Please tell me why hays high in NSC are bad for 'NORMAL' horses -- that are not obese, are not IR and are not foundered or laminitic?????
I think you mislead many people by telling them that all hay and grains the are high in starch and/or sugar are bad for all horses. That quite simply is not true.
OK, that's your opinion. IMO what you
say is 'quite simply not true'. While it does definitely depend on how much horses get, how little & often - or otherwise - they get it, how they're managed, how sensitive they are, how much exercise, etc, etc. I also do not say 'all hay & grain... for all horses' - it's a generalisation. But it is a very common problem & one that is only reasonably recently becoming understood better.
Basically it's like asking why - or denying that - lollies or other foods high in sugar are bad for humans. I don't think occasional junk food is generally a problem for people either - unless they're already IR, Cushings, etc - but if they live on it, it's not good for them & commonly causes a range of problems. Of course there are those that can seem to live on it, without obvious health probs, as you say your horses do(tho it appears that it's long term unhealthy diets that have the most effect on IR & Cushings, which is why many horses appear to 'do well' for many years before suffering), and there are those who's highly active lifestyles allow them to get by on more junk, but *generally speaking* living on high NSC diet is no better for horses as for people.
Horse's digestive systems are also built & work a lot different to ours, and 'hind gut acidosis' can also result from too sugary/starchy diets. Again it does depend on the hows & how muches of feeding, but basically horses aren't built to process high levels well. So you'll notice I generally say things like generally - but seeing so many common issues these days relating to too much & too rich feed, I tend to like to err on the side of caution.