Ruminant animals have evolved diversely and with the
flexibility to adapt to various plant feedstuffs. Hofmann
(1989) classified ruminants into three categories,
concentrate selector, intermediate and grass/roughage eaters,
according to their feeding behavior and anatomical
characteristics of the digestive tract. The difference in
anatomical characteristics and feeding behavior may affect
the inflow of urea-N into the digestive tract. Cattle and
sheep are grass/roughage eaters and have a larger rumen
and smaller hindgut compared with animals in concentrate
selector and intermediate groups. Furthermore, compared
with sheep, cattle have a relatively greater omasum and a
smaller large intestine (McLeod and Baldwin, 2000; Hata et
al., 2005).