Grazing Intensity Research in the Missouri Coteau of North Dakota


Livestock Response

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 R2 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 R2 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.

Table 3. Average daily gains, gains per acre, and condition scores from different stocking intensities from 1989-2000.


Desired
Grazing
Intensity
Average Daily Gains (lbs/head/day)
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Light
Moderate
Heavy
Extreme
LSD(0.05)
2.18
2.35
2.03
2.00
NS2
1.01
1.23
1.17
1.05
NS
1.42a1
1.13ab
0.91b
0.69b
0.48
2.04a
1.89a
1.70a
1.20b
0.44
1.56a
1.56a
1.68a
1.06b
0.40
1.10a
0.90ab
0.74b
0.20c
0.26
1.05a
0.94a
0.86a
0.55b
0.29
1.07a
0.93a
0.81ab
0.44b
0.39
1.63a
1.46a
1.20ab
0.83b
0.45
1.53a
1.31ab
1.03b
0.60c
0.38
1.40a
1.30a
1.19ab
0.96b
0.25
1.20a
1.07ab
0.97ab
0.82b
0.29

Average Gain (lbs/acre)
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Light
Moderate
Heavy
Extreme
LSD(0.05)
16.84c
33.27bc
41.28ab
61.00a
22.35
13.69c
27.63b
36.47b
52.87a
9.95
16.86b
43.10a
58.83a
61.90a
20.35
 18.60d
 54.33c
105.58b
129.22a
 22.49
 13.82c
 45.34c
119.31b
166.77a
 44.42
20.10b
38.70ab
57.23a
26.64ab
30.75
12.78c
42.37b
70.45a
77.04a
24.30
14.14c
30.10bc
53.25a
45.38ab
22.79
 30.27c
 66.05b
110.13a
 71.10b
 27.85
28.29c
62.25b
97.86a
67.98b
29.59
36.50b
59.73b
93.93a
108.49a
24.31
33.03c
42.39bc
58.24ab
74.44a
17.52

Condition Score
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Light
Moderate
Heavy
Extreme
LSD(0.05)




















5.19a
4.84ab
4.80ab
4.21b
0.64
5.08
5.13
5.16
4.74
NS
5.19a
5.11a
4.91ab
4.37b
0.58
5.35
5.24
4.93
-- 3
NS
5.81a
5.71ab
5.21b
4.65c
0.53
5.72a
5.65ab
5.54bc
5.41c
0.18
5.18a
5.20a
5.01a
4.61b
0.31

1Means in the same column followed by the same letter are not significantly different at p=0.05.
2
Means not significantly different.
3Not available

 

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 canít 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 10-year 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.



Table 4. Comparison of gain per acre from selected stocking rates (in lbs).

  A
B
C
  Stocking rate that would result in the maximum gain/acre in each year. Stocking rate that if held constant would result in the maximum gain/acre over the ten-year period. Gain/acre over the ten-year period if stocking rate were held constant at 0.97 aums/acre, the average of the moderate treatment over this period.
Year aums/acre gain/acre aums/acre

gain/acre

aums/acre gain/acre
1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2.26

2.68

3.41

2.27

3.08

2.04

1.92

2.08

3.18

2.81

62.5

134.8

175.8

58.1

84.7

57.0

92.4

91.2

111.4

76.6

2.47

2.47

2.47

2.47

2.47

2.47

2.47

2.47

2.47

2.47

62.0

133.9

161.1

57.7

81.3

54.0

83.6

87.5

105.3

75.5

0.97

0.97

0.97

0.97

0.97

0.97

0.97

0.97

0.97

0.97

41.8

78.6

76.2

38.7

43.1

39.4

66.4

61.0

52.6

43.3

10yr. ave. 2.57 94.4 2.47

90.2

0.97

54.1

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 canít 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 10-year 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.

 
Table 5. Comparison of return to land, labor and management from selected stocking rates.
  A
B
C
  Stocking rate that would result in the maximum return/acre to land, labor and management in each year. Stocking rate that if held constant would result in the maximum return to land, labor and management over the ten-year period. Returns/acre to land, labor and management over the ten-year period if stocking rate were held constant at 0.97 aums/acre, the average of the moderate treatment over this period.
Year aums
/acre
returns
/acre
gain
/acre
aums
/acre
returns
/acre
gain
/acre
aums
/acre
returns
/acre
gain
/acre
1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

10yr.ave.

0.88

3.13

2.39

0.67

1.44

2.06

1.11

1.01

3.24

2.19

1.81

$4.10

$97.11

$105.11

$1.99

$2.05

$31.83

$13.35

$2.11

$56.58

$18.05

$33.23

38.8

130.0

158.3

28.5

59.5

57.0

73.5

63.1

111.3

72.8

79.4

1.86

1.86

1.86

1.86

1.86

1.86

1.86

1.86

1.86

1.86

1.86

-$3.01

$80.65

$99.88

-$6.09

$0.84

$31.50

$6.60

-$5.10

$45.21

$17.57

$26.81

60.6

121.8

135.6

56.2

70.8

56.5

92.3

90.0

90.4

67.7

84.202

0.97

0.97

0.97

0.97

0.97

0.97

0.97

0.97

0.97

0.97

0.97

$4.04

$49.36

$67.22

$1.46

$0.59

$21.88

$13.11

$2.09

$25.82

$11.38

$19.70

41.8

78.6

76.2

38.7

43.1

39.4

66.4

61.0

52.6

43.3

54.1

 


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