The DM quality approach is not limited by
experimental forage quality data. Experiments or
experience with animal performances on specific
forages can be used to classify those forages. These
techniques, along with published data on ME∕kg,
were used to classify forages into three quality groups
by five periods of the year.3 The pasture DM quality
groups are pasture DM 1.8 including Mcal of ME∕kg
in the 1.71 to 2.0 range, pasture DM 2.2 with ME∕kg
from 2.01 to 2.35, and pasture DM 2.6 with ME∕kg
from 2.36 to 2.80. Hay 2.2 and hay 1.8 are
equivalent to pasture DM 2.2 and pasture DM 1.8,
respectively.
Energy density requirements for beef cattle range
from 1.71 to 2.0 Mcal of ME∕kg for dry pregnant
cows, from 2.01 to 2.35 ME∕kg for lactating cows
and steers gaining one pound per day or less and from
2.36 to 2.8 ME∕kg for stocker steers gaining more
than one pound per day [7]. In southcentral Okla-
homa, pasture DM 2.6 includes small grain forages
and clover pastures during rapid growth. Examples in
the pasture DM 2.2 category are berɪnudagrass in
spring and early summer and fescue with less than
200 pounds of nitrogen. Pasture DM 1.8 is produced
by any warm season forage deferred for winter
grazing.
A study centered on a livestock farm situation in
southcentral Oklahoma was used to develop and
evaluate use of the DM quality groups for beef-forage
planning. In the remainder of the paper, the forage
and cattle systems, the model and the results are
described.
FORAGE
Monthly total DM production was derived by
using forage yield data or converting experimental
data on steer grazing grains to forage production.
Agronomists and animal scientists reviewed produc-
tion estimates and made judgemental adjustments.
Total DM was then adjusted for grazing loss and
divided into quality classifications; pasture DM 2.6,
pasture DM 2.2, pasture DM 1.8 or hay by DM 2.2 or
DM 1.8 (Table 1).
The quantities of pasture dry matter were the
remainder of total dry matter after grazing losses of
15-50 percent and haying. Hay comprised approxi-
mately one-third of the total DM. Some pastures
produced three quality classes during the course of
the year. Interaction of fertilizer levels with quality
and timing of pasture is illustrated in Table 1.
CATTLE
The nutrient and DM requirements for cattle
were calculated on a monthly basis using a computer
program developed by Dillard [3] and by using
National Research Council and other experimental
data. Fall and spring cow-calf activities were identi-
fied according to the feedstuffs combined to maintain
the cow-calf unit during the winter period. For
example, the unit can be wintered on pasture 2.2, hay
2.2 or hay 1.8 with a protein supplement.
DM requirements by quality and quantity
through the production cycle are shown for cow-calf
and steer activities in Table 2. Pastures are supple-
mented with digestible protein or energy when
necessary. Three alternative cow-calf and steer sys-
tems are shown. It was assumed that October-May
DM 2.2 steers gain .75 to 1.0 pounds per day and the
steers on pasture DM 2.6 gain 1.5 to 2.0 pounds per
day.
THE LP MODEL
The LP model is summarized in Table 3 by
submatrices. Components of selected submatrices are
explained in the footnotes. The forage rows include
five pasture DM rows and eight hay rows. The pasture
DM rows are divided into three forage quality groups
for each of five time periods—March-April, May-June,
July-August, September-October and November-
February.
Fifty-two accounting rows are used to summarize
resources produced or utilized within the model and
to determine forages used by cow-calf and steer
enterprises. These rows also summarize pasture DM
yield by quality classification and production of DP
in each time period.
There are 11 pasture varieties: midland bermuda,
weeping lovegrass, tall fescue, native, improved
native, bermuda-lovegrass, bermuda-fescue, bermuda-
clover, fescue-clover, bermuda-vetch and bermuda
overseeded with small grains. Cropland can be utilized
by any of the improved pastures, small grain, or
Sorghum-Sudan pasture. Several nitrogen levels are
included with most pasture varieties.
Beef production activities consisted of five spring
calving cow-calf activities, five fall calving cow-calf
activities and seven stocker steer activities. They are
distinguished by winter feeding and calving programs
used and by selling weights.
Buy activities include inputs of nitrogen,
phosphorus, potassium, protein supplement, hay,
3Data and experience might support more groups—say 4 or 5. However, models implying infinitely many groups such as the
S-67 models probably have data requirements which exceed data obtainable.
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