Non-genetic factors influencing helminth infections in chickens: an emphasis on nutrition
Infections of laying hens with several helminth species are re-merging in the European countries. This is mainly because of the structural changes occurring in the housing systems of the modern husbandry. There are several environmental factors that affect establishment and further spread of the infections in layers. The most prevalent helminth species are the gastrointestinal nematodes, Heterakis gallinarum and Ascaridia galli, which have direct life cycles. Their eggs are thick-shelled and highly tolerant to the barn or external climatic conditions. Floor husbandry systems, particularly with outdoor access, enable completion of the life cycles and accelerate new or re-infections due to the efficient faecal-oral transmission route even if at lower stocking densities. Despite the growing interest in research, there is still no efficient vaccine against any of the chicken-helminths. Certain dietary factors (e.g., fibre) favour infections with nematodes, whereas some others (e.g., lysine) may reduce impact of the infection on chicken performance. Egg-shell degrading microfungi species may reduce environmental contamination. It seems that the nematode infections of chickens will be inevitable unless considerable changes in the housing systems take place in the future. Therefore, in addition to an improved hygiene and disinfection status in the farm, reducing adverse effects of the infections on animal welfare and performance may contribute to long-term sustainable solutions.