Table 3 shows the average daily gain, gain per acre and body condition scores
from the different grazing intensities in each year of the study. Grazing
pressure was too light on the heavy and extreme treatments in the first two
years of the study so there are no significant differences in average daily
gains in 1989 and 1990. Following that year average daily gain and animal body
condition scores decrease with increasing grazing intensity. The rate at which
average daily gain decreases with an increase in stocking rate varies greatly
from year to year. If all years are pooled together the relationship has an R^{2
}of 0.50, which means that stocking rate explains 50% of the variation in
average daily gain between pastures. When only one year is considered at a time
the R^{2 }varies between 0.72 and 0.98. Therefore between 72 and 98% of
variation in average daily gain is a result of the difference in stocking rate.
The differences between years may be due to variation in forage quality or
quantity, the effect of weather on the animals, their initial weight, or their
potential to gain. The relationships between stocking rate and average daily
gain are illustrated in figure 2. Reference lines indicate the average stocking
rates for each of the four grazing treatments.
Initially gain/acre increases as the stocking rate increases but there comes a
point when further increases in stocking rates result in reduced gain/acre (see
figure 3). Table 4A shows the stocking rate which would have resulted in the
maximum gain/acre in each year. Since we can’t predict ahead of time what
stocking rate would give the maximum gain/acre in a particular year it would be
impossible to stock each year for maximum gain/acre. In retrospect, if we were
to pick one stocking rate that would have resulted in the maximum gain/acre over
this 10year period it would have been 2.47 AUM/acre. This is the point labeled
optimum in figure 3. Table 4B shows what the gain/acre would have been each year
if we had stocked at that rate. Table 4C shows what the gain/acre would have
been each year if the stocking rate were held constant at 0.97 AUM/acre, the
average of the moderate treatment over this period.
Figure 4 shows the relationship between stocking rate
and economic return. Cost for land, labor and management are not included
because they vary greatly from one operation to another. If cattle prices were
constant then return/acre would peak at a stocking rate somewhere below maximum
gain/acre with the exact point depending on carrying costs (interest, death
loss, salt and mineral, vet cost, transportation, labor and land). However, when
cattle are worth more per hundred weight in the spring then they are in the fall
it causes the point of maximum return/acre to occur at a lower stocking rate and
when they are worth more in the fall it causes the maximum return to occur at a
higher stocking rate. Table 5A shows what the return/acre would have been if we
had stocked each year at the stocking rate which would result in the maximum
return for that year. These values correspond to the peaks of the curves in
figure 4. Obviously we can’t know ahead of time what the optimum stocking rate
for a particular year is going to be. If we were going to pick one constant
stocking rate that would have provided the maximum return/acre over this last
10year period it would have been 1.86 AUM/acre. This is the point labeled
optimum in figure 4. Table 5B shows what the returns/acre would have been each
year if we had stocked at this rate. Table 5C shows what returns/acre would have
been each year if stocking rates were held constant at 0.97 AUM/acre, the
average of the moderate treatment over this period. Although the average return
per acre is higher under the optimum rate there were three years with negative
returns while all years had positive returns under the moderate stocking rate.
(Costs for land, labor and management have not been subtracted). Comparing tables 4 and 5 it can be seen that in all but three years (1992,
1996 and 1999) the stocking rate with the greatest economic return was less than
the rate with the greatest gain per acre.
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Introduction  Forage Production & Utilization 
