These crops are members of the mustard family and belong to the genus Brassica. The forage brassicas are readily eaten by livestock and can be divided into two groups:
Under favorable growing conditions, rape and turnips are ready for grazing earlier than kale and rutabagas, but yield less. Brassicas can provide much needed high-quality forage during periods when the perennial forage supply is limited (October to December). They should not be used as the sole source of feed because they contain more than 90% water, are very low in fiber content, and contain substances that may become toxic upon prolonged (several weeks) feeding of an all-brassica diet. Flowers of turnips have a high content of mustard oil which can be toxic to animals. Also, turnips may cause an off-flavor in milk. Immature rape can be high in nitrate, especially with high nitrogen fertilization. Brassicas will grow on a wide range of well-drained soils.
Luginbuhl, J-M. 2006. Pastures for Meat Goats. In: Meat Goat Production Handbook, ed. T.A. Gipson, R.C. Merkel, K. Williams, and T. Sahlu, Langston University, ISBN 1-880667-04-5.