I fed top quality 'race horse oats' for many, many years, often with just a mineral salt block. The horses were very fit, glossy and full of energy. They were worked an hour 5-6 days a week. No matter how hard or advanced a work they were in they were never fed more than five pounds(big warmbloods or half Thb) a day of oats - often only 2 1/2 pounds of oats(15 hand horse).
I would give one caveat to feeding whole grains with the husk/hull on: horse's teeth need to be in good condition to chew up these products and get all the value out of them. Having the teeth maintained by a good dentist is a part of feeding whole grains.
For some time, when I was boarding, my horse was fed Purina products - 200 or Omolene. They did well on them, but the price went up and most boarding barns started feeding a molasses-oats-corn based feed. That's when I started feeding oats.
In all cases, if the horses had a day off, I reduced their grain/concentrate ration by half on that day. This is to prevent the horses from getting too much starch and carbohydrates, and tieing up(exertional rhabdomyolisis). The fitter the horses were, the more I was concerned about this. Tieing up was called 'Monday Morning Disease' because work horses were fed the same concentrate ration on Sunday as all work days, and on Monday, a few minutes into work usually, they'd tie up. Cutting their grain ration allowed me to control carbs.
The problem I have with most commercial concentrate products, is if I do that, I am not giving my horse enough of the minerals and other things he needs, independent of energy food related to work. That is why I continue to feed two separate products, one for energy, and one for the basics needed for maintenance. I feed the same amount of the one product and vary the energy feeds, based on amount of work.
The best thing about oats, is the covering made of fiber. You lose that if you feed rolled oats. The fiber hull of the oat goes right along with the starch, and creates a mixture in the gut that is perfect for digesting the nutrients safely, unlike corn, barley and other grains which do not have that.
I don't feed any concentrates to horses out of work or young horses. I feel as long as they have a ration balancer providing the NRC level of nutrients for their age group, they will do well. Especially with warmbloods, we have a very serious problem with them in the US, namely, them being porked up like American breeds traditionally have been - they get osteochondrosis at incredible rates when they are fattened up while growing, as well as poor bone growth and many other problems leading to unsoundness. They need to be slim while they are growing - not poorly, not starved looking, but slim. In Europe, Warmbloods were fed among other things, straw, or hay that is something close to it, as they were growing, to prevent overly fast growth.
If you have a good quality hay and salt/mineral block, there is generally no problem feeding oats. Old time horsemen always used to say oats produces strong muscles, but I think a consistent work program is what creates muscles. If a horse does nothing more than walk around a pen or pasture (even with the occasional sprint), he's not going to muscle no matter what he's fed. It's work that makes them beautiful. A decent diet of course, but work is what makes that beauty.
People have to be careful, because the marketing people at those big feed companies is very, very able to make us believe a whole lot of things. What they don't really tell us is that they themselves change their ingredients all the time - as long as the ingredients they use add up to the percentages on the label, they are allowed. Different products can be used to make up the protein, the fat, the carbs.
That's another reason I liked to feed oats. I knew what I was feeding. That and the price. I also just liked the idea of feeding a natural grain - not something cooked, extruded or pelletized.
Today, I don't have any oats in the bin. Since I am old and have some hot horses to contend with, I feed beet pulp shreds, soaked for at least 8 hrs. It compares to oats with the same DM, 9 instead of 12 % crude protein, about 2% of the starch, double the fiber, much less fat, a lower TDN. As with oats I feed it with a small amount of a ration balancer when we have our less good quality hay in the winter. Normally, our hay tests out as very, very nutritious. Our pasture also is very, very rich, with a lot of clover and alfalfa, so if they are also grazing, I cut back on the hay, at 1 hr grazing = 1 flake hay.
My Welsh pony gets hay, no beet pulp, a very small amount of ration balancer, maybe an eighth of a cup, and no grazing. My vet's orders. He was foundered multiple times before we got him. On this regime he is not having problems. It is extremely difficult to keep him at a healthy, slim weight. My vet says most ponies are a walking time bomb, they are so fat. In fact in his practice, he says, 'there are two kinds of ponies, ones that have had laminitis and ones that are about to'. He says he tries very hard to get people to stop feeding them so much or allowing so much graze, but few people actually listen, so their ponies get laminitis. A lot. He also says that many people don't even realize their pony has foundered, because ponies tend to be kind of stoic. If they are given unlimited grazing in spring, they will get laminitis every spring.
My horses seem to view the alfalfa and clover as roughly equivalent to crack cocaine. They eat it preferentially,, no matter what else is in the field. So I often have to make other adjustments, or they are getting too much protein for adults.
I have TRIED to eradicate the alfalfa and clover. It is extremely aggressive. Alfalfa exudes a poison into the ground to keep other plants from growing, even to keep other alfalfa plants from growing near it. And because we have clay, the alfalfa and clover love it here. So I have to accomodate that so that no matter what, my horse's diet always comes close to the NRC recommendations.
But stuff gets a little tougher with nutrition for baby horses and as they get older. We have some serious problems, industry wide, with babies and old horses. Old horses are getting an awful lot of insulin resistance and other disorders, babies are getting osteochondrosis, contracted tendons, and many other problems.
Some will say all of these are related, associated, linked, even caused by high-sugar rations like sweet feed. But is it? Maybe metabolic problems in babies are caused by overfeeding in general, and we see more IR because more old horses are living longer, due to use of wormers and other management changes.
The contention today, is that feeding a diet with a little more fat and protein is better for horses, and leads to fewer complications in old age, and fewer disorders in youngsters.
It is said very often by people selling products with more fat and/or protein, but it would be difficult to prove by designiing a study. You'd have to look at horses throughout their lifetime and track very accurately, disorders believed to be controlled by diet...but you'd also need some proof that these disorders ARE to any degree, controlled by diet!
