Biology Reference
In-Depth Information
predominant
Oesophagostomum
species and is most often found as
a single species infection on farms while mixed infections with
O. quadrispinulatum
are seen occasionally.
8
A. suum
is worldwide the most or second most (surpassed by
Oeso-
phagostomum
spp. in older stock) prevalent intestinal species in domestic
pigs, although the prevalence varies considerably with climate, produc-
tion system (indoor/outdoor/scavenging), farm practices, herd, age, and
breed, as evident from Chapter 16. High prevalences ranging from 17 to
35% have been reported from the Scandinavian countries by fecal analysis
in fatteners and gilts (
pregnant pig before first farrowing
9
) and more
recently 22% in Danish sows/gilts.
10
Adult worms were detected in 17%
of finishers at slaughter in Canada.
11
¼
In Japan, 15% slaughter pigs
129) were found positive by coproscopy.
12
African studies, also based
on fecal egg counts, revealed prevalences of 2% in growers on smallholder
farms in Nigeria,
13
13% in growers in Ghana,
14
and 40% with only small
variation across age groups in Burkina Faso
15
and Uganda.
16
More details
on prevalence in age groups and herds can be found in Chapter 16. Some
of these coprological studies undoubtedly overestimate the prevalence
14
as low or moderate egg counts may be due to coprophagia and therefore
represent false positive findings, especially if stocking rate is high.
17,18
In
contrast, infections with only one worm or all worms of the same sex will
result in underestimation of prevalence as compared to post-mortem-
based studies. A higher prevalence in females than in males (33% vs.
14%) was found in Burkina Faso
15
which confirmed an earlier observation
from Sweden that female finishers generally have higher egg excretion
than castrates.
19
A range of other studies have not reported such differ-
ences. One has to bear in mind that in most modern intensive systems
male piglets are castrated early in life whereas castration may take place
later or not at all in other production systems. This may influence
potential differences between sexes.
In the early 1990s 60% of Danish farms were infected with
A. suum
20
but farming practices have now changed to loose housing of sows in
dynamic groups, where sows in different stages of gestation move in and
out on a weekly basis, and recently 76% of the surveyed Danish farms
were found by coproscopy to be infected.
10
On 84 smaller organic farms
with traditional husbandry in Austria,
A. suum
was present (fecal
samples) in 30% of sow units and 59% of finishing units.
21
Corresponding
figures for
Oesophagostomum
were 66 and 43%. More than 50% of pigs at
slaughter had “milk spots” on the liver. In Germany, 7% of 144 breeding
farms (sows only) had
A. suum
infections.
22
In a small Dutch survey
including 36 farms, the prevalence of
A. suum
-positive farms (across age
groups) was 50% for free-range, 73% for organic, and 11% for conven-
tional farms (in-door with straw bedding).
23
The highest prevalences
were seen among finishing pigs with about half of the examined groups
(
n
¼
