When was the last time you wormed them? Still that would have been a slow weight loss.

I would mix a container of Activia and a water soluble vitamin/mineral/electrolyte (twice the recommended amount) in 1 gallon of warm (110F) water. Mix this with equal parts of a complete layer feed and serve it a rate of 3/4 cups per bird twice a day. Extra fortified water can be refrigerated for up to 5 days. Continue to have their regular dry feed available. Increase the protein level by offering cooked eggs/ground meat of some sort at mid day.

The probiotics in the yogurt will help balance their digestive systems; the vit/min/elec will balance their cardiovascular system (mainly blood calcium levels). The extra proteins will help maintain muscle mass.

Continue to rule out possible problems until you find what the problem is.

Hope all goes well.

Virgil