Pat - have you tried Dwarf Essex Rapeseed (or canola) in a side by side comparison with the turnips? Both are brassicas, and similar in feed/protein - I think the Rapeseed is alot cheaper though.

I tried the Rapeseed once as a Nurse Crop for clover - the big leafy leaves shaded the small clover all through a very dry summer, and I ended up with one of my best clover plots ever. I wish I could say the deer " turned on" to the Dwarf Essex Rape - but they never seemed to give it a second look, as they browsed the clover very heavily.