Long-Term Ecological 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 for the last five years, average gains by treatment from 1991 to 2004 and average body condition from 1994 to 2004. 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. 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.


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

Desired

Grazing

Intensity

Average Daily Gains (lbs/head/day)

2000

2001

2002

2003

2004

Average

1991-2004


Light

Moderate

Heavy

Extreme

LSD(0.05)

1.12

1.07

0.97

0.82

NS2

1.44

1.29

1.23

1.14

NS

1.34

1.47

1.00

0.78

NS

1.28a1

1.08b

0.89bc

0.87c

0.20

1.68

1.61

1.41

1.09

NS

1.41a

1.28a

1.12b

0.80c

0.14

 

Average Gain (lbs/acre)


 

2000

2001

2002

2003

2004

Average

1991-2002


Light

Moderate

Heavy

Extreme

LSD(0.05)

33.03c

42.39bc

58.24ab

74.44a

17.52

 43.18c

 59.88bc

 67.15b

108.27a

 23.74

20.06

37.90

33.57

38.96

NS

36.46b

51.58b

54.01b

84.41a

20.55

  53.11

  88.64

  96.15

113.32

NS

27.30c

51.60b

76.83a

83.51a

11.76

 

Condition Score


 

2000

2001

2002

2003

2004

Average

1994-2002


Light

Moderate

Heavy

Extreme

LSD(0.05)

5.18a

5.20a

5.01a

4.61b

0.31

5.78

5.52

5.43

5.24

NS

5.22

5.18

5.18

5.05

NS

5.46

5.36

5.18

5.26

NS

4.79

4.94

4.86

4.39

NS

5.34a

5.26ab

5.11b

4.79c

0.18

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

2Means not significantly different.



If all years are pooled together, the relationship between rate of gain and stocking rate has an R2 of 0.39, which means that stocking rate explains 39% of the variation in average daily gain between pastures. When only one year is considered at a time the R2 varies between 0.45 and 0.98, with the 0.45 coming from 2001. The next lowest was 2002 with an R2 of 0.48, and third was 1993 with an R2 of 0.59. Therefore ignoring 2001 and 2002, between 59% and 98% of variation in average daily gain is a result of the difference in stocking rate. 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). What happens at stocking rates beyond the extreme stocking rate reference line is mainly hypothetical because we have very few observations on which to base our regression lines. However all but 2001 and 2003 had at least one observation from a stocking rate higher than the projected rate that would provide maximum gain/acre for the year. Table 4A shows the stocking rate that would have resulted in the maximum gain/acre in each year. Since we can not 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 from 1991-2004 it would have been 2.21 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. We predict that if we had stocked at 2.21 AUM/acre each year gain per acre would have ranged from a loss of 54.3 lbs/acre in 2002 to a gain of 151.7 lbs/acre in 1993 but would have averaged 80.2 lbs/acre. Because so little forage was produced in 2002 the grazing season was cut short and none of the pastures were actually stocked that heavily.

 

 

 

 

The stocking rate on the extreme treatment averaged 1.18 AUM/acre for 2002 and, although gains were not good, only 11 out of the 189 animals in the trial had actually lost weight during the 55 days of grazing. Table 4C shows what the gain/acre would have been each year if the stocking rate were held constant at 1.01 AUM/acre, the average of the moderate treatment over this period.

 


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

 

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 14-year period.

Gain/acre over the 14-year period if stocking rate were held constant at 1.01 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

2001

2002

2003

2004

2.26

2.68

3.41

2.27

3.08

2.04

1.92

2.08

3.18

2.81


0.94


2.23

  62.5

134.8

175.8

  58.1

  84.7

  57.0

  92.4

  91.2

111.4

  76.6

*

41.5

*

112.6

2.21

2.21

2.21

2.21

2.21

2.21

2.21

2.21

2.21

2.21

2.21

2.21

2.21

2.21

62.5

130.5

151.7

58.1

77.6

56.5

90.0

90.8

100.0

73.0

102.4

-54.3

71.2

112.6

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

42.9

80.9

79.0

39.7

44.5

40.5

68.3

62.8

54.4

44.5

53.0

41.2

41.5

71.6

14-year Avg.

2.41

 91.6

2.21

80.2

1.01

54.6

* The regressions for 2001 and 2003 were not suitable to project the peak in gain/acre.



Figure 4 shows the relationship between stocking rate and economic return. Cost for land, labor and management are not included because these values 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, veterinary 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. Again returns for stocking rates beyond the extreme stocking rate reference line are hypothetical and again all but 2001 and 2003 had at least one observation from a stocking rate higher than the rate which would provide maximum return to land, labor, and management for the year. 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 14-year period it would have been 2.09 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 1.01 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 five years with negative returns while only one year had a negative return 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 four years (1992, 1996, 1999 and 2004) 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 14-year period.

Returns/acre to land, labor and management over the 14-year period if stocking rate were held constant at 1.01 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

2001

2002

2003

2004

0.88

3.12

2.39

0.67

1.44

2.06

1.11

1.01

3.24

2.19


0.31


3.04

$4.10

$97.11

$105.11

$1.99

$2.05

$31.83

$13.35

$2.11

$56.58

$18.05

*

-$1.49

*

$121.71

38.8

130.9

158.3

28.5

59.5

56.9

73.5

63.1

111.3

72.8


17.8


94.8

 

2.09

2.09

2.09

2.09

2.09

2.09

2.09

2.09

2.09

2.09

2.09

2.09

2.09

2.09

-$6.74

$86.11

$103.46

-$9.51

-$0.83

$31.82

$1.81

-$9.53

$48.69

$18.01

$48.68

-$43.89

$92.61

$108.69

62.2

128.1

146.7

57.8

75.6

56.9

91.6

91.2

97.1

71.5

98.0

-37.4

67.9

112.1

 

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

1.01

$3.98

$50.88

$69.06

$1.34

$0.80

$22.51

$13.22

$2.11

$26.76

$11.75

$26.63

-$8.04

$50.20

$61.78

42.9

80.9

79.0

39.7

44.5

40.5

68.3

62.8

54.4

44.5

53.0

41.2

41.5

71.6

14 yr. avg.

1.79

$37.71

75.5

 

2.09

$33.53

79.9

 

1.01

$23.78

54.6

* The regressions for 2001 and 2003 were not suitable to project the peak in returns to land, labor and management.


 

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