Figure 1. Typical isolation yard for gilts

Figure 2. PRRS is a big danger to incoming gilts

Figure 3. A warm dry bed is essential

Figure 4. Sunburn is a risk to gilts exposed for the first time

Maintaining a flow of gilt replacements into a breeding herd is integral to maintaining productivity. Across commercial herds, the replacement rates of breeding females can vary from 30 to 60 per cent in a year and the introduction of large numbers of gilts on a regular basis has the potential to disrupt the herd’s health either by introduction of new disease causing organisms or the introduction of gilts naïve to the organisms present on the recipient farm with which the gilts become infected and multiply. This can then tip over into the existing population, raising disease levels.

Given that replacement gilts constitute the future of the herd, careful thought, preparations, planning and execution are necessary to achieve maximum lifetime production and minimal health problems.

Whilst many of the comments in this paper refer specifically to the introduction of gilts from a third party farm, many of the later remarks are relevant to the home producer of gilts.

Health Status

Within the planning stage it is necessary to ensure that the incoming gilts match the health of the receiving farms as closely as possible. To achieve this, it is necessary to know the current health status of both farms.

In many cases the receiving farm’s health status will be known to the herd’s veterinary advisor based on clinical inspection, history of the herd, local knowledge and diagnostic investigation including abattoir data. However, this can change over time – e.g. herds – especially those producing weaners or moving growing pigs off site – can lose PRRS virus, which will affect both the choice and the management of gilts.

As a general principle the aim is to introduce gilts of as high a health status and standard as possible but ensure they are immune to the recipient herds’ disease picture on entry.

Breeding companies and seedstock suppliers of pedigree animals will have veterinary advisors and should have programmes of health monitoring such that they can declare the health of the gilts. This information is exchangeable at the veterinary level and purchasers of breeding stock should ask their veterinary advisor to liaise with that of the supplier.

This will help to ensure:

1. That you do not buy in a disease that you do not want
2. That you can manage the gilts to ensure they are immune on introduction to the main herd

Simply relying on statements from the sales representative is not advisable.

Quarantine (Figure 1)

Irrespective of the above considerations, there will always be a risk that incoming gilts will be carrying disease agents that will disrupt your herd. These may be:-

1. Sub-strains of agents that you have but are different to the strains present on your farm
2. incubating within the herd and not yet be overt
3. silent in the supply herd and not be detected by the health monitoring programme

To avoid health breakdown it is wise to isolate incoming stock away from your farm for a period of time. The principles of quarantining are:-

1. Choose a site away from the farm that will not allow spread of disease to your unit. There is however, little point in quarantine premises being further away from your farm than your nearest neighbouring pig farm.
2. Separate management of isolated stock from that of your farm – ideally with different stockmen. When this is not feasible, attend to the isolated gilts at the end of the day in dedicated boots and overalls and shower and change clothes overnight before returning to your unit.
3. The duration of isolation depends on the perceived risk but should be a minimum of four weeks. (For new and emerging disease it may need to be three months).
4. Constantly monitor the health of the gilts in isolation and seek veterinary advice if there are concerns.
5. The quarantine period can be used for vaccinations – see below.
6. Ask your veterinary advisor to check with the supplier’s veterinary advisor before removal of gilts to the main farm, that no new disease problems have occurred on the supply farm since the gilts left.

Acclimatisation

The aim of acclimatisation is to ensure that gilts are exposed, recovered and fully immune to the recipient herd disease causing organisms before entry to the herd.

Some favour starting this process in quarantine although this is unwise; if gilts become unwell it may be difficult to differentiate between what they have come with and what they acquire after arrival.

Therefore it is better to start the acclimatisation programme after quarantine but still within a semi-isolated area of the farm. Bear in mind that once gilts are exposed to the herds’ organisms these will multiply and be excreted which can contaminate the existing herd, overloading the environment and triggering disease.

Historically, acclimatisation has been achieved by the combined procedures of:

1. Contact with live animals – cull sows are often favoured but may be poor sources of organisms. Weaners housed next to gilts may be preferable. Hospitalised animals as sources of infections are high risk
2. Vaccination (see below)
3. Feedback – The feedback of animal protein (placenta, stillborn or mummified pigs etc) is illegal. The use of weaner faeces is of questionable legality

This acclimatisation procedure will take at least 4 weeks with exposure ceasing at least 2 weeks before the gilts are transferred into the main service area. During this time they should be in a separate air space with no direct faecal contact to the main herd.

Vaccination

The aim of vaccination is to provide gilts with a controlled ‘dose’ of an infectious agent to which they can develop immunity. It therefore takes time to work – very rarely will immunity have developed in less than two weeks following vaccine administration. The type and timing of vaccination will depend upon the health differences between the supply and recipient farms and the risk of disease. By way of examples:

1. If the supply farm is enzootic pneumonia-free but the recipient is positive, it is essential that gilts are fully immune before they arrive on farm. Therefore the vaccine course must be complete two weeks prior to entry. This can therefore be applied during quarantine or better still on the supply farm before dispatch (Most suppliers are prepared to do this). Similar consideration applies to PRRS but a PRRS-free supply farm will not administer live PRRS vaccine to gilts on site; this would have to be done in quarantine. Some veterinary surgeons advocate use of a single ‘primary’ dose of killed PRRS vaccine before dispatch, then applying a live dose in quarantine/isolation (Figure 2).
   
   
2. Where the disease concerned does not actually affect the health of the gilt, vaccination can be delayed until after removal from isolation. Parvovirus is only damaging to the unborn litter and thus can be given up to two weeks prior to service.
   
   
3. Where the disease concerned is a risk to the progeny of the gilt (e.g. E. coli) vaccine is best given in mid to late pregnancy.
   
   
4. Many advocate use of PCV2 vaccine in replacement gilts. Whilst one vaccine is specifically licensed for this purpose as part of a breeding herd vaccination programme, such use for other products may be regarded as ‘off licence’. Potentially, any immunity carried by the gilt at farrowing could interfere with subsequent piglet vaccination where used.
   
   
5. Other diseases that require vaccination application may include erysipelas, clostridial disease, Haemophilus parasuis and atrophic rhinitis

Veterinary advice should be sought to establish a sound programme of vaccination for gilts tailored to the needs of the farm and complementary to the established health status of both supply and recipient farm.

Timing

It is clear from this brief summary that time is needed to properly introduce and integrate gilts into the herd. The old fashioned idea of serving gilts on a transit heat on immediate and direct introduction is not satisfactory and will inevitably lead to both production and health issues.

Gilts have traditionally been supplied to farm either as weaner gilts (35 to 45kg) or at full weight (90 to 110kg). The choice will depend upon how long gilts are quarantined and acclimatised. In the absence of quarantine, a minimum of 6 weeks from entry to service is advisable with targets for service of a minimum of 225 days of age – 125kg live weight – although these targets may differ between breed types.

Other Considerations

Maiden gilts entering the farm are frequently exposed to some of the poorest accommodation available. Factors which can affect both their short term health and productivity and total lifetime performance include:

1. Hygiene – avoiding excessive challenge
2. Thermal comfort – avoiding chilling (Figure 3)
3. Sunburn – gilts are exposed to sunlight in gilt yards for the first time in their lives (Figure 4)
4. Lighting levels – 14 to 16 hours of daylight or equivalent artificial light will maximise stimulation of puberty and subsequent cycling
5. Boar contact; intermittent rather than permanent contact with mature boars (i.e. those over 14 months of age) will improve stimulation
6. Nutrition – A wide range of nutritional strategies have been advocated for gilts and specialist advice should be sought

Conclusion

Replacement gilts are the herds’ future. The correct approach to their introduction and integration will determine their long term successful productivity and producers should consider whether they are achieving the best from gilts and review policy on a regular basis.

Further Reading

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Find out more information on the diseases mentioned in this article by clicking here.