Performance of growing heifers fed urea treated fresh rice straw supplemented with fresh, ensiled or pelleted cassava foliage

Sixty-eight growing heifers were used in three experiments to evaluate the effects on feed intake, growth, liver enzymes and thyroid hormone status of four supplemental levels of cassava foliage: 0 (T0), 50 (T50), 75 (T75) and 100 g (T100) crude protein 100 kg− 1 LWt provided by fresh, ensiled or pelleted cassava foliage in diets based on urea treated fresh rice straw (UFRS) ad libitum, 0.72 kg dry matter (DM) of napier grass and 0.26 kg DM of cassava root meal (CRM) 100 kg− 1 LWt. The ensiled cassava foliage (ECF) supplement experiment was conducted from June to October in 2002, and the fresh (FCF) and pelleted (PCF) cassava foliage supplement experiments from February to June and August to December in 2003, respectively. The results showed that increasing the level of cassava foliage supplementation in the all experiments slightly decreased UFRS intake (p < 0.001), but to a lower extent than the added amount of cassava foliage. The highest total DMI was on the highest level of cassava foliage supplement (T100). At the highest level offered, of 100 g CP of PCF 100 kg− 1 LWt day− 1, the heifers readily consumed all PCF, while the daily intakes of the FCF and ECF were 80% and 94% of the amount offered, respectively. The daily intake of HCN on T100 for heifers fed FCF, ECF and PCF were 1.94, 0.52 and 0.17 g 100 kg− 1 LWt day− 1, respectively. Increasing the levels of ECF and PCF supplement significantly increased live weight gain (p < 0.001), while the increase was not significant for FCF. Daily live weight gains at T100 were 0.160, 0.233 and 0.266 kg day− 1 for FCF, ECF and PCF, respectively. Significant effects of FCF level were found on triiodothyronine (p < 0.01) and on thyroxin (p < 0.05) when comparing T75 and T100 versus T0 and T50, while the levels of free thyroxin, thyrotropin-stimulating hormone, aspartate aminotransferase and alanine aminotransferase were not significantly different at all FCF levels. Thyroid hormones and liver enzymes did not differ among treatments (p > 0.05) in the PCF and ECF supplement experiments. It is concluded that FCF with its high HCN and condensed tannin content was slightly unpalatable, had a negative effect on circulating thyroid hormones at higher supplemental levels and an adverse effect on growth rate, while ECF and PCF supplementation resulted in improved growth rate without adverse effect on thyroid hormones and feed intake when fed to growing heifers.