So one of my chicks is having a difficult time going to the bathroom but I really don't think it's pasty butt. I cleaned her butt off and she just keeps chirping loudly whenever she tries going to the bathroom. I also don't think she's constipated because the poop isn't stiff or hard. The vent gets swollen and the poop just stays there until I clean it off. The inside of her vent looks red. Here's a picture of what I keep seeing and then cleaning off. I do have Apple Cider Vinegar in the water.
