Morning, all, greetings from the duck pen! We have had such cold snowy weather - that to keep the ducks from going completely stir-crazy (I admit, to keep myself from doing the same), I spend more time right here with them. Glad I made the pen big enough for a person, too.
We struggle with soft shells here - I am doing some research, though not intense peer-reviewed stuff. Just trying this and that. I have found that some ducks do fine with just layer pellets. Several do not. Of those, a few do well with free choice oyster shell. But not all of them even try it. I currently add about 50 to 80 mg of calcium citrate, dissolved in water and added to their food, per duck, about 5 times a week. That has helped. While most of the flock are not laying right now, from my reading it appears that ducks can store and release some calcium, and one source indicated that fluctuating the amount of calcium enables them to retain that ability. Just sharing what I have read….
I also recently came across some research for people, that said that eating vegetables like kale enables a body to use vitamin D more effectively. And I have also read that vitamin D levels influence a duck's ability to effectively use calcium. Well.
Right now we have gone from two or three soft-shelled eggs every few days to one soft shelled egg a couple times a week, and one properly-shelled egg four to six times a week. No one appears egg-bound, so I wonder if in all this complex egg-laying, that soft eggs may be a symptom of calcium deficiency, and once calcium levels increase, the production of eggs stops till the calcium builds up to a certain level in their body.
One could make a life study of this, really.
I would check her oil gland also. Is she getting daily bath time? You could also try enrichment activities. The Ultimate Pet Duck Guidebook includes some really fun ideas for enabling ducks to express their (what Joel Salatin calls) duckness. And it appears to me, from my flock, there are emotions in the duck world. So maybe something to cheer her up will help her overall. Chopped cucumber in an unbreakable clear tumbler is something that Priss used to do for her Calls. They liked that.