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Detection and control of Salmonella What can be done to detect and control Salmonella on such farms? If monitoring shows a rising prevalence of positive sam- ples or a weaner buyer complains about a breeding farm, it is possible to take ‘sock and environmental swab’ samples. These samples are very sensitive and are the best method to assess the burden and spread of Salmonella on-farm. Alternatives are examination of classically ill pigs after death or to take faecal samples, especially when clinical disease occurs. These meas- ures allow identification of the type of Salmonella involved. Nowadays, most farms try to control Salmonella by using ac- ids in feed or water. They also try to improve hygiene proce- dures, but these efforts rarely lead to a satisfactory result. An abstract by Helen Lynch and others from Ireland, presented at the European Symposium of Porcine Health Management (ESPHM) in Dublin in 2016, showed that in-feed acids are not able to protect piglets from infection. Another publication in Dublin indicated that acids were, to some extent, able to lower serological titres, which is often the cause of failure of such programmes. Infection still takes place but, because titres are low, producers think they are buying healthy animals. However, after a while they will start shedding again and the farms become contaminated. That vicious cycle causes the Salmonella pressure to rise again.


Vaccination in breeding sows An oral presentation by Judy Bettridge from the UK’s Animal and Plant Health Agency, at the 2019 ESPHM in Utrecht, the Netherlands, described vaccination at the top of the breed- ing pyramid. It showed that it was possible to reduce the amount of S. Typhimurium shedding in animals on farms lower down the pyramid, though other types of Salmonella did not seem to have been reduced. A reduction, at least in the case of Salmonella Derby, which often can be seen as an accompanying infection of S. Typhimu rium, will show up – it is just a matter of time. Expe-


rience in Germany suggested that, while the vaccination of sows with Salmoporc (Ceva Animal Health) had the biggest influence on the shedding of S. Typhimurium, the oral vacci- nation of gilts still at the piglet stage – before expected in- fection – led to broader protection, with cross-protection against S. Derby. That was proven by a study with a S. Derby challenge strain. The result was that orally vaccinated pigs showed a significantly reduced detection rate in the ileocae- cal lymph nodes and in the caecum, as presented to the In- ternational Swine Health Service congress in Cloppenburg, Germany in 2019. If there is S. Typhimurium on a farm, whether accompanied by other Salmonella serotypes or not, the best effect of a vaccination protocol implemented on a farm can be seen when the whole herd is replaced with gilts that were twice orally vaccinated as piglets. With usual replacement rates, that normally takes about 30 months. The breeding herd within the UK study presented at ESPHM in Utrecht had not yet reached that stage. Nevertheless, despite the fact that the herd referred to had only reached the 18-month stage, the conclusion by the authors was that multiplier farm vacci- nation was effective as a Salmonella reduction strategy and provided ‘substantial benefits’ to the pyramid.


Early pig protection Protecting pigs early is key to control. Studies have shown that nurseries have the highest infection pressure. Piglets at that stage are very susceptible to infections. Having just been weaned they have not built up full protection against every pathogen with which they are confronted in the nursery and, at six weeks old, almost all of the maternally derived antibod- ies are dramatically decreasing. Since the piglets have come from small, litter-sized groups and are being grouped in larger batches, often having been sorted by size as well, there can be a considerable amount of mixing. As a result, even if there are only one or two sows in a


Work thoroughly with wipe samples, also on difficult places.


The ventilation system is a source of new contamination. ▶PIG PROGRESS | Volume 36, No. 4, 2020 19


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