Welsh Harlequins' eggs breaking

[yoyosma]

Hi all- I have 4 WHs, two years old last August. From 6 months old 'til this late Summer/early Fall, they laid darn near an egg a day apiece; then they started molting and have really gone down in egg production. Now it's none to one a day- rarely, two a day.
I feel like they've earned a rest! So I haven't supplemented their light as I have with the chickens. But I also am noticing that there's a broken egg in the nestbox quite often. I feed them (& have throughout) Layena and free choice oyster shell (same as the chickens, who still have nice strong eggs).
All of them range around during the day, eating green stuff and bugs; but that's been consistent all their lives. They all have food and water available in their night-time coops/runs. The ducks even have shell and grit available.
Some duck egg buyers were a bit put-off by how hard the eggshells were last year, but that's not the case any more, even with the ones that don't break.
My questions are:
Will they ever go back to that prolific egg laying? And, is it normal for eggshells to get less strong as the duck gets older? Is it just because of molting? (I gather that producing all those feathers takes a bit of effort....)
Should I change their feed?
And, should I supplement their light, more for their health than for more eggs? In other words, does less light affect the shell-making process?
I'm a bit worried about one of the eggs breaking INSIDE the duck. (Should I worry about that?)
Lots of questions- thanks, in advance, for your help!

 

[yoyosma]

Now the eggs have become soft-shelled; this hasn't happened much at all before ( a few when they were first starting to lay) and now it's consistent from at least one duck.
I read about Quackers (I think the poster's name is PetDuck) peritonitis and am really hoping that we're not heading in that direction.

 

[Amiga]

Since I don't like to worry people unnecessarily, let's say you need to be aware that this could lead to serious problems similar to what Quackers is dealing with.

I use calcium gluconate, dilute it in water and add that to the layer feed. There are about four or five ducks in my flock who either don't eat enough oyster shell or don't process calcium effectively. Low calcium can lead to egg binding, bone loss, and heart problems.

 

[yoyosma]

Thanks for your suggestion- is it OK for all of the birds to have the additional calcium? It would be hard to just target the one bird that's having trouble.

 

[Amiga]

I add the calcium gluconate to everyone's feed, and right now Hazel is the only one laying, but her eggs are getting a little thin. Since I have a few ducks that tend to get thin or no shells from time to time, I feel that I am building up the flock's reserves.

Granted, there are cautions about overdoing calcium. My choice for my situation, in consultation with our vet, is to boost with 1 teaspoon Ca gluconate per half cup of water added to feed. I do this 3 to 5 times a week.

And to add extra extra for only one duck, I mash it (so far, using prescription Neocalglucon) into peas that I feed just to the affected duck.

 

[yoyosma]

Thank you Amiga, for your help and for the additional details.
I couldn't find Neo-Calglucon (looks like it's made by Sandoz, and is available over-the-counter according to my pharmacist- but I googled away in vain, trying to buy it!).
I ordered pure calcium gluconate from an Amazon supplier... so I'll probably have questions about dosage, when it arrives. I'm thinking that the dosage of 1 tsp. in a half cup of water is not the pure calcium gluconate, but rather the Neo-Calglucon. Wish I could find it!
No shell-less egg today and Jo is looking pretty perky. Weird that this started happening so suddenly.
Thanks again.

 

[Amiga]

The Ca gluconate I use is a 23% solution, if that is any help

 

[yoyosma]

Just an update- my Welsh Harlequin duck, Jo, with the breaking eggs- she did die, despite the calcium gluconate.
The other ducks are fine; I didn't do light supplementation; they have now gone back to one egg per duck per day- pretty amazing productivity. They'll be 3 years old this August.
The eggshells of the surviving ducks (and chickens) are good and strong, with oyster shell available all the time.
Sad about Jo- .
One other duck died in early 2013; no weak eggshells for her, but I think she was eggbound. I did what was suggested here and in Holderread, but she went really fast- from looking fine to dying within a few hours.