Nutritional Value Of Forbs And Shrubs

The nutritional value of forage shrubs and forbs is variable, but can be high (Table 1). In many cases, the nutritional value of these species is high in comparison to tropical grasses. Because of this, forage shrub and forb species often work well as supplements in tropical areas. In temperate areas, the nutritional value of forbs can be competitive with alfalfa.[9] When considering management of these species, we need to consider not only forage quality, but other factors as well. Yield is often lower with forb species than with improved temperate grasses. In addition, there is wide variation in palatability and acceptability of forb species, which would affect a species' feeding value.[9]

Many forbs and shrubs contain materials that are deleterious to livestock. Some, such as Acacia and Leucaena, are rich in tannins, which can cause palatability problems. Tannins also bind proteins, which is deleterious when protein levels are low, but potentially beneficial at some level when protein levels and solubility are high. Species may contain cyanogens, saponins, nonprotein amino acids (such as mimosine), alkaloids, oxalates, or phytohaemagglutins, which have various deleterious effects on animals. In some cases, such as mimosine, ruminal microorganisms can adapt so that the toxic agent becomes ineffective. In other cases, limiting the amount of material eaten by the animal is sufficient to control deleterious effects.

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