I'm unable to see the album- facebook rarely works on here. Can you upload some via tinypic/photobucket?
If the colt is going on a year old, the first thing that you need to do is SEPERATE HIM FROM HIS DAM
they should NOT be together still. Especially if he is still a stud. I am very glad that you have taken him in. It sounds as if no one gave him the time of day where he was.
Once you've seperated them, you need to completely evaluate him. First, I would weigh him. If you don't have a scale, use an estimation chart such as this one. Estimate Your Horse's Weight
you then need to determine what he SHOULD weigh. You can do this by consulting a vet, or a horse nutritionist. If he is more than twenty pounds under what he should be, (I really have no clue what condition he is in, as I have seen no pictures) I would advise in talking to the vet or nutritionist and making a dietary plan for him. I'm sure that if he was in a pasture with his mother, he grazed- or if he was in a stall, he most likely took some of her food. (probably another reason she was underweight) So you shouldnt have to worry about him not knowing what to eat.
Yearlings- especially colts, do much of their growing between a year and two years old, so it is vital that you give him the right feed. Yearlings should generally get 1-1 1/2 pounds of food per 100 pounds of weight per day, plus unlimited, good quality haylage, but I would talk to the professionals. They'll know exactly what he needs.
I don't suspect that he will have too many growth problems if you catch this right now. There is a possibility of stunted growth if his mother's milk didn't have enough nutrience and he didn't get much roughage or anything, but he most likely battled for it and got most of what he needed. Either way, there isn't too much that you can do for a horse who's growth was stunted, besides being more careful with their early training when you begin to saddle train (as their bones may not be completely developed at the usual 3-4 years) I'd say just get a good feeding plan for him right now, and you won't have a problem. Those guys snap back pretty quick!
Oh, and also- it might do you some good to read this article. I found it very helpful. http://www.extension.umn.edu/horse/c...onWY_08456.pdf