Nutritional suitability of viscid and whitethorn acacia for ruminants

Leaves and pods of viscid acacia (Acacia neovernicosa Isley) and whitethorn acacia (Acacia constricta Benth) shrubs were analyzed for their nutritional suitability for livestock and wildlife. Leaves and pods were collected in mid-summer and at the end of the growing season in 1993 and 1994 from two sites in southern New Mexico in the Chihuahuan Desert. Chemical composition was determined by standard laboratory procedures. Pods of both species generally contained more crude protein, and phosphorus than the leaves. The difference in protein content between leaves and pods was not as great for whitethorn acacia as for viscid acacia. Calcium content of leaves for both species in 1994 (a drought year) was nearly double the calcium content measured in 1993 (near average precipitation). The amounts of crude protein, phosphorus and calcium in leaves and pods were adequate to meet the nutrient requirements of young immature animals and lactating females of livestock and wildlife during the summer and fall seasons. However, besides having thorns, both species also have secondary compounds including tannins and phenols, which reduce palatability and may limit intake and negate any benefit of the high crude protein content. Although a direct comparison was not possible, whitethorn acacia appears to have a higher potential forage value than viscid acacia because of higher protein content and lower tannin and phenol content. In southern New Mexico, desert grasslands, once common, are today dominated by many shrub species of low palatability. Both viscid acacia and whitethorn acacia species appear to have palatabilities similar to or higher than the two most common shrubs on these desert rangelands, mesquite (Prosopis glandulosa Torrey) and creosotebush [Larrea tridentata (D. C.) Coville]. With the continued decrease of herbaceous forage on these rangelands, and the continued expansion of the populations of these two acacia species, both have the potential to become more valuable as browse components in the diets of grazing animals. Key words: Viscid acacia, whitethorn acacia, crude proteins, condensed tannins, total phenolics, Chihuahuan Desert