Dispite what some people think not all horses in the same field need to be on the same worming schedule. Certain horses in the herd shed more worms then others, those are the horses that need to be wormed more vigilantly, but all of them should be tested for infestation. And not even a fecal test will give you a definate answer, there are worms that wont show up on a feecal test.
Instead of getting feeding advice from someone on this board, get it from your vet, as most people on here do not live in your area of the world. And not all products available in the US are available in every country.
My BO's had the vet out the other day, who dewormed them all. I think you guys were right. And he gave us a special feed for them that should put some weight on them in a few weeks :) called Afriwing or something like that. He also told us that the grass they ate wasnt helping cause it was kinda dry or something like that... but we did have a very dry summer so maybe.
Just thought I'd tell you guys, Im going to see them on Saturday so I'll be able to make sure their fed. I'll post pics soon, once I see results. So thank you all SO much for your thoughts and tips, Im sure it's going to work!! I'll keep you updated too :)