Effect and repeatability of Ascaridia galli egg output in cockerels following a single low dose infection
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Three groups of caged 20 Tetra-SL cockerels aged 1 day were orally infected with 30, 60 or 125 embryonated Ascaridia galli eggs. After 11, 12 and 13 weeks, faecal egg counts (FECs) were determined. All birds were slaughtered after the last sampling. A group of 25 control birds was sampled and slaughtered in parallel. The gastrointestinal tracts were examined for the presence of adult stages of A. galli. A random sample of 10% was also examined for the presence of immature stages of A. galli. The group with an infection dose of 125 eggs showed the highest average worm burden (p<0.05) and number of females (p<0.05), but the mean establishment rate was the lowest in this group. There was no significant difference in the mean logFEC between the groups. The logFEC per female worm was the highest in the low infection group (p<0.05). The average worm length and weight and the birds body weight were not significantly different among the groups. The estimated repeatabilities for mean logFEC of the different samples were reasonably high (0.55-0.87). This may open a way of genetic selection for A. galli resistance in chickens, which will be of importance for birds kept in alternative and organic farming systems.