Evaluation of the potential protein-sparing effects of sodium bicarbonate when added to grass silage for growing steers

Six Hereford-cross steers were used to determine whether or not the additio n of sodium bicarbonate (NaHCO3) to grass silage (GS) would reduce the need for supplemental protein from fish meal (FM). Grass silage (31% DM; pH 4.8 ) was either unsupplemented or supplemented with FM (10% of silage DM); NaH CO3 was added at 0, 2, or 4% of silage DM. Supplementation with FM increase d N retention (P < 0.01) but had no effects (P > 0.10) on feed intake or di gestibility of organic matter (OM). Urinary N excretion decreased (P < 0.05 ) linearly with the addition of NaHCO3 but due to an increase in fecal N th ere was no significant effect (P > 0.10) of NaHCO3 on N balance. Urinary ex cretion of bicarbonate (HCO3) increased linearly (P < 0.01) with NaHCO3 add ition, but there was no effect (P > 0.10) on urine pH or measures of blood acid-base status. Addition of NaHCO3 increased silage pH to 6.5 but had no effect (P > 0.10) an voluntary feed intake, or digestibility of OM and ADF. The results indicate that the addition of NaHCO3 to grass silage did not s pare dietary protein but led to a shift in the partition of N between urine and feces.