Well I can't think of any in relation to good gut function and a healthy weight and fibre in the form of chaff, hay or haylage encourage a horse to eat slowly. However I'm not a nutritionist, horses with weight gain problems would probably need something extra, someone else with more knowledge would know.
One problem I can think of would be the case of some poor doers with poor appetites. Because fibre is very filling, it can sometimes be difficult to get such horses to eat enough calories from fibre alone, so more concentrated food may be needed to maintain weight.
Ah now therein lies my problem. During the winter its not a problem as the minis are not working, just field ornaments!!
During summer i show Inky and i find it hard to maintain his condition with the fibre diet alone ( simple systems ) He doesnt need to gain weight but i find it hard to maintain his muscle tone and feel he isnt getting enough calories from the fibre diet alone. He isnt a big feed eater so i cant just give him more fibre as he just wont eat it. So thinking ahead to next year now ( how sad
) i was wondering how i could overcome this diet problem??? I have to be mindful he is still a youngster and a very small one at that, so riding isnt an issue to maintain condition or muscle tone!!
With a mini like him I would avoid cereal-based feeds, because of the risk of laminitis. The alternative is some form of oil in his feed - either straight oil of some kind, an oil-enriched chaff such as Alfa-A Oil or Spiller's Conditioning Fibre or perhaps an oil-rich supplement such as Outshine or Equijewel (the oil-rich supplements do work out the most expensive way of supplying oil, but you would only need small amounts for a mini).
Disadvantage - you won't believe how much poo I have to shift. When at grass, between Farra and Chancer I take off 8 - 10 barrows a week - when nights draw in I can only do this at the weekend and I feel like Hercules doing the Augean Stables
Showing - I get really good results with Chancer in the show season by feeding instant linseed, BSS and Equilbra. When I also want a bit more condition on him, though as he is becoming older he is holding his muscle and weight more - I find a bag of Spillars conditioning cubes over a few weeks before a show does the trick.
Obviously you won't need so much for your little tiddlers