Dairy goats, especially when milked twice daily will need additional multivitamins/trace elements/calcium/copper etc etc in their diet. There are several ways of supplying it - in powder from (like Caprivite and others) or in liquid drench (most sheep drenches with added copper are good enough for goats, there are also a few goat only ones available). Licks are usually not recommended for goats.
The disadvantage of powders is that most goats are really expert at leaving the powder at the bottom of the feed bowl, mixing it in with soaked sugar beet shreds will help. Drenching means that the dose they are getting is what you want them to get, but mine HATE being drenched...
However I am now planning to switch to a regular drenching, probably once a month - a small dose for the kids, and then adult dose for goatlings and nannies.
My hay this (last) year has also been failry low in nutrients I think as it wasn't harvested until late July...