10 May 2002

PMWSMAKESWEANING EVENMORECRUCIAL…

WEANING has always been a crucial time for the young pig but now, with post-weaning multisystemic wasting syndrome (PMWS) present, it is even more important to smooth the process, writes Suffolk-based pig vet Roger Harvey.

PMWS is not simply pigs succumbing to porcine circovirus type 2 (PCV2) infection – which is present in most herds and is the principal virus implicated in the disease. PCV2 infection alone usually causes few problems for the pig, but add another factor or factors and results are very different.

Most triggers involve the pigs immune system being initially over-challenged and then overwhelmed, pushing the pig into the danger zone that is PMWS.

Weaning is an ideal time to challenge the pigs immune system because of all the imposed changes in nutrition, environment, infection challenge and social interaction.

Solid food

The change to solid food requires pigs to establish a whole new intestinal environment, with appropriate enzymes and bacteria for efficient digestion.

When this process does not establish correctly, poorly digested food will reach the hindgut allowing bacterial overgrowth and diarrhoea, which will initiate an immune response by the pig. This environment will also allow any pathogenic bacteria present to multiply, possibly reaching a level to show clinical disease.

Food offered must be free from contamination by faeces, mould and dirt. Dirty food is simply asking for trouble and a waste of an expensive commodity, especially where creep feed is concerned.

No discussion about nutrition should ignore water – the often forgotten nutrient. Water must be clean and plentiful especially after weaning. Young pigs will rapidly dehydrate when their access to water is poor. Water supplied via a header tank is particularly prone to contamination and such systems need regular and thorough cleaning.

Disease

The actions of PCV2 in pigs are currently beyond our control and a vaccine is probably still two years away. Therefore, all efforts must be aimed at controlling secondary infections, which are likely to be the added factors needed to cause PMWS.

Porcine reproductive and respiratory syndrome virus (PRRSv) remains a significant factor on many farms and is usually active in growing pigs about the time PMWS typically occurs. Control of PRRS by management procedures – separating pigs by age – and using vaccines must be considered.

Other significant problems, such as enzootic pneumonia (EP), are often active around this time. There are effective vaccines to control this, either singly or combined with Glassers disease.

Some reports suggest the emergence of PMWS is related to the increased use of pneumonia vaccines over the past few years. However, EP vaccine has been used since early 1996 in the UK and I did not see my first case of PMWS until January 1999, so why the lag if there is a link? We also see PMWS in EP-free herds and those not using pneumonia vaccine.

Environment

All infectious organisms survive in the environment for a period of time; some only a few hours, others many months. Cleaning will physically remove them, but to be truly effective cleaning needs to be thorough and followed by a suitable disinfection routine.

Ordinary dirt in housing is a mixture of shed skin, dried faeces and, if straw bedding is used, pollen and fungal spores. These are all proteins which will stimulate the pigs immune system and are capable of being the trigger for PMWS.

The physical aspects of the environment play a vital role in the pigs well-being. Ventilation must be capable of providing clean, fresh air, free from dust particles and ammonia. Excessive ammonia stops the activity of minute hairs lining the airways, allowing dirt and infection to enter the lungs.

Social

By weaning time, the social hierarchy of litters is well established with each pig knowing its place and staying there. Mixing the litter with others is bound to upset this as the new group seeks to establish order, which always involves fighting.

Infections pass from one pig to another through wounds or the close contact that occurs. While the wounds themselves may not become serious, the added challenge to the pigs system from fighting infection may allow PMWS to take hold.

After weaning, water must be clean and plentiful to prevent stressing the pigs immune system and possibly letting in PMWS. It is the often forgotten nutrient, says Roger Harvey (inset).

&#8226 Reduce challenge to immunity.

&#8226 Good hygiene essential.

&#8226 Control secondary infections.