Abstract
The overall objectives of this thesis were to study the dynamics of gastrointestinal helminth infections in chickens kept in free-range or backyard systems under different environmental conditions. Studies were conducted on commercial laying hen farms in a temperate region in South Tyrol, Northern Italy and on small-scale farms in a tropical environment in Northern Thailand. In the first experiment (chapter 3), faecal egg counts of laying hens kept in mobile houses at two South Tyrolean farms in Luttach/Ahrntal (farm A) and Kastelruth (farm B) were conducted over one laying period. On farm A, sampling took place from September 2015 until July 2016 and on farm B from October 2016 until September 2017. In the mobile house of farm A 225 Lohmann Brown hens and on farm B two dual-purpose genotypes (purebred Les Bleues and crossbred New Hampshire x Les Bleues) were raised. Individual faecal samples were randomly collected from 20 to 40 individuals at monthly intervals throughout the laying period. Samples were analysed using a modified McMaster method for the number of nematode eggs (differentiated for Ascaridia galli/Heterakis gallinarum and Capillaria spp.) and coccidian oocysts. Averaged over the entire laying period, A. galli/H. gallinarum, Capillaria spp. and Coccidia were detected in 33.3%, 16.7% and 9.8% of the samples in farm A, respectively. In farm B the corresponding values were 2.7%, 3.6% and 15.5%. The average number of nematode eggs and coccidian oocysts per gram of faeces were 188 ± 395 and 35.9 ± 168 in farm A, and 9.2 ± 73 and 298.4 ± 2,136 in farm B, respectively. There was no significant difference in the prevalence of the different helminth species (P > 0.05) between the two genotypes of farm B. In summary, the infection rates and intensities were low during the entire laying period in both farms. For the second trial (chapter 4), a total of 280 hens were collected from 10 conventional and 4 organic free-range farms located in South Tyrol at the end of the laying period between September 2015 and July 2016. After slaughter, gastrointestinal tracts were examined for the presence of helminths. Individual faecal samples were taken to estimate faecal egg counts (FEC) and oocyst counts (FOC). Almost all hens (99.3%) were infected with at least one helminth species. Average burden was 171 ± 261 worms per hen. H. gallinarum (95.7%), Capillaria spp. (66.8%) and A. galli (63.6%) were the most prevalent species. Tapeworms were found in 30.7% of the animals. The percentage of FEC-and FOC-positive samples was 55.5 and 14.4%, respectively. On average, 258 ± 533 nematode eggs and 80 ± 421 coccidian oocysts were found in faecal samples. Overall prevalence did not differ between farming systems, but total worm burden was higher in organic than in conventional farms. Hens in organic farms had higher numbers of H. gallinarum and A. galli worms than conventional ones. Six out of the ten conventional farms used one or two anthelmintic treatments during the laying period. However, no differences were found regarding prevalence and infection intensity between these two groups of farms. For the third study (chapter 5), gastrointestinal parasite infections in a tropical environment in Northern Thailand were investigated in Thai indigenous chickens kept under extensive backyard conditions in small-holder farms. A total of 208 Thai native chickens (98 males and 113 females) were collected between December 2016 and May 2017. At the end of the fattening period (12 to 15 weeks of age), chickens were slaughtered and faecal and post-mortem parasitological examinations were conducted. One hundred and fifty six chickens were helminth-positive (73.9%). Out of the infected animals, 72.5% were infected with nematodes, while cestodes were found in 27.7%. An average worm burden of 33.0 worms per bird was found with the most prevalent species being the nematodes H. gallinarum (70.6%) followed by A. galli (60.2%) and Capillaria spp. (44.1%). The percentage of FEC- and FOC-positive samples was 33.7 and 55.4%, respectively. On average, 111 ± 328 A. galli/H. gallinarum eggs and 2,983 ± 11,641 coccidian oocysts were found in faeces. The prevalence of A. galli was higher in male than in female hosts, while the total infection rate and worm burden did not vary between sexes. The median worm burden was 15 (range 0 - 261) worms per male chicken and 8 (range 0 - 215) worms per female chicken. In summary, the results indicate that the vast majority of chickens kept either under mountain farming conditions in Italy or under the common extensive backyard production conditions in Thailand were infected with a broad spectrum of helminth species and coccidia. The high level of infections indicated that both geographical areas provide favourable conditions for helminth infections. Therefore, it is essential to adopt alternative control and management strategies in addition to the use of anthelmintics in order to minimize infection risks under the current production conditions.