Helminth infections in laying hens kept in alternative production systems in Germany - Prevalence, worm burden and genetic resistance

Abstract

The aim of this study was to investigate the spectrum and intensity of helminth infections, as well as to estimate seasonal effects on the prevalence and burden of helminths in organic free range layers in Germany. Furthermore, resistance of six common commercial laying hen strains to an experimental Ascaridia galli infection was compared. In a next step genetic parameters of resistance to a natural mixed infection under field condition were estimated for two commercial breeds. The experiments were conducted between 2007 and 2010 at the Department of Animal Sciences and on a commercial laying hen farm. For the first trail (chapter II), laying hens from organic free range farms were collected between 2007 and 2010. The hens were sacrified and the gastrointestinal tracts were examined for the presence and intensity of helminth infections with standard methods. Hens slaughtered from October to March were included in winter data, whereas hens slaughtered from April to September were included in summer data sets. Almost all hens harboured at least one worm of one helminth species. Average worm burden per hen was 218.4 worms. The most prevalent species were the nematodes Heterakis gallinarum (98 %) followed by Ascaridia gali (88 %) and Capillaria spp. (75.3 %), whereas the overall prevalence of the cestodes was 24.9 %. Total worm burden was significantly higher during the summer season when compared with animals slaughtered during winter season. Risk of being infected with any of the nematodes was higher in summer than in winter. Probability of infection with any of the tapeworm species was higher in the summer than in winter. For the second experiment (chapter III) six genotypes of commonly used commercial laying hens, namely Lohmann Brown (LB), Lohman Silver (LSi), Lohmann LSL classic (LSL), Lohmann Tradition (LT), Tetra SL (TETRA) and ISA Brown (ISA), were compared for their ability to resist an experimental Ascaridia galli infection. Laying performance, feed intake, change in the integument and faecal egg counts were determined during the experiment. The hens were infected at the beginning of laying period and slaughtered 105 d after infection i.e., at an age of 35 weeks, to determine their worm counts. Significant differences in average worm counts of the genotypes were quantified. LSL hens had the highest (25.8) and LT hens had the lowest (12.9) worms per hen. Although worm burden of LSL hens did not differ than those of TETRA and ISA, they had higher worm burdens than LSi, LT and LB hens. ISA hens also had higher worm burdens when compared with LT and LB hens. LSL and ISA hens had higher number of larva than LSi, TETRA, LT and LB hens. No large differences were observed among the genotypes for the performance parameters. For the third trail (chapter IV), groups of Lohmann Brown (LB) and Lohmann Selected Leghorn (LSL) hens were reared under helminth-free conditions and kept afterwards together in a free range system. Mortality rate, body weight development, laying performance and faecal egg counts (FEC) were recorded during a 12 month laying period. At the end of the laying period, 246 LSL and 197 LB hens were necropsied and worms counted following standard methods. LB hens showed a significantly higher average number of adult H. gallinarum, Capillaria spp. and tapeworms when compared with LSL animals. In total, LB had a significantly higher worm burden than LSL. The estimated heritabilities for total worm burden were on moderate in LSL and high in LB. It can be concluded that the vast majority of hens in organic production systems is infected with a broad spectrum of helminths. However, within- and between-breed variation and heritability estimates reported in this study suggest, that it is possible to select for helminth resistance in both breeds based on worm counts. Such an approach should be considered sustainable as an explicit genetic progress for resistance against each single nematode species can be achieved from short to long terms. This may be of importance for chickens kept in alternative and organic farming systems.