Serum thyroid hormone levels of heifers grazing leucaena leucocephala in southern Taiwan.

This study investigated the effect of prolonged ingestion of Leucaena leucocephala, a leguminous shrub with a potential as a source of animal feed in Southern Taiwan, by heifers on serum thyroid hormone levels. Ten crossbred beef heifers were divided into treated (grazing Hawaiian wildtype leucaena) and control (grazing Pangola grass only) groups of 5 animals each. The heifers grazing leucaena exhibited significantly (P less than 0.001) lower serum total triiodothyronine levels and also showed a tendency (P less than 0.10) for a lower thyroxine level. Growth rates to 90 days were 0.26 +/- 0.02 and 0.17 +/- 0.02 kg/day for heifers on Pangola grass and leucaena pastures, respectively. The difference was significant (P less than 0.05). Three of five heifers grazing leucaena showed severe hair loss from the tail and other parts of the body. Our results suggest that leucaena toxicity to animals may be present in Southern Taiwan.