One hundred medium-growth potential,
crossbred yearling steers (766 lb) were used to
identify the optimal level of urea in finishing
diets, based on growth and carcass traits. The
corn-base d diets had no urea o r contained .35,
.70, 1.05, or 1.40% urea (dry matter basis) and
no other supplemental protein. Alfalfa hay
(10% of DM) was the roughage source and
contained 16% crude protein. Feed efficiency
and gain were improved by .35% urea, with
little improvement from higher additions.
Regression analysis indicated that the optimal
level of urea for gain and feed efficiency was
.5% of dietary dry matter. Hot carcass weight
and dressing percentage responded
quadratically, being highest for steers receiving
.7 and 1.05% urea. Fat thickness and yield
grade responded cubically to the addition of
urea; these traits were also highest for steers receiving
.7 and 1.05% urea. Loineye area
decreased linearly with increased urea in the
diet. Marbling scores and KPH fat were
unaffected by urea addition. The increased
growth, carcass weight, and finish, with no
improvements in loineye area, indicate that urea
enhance d diet digestibility but did not increase
metabolizable protein supply. Optimal urea
levels (.5%) were less than those previously
indicate d for diets containing prairie hay as the
roughage source (.9%), suggesting that alfalfa
may supply a portion of the rumen degradable
nitrogen requirement when utilized as a source
of roughage in high grain diets.
