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The
Veterinary Journal
The Veterinary Journal 179 (2009) 240–246
www.elsevier.com/locate/tvjl
The relationship between infectious and non-infectious
herd factors with pneumonia at slaughter and productive
parameters in fattening pigs
Jorge Martı́nez
a,b,*
, Bernardo Peris a, Ernesto A. Gómez b, Juan M. Corpa
a
a
b
Departamento de Atención Sanitaria, Salud Pública y Sanidad Animal (Histologı́a y Anatomı́a Patológica),
Facultad de Ciencias Experimentales y de la Salud, Universidad Cardenal Herrera-CEU,
Edificio Seminario s/n, 46113 Moncada (Valencia), Spain
Centro de Investigación y Tecnologı́a Animal, Instituto Valenciano de Investigaciones Agrarias (CITA-IVIA),
Apdo. 187, 12.400 Segorbe (Castellón), Spain
Accepted 1 October 2007
Abstract
This paper explores the relationship between infectious and non-infectious herd factors with the occurrence of pneumonia at slaughter
and productive parameters in fattening pigs on 39 fattening herds. A questionnaire was used to obtain environmental and management
factors (non-infectious factors). Blood samples and lungs were obtained from 35 pigs in each herd at slaughter. Serological testing was
performed for antibodies against three respiratory pathogens (infectious factors): porcine reproductive and respiratory syndrome virus
(PRRSV), Mycoplasma hyopneumoniae (Mh) and Aujeszky’s disease Virus-gE protein (ADV-gE). Lung lesion classifications were catarrhal-purulent bronchopneumonia (CPBP), pleuropneumonia (PLP) and pleuritis. A mean lesion value (MLV) was calculated for each
lesion. ANOVA and logistic regression assessed statistical associations among MLV, average daily gain (ADG) and feed conversion ratio
(FCR) (dependent variables) with infectious and non-infectious factors (independent variables). Mh vaccination was associated with a
significant decrease in CPBP; high Mh seroprevalences was associated with an increased level of CPBP. FCR was negatively related with
high seroprevalences for ADV-gE and Mh. No significant associations were seen for ADG.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Swine; Pneumonia; Slaughter; Daily weight gain; Feed conversion ratio
Introduction
Respiratory disease in fattening pigs is a common health
problem all over the world in intensive production systems.
It causes important economic losses that are associated with
lower growth performance, and with high costs of medication and increased mortality (Maes et al., 2000). Respiratory disease is influenced by environmental and
*
Corresponding author. Address: Histologı́a y Anatomı́a Patológica.
Facultad de Veterinaria (Edificio V). Universidad Autónoma de Barcelona, 08193, Bellaterra (Barcelona), Spain. Tel.: +34 93 581 3145; fax: +34
93 581 3142.
E-mail address: [email protected] (J. Martı́nez).
1090-0233/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tvjl.2007.10.006
management factors (non-infectious factors); for infection
there is the inevitable influence of the nature of the respiratory pathogens to which the pigs are exposed (infectious factors). However, many respiratory infections are subclinical
in nature. The response to this is to replace treatment of
clinically affected individuals with a planned approach to
prevention and control that affects large populations. Prior
to implementation of these programmes it is useful to quantify the effect of factors that may be related to pneumonia.
To achieve this, inspection of pigs at slaughter has been
widely used in epidemiological studies of risk factors
associated with raised prevalence of lesions, especially
pneumonia. The presence of lung inspections permits an
investigation of the quantitative association between the
J. Martı́nez et al. / The Veterinary Journal 179 (2009) 240–246
241
occurrence of pneumonic lesions and production parameters, especially average daily gain (ADG) and the feed conversion ratio (FCR) (Pointon et al., 1990).
Some of the most important infectious agents involved
in respiratory disease in finishing pigs are porcine reproductive and respiratory syndrome virus (PRRSV), Mycoplasma hyopneumoniae (Mh) and Aujeszky’s disease virus
(ADV). These agents are distributed worldwide and are
known to play an important role in the appearance of
pneumonia (López, 2001).
A cross-sectional multivariate study in a large number
of fattening herds has been used in a number of epidemiological studies to investigate a wide range of factors
(Hurnik et al., 1994; Maes et al., 2001). However, the
conclusions may not be generalizable to other countries
because of differences in the type of farms, husbandry
systems, measurement procedures of lung lesions and respiratory agents targeted. Therefore, the objective of this
work was to investigate and quantify the possible relationships between non-infectious and infectious herd factors
with pneumonia and productive parameters (ADG and
FCR) in fattening pigs at slaughter.
precise definitions of the data to record. The number of questions was
restricted, and only closed questions for different categories were included.
They were summarised into continuous variables (herd size, stocking
density, number of pigs per compartment, and pig density in the municipality) and categorical variables (month of slaughter, company, PRRSV
and Mh vaccination programmes, purchase policy of pigs, wean-to-finish
management, biosecurity, type of ventilation, floor and feeding system),
following the criteria described by Maes et al. (2001) with a few modifications. Stocking density was calculated in m2/pig. A compartment was
defined as a subdivision of a building with its own ventilation system.
Vaccination against Mh (inactivated) and PRRSV (live vaccine) was
administered at the farm of origin during the lactation and nursery phases,
respectively.
The purchase policy of piglets was categorised as a purchase from a
single source or from various sources. Only two herds used wean-to-finish
management. Biosecurity was recorded positively when herds had a
perimeter fence, lorry wheel dips with disinfectant and anti-bird mesh in
windows and air chimneys at the same time. Ventilation systems were
classified as (1) automatic/manual windows and (2) the presence/absence
of air chimneys in the roof of the building. The type of floor was divided
into fully-slatted, partially-slatted and non-slatted. The type of feeding
was registered as (a) restricted/ad libitum; (b) dry/‘‘wet and dry’’ feeding
(water nipple placed inside the feeder) and (c) grinding/pelleting feed.
ADG (g/day) and FCR for each farm were supplied by the company, and
pig density in the municipality (pigs/km2) was supplied by the local
government.
Material and methods
Slaughter inspection
Selection of herds
Fattening pigs from the selected farms were slaughtered at 6–7.5
months of age with an average liveweight of 103.7 kg (SD ± 3). Pigs from
the same farm showed different growth rates and were sent to slaughter in
different groups depending on their weight (100 kg approx.). Moreover,
groups from the same farm were sent to different abattoirs in accordance
with market conditions. For this reason, only one group of pigs per farm
was examined at slaughter. Groups sent to abattoirs at a considerable
distance from our region could not be studied. Therefore, the first group of
pigs sent to any abattoir located in our area was studied. Hence in some
herds, the best growing pigs were investigated, whereas pigs with lower
growth performance were investigated in other herds. For this reason, the
group order analysed at slaughter (first/second/third/fourth) was recorded
and included in the statistical analysis to study possible differences in lung
lesions and serology between groups from different farms for each herd.
For each group, the first 35 pigs were blood sampled at slaughter.
Afterwards, 35 lungs were collected from the same group of slaughtered
pigs. Because of changes in the order of carcasses on the slaughter line, it
was not possible to ascertain which blood samples and lungs belonged to
each pig. Lungs were palpated and visually appraised by the same person
to detect pneumonia and pleuritis lesions. Lung lesions were classified as
catarrhal-purulent bronchopneumonia (CPBP), pleuropneumonia (PLP)
and pleuritis (Taylor, 1996). CPBP consisted of cranioventral consolidation, with a red/pink or grey-colouring, demarcated from the normal tissue, with a mucous to purulent exudate within the airways. PLP included
one consolidated focus or more in different lobes, principally in caudal
lobes, which were red–black coloured, with fibrinous pleuritis in some
cases, and which presented haemorrhages and necrosis on cut-sections.
Pleuritis was classified into grades 0–1–2 following the criteria described
by Wallgren et al. (1994) with minor modifications. Grade 0 represents an
absence of pleuritis. Grade 1 includes lesions affecting <5 cm2 of the
pleural surface, or adhesions between different lung lobes. Grade 2 consists
of lesions exceeding a surface area of 5 cm2, or adhesions of lung lobes to
the thoracic wall, the pericardium or to the mediastinum.
For CPBP and PLP, the percentage of pneumonia (lung score) was
calculated by weighing lungs separately (without trachea, bronchi and
other mediastinal viscera), and thereafter the pneumonic area which was
cut out separately (Hill et al., 1992). Although the slaughter protocol was
highly standardised between slaughterhouses, differences in weight
between lungs due to insufficient bleeding or the drying of tissues could
Ninety percent of the fattening farms located in the study area used an
integrated production system where the facilities and labour were supplied
by the farmer, while pigs, feed and veterinary practices were supplied by
vertically integrated companies. The companies were invited to collaborate and the six that agreed to do so are designated A–F. Two companies
were not interested in the study, and two others were not selected because
they sent their pigs to slaughterhouses at a considerable distance.
Because the selected companies had a variable number of fattening
farms during the study, it was not possible to know in advance which
farms would be studied. Therefore, companies were contacted every
month to find out which farms were going to send finishing pigs to the
abattoirs located in the study area. For the analysis, 39 finishing pig farms
were studied. No differential selection criteria were established regarding
the respiratory episodes which occurred during the fattening phase.
Study population
The work was performed in Eastern Spain (in the provinces of Castellón and Valencia) from 2002 to 2004. All herds participating in the
study were finishing pig herds with an all-in/all-out (AIAO) management.
This meant that farms did not acquire new piglets until all the pigs of the
herd were sent to slaughter. Pigs were placed on site with an average
liveweight of 18.1 kg (standard deviation (SD): ±3.9), and remained in the
herd until slaughter. Two farms had a wean-to-finish management where
piglets arrived at the fattening farm with an average live weight of 5.2 kg.
All farms used preventive medication at the start of the fattening
period which consisted of administering broad-spectrum antibiotics in the
feed against respiratory and enteric diseases, and anthelminthics. All herds
had a cleansing and disinfection protocol and a minimum 7-day standempty period. According to the producers’ information, two doses of
ADV attenuated vaccine were given during the fattening period. Protocols
varied depending on the farm.
Herd data collection
Once the farms were selected, herd data were collected using a questionnaire completed during a visit to the farm. This questionnaire had
242
J. Martı́nez et al. / The Veterinary Journal 179 (2009) 240–246
not be ruled out. However, such differences may have occurred in all
groups, hence it is improbable that these facts affected differences between
groups. A Mean Lesion Value (MLV) was calculated for each lesion as the
sum of all individual lung scores divided by 35. Potential values for herd
severity scores range from 0% to 100% for CPBP and PLP, and from 0 to 2
for pleuritis.
Serological testing
The potential infections herd factors were studied using serological
profiles. Thus, antibodies to PRRSV, Mh and ADV were detected using
commercial tests. Other respiratory pathogens, like Actinobacillus pleuropneumoniae or swine influenza virus, were not studied for reasons of cost.
The presence of antibodies against PRRSV was determined with an
indirect ELISA (CIVTEST suis PRRS, Hipra). A competition ELISA was
used to detect antibodies against Mh. This test detected antibodies against
a specific protein of Mh (p74), avoiding a cross-reactivity with other
species of Mycoplasma spp. (CIVTEST suis Mycoplasma hyopneumoniae,
Hipra). The presence of gE-antibodies against ADV wild virus was
determined with a competition ELISA (HerdChek Anti-ADV gpI, Idexx).
Statistical analysis
Statistical analyses were carried out using SAS (release 8.02, SAS
Institute). Associations were considered significant at the 0.05 level.
However, given the moderate number of herds involved in this study (39),
significant associations at the 0.10 level were included and considered as a
trend in the statistical results (Maes et al., 1999a). Analysis of variance was
used to analyse the continuous dependent variables assuming normality,
and a logistic regression was deployed to analyse dichotomous dependent
variables.
The relationship between lung lesions (dependent variables) and
infectious and non-infectious herd factors (independent variables) using
the herd as the experimental unit was studied by different methods.
Analysis of variance (PROC GLM) was used for the MLV of both CPBP
and pleuritis. The variable MLV for pleuritis was transformed by the
formula arcsinus square root in order to improve its normality. However,
the variable MLV for PLP could not be transformed into a normal distribution by any method. For this reason, it was considered as a dichotomous variable (presence or absence), and a logistic regression procedure
(PROC LOGISTIC) was used for this analysis. Logistic regression was
also used to assess the association between the proportion of seropositive
pigs in a herd for PRRSV, Mh and ADV-gE (dependent variables) and
non-infectious herd factors (independent variables). As previously
explained, the variable ‘‘group order examined at slaughter’’ was included
as an independent variable in all these models.
Associations between FCR and ADG (dependent variables) and noninfectious herd factors, lung lesions and infectious herd factors (independent variables) were tested at the herd level using analysis of variance
(PROC GLM). Lung lesions were included as the MLV for CPBP, PLP
and pleuritis. The two farms using a wean-to-finish management were
eliminated. They were not comparable with the other the herds because
the age, weight and growth rate of piglets at the beginning of this phase
differed greatly from those pigs starting the feeder-to-finish phase.
Moreover, only one farm for each company of two companies (E and F)
was investigated. Therefore, these two farms were also eliminated from the
analyses to avoid possible biases. Consequently, for this analysis only 35
farms were included.
For logistic regressions, a forward stepwise procedure was used to
explore the main explanatory variables, which were significant (P < 0.10).
A co-linearity test was used (PROC CORR) to analyse the possible correlations between the significant independent variables obtained in each
model. Significant correlations were considered if the Pearson’s correlation
coefficient was >0.75.
Results
Herd data
Categorical variables pertaining to non-infectious herd
factors are summarised in Table 1. Those herds with
PRRSV-vaccinated pigs were originally from the same
farm and belonged to the company A. Mh-vaccinated pigs
pertained to three integration companies (C–E). Only one
herd used a grinding dry feed system, and two farms
employed a restricted dry feeding system twice a day.
Two herds applied wean-to-finish management and
belonged to the company ‘‘B’’. The average and SD for
FCR and ADG were 2.8 (±0.2) and 657.8 (±50.6), respectively (Figs. 1 and 2). For other continuous variables, the
average and SD were: pigs/km2 306 (± 189.3), herd size
1124.7 (±620.3), pigs/compartment 480.4 (±301.1) and
stocking density 0.7 (±0.1).
Slaughter inspection
Regarding the MLV of lung lesions at a herd level,
CPBP showed an average of 8.4% (±5.1), PLP revealed
an average of 0.4% (±0.9), whereas pleuritis obtained an
average of 0.3 (±0.2) (Figs. 3 and 4). The first group of pigs
sent to the slaughter was analysed on 9 farms (23.1%), the
second group on 12 farms (30.8%), the third group on 11
farms (28.2%) and the fourth group on 7 farms (17.9%).
Table 1
Data from the categorical variables included in the non-infectious herd factors
Non-infectious factors
Categoriesa
Integration company
Slaughter season
PRRS vaccination
Mh vaccination
Multiple origins
Wean to finish
Biosecurity
Slat
Air chimneys
Automatic window
Wet and dry feeding
A 13 (35.9), B 12 (30.8), C 10 (25.6), D 2 (2.6), E 1 (2.6), F 1 (2.6)
Spring 6 (15.4), Summer 8 (20.5), Autumn 10 (25.6), Winter 15 (38.5)
No 33 (84.6), Yes 6 (15.4)
No 30 (76.9), Yes 9 (23.1)
No 22 (56.4), Yes 17 (43.6)
No 37 (94.9), Yes 2 (5.1)
No 24 (61.5), Yes 15 (38.5)
Partial 23 (59), Total 14 (35.9), Not slatted 2 (5.1)
No 9 (23.1), Yes 30 (76.9)
No 24 (61.5), Yes 15 (38.5)
No 16 (41), Yes 23 (59)
a
Number and percentages (in brackets) of herds in each category.
J. Martı́nez et al. / The Veterinary Journal 179 (2009) 240–246
% of farms
50
40
30
20
10
0
2.44-2.59
2.60-2.79
2.80-2.99
3.00-3.19
3.20-3.30
FCR
Fig. 1. The distribution of the feed conversion ratio (FCR) values at a
farm level.
% of farms
40
30
20
10
0
563-599
600-649
650-699
700-740
ADG
Fig. 2. The distribution of the average daily gain (ADG) values at a farm
level.
Serological testing
The average herd-level seroprevalences for PRRSV, Mh
and ADV-gE at slaughter were 96.1% (±16.3), 43.4%
(±34.8) and 31.1% (±44.8), respectively. Serological studies
for PRRSV revealed that only two farms (5.1%) showed
80
CPBP
% of farms
seroprevalences <97.1%, but no farm was completely seronegative. Serology for Mh revealed that 10.3% of farms
were entirely seronegative and only 2.6% (one farm) was
completely seropositive. Depending on the herd, a highly
heterogeneous pattern was seen for the distribution of
prevalences at the herd level for Mh. Serological analysis
for ADV-gE indicated that 59% of the farms were entirely
negative and 25.6% were completely positive. The herdlevel prevalences for ADV-gE showed a bimodal distribution with only 13% of the herds in the seroprevalence range
of 1–90%.
Statistical analysis
50
PLP
60
40
20
0
0
0.1-5
5.1-10
10.1-15
15.1-20
20.1-25
MLV
Fig. 3. The distribution of mean lesion values (MLV) for catarrhalpurulent bronchopneumonia (CPBP) and pleuropneumonia (PLP) at a
farm level.
80
% of farms
243
60
40
20
0
0
0.1 - 0.5
0.6 - 1
1.1 - 1.5
1.6 - 2
MLV
Fig. 4. The distribution of mean lesion values (MLV) for pleuritis at a
farm level.
Significant associations obtained by analysis of variance
(linear models) are represented in Table 2. No significant
associations were found using the logistic regression analysis or co-linearity tests. FCR was significantly higher on
farms with high seroprevalences for ADV-gE. An increased
FCR was found in herds with high seroprevalences for Mh,
and also on those farms where piglets were previously vaccinated against PRRSV. No significant associations were
found for ADG. The observation of CPBP increased significantly on those farms with high seroprevalences against
Mh, and a lower number of these lesions was detected on
farms with piglets previously vaccinated against this agent.
Discussion
The present study attempts to evaluate different infectious and non-infectious factors associated with the
appearance of pneumonia at slaughter and their production impact reflected in FCR and ADG. It is important
to clarify that it is possible that the results may not necessarily be extrapolated to other farms since herds were not
randomly selected. Moreover, some risk factors may not
appear significant because of a loss of variation in the independent variables cannot be ruled out since not all the companies working in our area participated in the study.
Lung inspection revealed that prevalence and the severity of CPBP were much higher than those reported in other
studies (Hurnik et al., 1994; Maes et al., 2001; Andreasen
et al., 2001b), but lower than those described by Wallgren
et al. (1994). The results of PLP and pleuritis were similar
to previous reports (Maes et al., 2001; Andreasen et al.,
2001b), although a direct comparison of the results of these
studies should be made with caution because some studies
comprised farrow-to-finish pig farms (Maes et al., 2001;
Andreasen et al., 2001b), or were based on different types
of herds (Hurnik et al., 1994; Wallgren et al., 1994).
The method of pneumonia quantification, particularly
concerning CPBP and PLP, must also be considered carefully. Some methods were based on the measurement of
the surface area of lung parenchyma affected by pneumonia
(Morrison et al., 1985). However this could underestimate
the real percentage of affected parenchyma (Maes et al.,
1996). For this reason, a method based on the weight of
244
J. Martı́nez et al. / The Veterinary Journal 179 (2009) 240–246
Table 2
Significant relationships (P < 0.1) in the analysis of variance, regression parameters (b), standard errors of regression parameters (SE (b)), and P values for
the feed conversion ratio (FCR) and catarrhal-purulent bronchopneumonia (CPBP)
Dependent variables
Significant independent variables
b ± SE (b)
P value
FCR
ADV-gE seroprevalencea
Mh seroprevalencea
PRRSV vaccinationb
0.03 (0.01)
0.02 (0.01)
0.2 (0.1)
0.05
0.08
0.08
CPBP
Mh seroprevalencea
Mh vaccinationb
2.09 ± 0.79
8.14 ± 4.02
0.02
0.06
a
b
Increase of 10% in seroprevalence.
Differences between non-vaccinated and vaccinated pigs.
affected parenchyma was described as being more accurate
for assessing the relationship between pneumonia and production (Hill et al., 1994). In order to avoid interpretative
subjectivity, lung inspection was carried out by the same
investigator. On the other hand, no statistical differences
in lung inspections were found between farms for the order
of groups analysed at slaughter. Thus, the analysis at
slaughter of the best growing pigs or of pigs with a lower
growth rate from the same farm did not account for differences with the rest of the farms for lung lesions.
Seroprevalence of PRRSV, Mh and ADV-gE were comparable to those found in other studies. Seroprevalence of
PRRSV at slaughter showed that almost all the herds
had a seroprevalence close to 100%, as reported by Nodelijk et al. (1997). Thus, no association between PRRSV
seroprevalence and pneumonia with productive parameters
could be established. Therefore, the time when this seroconversion occurred might have influenced the productive
parameters.
Serological studies for Mh and ADV showed that seroprevalences were lower than those reported by other
authors (Wallgren et al., 1993; Maes et al., 1999a, 2000).
Although it is important to take into account the year
when these studies were performed, it would seem that
the application of eradication programmes (ADV) in our
study area, the improvement of management practices
(AIAO management, Mh vaccination, strategic medication
and biosecurity measures) and farm facilities (many of the
studied farms were of new construction) in the last decade
have improved some aspects of swine respiratory disease,
particularly in relation to the two agents.
The distribution of seroprevalences against Mh at the
herd level showed a highly heterogeneous pattern depending on the farm. Thus, Mh colonisation and seroconversion
are greatly influenced by the effect of the individual farm
(Sibila et al., 2004). On the other hand, vaccination of piglets against PRRSV and Mh did not appear to be related
with the seroprevalences against these agents at slaughter.
Despite the application of vaccination programmes for
the eradication of ADV, the bimodal distribution of
herd-level seroprevalences for this agent indicated that, in
general, the majority of the pigs seroconverted within
infected herds. In this sense, ADV vaccination plays an
important role in the transmission of the virus. Although
producers stated that there were two vaccinations during
the finishing period, the efficacy of vaccination schemes
was not studied. Hence in the studied farms, incorrect
applications of vaccination protocols that could have influenced seroconversion against ADV-gE cannot be ruled out.
From all the studied infectious and non-infectious herd
factors that might be related to the appearance of lung
lesions at slaughter, only two variables were statistically
related with CPBP, namely ‘‘Mh seroprevalence’’ and
‘‘Mh vaccination’’. As expected, Mh seroprevalence
showed a positive association with CPBP as it is considered
the most important agent involved in the appearance of
this lesion (Taylor, 1996; Ross, 1999). Although Mh vaccination did not show a significant relationship with pneumonia, its application revealed a tendency to reduce the
prevalence and severity of pneumonia-related lesions at
slaughter, as reported by other authors (Le Grand and
Kobisch, 1996; Maes et al., 1999b; Dawson et al., 2002;
Sibila et al., 2007). One explanation for this tendency could
be that farms which have had to deal with important respiratory problems were more likely to use vaccination
schemes than farms without such problems. No statistical
relationship was observed between the rest of infectious
and non-infectious herd factors studied and the observation of lung lesions at slaughter. Therefore, it is possible
that the effect of Mh vaccination could be sufficient to mitigate the possible effects exerted by other factors.
Mh seroprevalence was also negatively correlated with
FCR. Although some authors did not find differences
between seroconversion to Mh and productive parameters
(Morris et al., 1995; Andreasen et al., 2001a), Wallgren
et al. (1994) reported that pigs that seroconverted in the
early phase of the fattening period had a lower growth rate.
Since the spread of Mh infection within a herd is considered slow (Meyns et al., 2004; Vigre et al., 2004), a high
seroprevalence at slaughter could suggest an early-stage
circulation of the agent during the fattening period. In
these herds, therefore, a large number of pigs could be
affected by mycoplasmal pneumonia over lengthy periods
of time, which could consequently decrease their feed
conversion.
Moreover, high ADV-gE seroprevalences were also negatively related with ADG and FCR. This negative effect
could be explained since ADV produces a decrease in the
J. Martı́nez et al. / The Veterinary Journal 179 (2009) 240–246
pig growth rate and also induces an immunosuppressive
state that is predisposed to infection by other infectious
agents (Kluge et al., 1999). In this way, an improper application of vaccination schemes could also be involved, as
previously discussed.
Another variable negatively related with FCR existed and
negative results associated with ‘‘PRRS vaccination’’ should
be considered with caution since all the piglets vaccinated
against PRRSV came from the same farm of origin. This
farm showed a poor health status, and PRRSV vaccination
was applied in an attempt to improve the productive parameters of piglets. Therefore, in this case, the farm of origin
could be taken as a confounding factor (Martin et al., 1997).
Finally, the observation of lung lesions at slaughter was
not associated with a loss of productive parameters, nor
was ADV-gE seroprevalence associated with the presence
of pneumonia at slaughter. This could be explained by
the temporary nature of lung lesions. Thus, the observation
of lung lesions at slaughter and their impact on productive
parameters could vary depending on the time that respiratory infections occurred (Sitjar et al., 1996). Moreover,
other infectious and non-infectious factors that were not
studied could be related with the appearance and duration
of pneumonia lesions in fattening pigs.
Conclusions
High seroprevalences to Mh increased the risk of CPBP.
However, a lower number of these lesions were observed
when Mh vaccination was applied. Moreover, high seroprevalences to ADV and Mh were negatively related to
FCR. Therefore, accurate vaccination programmes for
ADV should be designed for each farm.
Acknowledgements
This study was financed (A-2001) by the Conselleria
d’Agricultura, Pesca i Alimentació of Generalitat Valenciana (C.A.P.A.). The authors are grateful to M. Láinez, J.
Peinado, C. Caballero and M.A. Escribano from the
C.A.P.A., P. Segura, J. Ortega and V. Cayo from Universidad Cardenal Herrera-CEU, and all the veterinary practitioners, farmers and slaughterhouses personnel who helped
make this study possible. The authors also wish to thank
Dr. Joaquim Segalés (Universidad Autónoma de Barcelona) for the reviewing the manuscript.
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