w/ the corn oil start out very lightly. Just spritz it on or you'll get them too loose. I like a little cherry flavoring too. Just a couple of drops.
I'd cook some corn and/or barley - top dressed with the normal ration. Can be cooked in a crock pot.
As Red stated, a small amount of oil/sunglo... too much oil & they will get runny!!
A few ounces or work up to a 1 lb. per day of a high fat content Lamb's milk replacer - top dressed. (Might be your best bet for quick results).
Work up to about a 1 lb. per day of any high fat content horse feed - top dressed.
In a nutshell... the cooked grain increases digestibility & absorption (more calories) + fat calories convert into fat cover quicker than carbs calories, IMHO (more calories). Just be careful & don't go overboard with the cooked grain or the fat supplements.
You might also consider giving them a probiotic to add more good bugs to the ruminant. I love Fastrack (but, I am a Fastrack dealer!
) & I think that it is by far the best probiotic product that I have ever used (I've tried several), but it needs to be purchased FRESH (not off a store shelf!!) & it needs to be stored in a cool environment or else it will kill the good bugs in the product & it makes the product less effective. Once you've added the good bugs, I'd also add a yeast supplement to feed those bugs. I've even poured beer on cattle feed for that exact same reason... it helps to feed the bugs. You want the digestive system hitting on all cylinders & probiotics + yeast will do that for you.
And of course the obvious... make sure that he has been recently treated for worms/parasites.
1 more thing... make sure that he is getting a high quality mineral supplement & that all the nutritional bases are covered and they need to have fresh, clean water at all times!!