dc.description.abstracteng | Regarding to a lack of experimental infection models and different maturation ability
of Ascaridia galli egg sources (Worm uteri and faeces) in a first study (Paper 1),
A.galli eggs isolated from two different sources were investigated for different
embryonic development capacities. The second study (Paper 2) showed no
protective maternal immunity against A. galli in chicken. The objective was to
investigate whether maternal antibody positive chicks are more resistant to A. galli
infection than maternal antibody negative chicks. Free-range chickens are exposed
to a high risk of nematode infections. Genetic selection for increased immunity could
be an important tool to reduce problems due to infectious diseases - estimating the
number of parasite eggs for an infectivity diagnosis can be unreliable in a free-range
system. Thus the objectives of a third study (Paper 3) were to estimate genetic
resistance to naturally acquired immune systems and infectivity diagnosis by
estimating the total specific antibody responses against most prevalent nematodes in
the free-range laying hen system.
The first experiment (Paper 1) was performed to investigate the embryonation ability
of A. galli eggs, isolated from two different sources originating from 12 worm
infrapopulations both from faeces of the living host (faecal eggs) and directly from
worm uteri after host necropsy (uterine eggs). The isolated eggs from each
infrapopulation and source were incubated in Petri dishes (n=24) containing a
potassium-dichromate (0.1%) medium for 28 days at room temperature. In ovo larval
development was evaluated every second day by examining morphological
characteristics of 200 eggs/ Petri dish starting from the day of egg isolation (d0). A
total of 72,000 eggs were classified into undeveloped, early development, vermiform
2
or fully embryonated stages. Isolation procedures caused similar damage to uterine
and faecal eggs (2.2% and 0.5%, respectively; P=0.180). The first sign of in ovo
embryonic development in faecal eggs (7%) was observed during the 24-hour period
when faeces were collected. On d28, a higher percentage of uterine eggs remained
undeveloped when compared with faecal eggs (58.6% vs 11.0%; P< 0.001).
Although a higher (P<0.001) percentage of faecal eggs entered both the early
developmental and vermiform stages, which took place primarily within the first two
weeks of incubation, there was no time-shift between the development of faecal and
uterine eggs. Starting from d10, higher (P<0.05) percentages of faecal eggs
completed embryonation compared with uterine equivalents.
The second experiment (Paper 2) was demonstrating whether chicks descending
from nematode-infected hens are more resistant against Ascaridia galli, a prevalent
gastrointestinal nematode, infection than infected offspring from nematode-free
mothers. One-day-old chick offspring (N=153) from infected (mab+; maternal
antibody+) or uninfected control dams (mab-) were experimentally infected with A.
galli at two different concentrations (100 or 1000 eggs/chick). Female chickens
exhibited significantly (P<0.05) higher specific antibody concentrations (2.355 ±
0.211). The worm burdens of the chicks were determined at 6 weeks after infection.
There was a high correlation (r=0.89, P<0.001) between A. galli-specific antibody
concentrations in dam plasma and egg yolk. Dam and chick infection doses
interaction had a significant effect (P<0.05) on worm burden and the highest infection
rate (21.2 ± 2.95) occurring in mab+ chicks challenged with +1000 A. galli eggs. In
chicks, lower doses of infection caused a difference in worm burden between the
mab +/ - groups. Chick infection dose had a significant effect on female/ male
3
harvested worms. There was also an interaction effect between maternal infection
and chick infection with respect to worm weight.
The final study (Paper 3) was conducted on two genotypes of Brown hens (LB
classic and LB plus) under practical free-range farm condition. Aims of this study
were to describe genetic resistance to immune systems and infectivity diagnosis by
estimating total specific antibody concentration (TsAb) against the most prevalent
nematodes in free-range chicken systems. Chickens (17 weeks old) of two Lohmann
brown genotypes (LB plus/ LB Classic) were examined for a laying period of one and
a half years. Individually obtained plasma of the genotypes, LB plus (n= 200) and LB
classic (n=200) were used for detecting TsAb via the ELISA test before necropsy.
Some birds were subjected to post-mortem parasitological examinations at 79 weeks
(LB plus, n= 162) or 88 weeks (LB classic, n=139) of age. There was a significant
(P<0.05) difference in total worm burden (TWb) and TsAb in relation to the genetic
background of the chickens in their response to naturally acquired nematode
infections. Positive phenotypic correlations (r=0.1, P=0.014) of TsAb with the total
epg (Tepg) before necropsy and no significant correlation (r=-0.13, P=0.1) with TWb
at necropsy were moderated. Slightly fluctuating increases of TsAb by age (weeks)
were observed.
It is concluded that isolated A.galli eggs from both sources reached a plateau of
embryonation by the end of the second week of incubation, with faecal eggs having
more than a two-fold higher embryonation ability. Cumulative mortality was higher in
uterine eggs (14.3%) when compared to faecal eggs (0.2%). Although lower worm
burden in mab- chicks with resistant tendency against A.galli pathogen in maternal
antibody positive (mab+) offspring was demonstrated, no protective immunity against
A. galli infection was observed. In this free-range chicken system, the LB classic
4
genotype was more susceptible to gastrointestinal nematodes than the LB plus
genotype with higher total antibody responses before necropsy and lower total
antibody responses at necropsy. Estimating total specific antibody responses is
meaningful for infectivity diagnosis in a free-range chicken system. | de |