Epidemiological studies on gastro-intestinal nematode infections in chickens

The first objective of this study was to monitor the establishment and development of gastro-intestinal helminth infections in laying hens over two production years (PY) on a free-range farm operating with two mobile stalls in Lower Saxony, Germany. The Second objective was to estimate the genetic parameters of worm burdens with the most common gastro-intestinal nematode (GIN) in two chicken genotypes after being exposed to free-range farming conditions for a laying period. Since the sampling time of faeces may influence information quality of faecal egg counts, the third objective was to investigate whether nematode egg excretion in naturally or experimentally infected chickens follow certain fluctuations patterns throughout the day, which may allow for determining the most appropriate sampling time. The first experiment (Chapter 2) was performed between July 2010 and June 2011 (PY1) and July 2011 and January 2013 (PY2), respectively. During PY1, Lohmann Brown classic hens (LB classic) was tested, while in PY2 two different genotypes (LB classic and LB plus) were used in parallel. In both PY1 and PY2, 20 individual faecal samples per stall were randomly collected at monthly intervals in order to calculate the number of internal parasite eggs per gram of faeces (EPG). At the end of the laying periods, approximately 10% of hens for PY1 or more than 50% of hens for PY2 were subjected to post-mortem parasitological examinations. No parasite eggs were found in the faecal samples during PY1, whereas almost all of the hens (97.6%) were infected with Heterakis gallinarum (36 worms/hen) at the end of the period. In PY2, nematode eggs in faeces were found beginning in the third month at a relatively low level, while increasing considerably towards the final three months. The average worm burden was 207 worms/hen. The caecal worm, H. gallinarum was the most prevalent nematode (98.5%), followed by the roundworm Ascaridia galli (96.2%) and the hairworms Capillaria spp. (86.1%). Capillaria spp. were composed of C. obsignata (79%), C. caudinflata (16%) and C. bursata (5%). The mortality rate of chickens ranged from 18.3 to 27.4%, but did not differ significantly between genotypes or production years.