Forage Potential of <i>Opuntia</i> Clones Maintained by the USDA, National Plant Germplasm System (NPGS) Collection

Short term gas exchange measurements and long term field trials have confirmed the several fold greater water to dry matter conversion efficiency of cactus than C3 and C4 plants. The protein and dry matter digestibility of Opuntia typically are in the 60 to 70% range and are on par with other high quality forages. While the protein content is low (ca. 6%), as is usually observed in unfertilized rangeland, fertilization can increase the protein to 10 to 15%. The high mineral content (4.2% Ca and 2.3% K) would appear to be beneficial to lactating animals. The high water content, maintained in drought periods, is useful in meeting animal water requirements. In both Mexico and the USA spiny varieties have been utilized by burning off spines in the field with propane torches, or by use of stationary forage choppers at the dairy/feedlot. Spineless varieties require intensive fencing for protection against wildlife and uncontrolled livestock. Spineless varieties generally have less tolerance to freezing weather than spiny varieties. It has been estimated that about 400 000 ha of spineless varieties have been planted in Brazil, from 700 000 to 1 000 000 ha in northern Africa and that cactus was an important forage component on 3 million ha of grazing lands in northern Mexico. The majority of the spiny and spineless types used worldwide for forage are preserved in the USDA NPGS germplasm collection. This paper reviews the environmental adaptability and most important nutritional characteristics of major forage clones. Spineless clones are described that are adaptable to USDA cold hardiness zones 7, 8, and 9.