Enzootic (mycoplasmal) pneumonia is widespread throughout the United Kingdom, with well over 90% of herds infected. Surveys have shown in the past that 45% of pig lungs at slaughter have the classical lung lesions but whether this has increased over recent years with the arrival of PRRS virus and circovirus (PCV-2) has not been recorded. Our cool and damp climate helps the mycoplasma spread within the farm, as it needs a moist atmosphere to survive and can travel for upto 3 kilometres between farms. Our autumn, winter and spring conditions are ideal for the spread of the disease, especially as we tend to reduce ventilation to maintain house temperatures and thereby increase microbial numbers in the atmosphere and therefore the severity of the challenge. The number of lungs affected and the size of lesions increase during the winter through to about May, when it warms up and the ventilation increases and the lesions start to fall. Many authors have described an association between the size of the lesions and their depressing effect on growth rates, as well as the increase in the severity of other infections such as Pasteurella multocida and PRRS.
How does this help us to choose which vaccination program to follow? It does highlight that the disease is dynamic and each farm must select a program to suit its particular situation, based on the season, production system and concurrent infections both bacterial and viral.
In the US, a Minnesota practitioner Paul Yeske (2001) described the criteria he used.
Table 1. Situations for one or two shot mycoplasma vaccination programs in the US
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Relatively stable herds with low infection pressure from say PRRS and SIV (influenza) and they practice all-in all-out systems |
Disease pressure is high from other active pathogens such as PRRS, and immunity is unstable in the young pig. |
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Vaccinate at the end of the nursery (grower ) period, 9-10 weeks of age |
Seasonal vaccination in summer and autumn for those pigs going to finish in the winter and spring |
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Compliance to vaccinate is high |
Commingled pigs from different nurseries or different sources – (essential for fattening scheme pigs) |
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All-in all-out rooms within one building or in close proximity – multi-age site. |
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Continuous flow facilities |
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Where compliance is unreliable |
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Vaccinate first 6-8 weeks and secondly 8-10 weeks of age (minimum 2 weeks between each vaccine and 6 weeks before the occurrence of clinical signs). |
How does this apply to the UK? Firstly the majority of our farms are relatively small and stable in comparison with the large corporate farms in the US, where they are practicing three-site production. PRRS is seen but is not considered a major problem in the UK neither is SIV and vaccination is not widely practiced. PCV-2 or circovirus on the other hand is considered a major problem here and has a major damaging effect on the pig's immune system; hence vaccination should be used earlier when the pigs can respond. In the UK we used successfully the 1 week and 4 week programs for a number of years and more recently the one shot in the 4th week. We tend to wean later in the UK at 26 days rather than the 19-21 days in the US so the pigs are a little older and the maternally derived antibodies (MDAs) from colostrum have fallen even more. MDAs or passive immunity are important as they can neutralise mycoplasma vaccines making them ineffective, so it is currently advised not to vaccinate sows. The first vaccination at week one may help reduce the MDAs, so that the second vaccination in the 4th week is more likely to work. The single dose products contain a higher level of antigen to help counter this but it does depend on the level of MDAs as it has been shown the vaccines can be neutralised. (Hodgins et al, 2002)
Many of our farms are relatively small and do not have the facilities for all-in all-out separate-site production, so commingling of pigs, multi-age sites and continuous flow can be considered the norm, suggesting two shots would be more suitable and reliable. To counter this there is the 'convenience factor' of one shot and the extra labour costs required for two shots, which have to be put into the balance.
Compliance is an interesting aspect, are the pigs regularly and reliably vaccinated? With the current squeeze on the industry and cut backs on labour this may be an important problem, but one, on which there is no information. However the estimate is that nearly 60% of pigs are being vaccinated for mycoplasma based on doses sold, suggesting that it is not so important here.
Robyn Fleck, a field services veterinarian with Schering-Plough Animal Health in the US, where they have their product M+PAC approved for both single and double dose programs, devised a more simplified plan, which can be adapted to UK herds.
Table 2. UK situations for either a one or two shot mycoplasma vaccination program
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Use in PRRS stable herds (usually <250sows) |
Use in unstable herds with higher health challenges - PRRS and PCV-2 (>500 sows) |
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Use when mycoplasma challenge is lower - Single source pigs, all-in all-out by site - Pigs placed in late winter, spring and early summer |
Use when mycoplasma challenge is high - Late summer, autumn and early winter placed pigs - Multiple sources, multi-age sites and continuous flow farms |
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Use when MDAs are known to be low (older unvaccinated sows) |
Use when MDAs are unknown, variable or high (high gilt replacement >40%) |
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Use when vaccination compliance is high |
Use when vaccination compliance is questionable |
References:
Hodgins, D.C., Shewen, P.E. and Dewey, C.E. (2002) Influence of age and maternal antibodies on antibody responses of neonatal piglets to Mycoplasma hyopneumoniae.
Proceedings of the International Pig Veterinary Society Ames, Iowa, USA, 1, 255Yeske, P. (2001) Experiences with mycoplasma vaccinations: what to do if vaccination doesn't live up to expectations.
Proceedings of the Allen D. Leman Conference University of Minnesota, USA, pp 108-110
More on Mycoplasma vaccination: Octagon Technical Papers