Mine can get a bit hyper on too much sugarbeet even unmolassed but as it's only one of the ingredients I can't see feeding the quantities needed to have this effect being very likely.
Thanks, I tend to have fed 3/4 scoop once a day, but I've been accused,on Facebook no less, of feeding him nearly a whole bag over 3 days. I managed to overlook the hyperbole on that occasion, but it does get old.
Feed gets a bad press when it comes to behaviour. Feed only affects behaviour if the source of energy from the feed comes from cereal starch so unless fast fibre contains cereals it probably isn't affecting your horse. If your concerned check the starch content of the feed. A non heating feed is considered 20% starch or less, how ever some sensitive horses would need 15% or less.
There's always one that gets heated up on anything more than a bucket of water haha. Ignore them, I thought fast fibre was so low in calories it actually can be fed in huge quantities as a sort of forage replacer for a poor doer? That's just what I've seen on here anyway, a bag in 3 days would be pretty epic!
They are probably the same people who go crazy if you mention sugarbeet because sugar is bad, and you have to explain that it is a by-product of sugar production and therefore the sugar has been removed... Unless you add molasses.