Toxicity of Leucaena leucocephala for steers in the wet tropics.

Brahman crossbred steers grazed Leucaena leucocephala (cv Peru) for 0, 1/2, 1 1/2, 2 1/2, 3 1/2, 4 1/2, 5 1/2, or 6 1/2 days per week grazing Buffel grass (Cenchrus ciliaris) for the 1 1/2, remainder, for at least 50 weeks. Animals grazing Buffel grass only or Leucaena for 1/2 day only grew faster than all other groups in the wet season (0.75 dg/day) but not in the dry season (0.44 dg/day) and had normal thyroxine concentrations in blood. All other groups grew more slowly, had reduced blood thyroxine, fatter carcasses and in some cases showed alopecia, excessive salivation and goitre; 1 steer died. Poorest growth rates in the wet season (0.44 dg/day) were achieved with signs occurred with 4 1/2, 5 1/2 or 6 1/2 days of Leucaena. The frequent observation of toxicity of Leucaena when grazed by cattle under irrigated or wet tropical conditions suggests that its use as a browse legume under these conditions needs further examination.