Biology Reference
In-Depth Information
rapidly be expelled, and by day 25 p.i. only a small number of worms will
remain and mature into egg-producing (patent) adults. These may stay in
the intestine for 1 year but some may be expelled earlier.
33
If this happens,
pigs may become reinfected.
34
The intestinal phase is associated with
pathological changes in the mucosa.
35
While the influence of
A. lumbricoides
on cognitive abilities has been
recognized for years,
36
there is no experimental data to support this
finding for
A. suum
in pigs.
IMPACT ON GROWTH AND PRODUCTIVITY IN
PIGS
EXPERIMENTAL STUDIES
e
Though based on very few observations, early studies describing severe
clinical disease in
A. suum
-infected pigs also reported dramatic reductions
in weight gain (e.g. Spindler
32
). A later study showed beneficial effects (a
9% increase in weight gain and 10% better feed utilization) of pyrantel
treatment in growing pigs naturally exposed to
A. suum
on contaminated
soil.
37
The pigs were, however, exposed to mycoplasms at the same time.
The first detailed nutritional balance studies with
A. suum
in experimen-
tally infected pigs were performed in the 1980s. Young pigs, fed low or
high protein diets, and infected with 200 2-week-old
A. suum
-larvae,
showed reduced nitrogen absorption and retention, and reduced weight
gains as compared to uninfected controls,
35
but none of these often cited
differences were statistically significant, despite a remarkably high
establishment of adult worms. However, the study clearly showed
a significant influence of these luminal stages on the pathology of the small
intestine at both dietary protein levels: increased wet and dry weight
correlated with worm burden, hypertrophy of
tunica muscularis
, increased
crypt length, and a trend of decreased villus height. In pigs on a (very) low
protein diet (7.8% protein), Forsum et al.
38
found reduced weight gains in
experimentally infected pigs (600 eggs/pig) during patency but not in the
early stages of infection. The infection was associated with a 28% reduction
in feed intake and heavier small intestinal tract (thickened muscular layer
as in the previous study). In general, these trends were positively corre-
lated to worm burden, but in pigs fed a normal protein-level diet statistical
significance was not obtained. A Swedish study on naturally infected
growers showed that female pigs but not castrates with a high parasite
load (
20 worms at slaughter) had
a 6% lower daily weight gain as compared to pigs with low (or nil) load.
19
The pigs were co-infected with
Oesophagostomum
spp. at low levels.
A study with single infections of 600, 6000, and 60,000 eggs per pig did
not affect feed intake.
39
However, uninfected pigs grew 10% faster than
the high infection group (not significant) and the same animals had 13%
>
10,000 epg at start of fattening and/or
>
