I'd go for plenty of fibre plus some source of oil. Make sure horse is getting adlib hay/haylage, then perhaps you could change your chaff for an oil-enhanced one such as Alfa A Oil or Spiller's Conditioning Fibre. (Should point out that I have heard some people say that their horses get fizzy on alfafa, but mine have always been fine - I suppose it is a case of trial and error).
Not only will the oil add extra calories, it will also add a nice coat shine which is always a good thing for showing!
what about calm & condition. it kept the weight on my TB. i did try the cherry chaff but it gave them both the runs. i think it might have had to much oil in it .
My mare is on Calm & Condition and Alfa A Oil to put weight on and everyone is commenting on the difference in her. Hasn't sent her loopy (no barley in the C&C) whereas the cereal based D&H veteran conditioning mix did make her quite fizzy.
Plenty people swear by C&C. Maybe worth calling Allen & Page for advice?
i use spillers fibre cubes or speedi beet for weight gain without the fizz. good thing about the fibre cubes is that you can also put some in a snack ball in stable or field too!
Im with tgm alpha with oil, if your boy is already on pasture mix you could move on to build up from d and h I use build up if my skinny tb looses weight it doesnt fizz him up
I had my chap on Spiller Conditioning cubes but he was a bit loopy - their advisers recommended slow release comp vubes as they have less starch worked well if you want a horse well covered & fit rather than showing podge!
I feed my show horses C&C, alfa oil and copra meal for those that need extra conidtion - cant recommend c & c highly enough - for condition without fizz