Diarrhoea is a common clinical sign in young pigs, indicating that there is likely to be an enteric infection present, which may be eating into the pig's performance as well as the farmer's profits.
In the weaned pig of 3-4 weeks of age diarrhoea is primarily associated (over 95%) with Escherichia coli infections, which usually start 5 days after weaning and recover 5-7 days later. With improvements in management, hygiene and the widespread use of zinc oxide in the feed, many of these problems have been overcome. However in the grower stage, between 7-8 weeks and 12 weeks of age a separate infectious syndrome often appears, 'the grey scour syndrome or colitis complex.' Many of the organisms are slow growing and take 1-3 weeks to colonise the gut to a level to cause disease, hence it is seen usually in the grower stage and in only 10-30% of the pigs.
Colitis, or inflammation of the large intestine, which causes the diarrhoea, may be caused by a single infectious agent such as Brachyspira pilosicoli, or B. hyodysenteriae (swine dysentery agent), Lawsonia intracellularis ('ileitis agent'), Salmonella spp, Yersinia spp, E. coli and Clostridium perfringens or more commonly by a mixture of two or more bacteria.
In an excellent survey carried out in Scotland on 85 pig units with grower diarrhoea problems, Brachyspira spp were involved in 55% of the cases and L. intracellularis in a further 12%. (See table 1.) This was interesting, as in survey of UK and Irish farms 95% of farms were infected with L. intracellularis but it was only considered 'problematic' in a few.
Depending on the bacteria involved, the severity of the condition will vary, from a severe haemorrhagic ('bloody') diarrhoea, associated with swine dysentery, to a moderate watery to soft grey diarrhoea with mucus, to no clinical signs at all. Performance is affected especially in the severely affected pigs, with poor growth and feed conversion efficiency, often reduced by 10-30% depending on the severity and type of condition. Mortality rate increases are variable depending on the organism involved; they tend to be higher with B. hyodysenteriae and S. enterica Typhimurium but lower with B. pilosicoli and L. intracellularis. A mixed infection tends to increase the severity of the individual disease and in some herds the constant straining may increase the incidence of rectal prolapse and its sequelae, rectal stricture. The pig cannot pass any faeces and the abdomen swells up, usually resulting in death or the need to cull.
In the DEFRA Veterinary Investigation Surveillance Report, 2000, a changing pattern in the infections has been observed. (See graph 1.)
Graph 1. Disease incidents and trends, reported by year
(Source: DEFRA, Veterinary Laboratories Agency, 2001)
There has been a decrease in the number of incidents involving swine dysentery and non-specific colitis, the latter, probably due to improved diagnosis and recognition of B. pilosicoli, which has increased as well as ileitis. S. Typhimurium has been quite stable even though the number of pigs slaughtered in the UK has fallen by 22% over the same time scale. It is probably due to its association with PMWS. It also has to be remembered that the incidents reported are usually the more severe cases, such as swine dysentery and salmonella cases have to be reported. It does indicate a useful trend however.
A variety of products are available to prevent and control these infections. Tiamulin, valnemulin, lincomycin and tylosin are all used for controlling the Brachyspira and Lawsonia infections. A recent review showed there is some marked variation in the relative sensitivity of 76 isolates of B. hyodysenteriae to these antibiotics, with valnemulin being the most active followed by tiamulin, lincomycin and tylosin, the latter two showing clear signs of resistance development. The percentage of isolates with the same minimum inhibitory concentration (MIC) to each antibiotic are presented in Graph 2. A low figure means the antibiotic is more active, a high figure i.e. above 2 µg/ml for tiamulin and valnemulin, 32µg/ml for lincomycin and 50µg/ml for tylosin indicates likely resistance.
Graph 2. Comparative MICs (µg/ml) of various antibiotics against B. hyodysenteriae
(Source: Karlsson and others, 2002)
If Salmonella spp, Yersinia spp or E.coli are involved then other antimicrobials will be required e.g. apramycin, neomycin, trimethoprim/sulpha, spectinomycin or tetracyclines, in order of activity.
When faced with these problems it is essential to diagnose which organisms are involved by faecal testing and necropsy, so the correct treatment can be prescribed. Antimicrobial sensitivity testing is also helpful but difficult to do on some organisms. Where mixed infections have occurred, causing diarrhoea in 20-30% of pigs, it is beneficial to medicate the feed at the treatment level for 3-4 weeks, not only to reduce the infection in the pigs but also to reduce the infectious challenge and contamination from the environment. L. intracellularis will survive for up to 14 days in faeces and B. hyodysenteriae can survive for up to 40 days in moist faeces and 60 days in slurry in cold weather. Once the disease is under control the level of medication can be reduced to prevention levels, with the subsequent cost savings. A concurrent hygiene program is also of benefit, as frequently pens have not been cleaned for some time.
A close cooperation and consultation with your veterinary surgeon is essential to diagnose the causative agents involved, choose the most effective medication for those organisms and provide the necessary treatment and hygiene program for future control.
References:
Thomson, J.R., Smith, W.J. and Murray, B.P. (1998) Investigations into field cases of porcine colitis with particular reference to infection with Brachyspira pilosicoli. Veterinary Record, 142, 235-239.
Karlsson, M., Oxberry, S.L. and Hampson, D.J. (2002) Antimicrobial susceptibility testing of Australian isolates of Brachyspira hyodysenteriae using a new broth dilution method. Veterinary Microbiology, 84, 123-133
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