Biology Reference
In-Depth Information
condemnation? A recent study from England reported a prevalence of
4.2% milk spot livers based on post-mortem examination performed on
the slaughter line in an abattoir on more than 12,000 pigs monthly for 5
years (2005
2010).
49
The prevalence showed a clear seasonal pattern:
increasing in summer/early autumn, peaking in September and declining
in winter/spring. This marked seasonality, also reported from
Denmark,
50,51
is probably related to lack of development of eggs to
infectivity under temperatures of 15
C and increasing rate of develop-
ment with increasing temperature, e.g. during the late spring and summer
both indoor and outdoor in northern temperate climates.
19,52
An abattoir
study in Northern Ireland in 1969
e
1989 supports this explanation by
describing a strong positive correlation between annual prevalences of
liver condemnations due to cirrhotic lesions with mean air temperatures
in May.
53
Any year was strongly correlated with the previous year,
probably indicating that high contamination levels were carried over to
the following year. The same study reported an increase in prevalence
from 4 to 9% during the period investigated and this was attributed to
increased transmission. However, as pointed out by Roepstorff
26
inten-
sification and increased use of anthelmintics during this period are more
likely to cause reduced transmission, and the increase observed is thus
perhaps due to acquisition of infections later in life as white spots only
reflect recent exposure, as discussed above. From tropical regions, 8% of
livers were reported condemned at slaughter slabs (basically equipped
abattoirs) in Dar es Salaam, Tanzania (
N
e
731).
54
Surveys using extended examination at slaughter have, for obvious
reasons, in many cases reported higher prevalences of milk spot livers as
compared to abattoir condemnation data after routine meat inspection:
44% in Saskatchewan (
N
¼
2500),
11
24% in Denmark (
N
9186),
50
36% in
¼
¼
20,758),
55
and 31% in Poland
Belgium during expected high season (
N
¼
1000).
56
The Danish study reported a markedly higher prevalence in
females than entire males (26% vs. 11%) while females and castrated
males (29%) were not significantly different. Production of entire males is
a niche production in Denmark, and these animals are usually kept
separately from the rest. The Belgian study reported that livers with few
(number not mentioned) milk spots were trimmed while the Polish study
(range: 1
(
N
¼
7 milk
spots were trimmed and the remaining part approved for consumption
while 8 or more spots lead to total condemnation.
A number of recent on-farm studies have estimated the production
losses associated with
A. suum
by comparing treated with untreated
groups within infected herds, whereas comparison of infected and
uninfected herds have not been attempted, probably because it is very
difficult, if not impossible, to declare any herd totally free of
A. suum
.
26
In
a Croatian farm, three groups of piglets (
n
e
30 milk spots per liver) mentioned that livers with 1
e
¼
90)
(1) indoor, remaining
e
