Few health questions...

Alright, so I've noticed Loki coughing. Not a 'hack-hack-hack' cough but just one big 'HACK' when he's been out grazing. Kinda like when you get something in your throat and you 'grunt' it loose.
It's happened twice so far, once the day before yesterday and once yesterday.(it's rather loud and easy to hear) Haven't seen this at all in the other two, everyones getting exactly the same hay and grain. He has clean water, clean hay, clean grain, etc. Poop is regular.
Is the grass maybe tickling his throat? He is perfectly healthy otherwise, absolutely no changes. Let him out today, nothing.

Second, how much corn oil do you add per pound of feed? I picked up a huge bottle the other day and would like to add a little bit just for overall shine and hopefully some extra weight gain on my rescue.
My rescue is pretty darned shiny to begin with, and my youngster is also pretty shiny under his shedding coat. Loki's a bit harder to see since he's so light colored.

Third, my three-year MFT gelding, Red, really seems awfully thin on the top line and hindquarters. He just seems really narrow. He's getting five pounds of Strategy plus a square bale of hay (shared) twice a day and daily turnout onto lush grass pasture at LEAST two hours a day weekdays. Plus clean water and whatnot. He'll be going on full pasture just as soon as I can get more fence posts.
You really can't see any ribs, but they can be felt, and he actually has a bit of a belly going on. Healthy otherwise. Is he just going through another spurt? He's around 14.2 currently and should mature at 15-15.2hh. Is this normal?

Fourth, should I feed alfalfa in addition to my prairie? My rescue is happy and healthy, but he seems to be gaining weight a lot slower than before. I'm kinda hoping the corn oil I would like to ad to his feed will help out a little.
He's currently getting 10 pounds Strategy per day, plus the square bale that he shares with Loki and Red twice a day, plus the daily turnout. I barely work him, save for the once-a-week or so practice riding for 15-20 minuets.
He does love to run and buck, all three go tearing up and down the pasture at least once or twice per turnout.

Thanks guys :)

I wouldn't worry too much about the cough unless it is more than once a day or is accompanied by other signs of a problem.

You can add up to 1-2 cups of oil to a full-sized horse's feed per day. Start slowly and expect it to take a couple of weeks to see good results.

For Red, the lack of topline is most porbably lack of muscling as it sounds like he's probably getting plenty of groceries. Daily work with trotting and work over ground poles should help build his topline.

You probably don't need to add alfalfa, especially with adding oil to the diet for weight gain.

Thanks Ryle

I'll hunt down some poles and work Red over them. He's wormed and everything, it just bothers me how scrawny he looks. He IS growing though...I should just stop fretting >.<