By David Burch
How to prevent five major pig diseases from ?occurring? The key to the answer often lies in the breeding herd. After all, negative sows breed ?negative piglets. In order to eradicate pathogens from the breeding herd, vaccines and especially ?antibiotics play a pivotal role.
As a veterinarian, prevention of infections is a subject that is very close to my heart. Any article on dealing with pathogens and how to prevent them should touch on some basic rules that can avoid a lot of trouble.
Starting with high health is the best place to be. Get reports of the health of breeding herds before purchasing stock. Get your vet to talk to their vet. Check the reliability of the breeding company from a disease perspective, not just on the genetic potential. If it brings disease on to the farm, it can blow away any of the genetic potential improvements you were hoping for. I have recently seen this with a hyper-prolific breeding herd but it spread Streptococcus suis as well.
Don't merge farms. I am a great believer in closed herds, if possible; it stabilises immunity and reduces the risk of disease introduction. Every time new animals (gilts mainly) are brought on to the farm there is a risk of disease introduction and also they have to acclimatise to what infections are present. Importing semen is usually the safest option for limiting disease risk, whilst still being able to improve the herd's genetics. There have been recent occasions where boar studs have broken down with Porcine Reproductive and Respiratory Syndrome virus (PRRSv), so nothing is totally risk free. Purchasing of pigs for finishing is always potentially high risk.
Biosecurity is still the most important way of keeping disease out. It is critical for staying disease free or maintaining your current health status and must be a part of any eradication programme; otherwise the chances of long-term success are severely limited. On many farm visits, one finds biosecurity is minimal and surprisingly, when you ask “how did the disease come in?” the farmer knows but has not really done anything to stop further infections coming in – too much trouble? Or if they have carried out eradication before they expect it to break down within 6-12 months “like it did the last time.” I frequently say “think of the farm as a fortress and how best you can defend it and keep infections outside.”
More specific pathogens and prevention
If we look at prevention of disease we have been fortunate to have usually an array of vaccines, therapeutic drugs etc to control the effects of the disease. Improvements in management, housing, heating and ventilation, nutrition all have played a part. It is when we have got one infection, then another, then another, the effects of disease complexes can make a major impact on a farm's productivity and profitability and then the farmer usually considers the eradication option.
A combination of PRRSv, which is immunosuppressive, Enzootic Pneumonia (EP), which can also be immunosuppressive and a pathogenic strain of Actinobacillus pleuropneumoniae (App), leading to the porcine respiratory disease complex (PRDC) is a classic example. If the App isolate has developed resistance to the cheaper antibiotics like tetracyclines or trimethoprim/sulphas it is almost a necessity to go for the eradication option. Breaking down with swine dysentery is also a common reason to go for eradication because of its severity.
Most eradication programmes are focused on eliminating infections from the breeding herd. There they usually have some immunity, a low level shedding of the virus or bacteria and a good chance of getting rid of the bug. Trying to eradicate infections from growing pigs is very difficult and also costly, so partial depopulation of the growing/finishing herd is important.
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