Abstract :
Four ruminally fistulated Holstein heifers (BW5264612 kg) were used in a 434 Latin square design experiment to
determine the effect of increasing levels of sodium bicarbonate (BICARB; 0%, 1.25%, 2.50% and 5%, on concentrate dry
matter (DM) basis) on DM intake (DMI), water consumption and ruminal fermentation. Sampling was carried out in the
last week of each four 21-day experimental periods. Heifers were offered concentrate (13.460.04% crude protein (CP),
13.360.44% NDF, 51.760.97% starch) and barley straw once daily at 0830 h ad libitum. There was a linear decrease in
concentrate DMI and a linear increase in straw DMI with increasing buffer level in the diet, resulting in a tendency towards a
linear decrease in total DMI. Intake of concentrate was 6.89, 7.66, 6.72 and 5.7260.83 kg/day, whereas straw intakes were
0.73, 0.84, 0.94 and 1.0660.14 kg/day, for the 0%, 1.25%, 2.5% and 5% BICARB, respectively. Water consumption was not
affected by treatments when expressed as l/day or percentage of BW, but increased linearly when expressed as l/kg of DMI.
The percentage of total daily water drunk in the morning (from 0830 to 1230 h) increased linearly with the level of buffer.
Mean ruminal pH and total area under the pH curve were not affected with increasing buffer level. The lowest daily pH
(5.6560.09) was not affected by treatments. A quadratic tendency (P<0.10) was observed in the number of hours and the
area under the pH curve in which ruminal pH was below 5.8, with high values only at the 0% BICARB. Additionally, increasing
bicarbonate level caused a linear increase in the ruminal pH at 2 and 4 h after feeding. Daily average NH3 N (2.460.9 mg
N/100 ml) and total volatile fatty acids (VFA) (143612 mM) concentrations were not affected by treatments. Daily average
molar proportion of propionate decreased linearly, and acetate proportion and the acetate-to-propionate ratio were increased
with increasing buffer level in the diet. Molar percentage of butyrate, isobutyrate and isovalerate, and branched-chain VFA
concentration increased linearly as the level of bicarbonate increased in the diet. Results indicate that high levels of BICARB
to finishing heifers fed high-concentrate diets may result in a decreased DMI without significant effects on mean ruminal pH,
which may affect animal performance. All individual VFA proportions, except valerate, were changed by the addition of
bicarbonate.
