Ascaridia galli and Heterakis gallinarum are the two most important gastrointestinal-nematodeParasitic worms with long narrow and threadlike bodies that reside in the gut of an host animal. The… species, challenging the health and welfare of chickens. They impair host performance through reduced feed intake and lower feed conversion efficiency. However, infected chickens can expel vast majority of worms through humoral and local immune responses. Previous data indicate that there might be trade-offs in allocating metabolic resources between defense and performance functions in high performing chickens exposed to pathogenic challenges.