Now the one thing yall are missing is: How big is the OP's horse?
Horses under 1100 lbs can maintain very well on a good-quality hay if they're not in heavy work. Pasture ornaments and light riding of those weights can meet their nutritional requirements through hay alone in some cases, especially if the hay tests well.
This is not always the case for a horse over 1100 lbs who is working harder than a trail ride or a 30 min leisurely ride once or twice a week.
It comes down to nutritional density per lb. Smaller horses have smaller nutrition requirements. Big horses have bigger nutritional requirements. Sometimes the big horses simply cannot eat enough of a particular hay or forage to meet ALL of their requirements, especially while in moderate to heavy exercise, and especially in sports like racing, jumping, and barrel racing which also require some level of starch present to fuel anaerobic muscle activity.
Hay alone, even grass alone, is simply not dense enough in minerals to meet the daily intake of a 16hh 1250 lb barrel horse (for example). Whereas, it might totally be with a couple lbs of oats for a 14hh, 950 lb trail horse or casual riding horse.
The question is not "horses can/can't live only on hay".... mineral deficiencies can be silent. Magnesium deficiency = tying up. Calcium deficiency = epiphysitis in young horses, Bighead syndrome, fractures, weakness of bones. (Because no yearling halter horse ever got epiphysitis, right... I mean, they have SO MUCH body condition!)
Body condition is not everything. Mineral imbalances and deficiencies (and rarely, excesses), can cause serious health and soundness problems down the road. If you're raising a weanling, you need to make sure they're getting enough minerals and that their calcium : phosphorus ratio is 2:1. Too often it ends up in reverse with high phosphorus and then hey presto, people wonder why that foal later needs joint injections.
We don't know if the OP's horse can make do with JUST hay right now, because:
1) We don't know the age and weight of the horse.
2) We don't know the current workload or type of workload of the horse.
3) We don't know what her hay tests at or how many kg's/lb's she currently feeds, roughly. (Unless the horse is out on a round bale free-choice 24/7).
Maybe her horse needs just the minerals balanced, maybe it needs nothing at all... maybe a complete feed would be better, maybe a complete feed with starch, maybe a complete feed with low-starch.
OP, I'm in Ontario, too... if you're in Eastern Ontario, you can get Triple Crown feeds in some areas. The next best is Buckeye, but it's bloody expensive right now. Purina is third on that list--- the Equilizer, Integri-T, and Evolution Elite are my personal choices of all their feeds.
Depending on the answers to those three questions, something from Purina could easily fit the bill. I fed those three Purina feeds for a few years before switching to Triple Crown, and they did all right.
At one time, I also fed beet pulp with whole oats and a top dress of Purina Equilizer... pretty sure Sugar Bear won his first Congress polebending championship on that mix, so I guess I'll say it works all right for barrel horses. Lol
13 year old Quarter Horse gelding weighing approx 1100lb as of spring 2012 (I would need to re-tape to get an updated estimate). Free choice grass hay that has not been tested. Worked currently twice a week for ~two hours each time of mainly trot & canter arena work. Previous work load was a mix of arena and trails 3-4 times per week at about 2 hours each time with again a lot of trot, canter and hill work. Actually started looking at the clock recently. Hope to be team penning this season. Health concerns: arthritis both hocks, hoof concerns: previous very slight rotation of left front coffin bone and has previously had caudal heel pain in both fronts (mild calcification of navicular bone on right front 3 years after diagnosis). Previous bad thrush problems. Previous veterinary concerns of IR/Hypothyroidism ... blood work normal and re-checking this spring if funds are available.
This winter we had a very bad problem with rain rot and mud fever. That is why he has been getting supplemented with oral Vitamin AD from Jeffers. I did not start this until the end of December so we're just finishing the first month and it will no longer be a weekly supplementation ... I have been fallowing directions laid out by a member here.
This is why I do not want to take him off a RB or supplement altogether as I don't think he will thrive on hay alone. He would survive, no doubt. However to me surviving is just not enough ... especially the winter months where the hay is more then likely lacking in areas. The BO has not tested and I cannot afford to test at this time (cannot afford to purchase the hay probe to get samples let alone the cost to send it off). Maybe in a few months the situation will be different. I would certainly love to know but at this time I have limits.
I have contacted the area rep for Purina and she provided me with information on the Equilizer and Optimal. Currently awaiting NSC values on both of those products. I would most likely use Equilizer. It's not far off from the Gro n' Win apart from a little lower in vitamin/minerals in comparison and does not contain biotin or omega 3's as far as I can tell from what was provided to me (will need to double check the website) nor do I know the NSC content at this time.
The option I wanted to consider for a loose vitamin/mineral supplement to top dress over something like beet pulp ... defiantly not going to be an from what I can find locally. It's simply not going to come close to what a commercial pelleted RB is going to give me. For this reason it's out unless I can find something different OR get the hay analyzed to know for sure.
I created sheets in excel to compare the different feeds (Gro n' Win, Purina's, KER All Phase) so I will have to post these shortly when I am off work. This is helping me make a more informed decision ... sitting down and looking at values to compare and then comparing cost.
Thank you everyone for the advice and product recommendations. Unfortunately I am unable to get some of those products around here. If I can't get the bill down then I'm not going to be overly upset but it never hurts to look and it certainly makes you analyze things a little closer.