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. 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 from1989-2001.

 


Desired

Grazing

Intensity


Average Daily Gains (lbs/head/day)

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

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

1.12

1.07

0.97

0.82

NS

1.44

1.29

1.23

1.14

NS

 

 

Average Gain (lbs/acre)


 

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

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

 43.18c
 59.88bc

 67.15b

108.27a

 23.74

 

 

Condition Score

 


 

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

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

5.78

5.52

5.43

5.24

NS

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

2Means not significantly different.

3Not available


2001 was an unusual year. Precipitation was well above average in June and July and well below average in August and September (see precipitation table). This resulted in the quantity of forage produced being less than average (see table 2) but in these situations the forage often cures at a higher quality. The lack of forage forced us to remove the cattle on September 11, the earliest they had come off since 1992 (see table 1). The theory that forage quality was higher than average is supported by the fact that there was no significant difference in animal body condition scores between treatments, the first time this has occurred since 1995 (condition scores for cattle on the extreme treatment were not available in 1997). It was also observed that the quality of animals stocked on the study was better than usual. They were not as wild and they fed better. The cattle probably gain well on all treatments at the beginning of the grazing season and reduce their rate of gain on the heavy treatments as forage quantity becomes limiting. In years when the grazing season ends early as in 2000 and 2001 there is less chance for the differences in rate of gain between the light and extreme treatments to become significant. If all years are pooled together the relationship between rate of gain and stocking rate has an R2 of 0.43, which means that stocking rate explains 43% 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 1993 with an R2 of 0.59. Therefore ignoring 2001, 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 had at least one observation from a stocking rate higher than the projected rate which would provide maximum gain/acre for the year. 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 11-year period it would have been 2.58 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 0.99 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 11-year period.

Gain/acre over the 11-year period if stocking rate were held constant at 0.99 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

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

*

2.58

2.58

2.58

2.58

2.58

2.58

2.58

2.58

2.58

2.58

2.58

61.2

134.6

164.3

57.0

82.4

52.4

79.8

85.1

107.0

76.1

115.6

0.99

0.99

0.99

0.99

0.99

0.99

0.99

0.99

0.99

0.99

0.99

42.4

79.8

77.6

39.2

43.8

40.0

67.4

61.9

53.5

43.9

52.3

11-year Avg.

2.57

  94.4

2.58

92.3

0.99

54.7

* The regression for 2001 was 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 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. Again returns for stocking rates beyond the extreme stocking rate reference line are hypothetical and again all but 2001 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 11-year period it would have been 1.97 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 0.99 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 11-year period.

Returns/acre to land, labor and management over the 11-year period if stocking rate were held constant at 0.99 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

0.88

3.12

2.39

0.67

1.44

2.06

1.11

1.01

3.24

2.19

$4.10

$97.11

$105.11

$1.99

$2.05

$31.83

$13.35

$2.11

$56.58

$18.05

*

38.8

130.9

158.3

28.5

59.5

56.9

73.5

63.1

111.3

72.8


1.97

1.97

1.97

1.97

1.97

1.97

1.97

1.97

1.97

1.97

1.97

-$4.71

$83.42

$101.86

-$7.66

$0.13

$31.76

$4.45

-$7.10

$46.97

$17.84

$46.30

61.5

125.1

141.2

57.1

73.2

56.9

92.3

90.9

93.8

69.7

93.4

0.99

0.99

0.99

0.99

0.99

0.99

0.99

0.99

0.99

0.99

0.99

$4.01

$50.14

$68.16

$1.40

$0.70

$22.21

$13.17

$2.10

$26.30

$11.57

$26.28

42.4

79.8

77.6

39.2

43.8

40.0

67.4

61.9

53.5

43.9

52.3

11 yr. avg.

1.81

$33.23

79.4

1.97

$28.48

86.8

0.99

$20.55

54.7

* The regression for 2001 was not suitable to project the peak in returns to land, labor and management.



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