continued to use this method very successfully.

Most combined breeding and finishing farms, even if established as high health herds, ultimately become infected with one or more pathogens. These become endemic due to the continual use and management of pig houses (Fig.3-47) with worsening feed efficiency, reduced daily liveweight gain and poor profitability. Furthermore when a pig is moved into a house already occupied with other pigs it is exposed for the first time to a new range of organisms, both pathogenic and non pathogenic. It is now recognised that this exposure, even though there may be no clinical disease, stimulates the immune system, with increased demands for energy and lysine and the result is poor growth. Segregated weaning systems break the cycle and production and health can be maintained by continuing SDC principles on the farm.

Infections of the respiratory tract seem to have the biggest adverse effect on efficiency of lean meat growth. This is probably because a disproportionately large portion of the body's immune cells are in or associated with the respiratory tract. Every time the pig breathes in air it inhales bacteria and viruses along with dust and toxic gases. The effect of this on a respiratory tract that is already chronically infected and diseased is to repeatedly stimulate the immune system to fight off the insult. The energy required for this is very high. It has to be derived from the pig's food to the deprivation of growth.

The respiratory tract is the main antigen sampler and immune stimulator of the pig's body.

To illustrate this a trial experiment was carried out on a breeding finishing farm where respiratory disease was endemic. 128 pigs were weaned at an average of 27 days of age and immediately moved off site to a clean straw yard with no other pig contact. 143 pigs were left on the farm as controls. See Fig.3-48. The growth rate differences were spectacular, a 16% improvement in feed conversion efficiency and a 74% improvement in daily liveweight gain (dlwg) at the end of 49 days. Half the healthy pigs were then returned to the farm where FCE became worse by 21% and dlwg by 40% over the next 48 days.

It is significant to note that the off site weaned pigs were still infected with enzootic pneumonia and PRRS.

SDC can also be carried out by building, instead of total weaner/finisher depopulation but the decision would depend upon the siting and distances apart of the buildings. Systems using SDC in pig dense areas would wean between 21 and 24 days of age. At these ages EP and PRRS will be maintained but other pathogens eliminated or controlled.

Factors to consider when adopting partial depopulation - SDC

  • Discuss with your veterinarian the disease profile on the farm. It should be possible to eliminate from the breeding herd the following diseases if they exist.
  • Mange - by medication. (See chapter 11).
  • Atrophic rhinitis - by sow vaccination after a six month period.
  • Severe pleuropneumonia - by preventing droplet spread, and vaccinating and medicating the sow herd.
  • Swine dysentery - by medication. (See chapter 9).
  • EP - will not be eliminated but it can be controlled effectively by vaccinating piglets at one and three weeks of age.
  • PRRS - may remain but its effects will be minimal with endemic diseases removed and a segregated all-in all-out system.
  • The weaning age could vary between 16-26 days depending upon the level of disease control required.
  • The SDC programme is best carried out during warmer months of the year.
  • All houses or sections of houses must be adapted for all-in all-out use.
  • All weaner and finishing pigs should be sold from the farm before the segregated weaners re-enter the building again. Pigs may enter the houses after they have been cleaned and empty for 14 days.
  • A study of the pig flow should be made to see if by better use of houses, greater control of the system can be achieved.
  • Allow a two week period between depopulation and repopulation of each house.
  • If a swine dysentery eradication programme is being carried out allow at least 4 weeks depending on disinfection procedures. (See chapter 9).
  • Consider batch farrowing to give better use of buildings.
Field experiences and the advantages of SDC
  • There is no loss in pig production and minimal loss in sale weight of pigs and cash flow.
  • Respiratory and enteric diseases can be controlled effectively.
  • Post-weaning mortalities have been reduced from 12 to 4% and maintained.
  • Continuous in-feed medication can be removed and only occasional strategic medication may be required.
  • Increases in daily liveweight gains of up to 22% have been achieved.
  • Buildings can be altered and maintenance carried out.
  • Significant improvements in health status can be maintained.
  • Mange, atrophic rhinitis, pleuropneumonia and swine dysentery may be successfully eradicated.
Successful systems have been maintained for at least 3 years. (At the time of writing).

SDC is an effective method of upgrading health status without total depopulation of the herd, which might not be advisable in a pig dense area.

Two site production

Traditionally, weaners have been reared to about 30kg on the same site as the dry sows and farrowing accommodation. However, the term "Two Site" in the present context implies that the piglets are weaned at three weeks of age to a second separate site where they are housed to slaughter weight. (Fig.3-49)

Aim: To produce healthy growers and finishers.

Here the breeding farm produces only piglets to weaning and moves these to a separate combined nursery and finishing farm.

The finishing farm would ideally have separate houses but more likely separate sections for each weeks supply of weaned pigs. To reduce droplet spread infections each house should be separated by at least 15m.

In this system it would be advisable to vaccinate pigs against mycoplasma pneumonia and wean between 16-24 days of age depending upon the disease status to be achieved. In the European Union routine weaning under 21 days is not allowed unless for health reasons.

Three site production

The sows and boars are on the first site where the piglets are born and suckled. They are then weaned to a second site and at 25-30kgs are moved to the third site for growing and finishing. (Fig.3-50)

Aim: To break the cycle of infection.

Here as the name implies the system is separated into breeding, nursery and finishing sites. The latter site can be further adapted by housing separation as in two site SEW to allow all-in all-out on a weeklybasis.

Co-operative production

Groups of producers can combine to take advantage of 3-site or multi-site production in many different ways including changing some farms to breeding only, some to nursery production and others to finishing..

Batch farrowing

Instead of farrowing weekly the mating programme is adjusted to farrow larger groups less frequently and thus wean larger populations of similar aged pigs. The segregated weaning principle then becomes easier to apply. Other advantages include better use of buildings, all-in all-out, greater attention to detail at farrowing and the more efficient use of AI. Furthermore pigs in the growing finishing periods can be fed more specialised diets along their growth curve.

Multi-site production

The sows are all on one or more sites where they farrow. On the same day of the week the piglets are all weaned away to an all-in all-out nursery where they are reared for seven weeks. In each successive week all the suckled piglets are weaned to different all-in all-out nursery sites. After 7 weeks the first nursery is emptied, cleaned and disinfected and refilled with young weaners again. There are thus 8 separate nursery sites. Each successive week when a nursery is emptied the 30kg weaners are moved to separate all-in all-out grower/finisher sites. There are 16 of these filled and emptied in rotation

Aim: To break the cycle of infection and maximise growth and feed conversion.

Effectiveness: This is very effective on a commercial basis for large scale commercial production. The all-in all-out system mitigates against the occasional leak of single pathogens coming through, however they will only affect one nursery site and one finisher site. Producers have made the mistake of mixing up SEW and SW, weaning too young.

Using this system a number of breeding farms may co-operate and supply piglets all of similar ages together on a week by week basis to the separate weaning units. See Fig.3-51. For it to be successful however the age at weaning needs to be tightly controlled and pigs of older age must under no circumstances be fostered backwards. They should be removed from the system. Furthermore if there is a disease outbreak such as TGE on one of the breeding farms the result can be disastrous.

The distances between breeding farm, nurseries, growing buildings and finishing houses should ideally be at least 3km (2 miles) apart to take full advantage of SEW. The closer to each other they are the greater the risk of windborne spread of diseases such as enzootic pneumonia, PRRS, flu and aujeszky's disease. However for droplet spread disease such as rhinitis, meningitis, pleuropneumonia and dysentery 500m is adequate but clearly the risk is slightly increased.

Single sow herd multi-site production

This principle is illustrated in Fig.3-52. There are eight separate nurseries holding pigs until 10 weeks of age. They are then moved to separate finisher accommodation each week, again all-in all-out. For this to operate in practice, the sow herd has to have at least 1500-2000 sows.

Multi-sites, and variations of it, have been applied successfully and on a large scale in the USA, Mexico and Chile and it is now catching on in the UK and Spain. It has the huge advantages of combining all-in all-out production by site with those of segregated weaning. Ideally it requires 45,000 sows in the combined first site if the sows are treated separately or 24,000 if they are not but effective systems can be achieved with fewer numbers. The development of outdoor sow herds to provides an ideal base for multi-site production.

The SW principle can be adopted with advantages to disease control in many different ways and that method best suited for the farming system must be identified.

It should be pointed out that SW is not a fool proof system and it can create considerable problems if there are a few piglets are carrying disease amongst a naive population. Typical examples would be mycoplasma pneumonia, actinobacillus pleuropneumonia or TGE. Streptococcal meningitis is not controlled by SW and serious outbreaks have occurred.

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