Amanda - 2 buckets between 32 ewes twice a day sounds a lot. But so much depends on the breed and genetics; ours are prone to growing overlarge lambs if overfed and in a good year nothing but the mules would get cake until 4 weeks before lambing, some Texel types not until after lambing.
Your 'lacklustre' sheep could be ailing something - my 'go to' remedy would be a good chelated mineral drench, if that doesn't pick them up, I'd be wondering about lice or something making them feel below par? Or fluke?