While it may seem counterintuitive, we personally feed MORE hay, not less, to these slower eaters. I am of the opinion that very often the problem is chronic acidosis. Feeding additional hay helps to balance the rumen and will usually lead to an increased appetite within a few days to a couple weeks. Even alfalfa may be too rich. Grass hay may be more effective. B12 crumbles certainly won't hurt, but a healthy rumen is still essential.