Mites feed on a chicken’s blood. Leading to anemia, causing weakness and affecting the chicken's ability to properly absorb nutrients, like calcium, which is crucial for strong eggshells.
The irritation caused by mites leads to stress which can cause soft or shellless ones.
If a hen is battling mites, she may not eat or drink properly, which leads to deficiencies in critical nutrients like calcium, vitamin D, and phosphorus.
Mite infestations can weaken the hen’s immune system. A weak immune system means the hen may struggle to metabolize calcium and other nutrients effectively.
I'm glad you are working on the mites. Elector PSP is particularly effective if you haven't tried it yet and you can use it directly on chickens - as well as their coop.
I was just dealing with a hen laying shelless. I gave her 300 mg of calcium with D3 (just the OTC from Walmart) and she's back to laying regular eggs. Her issue isn't mites though. However, I hope you manage to eliminate the mites for her health. I would wait to see if she improves after the mites are gone first though.