Lung lesions in slaughter pigs in 2017

Pulmonary diseases still represent one of the major threats for the economy of current industrial pig farms. With the aim to reduce the use of antimicrobials in their control, they are becoming even harder to control. Among the variety of different agents involved, Mycoplasma hyopneumoniae (M. hyo) as a primary cause of enzootic pneumonia (EP) and Actinobacillus pleuropneumoniae (A.p.) causing porcine pleuropneumonia are one of those most largely present in European swine herds. Despite their known common presence, the real prevalence and impact on pig performance is not easy to assess.

Serious reduction of performance

M. hyo is supposed to be present on over 80% of all farms and can cause serious reduction of the production performance and profitability of pig herds. Mycoplasma infection can be hard to detect but the negative impact on productivity remains hugely significant. Part of the reason for this is that M. hyo infection does not always lead to the development of clinical disease. Indeed, M. hyo infection often appears to have a subclinical course, where only pig growth performance is reduced. This means that apparently healthy pigs may be carrying mycoplasma with no clinical signs until EP may develop as a result of other factors such as stress or co-infection. For this reason a range of accurate diagnostic methods is required to identify and monitor the progress of the disease and the effectiveness of treatment and control practices.

Figure 1 – Median EP-Index values of lung batches scored in different regions of Germany and Austria.

A.p. has been positively found in up to 90-100% farm prevalence in some studies. Acutely infected pigs are relatively easy to be diagnosed. These pigs usually progress in disease severity and die a few days after the beginning of the clinical signs or resolve and become chronic carriers. The chronic or subclinical carriers are the hardest to identify and are usually the cause of further disease outbreaks. Some signs, such as decreased appetite, decreased weight gain, and exercise intolerance may be seen, but many chronic carriers show no obvious clinical signs and are only identified with testing during pleuropneumonia outbreaks.

Cranio-ventral consolidation in lungs on the slaughter line. Photo: Ceva Animal Health

Lung scoring

Scoring of lung lesions in the slaughter pigs provides very important information about the respiratory health in the pig population. Lesions suggestive for previous M. hyo or A.p. infections and their scoring have been described in an earlier stage. The Ceva Lung Program (CLP) was set up to quantify and record EP-like and A.p.-like lung lesions, based on typical changes in the lung parenchyma and pleura. Scoring of those lesions allows evaluating the problems with EP and pleuropneumonia. These results provide important information to assess the level of disease on the farm, see its dynamic in time and even benchmark it with other sites of the same company or other producers. Based on it the decisions, whether an intervention such as vaccination or therapy should be introduced, can be made. Afterwards the results of such interventions can be assessed.

The programme collects a sufficient amount of data from different regions, countries and production systems which allows also comparing the situation and approaches in those locations, the evolution, seasonal effects etc. An extensive survey using CLP scoring methodology at the slaughterhouses was performed in 2017 in European pig producers. The aim of this survey was to collect the results of lung scoring performed in most of swine producing European countries in 2017.

Collecting results

The results were collected from 19 European countries in the 12 months period from December 2016 until November 2017. The mean values and quartiles were calculated for the:

• percentage of lungs with bronchopneumonia;
• the percentage of affected lung parenchyma out of sick lungs; and
• the percentage of dorso-caudal pleurisy and the A.p. index (APPI).

For the two latter indicators the results from France were not included, because there they were not scored routinely.

The total number of scored lungs was 325,624 from 2,918 reports with the average of 112 lungs per batch. The distribution values corresponding to of various types of lesions have been summarised in Tables 1 and 2.

The data set from 19 European countries in 2017 shows very similar distribution of the values as the analysis made in 2016. This confirms the programme as a repeatable, relevant scoring methodology considering that fact that the amount of reports in 2017 increased by 50% compared to 2016. The incidence of especially EP-like lesions remains high despite the decrease of 8.5% vs 2016. The control of M. hyo infections seems still to be a major challenge.

Extent of the survey

Several surveys in slaughter pigs evaluating the lung lesions have already been conducted in some EU countries in the past. It is unlikely that they have ever been performed to such a large extent, involving all European important pig producing countries.

Besides the overall picture of the continental situation, the database allows breaking down the results and evaluating different risk factors, which might contribute to the high or low prevalence of EP and pleuropneumonia.

One of those seems to be the density of pig production in different regions and types of farms. This effect was demonstrated in Germany and Austria, with the statistically lowest EP scores found in Eastern Germany, probably reflecting the high health status of large and isolated herds in that region.

Another important factor is the climate and season. Based on the results collected in Spain from 1,145 commercial pig batches classified in four different trimesters according to slaughter dates, the seasonal effect was demonstrated. The significantly worst lungs in terms of EP-like lesions were found in pigs slaughtered the third semester of the year.

Efficiency of prevention measures

The efficiency of the prevention measures can be estimated including the financial benefits/losses according to the lung score results and previously described predictive impacts on the performance.

A study in 27 farms in France, finished in 2017 compared the data from farms vaccinated with Hyogen (a vaccine by Ceva Animal Health), with database results previously gathered when other vaccines were used. A six-month period for each protocol was considered. In total 16,000 lungs were scored, also see Table 4. These findings help producers to choose an appropriate respiratory health programme (including vaccination protocols) for their farms, and to monitor the effectiveness of these programs once implemented.

Lung scoring and evaluation using Ceva Lung Program is providing high value data and can be used by pork producers and veterinarians to assess respiratory health on their farms. It allows monitoring the situation in time and assessing various factors influencing the prevalence and severity of diseases. Consequently using this information can improve the health of the herd and reduce the cost of production. Yearly regular evaluation of data sets from CLP, which continues in 2018 will provide more information about the trends in swine respiratory health.