Beef production based on cassava products and legume foliage in Vietnam

Abstract: The overall aim of this thesis was to determine the associative effects of supplemental sources of protein, or protein and energy, using cassava products and legume foliage on rumen degradability, in vivo digestibility, feed intake and growth rate of crossbred growing cattle. First it was hypothesized that the substitution of a part of a conventional concentrate with mixed cassava and legume foliage will positively influence rumen degradability and improve the performance of growing cattle. The results showed that there were significantly higher values of rumen degradation with a mixture of cassava and Phaseolus calcaratus legume (CA-LE) feed compared to the control feed. With the same dry matter intake (DMI) of concentrate, the level of CA-LE feed did not have any effect on total DMI but live weight gains in CA-LE40 and CA-LE60 were significantly higher (551 and 609 g/day, respectively) than in the control group. Secondly, it was hypothesized that a combined protein source will result in at least the same feed intake, digestibility and growth rate as in growing cattle fed concentrate. With the same nitrogen supplement, there were no significant differences in DMI, but 30% and 19%, respectively, higher live weight gain in the group fed a mixture of foliages as compared to the groups fed only cassava or stylosanthes. The third hypothesis was that a synchronisation of energy from cassava meal and protein from the mixture of foliages would improve feed intake and growth rate of cattle. The highest nutrient digestibilities were found in the group fed both high crude protein and metabolisable energy (ME), resulting in a significantly higher daily gain, 558 g/day. In order to overcome the negative effect of hydrogen cyanide, cattle fed high amounts of cassava foliage should be supplied with extra energy in the diet. The rumen degradation characteristics of some tropical legumes mixed with cassava foliage and cassava root meal were evaluated using the in vitro gas production technique. The potential gas production of the mixture samples, indicating the level of solubility and degradability of substrate in rumen, ranking from highest to lowest, were: cassava root meal with Stylosanthes guianensis, Leucaena leucocephala, Phaseolus calcaratus, Flemingia macrophylla, and Trichanthera gigantea, and cassava foliage with Stylosanthes guianensis, Phaseolus calcaratus, Leucaena leucocephala, Flemingia macrophylla, and Trichanthera gigantea. The highest estimated values of organic matter digestibility, short chain fatty acids and ME were in cassava root meal mixed with legumes at the level of 75%. There was a negative relationship between ash content and potential gas production in individual feed substrates. No effect of hydrogen cyanide on fermentation kinetics in rumen could be detected in this study.