Sick Legorn... Help!!

I have around 30 leghorns (mixed colour) 15-17 weeks old in a 80 x 80 ft pen (movable fence) with fresh grass. I found one in the shade yesterday which seemed tired and weak, didnt want to stand. I took it in overnight with water & feed. Didnt seem to drink but had a go on a banana which seemed promising. It did stand overnight but during the day would just sit. I noticed its dung was mainly just a bound string of undigested grass and was about 5-6 inches long and unbroken from its cioaca so i gave it helping hand and gently pulled the rest out (about another inch)..... it died about 30 seconds later. Not sure how long it had been sitting sick in the pen could of been days? Some of the hens are are a little older than others and not sure if this was a younger one or not, its comb was fairly undeveloped but also seemed quite small and dry while sick. Its eyes were more black than colour. I have no roosters in with them. Hope someone can help.
Dean from New Zealand