Effect of molasses or rice gruel to urea supplemented rice straw on its intake, nutrient digestibilities, microbial N yield, N balance and growth rate of native (Bos indicus) growing bulls

The possibility of using gruel compared to that of the cane molasses as a source of readily fermentable energy for a urea supplemented straw diet has been studied. Twelve native growing bulls of 237+_ 8.7 kg live weight and 35 months old were randomly allocated to three treatments fed solely rice straw enriched with: (1) 3% urea (US), (2)3% urea + 15% molasses (UMS) and (3) 3% urea + 30% rice gruel (UGS). The feeding trial continued for sixty days. Organic matter (OM) intake was significantly (p0.05) higher in the UMS (64 g/kg W0.75/d) followed by UGS (53 g/kg W0.75/d) and US (49 g/kg W0.75/d). Estimated (from digestible OM intake) metabolizable energy (ME) intake were 396, 348 and 301 kJ/kg W0.75/d for UMS, UGS and US respectively. The maintenance (i.e., no change in live weight) ME intake calculated to be 308+_ 7.4 kJ/kg W0.75/d. Urinary purine derivatives excretion was nonsignificantly higher in the UMS (51.73 mmol/d), followed by UGS (42.53 mmol/d) and US (35.26 mmol/d). The estimated microbial N (MN) yield were 21.10, 14.00 and 11.60 g/d for UMS, UGS and US respectively. For each MJ increase in ME intake, MN yield increased by 1.29 +_ 0.134g. Observed live weight changes during the experimental period were 292, 125 and -19 g/d respectively for UMS, UGS and US. It was concluded that supplementation of readily fermentable N (urea) alone was not enough to optimize the rument function anda source of readily fermentable energy was required. Rice gruel was less effective than molasses as fermentable energy source to remove a restriction on voluntary intake and provide less amino acids of microbial origin for absorption from the small intestine, thus more substrate for protein synthesis and gluconeogenesis were available for growth in the molasses than the rice gruel supplemented animals. However, in situation where molasses is not available or costly, rice gruel does appear to have a place as readily fermentable energy source on a urea supplemented straw diet.