Abstract :
Four Holstein heifers (264612 kg initial BW) were used in a 434 Latin square design with 21-day experimental periods to
determine the effect of increasing levels of sodium bicarbonate (BICARB) (0%, 1.25%, 2.5% and 5%, of concentrate dry matter
(DM) basis) on chewing and feed intake behavior when fed high-concentrate diets. Concentrate (13.41% CP, 13.35% NDF) and
barley straw were fed once a day at 0830 h ad libitum. Feed bunks placed on scales and video recording were used to measure
24-h feed intake and chewing behavior, respectively. The patterns of feeding behavior (feed intake, meal size and length) and
chewing behavior (eating, ruminating and total chewing) were studied by dividing the day into 12 intervals of 2-h each,
beginning at feeding (interval 1 through 12). Number of meals per day and eating rate decreased linearly with increasing buffer
level, but meal length increased linearly. No treatment effects were observed in sum of daily meal lengths or average meal
size. The treatment3interval interaction was significant on meal size, length and feed intake. The size and length of those
meals occurring during the 4 h post-feeding increased linearly. However, meal size tended to decrease in the evening between
8 and 12 h, whereas feed intake decreased linearly from 6 to 10 h and from 12 to 14 h post-feeding. Buffer concentration did
not affect the percentage of time spent ruminating, eating or drinking per day but the buffer level3interval interaction was
significant. Time spent eating expressed as min per kg of DM or organic matter (OM) intake increased linearly with buffer
levels. Proportion of time spent eating increased linearly during the intervals between 0 and 4 h post-feeding. Time spent
ruminating decreased linearly during the 2 h post-feeding, and also in the evening from 12 to 14 h, and at night from 18 to
22 h post-feeding, but the effect was quadratic between 8 and 10 h when intermediate buffer levels showed the greatest
ruminating time. Time spent drinking decreased linearly from 6 to 8 h but increased during the 2 h following feeding and from
10 to 12 h post-feeding. Daily eating rate and meal frequency decreased linearly as the buffer level increased, but average meal
size and daily chewing times were not affected. However, significant time of the day3buffer level interactions were observed
for feed intake, meal size and length and chewing behavior.
