My pigeons have a problem of vomiting, not eating and then dying?

Once the young pigeons reach 20 days old they vomit , no appetite, lameness and they die?

This morning when feeding my pigeons i noticed one pigeon sitting on the perch whith its eye lids half closed?

The birds drink water and the water stays in the crop. The birds crop swells and the bird will die. Could you advise?

What do you suggest with pigeons with swollen heads, watery eyes ans yellow streeks in the mouth?

Mijn duiven stoppen met eten, en de spijsvertering stopt. Welke ziekte is dat en wat kan ik er aan doen?

Hoe komt het dat mijn duif geen eetlust heeft?