I took the remaining wheat back to the shop and they gave me a replacement bag. That doesn't help my birds, but it's good enough (and frankly I was surprised that the store attendant took me seriously). However I think she soon realised it wasn't coccidiosis and I do know what I'm talking about.
At any rate, three days after removing the suspect wheat, I'm seeing my first eggs from these layers. The two (rooster and hen) that were ailing have improved to being indistinguishable from the others.
It's a great relief, but also a reminder as to how easy it is to forget a basic principle (the basic principle being, examine feed closely and don't use it if there's anything amiss). Wheat that doesn't sprout well is surely a huge sign of a problem.
Silly me, but it's fixed now... hopefully.
A couple of weeks ago my usual grain store was shut, so I bought 2 bags of wheat from the more expensive place up the road.
Straight away it went into plastic drums with good lids, so I had no reason to think there would be any problem. However I noticed over the following week that this wheat doesn't soak up water quite as well as normal, and its sprouting rate is somewhat reduced. That is, only about half the grain will sprout at all, and it's usually beginning to moulder before the second day. I've never had wheat behave like this before, and I've been sprouting for years now!
Meanwhile some point of lay birds I got earlier have still not come into lay and two of the commercial meat hybrids had a few days in which I could see that they weren't well. Both carried their tails low and were a little listless.
The little chicks are eating exactly the same food as the older birds, with one difference: instead of sprouted wheat forming the chief grain, they've been getting mainly bran and pollard (mixed with all the other things I usually mix). They've also been given extra soy and kefir. They're doing incredibly well and look absolutely super.
I've realised the wheat is most likely very old, and has been improperly stored, or damaged, perhaps by beginning to germinate some time ago. Whatever the case, it's bad.
Now that can happen with other feeds as well, so please don't be put off sprouting. If I look close I can see that this wheat is slightly greyer than usual, and has a dimpled appearance, as though it's been withered. I can't see signs of weavils (which I've had in the past when wheat is poor) but it does appear the seed coat is damaged. Most importantly though, it's barely sprouting even though conditions are perfect (good clean water at 3/4 of the bucket, only 1/4 being wheat; good storage here; hanging in shade; and daily rinsing).
If I haven't poisoned my birds completely, I should start seeing eggs within a week or so of taking that wheat out of their diets...
But it's a wake-up call, at any rate.