Eight ruminally-cannulated beef
heifers (451 ± 21 kg BW) were used in a replicated 4
×
4 Latin square design. Four experimental diets were
prepared and fed once daily for ad libitum intake:
control, 1%, 2%, and 3% EN (0.15, 0.9, 1.5, and 2.5%
NO
3
−
in dietary DM, respectively). The control diet
(55% forage and 45% concentrate) included encap
-
sulated urea, which was gradually replaced with EN
for the EN diets (iso-nitrogenous; 12.5% CP). In each
period, EN was increased stepwise by 1% every 4 d
during adaptation. A 7-d washout period (control diet
offered to all heifers) was provided between experi
-
mental periods. Dry matter intake tended to decrease
(10.4 to 10.1 kg/d; linear,
P
= 0.06) with EN levels.
Enteric methane yield was linearly decreased (21.3 to
17.4 g/kg DMI;
P
< 0.01) by EN, and methane produc
-
tion (g/d) recovered to the level from heifers fed the
control diet on the first day when EN was withdrawn
from the diet. Apparent total-tract digestibility of DM
and OM increased (
P
= 0.03) or tended to increase
(
P
= 0.06), respectively, with EN levels.