When to stop grain

[Saltlick]

My guys never get grain, especially since my Saanen got UC last summer from (unknown to me for a long time) eating grain that was slipping through the cracks in the floor of the horse in the neighboring paddock (but he got lucky and survived with minimal treatment - it scared the shit out of me though!). I do feed the other two timothy pellets with a little black oil sunflower seeds mixed in from time to time during the winter, especially since the Saanen (well, turns out to be a mix with maybe a little Boer) is a jerk and gets the most to eat. Other than that they only get grass hay.