Firstly, why/to which horses/how much do they feed the horses at this barn? There may be good reason for them doing what they do, so look at the specifics. Perhaps for eg, they are feeding alfalfa as a supp to adequate grazing? (Altho 6 biscs a day is a lot) Surely they don't just feed all the horses the same? If they do that, it's not a good practice at all & I would look at suppling your own feed for them to dish out.
Lucerne/alfalfa is generally a pretty good feed for horses, being rich in a number of nutrients, high energy and low in sugar. However, being high energy, it may not be appropriate & should be fed sparingly to 'easy keepers'.
Being very high in protein it may not be appropriate for older horses. Being high in calcium, phosphates, potassium, etc it also needs to be fed *as part of* a balanced diet, or else it is liable to cause other problems associated with overdose & imbalance of nutrients. It also depends where it's grown, the season/growth stage it was cut as to what exactly is in it, and some recent studies by my nutritionist suggest it can sometimes be so high in something(sorry, forget, but think it's phosphorus) that it causes severe magnesium deficiency(excess Phos. suppresses Mg), which can lead to a number of probs, including laminitis.
So while it may be good for your horse to have some alfalfa, I would definitely NOT be feeding it as the primary, let alone only source of forage.
As for the grain, why is it fed? Perhaps it's a 'ration balancer' that is effectively a pelleted supplement. If not, your horse will likely also need a supp that balances his nutrition. 12% protein is not low, so I'd want to look at how much/whether this is needed to balance the ration. Also depends what is in it. Eg. is it grain(some use that term ambiguously)? Is it sweetened? Generally unless fed for a good reason, grainy, starchy feeds can be lumped together with sweetened feeds & 'cookies' etc - they are junk food & not good for health.
Why do you give the horse grain at all? I don't understand, other than feeding some vitamins or minerals that are missing from a particular region's hay, why do we feed grain? I hope I don't come across as preachy. I genuiinely don't know why this is done. I dont understand why horses can't get enough calories from good hay?
Tee hee! Because that's just What You Do of course!
There are some good reasons for feeding grain - such as to help balance nutrients - phosphorus, especially, to provide extra 'fast' energy for hard working horses, etc. In these cases & fed properly(ie little & often, well processed because horse's systems don't digest it well), it is generally OK. But even then can be problematic and IMO there are generally better, safer feeds for energy & nutrition. Unfortunately you're right, that a lot of people just feed grain without understanding why - just because it's the traditional 'Done Thing' in their neck of the woods.