Sweet potato vs. Sugar beet
Feedipedia,
Rabbits
Dried sweet potato tubers profitably replaced 100% of maize grain in rabbit diets, without adverse effects on performance and blood characteristics (Agwunobi et al., 1997).
Sweet potato forage [the vine ] is mainly a source of protein and contains about 15-30% CP in the DM, but the forage quality depends on the proportion of leaves and stems, the latter containing much less protein than the leaves. Lysine is the main limiting amino acid (Le Van An, 2004). Unlike legume forages, it does not contain notable quantities of antinutritional factors.
Digestibility and degradability [Ruminants ]
Dry matter digestibility was found to be 70% (Ffoulkes et al., 1978a) and dry matter degradability was in the 40-50% range (Etela et al., 2008a). Rumen protein degradability of fresh sweet potato forage was quite high (about 70%), but the undegradable dietary protein was lower than that of other protein supplements of similar degradability (cottonseed meal and Gliricidia sepium). This resulted in less digestible true protein being available to the animal for metabolism after digestion and absorption (Kabi et al., 2005).
Rabbits
Sweet potato vines are palatable to rabbits and have been found to be more palatable that Leucaena leucocephala and the foliage of other legume trees (Raharjo et al., 1985). In rabbits fed a concentrate diet, fresh sweet potato vines resulted in a slightly lower intake and daily gain (21.1 g/day) than water spinach (Ipomoea aquatica). The best DM intake and growth rate were obtained when adding Guinea grass (Megathyrsus maximus) to sweet potato vines, water spinash or a mixture of both forages, though the digestibility of DM and crude protein was lower for these diets supplemented with Guinea grass (Doan Thi Gang et al., 2006). Groundnut haulms and soybean forage were more cost effective than sweet potato forage for feeding rabbits (Iyeghe-Erakpotobor, 2007).
My thoughts,
I think those living in warm humid areas should think about growing sweet potato for rabbit feed, - When I lived in Florida.. I grew them for myself as well as rabbits, . in my opinion, - the vines were at least as valuable as the roots, [for all of us, as the vine tips [first 8 inches] and young leaves, are wonderful steamed, or stir-fried] Sweet potato vines, and leaves are readily eaten by rabbits, and sweet potato plants produce a huge amount of harvestable vine. -- both the vines and the root are low in "long stem fiber" which is a necessity for rabbit feed rations. so- a source of long stem fiber must always be available to the rabbits. [grass hay , or even corn stalks fill this need.]
People who live in areas with a frost free growing season less then 180 days, should think about sugar beet production for rabbit feed. -- as far as utilization of garden space is concerned, ..Both sugar beet, and sweet potato have a great calorie/ square foot yield. Both store well in their respective growing areas. [in the south,- sweet potatoes can be left in the garden, and harvested throughout the winter.]
I think the sugar beet is a better nutrition source then the Sweet potato [as far as rabbits are concerned] and can completely replace, grain, in rabbit rations] with good results achieved from just sugar beet and timothy/alfalfa hay. --but in the south, the long term yield of usable vine in addition to the tubers, makes the sweet potato a much better choice.
For those living in the north, kale is a great feed crop, and for those in the south both kale and collard [just another "kale"] work well to help fill the rabbit nutritional needs.
-- just a note-
-- in Florida, the soil is for the most part, devoid of most minerals for the plants to use, and very low in nitrogen as well., so feeds raised in the "sugar sand" need a lot of soil amendments, and will have a lower feed value than the same crops raised in the north, [in better soils] -so- a good mineral supplement is even more important. as well as something added to boost protein levels in feed rations.[along with coastal Bermuda, I fed perennial peanut hay, getting better results than when using the much more expensive alfalfa hay]. JMHO...
buying sweet potatoes at .20 cents/ pound, is not nearly as cost effective as buying rabbit pellets at .30 or .40 cents / pound.