The productivity and profitability of pig production depends very much on the health status of the herd and the way it is managed. Viral, mycoplasmal, bacterial and parasitic infections are very common especially in the young, growing animal and it is critical to control these infections.
Vaccines, both in the sow for early protection of the piglet or directly into the growing pig, or alternatively, the use of strategic medication to prevent diseases from developing and spreading through the whole herd, are the most common forms of disease control.
These must be coupled with herd high-health management by the selection of breeding or growing stock not infected with diseases such as Mycoplasma hyopneumoniae, the cause of enzootic pneumonia, or Brachyspira hyodysenteriae, the cause of swine dysentery. Good biosecurity is also essential to keep diseases out of the farm.
Since the control of PMWS (post-weaning multisystemic wasting syndrome) caused by porcine circovirus type 2 (PCV2) by the widespread use of vaccination in the growing pig population, the overall health of the national herd has improved substantially. In many ways we have returned to a more normal production situation before the epidemic. Porcine reproductive and respiratory syndrome (PRRS) virus is still circulating but in the UK we are fortunate to have just the European low pathogenic strain, in contrast with the EU where the more virulent US strains are also circulating.
Viruses – lowering immunity
These viruses both have a depressing effect on the immune system so that pigs cannot fight off the infection and are more susceptible to the more common infections, especially on the respiratory side, such as enzootic pneumonia, Streptococcus suis, the cause of meningitis, Haemophilus parasuis (Glässer’s disease) and especially Actinobacillus pleuropneumoniae, the cause of pleuropneumonia.
Not all of these bacterial infections could be vaccinated against hence the common use of antimicrobial medication to control infections. When PRRS virus, M. hyopneumoniae and common, secondary-invading bacteria such as Pasteurella multocida were involved it was referred to as PRDC (porcine respiratory disease complex) and could be very difficult to control, requiring a mixture of vaccination, medication and environmental improvements.
On the enteric or gut side, Escherichia coli infections in the young piglet is a common problem and vaccination of the sow will help prevent problems in the neonatal piglet. Coccidiosis is common in the 7-10 day old piglet still but one major improvement has been the reduction in the severity and duration of post-weaning diarrhoea, since the introduction of 4-week weaning and the widespread use of therapeutic levels of zinc oxide in the feed.
Colitis and ileitis
From about 7-8 weeks of age and older is the common time for the spirochaetal infections such as B. hyodysenteriae and B. pilosicoli the cause of dysentery and ‘colitis’ in growing and finishing pigs. At the same time Lawsonia intracellularis, the cause of ‘ileitis’ is challenging growing pigs and can also cause a reduction in growth rate, feed conversion efficiency (FCE) and diarrhoea.
On occasion, there can be mixed infections especially at the end of the nursery period and they are also more commonly reported in Scotland. Over 95% of herds in the UK are exposed to L. intracellularis infection, but fortunately not all will develop severe clinical disease. A per-acute, severe form can be seen in finishing pigs, when they are commonly found dead with pale carcases.
Eradication of swine dysentery has recently become a top priority in many pig farms in regional health schemes in the UK and is achievable. Lawsonia intracellularis eradication is possible but appears to be much more difficult and more likely to breakdown. Salmonella infections are still common in UK pigs but generally it is more of a public health issue than a clinical problem in pigs, however worm infections involving Ascaris suum are also still common place and cause typical ‘white spot’ livers, which result in their condemnation at slaughter. Anthelmintic medication is required for this.
Some of the common respiratory and enteric diseases patterns are highlighted in Figures 1 and 2, respectively.
Figure 1. Common respiratory disease infection patterns
Figure 2. Common enteric disease infection patterns
Infectious agents are a major problem affecting pig health and welfare but generally they can be controlled by vaccination and medication if a farm becomes infected. However, high-health options are available and coupled with good biosecurity and pest control (against rodents, flies, wild birds) it is possible to maintain health and improve performance and profitability.
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