because she eats 2lbs of strategy and hay all day until it runs out and she is slim.i would not say she is under weight,
It actually doesn't hurt horses(or us
) to lose a bit of weight. In fact it's long term 'good condition' or being overweight, no regular 'hard seasons' to use up fat stores that commonly causes metabolic diseases. Of course you don't want your horse getting too thin, but I'd wait until/if she might need extra before feeding, rather than pre-empting & feeding her extra 'for Justin'.
As desert said, first & foremost, I'd ensure she doesn't run out of hay, but if you use a slow feeder, she won't be able to gorge on it either, so it may not mean she needs more
If fed 2lb of strategy all at once, only once a day, she's probably not getting a lot from it & may also be suffering gut probs which cause her not to be an 'easy keeper'. It's possible that simply stopping feeding that will allow her to digest/process her feed better.
also are alfalfa cubes and alfalfa pellets considered equal or are cubes better ?
I don't know about cubes - are they just compressed hay/chaff? If so, that would be better than more processed pellets. But remember the more processed stuff like that often is made from sweepings & such, the more processed the less nutrients it may retain, and horses' digestion also benefits from chewing of long stemmed fibre, so if feeding lucerne/alfalfa, I'd opt for hay, or at least chaff, rather than the more 'fast food' type.
So... all types of feed are best fed little & often, and you need to start gradually anything new - for eg. if you wanted to feed a whole cup of flax daily as Desert suggested, I'd start with a 1/4 cup & increase gradually over a week or so. If feeding starchy &/or fatty/oils, it's more important not to feed infrequent/large meals. But as per previous, if/when there is a need for extra energy, there are healthier, more easily digestible options such as rice bran, beet pulp, etc.