Four rumen-cannulated cows (330 kg average weight at 4 years) were used to evaluate the supplement of ensiled cassava tops (ECT) (variety KM 94, 39% DM) on rumen functions, thyroid hormones and liver enzymes. The treatments, arranged in a 4 x4 Latin square design, were ECT at 0, 50, 100 and 150 g CP 100 kg -1 body weight (BW), and a basal diet of urea-treated fresh rice straw (UFRS) ad libitum and 1.1 kg dry matter (DM) cassava root meal (CRM) in each 30 day study period. The results showed a continuous decrease in dry matter intake (DMI) of UFRS with increasing level of ECT supplement (p<0.001). The highest total DMI was observed for treatment ECT150 (2.68 kg DM 100 kg-1 BW day-1) followed by treatments ECT100, ECT50 and ECT0, with 2.47, 2.24 and 2.06 kg DM 100 kg -1 BW day-1, respectively. Increasing levels of ECT supplement increased the concentration of total volatile fatty acids (p<0.05) and ammonia nitrogen (p<0.05) and resulted in a decrease in pH (p<0.05). Overall average plasma triiodothyronine and thyroxine concentrations were 0.80, 0.82, 0.85 and 0.69 ng ml-1 (p>0.05), and 50.9, 49.5, 50.7 and 42.4 ng ml-1 (p>0.05) for treatments ECT0, ECT 50, ECT100 and ECT150, respectively. There were non-significant differences in alanine aminotransferase and aspartate aminotransferase among treatments. It is concluded that ECT is a valuable protein-rich feed supplement to cattle, and the highest level of on average 2.48 kg DM ECT per cow and day (28% of total DMI) did not significantly affect thyroid gland hormones and liver enzymes in cows.
