Abstract |
- Two studies were conducted to compare lamb feedlot
performance and digestibility of nutrients by lambs fed
rations containing bird-resistant and bird-susceptible
sorghum grain with 20 or 40% tall fescue hay as a source
of roughage.
Four rations were fed ad libitum on the performance
study and at 80% of ad libitum on the digestibility trial.
All rations included cottonseed meal, animal fat, urea
and limestone. Rations 1, 2, 3 and 4 contained 39.2, 66.9,
39.3 and 67.0% grain sorghum and 40.9, 20.6, 40.8 and 20.6%
hay, respectively.
Results indicated lambs on high roughage treatments
with depression in dry matter (-4.8%), organic matter
(-3.6%), crude protein (-4.9%), ether extract (-1.6%), nitrogen-free-extract (-1.5%) and energy (-2.3%) digestibility
and decreased copper excretion (-10.7%). CWC
(202.66%), cellulose (18.00%), acid detergent fiber (24.6%)
and total ash (11.2%) digestibility and NR (11.3%) indicated
some improvement in high roughage diets. When digestible
energy was considered on the basis of concentrate consumed
daily, it showed an increase of 31.2% over the low roughage
treatments.
Lambs on high tannin treatments showed depression in
dry matter (-2.3%), organic matter (-3.7%0, crude protein
(-5.6%), nitrogen-free-extract (-2.3%), energy (-3.7%),
CWC (9.1%) and cell contents (-3.3%) digestibility, and in
nitrogen retention (-1.7%) and total phosphorus (-6.2%)
excretion. Ether extract (4.6%), ADF (12.7%), total ash
(41.7%, p<.01) and cellulose (16.8%) digestibility showed
improvement, while copper (9.7%) excretion increased.
Lambs receiving high roughage rations experienced some
improvement in feed intake per pen (7.9%), ADG (3.7%),
YG (8.8%), percent kidney fat (15.2%, p<.01), quality
grade (.4%) and loin eye area (3.6%). Leg conformation
score (LCS), fat thickness (FT) and dressing percent were
depressed by 1.0, 18.0 and 6.8% compared to low roughage
treatments.
Lambs on the high tannin treatments experienced some
improvement in FI (4.6%), YG (4.9%), kidney fat (7.0%),
loin eye area (7.5%) and dressing percent (2.9%). Leg conformation score seemed to be depressed by the high tannin
level (-3.8%). Lambs on high roughage treatments had a
poorer FE ratio (7.8) than those consuming the low roughage
ration (7.5). A similar trend was observed with high
tannin (8.1) as compared to low tannin treatments (7.4).
Cost per kilogram of gain in liveweight or carcass was
higher (18.1 and 26.9%, respectively) for lambs on high
roughage treatments than those consuming low roughage
rations. Observations on high tannin versus low tannin
rations showed similar trends (7.2 and 4.2%, respectively).
High roughage diets seemed to give an increase in
TVFA (13.5%), NH3-N (67.7%) and acetate:propionate ratio
(59.7%). Increased amounts of TVFA (13.5%) and NH3-N
(13.7%) and a wider acetate:propionate ratio (4.2%) were
observed in the high tannin diets.
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