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Strategies for preventing disease entry

(166) These need to be simple, practical and cost effective in meeting the objectives. At the onset there is no one method that can be adopted across all farms because of different organisms, herd sizes, facilities and breeding policies. However ground rules can be considered in conjunction with the information given in Fig.4-6. These will help to establish the best methods for your herd.
  • Monitor the reproductive performance and health of the breeding stock as a guideline to success.
  • Always buy replacement stock from the same source if possible and one with good biosecurity and health documentation.
  • Determine the required isolation period.
- No isolation You are at the mercy of the donor herd. Diseases such as PRRS and enzootic (Mycoplasma) pneumonia (EP), have long incubation periods and they should at least be present in the recipient herd. Many farms adopt this strategy and introduce stock quite successfully. Sometimes it is necessary to medicate the feed with 300-500g/tonne of CTC or OTC or 100g / tonne tylosin over the first 3-4 weeks of introduction to suppress any development of disease.

- 21 days complete isolation - Allows for a check (albeit short) to see that no diseases are incubating in the donor herd. Pigs can be blood tested during this period. Not recommended if EP or PRRS are absent in the recipient herd as at least 56 days are required.

- 21 days on farm isolation - It may be necessary to medicate in-feed during this period. Pigs can be blood tested but 21 days may be insufficient for some diseases.

- 56 days complete isolation - This is necessary for herds believed free of enzootic pneumonia and PRRS. Sentinel pigs from the recipient herd can be slaughtered and tested as well.

- 85 days complete isolation - This is an extended period advocated by some veterinarians to allow time for PRRS negative animals to become infected and ultimately become non viral excretors. This is particularly so when live vaccine is used in countries where it is available. Live vaccines are not available in some countries and therefore do not complicate procedures such as the introduction of new strains of virus.

Age of incoming animals
Traditionally this is around 180 days to allow 6 weeks of acclimatisation prior to mating although weaner gilts (30kg weight) are becoming more popular. PRRS has created major problems particularly if negative gilts are introduced directly into positive herds. Three site production by breeding companies also reduces the availability of PRRS positive animals. The age when gilts are purchased may drop to 28 days to allow for prolonged PRRS exposure.

Experiences in the UK and in Europe confirm that the introduction of pigs either naturally exposed to enzootic pneumonia and PRRS or negative to both these diseases (enzootic pneumonia vaccinated) can be successfully integrated into similar herds, by adopting suitable isolation and acclimatisation protocols.

Suggested procedures
(Discuss these with your veterinarian)

Procedure A - High health status pigs to a high health status herd (indoor or outdoor).

Typical example being. EP, PRRS, Actinobacillus pleuropneumonia (APP) negative in both donor and recipient herds.

  • Weight of gilts 25-95 kgs.
  • Complete isolation required for 8 weeks with no farm contact.
  • At the end of the first 7-10 days introduce sentinel weaner pigs 8-14 weeks of age either directly into the gilts or provide nose to nose contact. 1 sentinel (minimum of 5) per 4 gilts is advised.
  • At the end of 8 weeks the sentinel pigs can be slaughtered and examined for disease.
  • The group can be tested for EP, PRRS and other specified diseases.
  • Check with the donor herd that pigs can move into the herd.
  • When all is clear introduce the gilts to the service area.
Procedure B - High health status pigs to a lower status herd

Typical example is EP, PRRS negative pigs to an EP, PRRS positive herds

Indoor herds

  • Vaccinate all incoming breeding stock 6 weeks and 4 weeks and again on entry to the herd against EP and other diseases as required during isolation. If PRRS vaccine is considered safe to use, the isolation period will need to be extended.
  • Age of gilts 12-24 weeks.
  • Complete isolation or on farm isolation. Direct integration is not recommended.
  • At the end of 7-10 days isolation introduce challenged weaner pigs (EP, PRRS +ve) 8-14 weeks of age as for Procedure A.
  • If PRRS vaccine is not used medicate the feed with 300-500g/tonne of oxytetracycline or chlortetracycline or 100g / tonne tylosin for the first 5 weeks of isolation or as advised by your veterinarian. Medication may or may not be required.
  • Blood sample 50% (minimum of 5) of the gilts in week 7.
  • Check sentinels at slaughter if post-mortem examinations are required.
  • Check with the donor herd that the pigs can move into the herd
Outdoor herds

  • Weight of gilts 25-90 kgs.
  • Because the exposure to respiratory organisms is low, medicated feed is not usually required.
  • Vaccinate for EP as for indoor herds
  • Mix challenged weaner pigs into the group whilst in isolation as for indoor herds. It may be necessary to change these pigs after 2 weeks.
  • If PRRS vaccine is used then a 12 week total isolation must be considered.
  • Blood sample gilts for PRRS in week 7 in one batch to establish the success of the system.
  • Move gilts to the service area.
Procedure C - Normal health herds

Typical example being EP, PRRS positive pigs to Normal Health herds also EP, PRRS positive.

  • Age of gilts 30-95 kgs.
  • Isolation on farm or direct integration. The former recommended.
  • Incoming gilts are best vaccinated for EP although they should have been exposed.
  • Hold in isolation or a pen for 7 days.
  • In-feed medicate on arrival as in Procedure B for 5-6 weeks if required.
  • Introduce challenged weaner pigs after 7 days or if integration is direct, expose the gilts to the grower house environment for 20 minutes on two occasions, 5 days apart.
  • Blood test the first group through the system to assess the PRRS status at 7 weeks after entry.
  • If PRRS vaccine is used total isolation for 12 weeks is required.
If the programme does not seroconvert gilts or boars to PRRS, exposure procedures need to be intensified by rotating weaner pigs more frequently. Expose animals to the infected environment for longer and more frequent periods.

Gilts should remain in their isolation pens for the full 8 weeks. In countries where live vaccine is used gilts are totally isolated for 12 weeks to prevent excretion of the vaccine virus into the herd. In some breeding herds the use of vaccine has been associated with severe disease and its use in any case may not be advised for risks of incompatibility.

Checklists for the health of your gilts
Assess health and disease. Do you have?:

  • Variable growth
  • Coughing
  • Evidence of rhinitis
  • Mange
  • Pneumonia
  • Lameness and stiffness on movement
  • Failure of the gilt to stand to the boar - Osteochondrosis or leg weakness
  • Poor feed intake or an incorrect diet.
Provide good nutrition
The methods of feeding the gilt and the composition of the diet will depend on the genotype. They will also depend on the environmental needs of the gilt relative to housing, temperature and insulation of the buildings. To determine the best system requires a degree of trial and error on the farm - the objective being to produce the second or third oestrus cycle within a predetermined time span so that the service programme can be accomplished satisfactorily.

Key points to success:

  • Gilts should arrive on the farm at approximately 85kg and be fed a dry sow diet until 100kg. This will also allow time for acclimatisation.
  • It is necessary to increase backfat in the modern genotype to 18-20mm at the P2 measurement. This is best carried out feeding a low lysine ration, such as that contained in a sow breeder ration (13.4MJ DE/kg and 0.8% lysine). Feed to appetite.
  • Approximately 2-3 weeks prior to moving into the service area for mating ad lib feeding should take place. This is to maximise ovulation rate. Use a good lactator or grower diet containing 14MJ DE/kg and 1 % lysine.
  • Low protein, low energy, or poor quality diets in the period leading up to puberty will often produce a deep state of anoestrus that in some cases is permanent. Assess the response to the diet used.
  • Do not leave gilts in a finisher house to point of service, many will never cycle and nutritional requirements may not be satisfied.
Satisfy the gilt's physiological needs
Oestrus should commence from approximately 165-200 days of age. Movement from one pen to another with close boar contact provides the greatest stimulus.

Key points to success:

  • Age at puberty is dependant on breed. Pure breeds are often slower coming into oestrus.
  • House a vasectomised boar in the group.
  • The major chemical substances that stimulate oestrus are pheromones found in boar's saliva and in preputial secretions. These are more powerful in old boars, however make sure they cannot mate.
  • Provide direct pheromone contact.
  • Rotate boars to give a different contact every 7-10 days.
  • Provide a dry, warm well lit environment. Would you be comfortable in your gilt housing? If so, then it will satisfy the gilt.
  • Provide 14 hours of good light (you should be able to read a newspaper in the darkest corner).
  • Wherever possible always move gilts to the boar for contact.

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