At what age should I worm my chicks for the first time? My Welsummers and Sebrights are about 9-10 weeks now, I have some others in the range of 6-8 weeks. Okay time to worm with Ivermectin? Or should I let them grow some more? I've been wanting to worm them badly but was afraid of doing it to early and either killing them or causing serious digestive upset.