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Effects of supplements of urea and
minerals on steers fed maize silageT. F. Reardon
a
aRuakura Animal Research Station, Ministry of Agriculture and
Fisheries, P.B., Hamilton, New Zealand
Version of record first published: 18 Jan 2012.
To cite this article:T. F. Reardon (1980): Effects of supplements of urea and minerals on steers fedmaize silage, New Zealand Journal of Experimental Agriculture, 8:2, 101-104
To link to this article: http://dx.doi.org/10.1080/03015521.1980.10426242
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N.Z. Journal
of
Experimental Agriculture 8 (1980): 101-4
101
ffects of supplements of urea and minerals on steers fed
maize silage
T. F. REARDON
Ruakura Animal Research Station, Ministry
of
Agriculture and Fisheries,
P.B., Hamilton, New Zealand
A mineral mixture (Ca, P, Na, Mg, S, Cu, Co, Zn, Mn, I, Fe) and urea (10 g/kg silage
DM) were added separately and in combination to sole diets
of
maize silage (33 DM)
fed to 16-month-old beef steers initially weighing 303
kg.
Urea increased silage
DM
intake from 7.3 to
8.1
kg/day and increased carcass gain from 0.20 to 0.48 kg/day.
Minerals increased silage DM intake from 7.1 to 8.3 kg/day and increased carcass gain
from 0.22 to 0.46 kg/day with an indication (P < 0.1)
of
a positive interaction between
urea and minerals on both intake and carcass gain. There was a significant interaction on
live-weight gain with urea improving gain from 0.77 to 1.43 kg/day in the presence
of
and from 0.37 to 0.80 kg/day in the absence of, supplementary minerals. '
Keywords
Zeal mays
L., silage, steers, weight gain, urea (nutrient), minerals
(nutrient)
INTRODUCTION
In contrast to the North American (Goodrich
Meiske 1971) and British and European industries
(Mal terre 1976) the New Zealand beef industry uses
little maize silage. Low returns for beef, year-round
availability
of
pasture dry matter (DM) at less than one
half
of
the cost
of
maize silage DM (Hutton 1973), and
the need to correct protein and mineral deficiencies
of
maize have limited the use
of
maize silage. However, a
low-cost system
of
protein and mineral supple
mentation, consistent with reasonable levels
of
animal
production, could enable maize silage to contribute to
beef production in the warmer areas
of
New Zealand.
The present study examined the effects
of
supplements
of
minerals and urea added separately, or
in combination, to maize silage when fed to
beef steers.
MATERIALS AND
METHODS
Forty-five Angus-Hereford crossbred steers, aged
about
16
months, were divided into groups
of
5 by
stratified randomisation using live weight. They were
held on a sawdust pad with continuous access to feed
Received 30
july
1979;
revision
16
November 1979
and water. During days
1-9,
all groups were offered a
diet
of
hay and maize silage with reducing proportions
of
hay. On day 10, one group was slaughtered after a
24-h fast and carcass weight was recorded to establish a
regression
of
carcass weight on unfasted live weight.
From day 11, the remaining groups formed 2 replicates
of
a 2 x 2 factorial experiment in which maize silage
was offered to appetite (at least
5
refusals) together
with urea at levels
of
0 or
10
g/kg silage
DM
and with a
mineral mixture at levels
of
0 or 22.5 g/kg silage DM
added daily as fresh silage
was
offered. Levels
of
urea
supplementation were progressively increased from 4
to 109/kg silage D M from day 11 to day
17.
The
mineral mixture, offered at the full rate from day 11,
consisted
of
(g/kg mineral mixture): bone flour (627),
calcined magnesite (96), common salt (189), finely
ground sulphur (63), and trace minerals (25). The
trace mineral mixture consisted
of
(g/kg trace mineral
mixture):
CuS0
4
.5HP (70.6), CoS0
4
.7HP (0.6),
ZnS0
4
.7Hp
(393.3),
MnS0
4
.4Hp
(280.9), KI (1.6),
FeCI
3
.6Hp (252.8). Daily silage samples were bulked
into weekly samples for analysis.
Nitrogen was determined by a macro Kjeldahl
digestion using K
2
SO/Se
catalyst and steam
distillation. Na, K, Ca, Mg, and P were determined by
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102
N.Z. Journal of Experimental Agriculture, Vol. 8,
1980
atomic absorption spectrophotometry after digestion in
nitric:perchloric acid
(2:
1) with wet digestion being
followed by reduction to molybdenum blue for the
determination of P. Sulphur
was
determined
gravimetrically as BaS0
4
after oxidation in an oxygen
bomb.
Between days 62 and 72,
all
animals were
slaughtered after
24
h without feed. Rate oflive-weight
change was calculated as the regression coefficient of
weight (recorded weekly) on time from days 16 to 57.
Carcass gain was calculated from actual carcass weight
when slaughtered and carcass weight on day 10
estimated by the regression of carcass on live weight in
the initial slaughter group. Variation between animals
within replicates was used as the measure of
experimental error for gains of live weight and carcass
weight.
R SULTS
Compositions
of
feed and supplements are presented
in Table 1. Dry matter percentage
of
maize silage
by
toluene distillation (33.1 ) was slightly higher than
that found
by
oven drying (32.6%). The Kjeldahl N
content of the mineral mixture was higher than
anticipated when the mixture was formulated.
Intake of silage DM was increased
by
the addition of
minerals
(7.1
v.
8.3
kg/day, P
< 0.001)
and
of
urea
7.3 v. 8.1 kg/day, P
~
o
O:OA
2
0
o
O - - - - - - - r - - - - - ~ - - - - - - ~ - - - - - - ~
6 7 8 9
10
Silage OM
(kg/day)
Fig. 1 Mean silage intake for groups of 5 steers and rates of
gain
of
live weight (solid symbols) and carcass weight (open
symbols) on maize silage diets without supplements
(0, . ,
with urea only
A ,
with minerals only (V,. .. ), and with
both urea and minerals
(0, . ) .
Line relates intake by a 300
kg
steer
to
rate
of
live-weight gain estimated from National
Research Council (1976) tables assuming net energy values
of
6.53 and 4.14 MJ/kg OM for maintenance and gain
respectively.
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104
N.Z. Journal of Experimental Agriculture, Vol. 8, 1980
diets supplemented with NPN to higher levels of crude
protein (up to 90 g digestible crude protein/kg DM)
(Cottyn et al. 1977).
Part of the improvement in rates of gain as a result
of
supplementation can be attributed
to
increased
intake (Table 2). In Fig. 1, intake of silage DM and
rates of gain of live weight and carcass are plotted
together with the relationship between live-weight
change and dry matter intake estimated (National
Research Council 1976) for a 300 kg steer assuming
net energy contents of maize silage of 6.53 and 4.14
MJ/kg DM for maintenance and gain respectively. In
the present data, an increase in daily DM intake of 1 kg
was associated with increases in daily gains of about 0.5
and 0.25
kg
respectively in live weight and carcass
weight whereas the theoretical relationship (Fig. 1)
indicates an increase
of
about 0.2 kg oflive-weight gain
per kilogram of extra DM. This additional
improvement in animal performance, beyond that
attributable to increased intake, represents
improvement in efficiency of utilisation from a
deficiency situation up to a situation where utilisation
of the energy content of maize probably approaches
maximal values.
Some reservations must be held on the reliability
of
live-weight gain measured over a relatively short
period such as that used in the present experiment. In
addition,
all
groups lost weight during adaptation to the
experimental conditions and rations (Table
2, days
1-16). The results for carcass gain are less equivocal
with the largest source of error being the estimation of
initial carcass weight from live weight, measured
before differential feeding began. Thus, the low
proportion of carcass gain in live-weight gain (Table 2)
possibly indicates that live-weight gain was
overestimated in
all
groups.
Rate of carcass gain provides a convenient measure
for the practical assessment of these results. In a
preliminary report (Reardon
et al.
1976), the mineral
mixture and urea were estimated to each add 0.3 cents
to the cost of a kilogram of silage DM but together
produced sufficient extra carcass, relative to
unsupplemented maize silage, to more than cover the
costs of their addition. However, at the assumed prices
of
3 c/kg DM for unsupplemented maize silage and
50 c/kg for carcass, total daily feed costs exceeded the
value of total daily carcass gains by a wide margin for
the unsupplemented group and
by
a narrow margin for
the fully supplemented group. At more favourable
relative prices for carcass and silage, the results in
Table 2 indicate that total feed costs of a fully
supplemented maize silage diet would be recovered
from the value of carcass gained. Evaluation of this
profit margin against non-feed costs and against profits
from alternative means of producing beef and of using
the maize crop
is
beyond the scope of this discussion.
Acknowledgments
Mr W. Ferguson for the feeding and care of the animals;
Mr R. P. Newth and Mr D. Karl for chemical analyses.
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