my opinion is that it partly depends on the state of your land and stocking rates, , partly depends on what else you feed them and partly depends on time of year. I always have salt out as I believe that a ruminant needs sodium available at all times for good rumen health, and there's not usually much in grass. apart from that i'm never sure whether there's enough trace elements in most buckets, or just a big block of molasses but still stick one out through tupping and up to and after lambing just in case. I favour lifeline buckets, with selenium, iodine which are vital in ensuring good health, there's also zinc for feet, calcium for good bones teeth etc, the list is fairly endless. poss test your land and fresh leaf grass to see if anything lacking