Effects of brown midrib 3 mutation in corn silage on productivity of dairycows fed two concentrations of dietary neutral detergent fiber: 2. Chewingactivities
M. Oba et Ms. Allen, Effects of brown midrib 3 mutation in corn silage on productivity of dairycows fed two concentrations of dietary neutral detergent fiber: 2. Chewingactivities, J DAIRY SCI, 83(6), 2000, pp. 1342-1349
The effects of digestibility of corn silage neutral detergent fiber (NDF) a
nd dietary NDF content on chewing activities were evaluated with eight mult
iparous high producing dairy cows in a duplicated 4 x 4 Latin square design
with 21-d periods. Experimental diets contained corn silage from a brown m
idrib (bm3) hybrid or its isogenic normal control at two concentrations of
dietary NDF (29 and 38%). The NDF digestibility estimated by 30-h in vitro
fermentation was higher for bm3 corn silage by 9.4 units (55.9 vs. 46.5%).
Feeding behavior of animals and ruminal pH were monitored continuously for
4 d in each period by a computerized data acquisition system. Ruminal diges
ta were evacuated twice per period to determine the ruminal NDF pool and it
s turnover rate. There was no effect of NDF digestibility on total chewing
time either per day or per kilogram of NDF intake, or on ruminating time ei
ther per day or per kilogram of NDF intake. Although bm3 treatments increas
ed the turnover rate of NDF in the rumen, they increased dry matter intake
and had no effect on ruminal NDF pool size. Total chewing time and ruminati
ng time per day were related positively to NDF intake and ruminal NDF pool
size, but were not related to ruminal turnover rate of NDF. These results p
rovide no evidence that enhanced NDF digestibility decreases the physical e
ffectiveness of NDF of corn silage.