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Background

During the past six years, as PRRS virus has become more widespread, there have been significant changes and a deterioration in disease profiles in many herds. The major long term effects of these changes have been seen in disease patterns in weaned, growing and finishing pigs. Between 1984 and 1996, there has been a significant deterioration in levels of health particularly associated with the appearance of Porcine Reproductive Respiratory Syndrome (PRRS) in 1991 and its effects on Enzootic Pneumonia and Actinobacillus pleuropneumonia.

The appearance of PRRS also highlighted the low-grade endemic infections that were already present in many herds, particularly those involving the respiratory system. Chronic respiratory disease has become a major limiting factor to profitable pig production. A survey of 163 indoor herds in 1996 showed over 90% to be infected with swine influenza and enzootic pneumonia and 72% of herds also infected with PRRS. Streptococcal meningitis was recorded in 22% of herds but only 9% of herds appeared to have problems with Actinobacillus pleuropneumonia. From 1996 however the incidence increased significantly. More alarming was the fact that 27% of herds were affected with chronic endemic respiratory disease. The combination of segregated disease control (SDC) (described later in herd 2 in this paper) combined with mycoplasma vaccination and controlled pig flow has dramatically improved the health status, post weaning mortalities and feed efficiency in many herds since 1997.

Key factors that affect disease levels

It is important to appreciate the factors that affect the levels of disease in any one herd. These can be grouped into six distinct, but inter-relating entities. First, the presence of primary pathogens causing respiratory and enteric diseases and if these are active in the herd, then the disease(s) will also be present at a varying level. Second, the severity of disease is dependent upon the organism itself, the numbers that the pig is exposed to at any particular time and the degree of pathogenicity.

The third and perhaps little considered factor in breeding/finishing farms is the presence of many different bacteria, viruses, fungi and other agents that permanently reside in a continually populated pig house. In themselves, they may not produce disease but are responsible for several secondary infections. The significance of this is highlighted by the improvements that can be achieved by converting the pig flow system into all-in/all-out procedures, or the significant advances by adopting three site production methods and SEW (2).

The fourth and a most important factor, is the influence of the management of the system and the control of the environment. Permanently populated houses with varying ages of pigs continually entering and leaving will invariable result in high levels of pathogenic organisms being perpetuated in the environment that result in chronic endemic diseases. The total removal of these organisms (and pigs) from the environment at the onset of SDC is a vital component of its success.

The age structure of the herd, in particular the proportions of young breeding animals to older ones, determines the levels of infectious agents exposed to pigs at a young age. The age structure of the weaned and growing herd is also important as maternal antibody drops and pigs become exposed to pathogenic organisms. The continual introduction of breeding females may also influence health status and in particular disrupt breeding herd stability in respect of PRRS.

The final factor affecting the prevalence of disease is the level of immunity received by the pig through colostrum and the time when it first becomes exposed to disease. An appreciation of this latter fact, is embodied in segregated early weaning (SEW) and 3 site production and its adaptation through SDC.

Methods of controlling disease

These are highlighted below and can be grouped into three areas, although many control programmes will involve parts of each. Freedom of herds from specific pathogens has been a method of control used for the past 25 to 30 years. The major epizootic diseases such as Swine fever, African swine fever, Swine vesicular disease and Pseudorabies, are in most countries controlled by slaughter policies or eradication programmes. At an individual herd level, freedom from a number of specific diseases can be maintained for a considerable period of time. Such diseases would include Enzootic pneumonia, Actinobacillus pleuropneumonia, Mange, PRRS, Atrophic rhinitis and Swine dysentery.

However, even with the most extreme precautions, a number of diseases may still be present or introduced in a high health herd. These would include; Glässer's disease, Proliferative enteropathies and Ileitis, Streptococcal meningitis, PRRS and Enzootic pneumonia. Most herds will contain one or more pathogens if the farm is in a pig dense area. It is necessary therefore to consider alternative disease strategies to SEW and 3 site production particularly in the UK and some European countries because pig densities are high and landmasses are small. Weaning also is not allowed under 21 days on welfare grounds which dilutes the advantages of weaning at 10-14 days of age.

Respiratory disease and methods of control

The following outline the options for controlling respiratory diseases, some which are obviously dependant upon the location and circumstances of the farm.

Disease freedom:

• National basis
• Individual herd level
• Maintenance of freedom

Disease eradication:

• Depopulation and repopulation
• Medication
• Medicated early weaning
• Vaccinate/test and removal
• Segregated early weaning (SEW)
• 3 site production
• Segregated disease control (SDC)

Disease control:

• Medication
• Vaccination
• Management
• Segregated Early Weaning (SEW)
• 3 site production
• Segregated disease control (SDC)

Eradicating disease

This can be achieved on a herd basis, either by depopulation and repopulation with disease free stock or the application of eradication techniques to an existing permanent population. In the latter, a combination of medicines, vaccines and management manipulation of pig flow are the criteria for success. Medicines can be used to prevent and control disease by strategic medication, that is, the application of the drug at a selective point in time just prior to the development of disease. Infections can also be suppressed by continuous or intermittent in-feed or water medication or by early weaning the pigs away from the sow and the infected environment together with medication.(MEW). Medicines can also be used to eradicate the disease organism totally and typical examples would be Swine dysentery or Mange. Economic pressures today however will not sustain herds with costly diseases or those that are antibiotic dependant for their control. Current control procedures of MEW (1) or SEW (2) have provided new advances in disease control and elimination. However in countries with intensive areas of production, such procedures are difficult to apply and maintain health status. In 1993 an adoption of SEW principles was applied to a combined breeding feeding herd (and many others since). This was called Segregated Disease Control (SDC)(3).

Segregated disease control

The principal adopted was to make a break in the disease cycle by weaning pigs to separate accommodation from the endemically infected and permanently populated houses on the farm and then to bring them back into the system after the complete removal of all pigs weaned to slaughter on the farm. There is thus no loss in production.

Detailed Procedures

Pigs at weaning are either moved into straw baled kennels under large Dutch barns or into outside weaner arcs or straw yards for 6 to 8 weeks or alternate buildings. During this period, whilst these pigs are segregated away from the endemically infected pigs, the latter are sold from the farm, ideally over an 8-week period. The segregated pigs are then returned into the cleaned disinfected houses. It is essential to totally depopulate the herd from weaned pigs through to slaughter before the segregated pigs are returned to the buildings. Prior to the pigs returning however, a study must be made of the pig flow and the mating programme. Buildings should be sectioned such that the system can contain each week's weaned pigs all-in/all-out. Most endemic infections remain on the farm because the weaned pigs enter infected environments, become infected and thus maintain the status quo. The objective of SDC is to "clean up the system" and then prevent droplet spread between batches as far as is practical. This maintains equality of immunity at age and dramatically reduces micro-organism challenge.


To establish whether this principal of segregated disease control would be of value, a simple experiment of moving pigs from an endemically infected herd (EP, App, PRRS, Flu) at approximately 24 days of age was carried out in 1993 (Table 1). A group of 128 pigs was moved into a clean straw yard with no other contact with pigs and the growth rates, feed efficiency and mortality were monitored. The significant advantages can be seen when the pigs were just moved from the infected environment, although they had still been exposed to EP, App, PRRS and Flu. Half these pigs were then returned to the farm and growth rates monitored.

The results were quite dramatic. The daily gain of the pigs being returned to the farm dropped to 540 grams per day compared with 899 grams of the straw yard pigs (Table 1). There was also a very significant difference of 0.58 in feed conversion efficiency (FE). It is important to note that these pigs were not early weaned.

After 49 days, half of the SEGREGATED Pigs were returned to the farm.

Field Applications of SDC

This small experiment was then tested in 1994 on a 230 sow herd producing slaughter pigs at 95 kilograms. This herd (numbered as 2 in the study) used continual production systems and was infected with the following diseases:

• Mange
• Atrophic rhinitis
• Actinobacillus pleuropneumonia types 3 and 8
• Enzootic pneumonia
• Swine influenza
• PRRS

Endemic respiratory disease had developed on the farm, to the extent that is was almost non-viable. The main problem area was the 1st stage weaner accommodation housing pigs from 4-8 weeks of age. There was a 5% mortality, 25% of pigs required individual treatment and all feeds were medicated with 500g Chlortetracycline. The owner would only consider total depopulation as a last resort and therefore in March 1994 SDC was adopted as an experiment. SDC pigs (designated "clean") were weaned into naturally ventilated straw based kennels at approximately 24 days of age. They remained there until 9-10 weeks of age and during this period of time, the infected weaned/growing pigs were moved to the finisher houses. The first stage accommodation was depopulated, totally washed with hot water and detergent, disinfected and then split into sections, to allow all in/all out on a weekly basis. The principle was to prevent droplet spread between batches. The results were dramatic with a significant drop in mortality and pigs requiring treatment and a marked improvement in health. This was maintained for 13 months. However when the "clean" pigs were moved into the infected finishing houses severe and worse disease developed. In April 1995 it was decided to repeat the SDC but apply it to both weaner/grower and finisher accommodation, due to the success of the initial attempt in the weaners. At the same time disease eradication/control was carried out in the breeding herd.

Disease Eradication/Control

Mange
The sow herd was treated topically with phosmet followed by Ivomectin (Ivomec) in feed for two ten day periods ten days apart. The segregated weaners were given Ivomectin (Ivomec) for 7 days post weaning during the sow treatment period. Mange was successfully eliminated.

Atrophic Rhinitis
The sow herd commenced vaccination in March 1994 twice 3 weeks apart and thereafter one month before farrowing. At the onset of SDC all breeding stock was treated with trimethoprim/sulpha for 14 days in-feed. Clinical disease disappeared and nasal sections showed no turbinate atrophy. Toxigenic pasteurella were however identified from nasal swabs in 14 week old pigs. No clinical disease has been seen subsequently (5 years to date).

Actinobacillus pleuropneumonia (App)
App types 3 and 8 had been isolated subsequent to PRRS infection of the herd with lung lesions at slaughter. After medication of the sow feed with trimethoprim/sulpha no other specific controls were adopted. No further clinical disease has been seen and no lesions detected at slaughter (5 years to date).

PRRS
Control procedures included strict all in/all out throughout the altered system. Special attention was given to the environmental and nutritional requirements of the pigs from 8 to 15 weeks of age. Whilst low levels of clinical disease have been evident intermittently, they have had little effect on the pigs. After each pen was cleaned and disinfected between batches, it was sprayed with disinfectant

Enzootic pneumonia (EP)
Five months after SDC in November 1995 an apparent breakdown of EP occurred which was mild and lasted for 6 weeks but with low mortality. It appeared that the SDC had produced a naïve population of growing pigs. Vaccinations using Suvaxyn Pig Vaccines (Fort Dodge) were commenced in piglets at 1 and 4 weeks of age. No clinical evidence of mycoplama infection has been evident since and only very small lesions detected at slaughter.

Results
The records (4) before and after SDC in the breeding herd are shown in Table 2 and in the grow/ finisher herd in Table 3.



In the breeding herd there was an improvement in fertility with farrowing rates increasing from 78 to 85% and as a consequence pigs reared per sow per year rose from 22.3 to 24.5. However this also coincided with a change to single natural matings and a change in management in the feeding herd. The improvements have been sustained over a 5-year period.

• Feed efficiency improved from 2.87 to a current figure of 2.18 (table 3) with average P2 backfat measurements of 10.1mm (0.4"). Mortality wean to slaughter dropped from 12.2% to 3.5%. (Currently 3.1%).
• Treatment levels dropped from a peak of 34% to 3% of pigs weaned and days to slaughter at 95kg improved by 24.
• The effects of vaccinating piglets at 1 and 4 weeks of age against EP and sows for AR in the herd has played a crucial role in health maintenance. Lung examinations have shown no evidence of App and few consolidating lesions indicative of EP.

From 1995 SDC methods have been adapted to over 30 breeder finisher herds from 200 to 600 sows (5). Procedures have included:

• Conventional SDC as described above
• Strict all in/all out policies
• Removal of the complete weaning/feeding herd off site for a 6-8 week period.
• Farrowing once every 3 weeks
• Vaccination of the piglet against EP at 1 and 4 weeks of age.

The above adaptations have given improvements in mortality in the herds studied ranging from 4 to 43%, reductions in medication costs ranging from 19 to 49%, improved feed efficiencies of 3 to 10% and daily gains of 1 to 9% (5).

Field experiences are outlined in table 4 showing diseases that can be controlled or eliminated by SDC combined with vaccination and medication.

In the UK weaning at less than 21 days is not allowed on welfare grounds. Furthermore because herds are often situated in close proximity to one another it is impossible to remain free of EP and PRRS. The UK strain of PRRS may be less pathogenic than US strains but very severe disease has been experienced in some herds. Weaning at a mean of 24 days maintains infections with Mycoplasma and PRRS.

Therefore, SDC allows such herds to remain infected or exposed, with minimal effects on economy of production. For the procedures to be successful the following points need to be considered:

• At what age should pigs be weaned?
• What diseases are to be controlled or eradicated in the breeding herd.
• What is the distance of segregated pigs from infected ones? Only droplet spread diseases will be controlled.
• Removal of both weaners and feeder at the onset.
• Adapt housing to all-in/all-out by each week's production.
• Consider farrowing every 2-4 weeks.
• Empty houses for 2 weeks.
• Wash down houses - use detergent
• Empty slurry channel or pits to the bottom.
• Disinfect with iodophor chlorine or peroxide based disinfectants.
• Control vermin
• Vaccination/medication.

Finally there is no loss of production in carrying out segregated disease control and field results show it to be another successful tool that can be adopted for long term improvements in health and production on breeder/finisher farms.

References

1. Alexander, T.S.L. 1982. The Establishment of new herds by medicated early weaning. Proc Int Pig Vet Soc 7:64
2. Harris, D.L. - 1988. Alternative approaches to eliminating endemic diseases and improving performances of pigs. Vet Rec. 123:422-423. - 1990 The use of isowean and 3 site production to upgrade health status. Proc Int Pig Vet Soc 11: 374
3. Muirhead, M.R. and Alexander T.J.L., 1997. In Managing Pig Health and the Treatment of Disease p 97. Publisher 5M Ltd, Sheffield UK. S35 OAF
4. Easicare Data Recording Systems 1998. Beverley, UK, HU17 OAA.
5. Kingston, N.K., 1998 New Approaches to Controlling Disease. 2nd International Congress for Veterinarians and Farmers. Eurotier, Hanover 1998

Further Reading

Further information on Segregated Disease Control and other topics such as two/three Site Production, Segregated Early Weaning (SEW), Medicated Early Weaning (MEW) and Modified Medicated Early Weaning (MMEW), can be found in our:

Pig Health Database....Simply click the link and conduct a search. To find all references to a search request select the "Full Text" check box by the Search button before you conduct the search.

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Below are some additional links to related topics that might be of interest.

Segregated Early Weaning
A thorough article explaining Segregated Early Weaning written in January 1999 by Allan R Carlson, DVM, Swine Health Center, Morris, Minnesota.

Should I Consider Segregated Early Weaning?
Swine Management: The use of Segregated Early Weaning, by Mississippi State University Extension Service.

Economic Advantages of Multiple-Site Production
An article looking at two-site production, three-site production, multiple-site production, and segregated production by Joseph F. Connor, DVM, Carthage Veterinary Service, Ltd., Carthage, IL 62321, Jerry Torrison, DVM, MS, PIC USA, Franklin, KY 42134

Feed Costs in Single Site Versus Multi-Site Production Systems
Pork producers owning single site traditional production systems have looked at the multi-site complexes, questioning whether their production methods are becoming obsolete. The article covers; Single Site versus Multi-Site; Performance of Multi-Site Production and 3-Site Production.

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