Four Black Angus heifers (approximately 15 mo of
age at the beginning of the experiment) with ruminal and
duodenal cannulas were used in an experiment designed
as a 4 × 4 Latin square with 4 dietary treatments and 4
periods of 28 d (9 d for dietary adaptation and 19 d for
measurements and sample collection). The heifers were
spayed and surgically fi tted with fl exible permanent ruminal
and duodenal cannulas by a licensed veterinarian
8 wk before the start of the experiment. Ruminal cannulas,
manufactured of fl exible polyvinyl chloride, with
a 7.5 cm i.d. opening (number 4C; Bar Diamond, Inc.,
Parma, ID) were used for the fi rst 6 to 8 wk after surgery
and then replaced with a cannula with a 10 cm i.d. opening
(number 9C; Bar Diamond). The surgical technique
for placement of ruminal cannulas was as described by