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Long-Term 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. Grazing pressure was too light on the heavy and extreme treatments in the first two years of the study, so no significant differences in average daily gains were observed in 1989 and 1990. Since 1990, average daily gain and animal body condition scores have decreased 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, the animals’ initial weights, or their potential to gain. Starting in 2008 we began taking a mid-season weight on the cattle. This will allow us to determine if the animals on the heavily stocked pastures gain consistently less throughout the grazing season or if they gain well in the first half of the grazing season and then lose weight or gain more slowly in the second half of the season. In 2008 all the cattle on all grazing treatments gained at a slower rate in the later part of the grazing season, August 1st to August 25th, than they did in the first part of the grazing season, May 20th to August 1st. The extreme grazing treatment had a significantly slower rate of gain in the first part of the grazing season than the other treatments, but there was no significant difference in the rate of gain between treatments in the last 25 days of the grazing season.

 

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

Desired Grazing Intensity

Average Daily Gains (lbs/head/day)

2004

2005

2006

2007

2008

Average 1991-2008

Light

1.68

0.93a1

0.57

1.36

1.75a

1.35a

Moderate

1.61

0.87a

0.62

1.22

  1.58ab

1.24a

Heavy

1.41

0.71ab

0.48

1.33

1.35b

1.08b

Extreme

1.09

0.39b

0.13

1.16

0.95c

0.77c

LSD (0.05)

NS2

0.36

NS

NS

0.38

0.14

 

Average Gain (lbs/acre)

 

2004

2005

2006

2007

2008

Average

1991-2008

Light

53.11

34.17

11.01

44.41c

39.73b

28.42c

Moderate

88.64

63.20

20.82

69.27bc

68.61ab

54.46b

Heavy

96.15

65.68

20.77

107.47ab

82.15a

75.10a

Extreme

113.32

52.51

7.48

122.96a

76.10a

79.61a

LSD (0.05)

NS

NS

NS

42.67

29.04

10.97

 

Condition Score

 

2004

2005

2006

2007

2008

Average

1994-2008

Light

4.79

5.58a

5.08

5.60

6.99a

5.47a

Moderate

4.94

5.30a

5.17

5.50

6.51b

5.36ab

Heavy

4.86

5.27a

5.02

5.54

6.38b

5.23b

Extreme

4.39

4.83b

4.81

5.41

5.82c

4.91c

LSD (0.05)

NS

0.41

NS

NS

0.39

0.20

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 0.28, which means that stocking rate explains 28% of the variation in average daily gain between pastures. When only one year is considered at a time, the R2 varies between 0.09 and 0.92, with 0.09 coming from 2007. The next lowest R2 was 2006, with an R2 of 0.25, and third was 2001, with an R2 of 0.45. Therefore, ignoring 2006 and 2007, between 45% and 92% of variation in average daily gain is a result of the difference in stocking rate. Forage production was well above average in 2007 and gains had not become forage-limited on the heavily grazed pastures by the time the cattle were removed (Table 2.). Forage production was well below average in 2006 and cattle were removed early, before the stocking rate had much opportunity to influence average daily gains (Tables 1 and 2, Figure 1). 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 increased as the stocking rate increased, 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, 2003, and 2007 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 cannot predict ahead of time which stocking rate will 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 1991-2008, it would be 2.15 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 2.15 AUM/acre each year, gain/acre would have ranged from a loss of 45.3 lbs/acre in 2002 to a gain of 149.1 lbs/acre in 1993 but would have averaged 74.6 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. Similarly, in 2006 the grazing season was cut short and the stocking rate on the extreme treatment averaged 1.55 AUM/acre. However, in that year, 46 of the 191 animals in the trial had lost weight before they were removed at the end of the 77-day grazing season. Table 4C shows what the gain/acre would have been each year if the stocking rate had been held constant at 1.09 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 18-year period.

Gain/acre over the 18-year period if stocking rate where held constant at 1.09 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

2.26

62.5

2.15

62.4

1.09

45.4

1992

2.68

134.8

2.15

129.3

1.09

86.1

1993

3.41

175.8

2.15

149.1

1.09

85.5

1994

2.27

58.1

2.15

58.0

1.09

42.0

1995

3.08

84.7

2.15

76.6

1.09

47.6

1996

2.04

57.0

2.15

56.8

1.09

43.0

1997

1.92

92.4

2.15

90.9

1.09

72.5

1998

2.08

91.2

2.15

91.1

1.09

67.0

1999

3.18

111.4

2.15

98.5

1.09

58.7

2000

2.81

76.6

2.15

72.3

1.09

47.4

2001

*

2.15

100.1

1.09

56.7

2002

0.94

41.5

2.15

-45.3

1.09

40.1

2003

*

2.15

69.5

1.09

43.3

2004

2.23

112.6

2.15

112.5

1.09

76.9

2005

2.73

67.0

2.15

63.4

1.09

38.1

2006

1.01

20.8

2.15

-24.3

1.09

20.6

2007

*

2.15

100.3

1.09

54.3

2008

1.90

82.2

2.15

80.8

1.09

67.0

18-year avg.

2.30

84.6

2.15

74.6

1.09

55.1

* The regressions for 2001, 2003, and 2007 were not suitable to project the peak in gain/acre.

 

Figure 4 shows the relationship between stocking rate and economic return. Costs 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 cost, veterinary cost, transportation, labor, and land). However, when cattle are worth more per hundredweight in the spring than they are in the fall, the point of maximum return/acre occurs at a lower stocking rate. When the cattle are worth more in the fall, the maximum return/acre occurs at a higher stocking rate. Again, returns for stocking rates beyond the extreme stocking rate reference line are hypothetical and again all but 2001, 2003, and 2007 had at least one observation from a stocking rate higher than the rate that would provide maximum return to land, labor, and management for the year. Table 5 shows what the optimum return/acre would have been for each year if stocking rate were set for the optimum for that year (A), if the stocking rate were held at a constant optimum rate (B), or if held the stocking rate were held constant at the moderate stocking rate (C). The peaks of the curves in Figure 4 correspond to these optimum stocking rates. If we were to pick one constant stocking rate that would have provided the maximum return/acre over the last 18-years, it would be 2.09 AUM/acre. This is the point labeled “optimum” in Figure 4. Although the average return/acre is higher under the optimum stocking 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 shows that in all but five years (1992, 1996, 1999, 2004, and 2006) 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 18-year period. Returns/acre to land, labor, and management over the 18-year period if stocking rate were held constant at 1.09 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

0.88

$4.10

38.8

2.09

 ($6.74)

62.2

1.09

$3.77  

45.4

1992

3.12

$97.11

130.9

2.09

$86.10 

128.1

1.09

$54.43  

86.1

1993

2.39

$105.11

158.3

2.09

$103.46

146.7

1.09

$73.25  

85.5

1994

0.67

$1.99

28.5

2.09

($9.51)

57.8

1.09

$0.98  

42.0

1995

1.44

$2.05

59.5

2.09

($0.83)

75.6

1.09

$1.23  

47.6

1996

2.06

$31.83

56.9

2.09

$31.82  

56.9

1.09

$23.92  

43.0

1997

1.11

$13.35

73.5

2.09

$1.81  

91.6

1.09

$13.34  

72.5

1998

1.01

$2.11

63.1

2.09

($9.53) 

91.2

1.09

$2.05  

67.0

1999

3.24

$56.58

111.3

2.09

$48.69  

97.1

1.09

$28.93  

58.7

2000

2.19

$18.05

72.8

2.09

$18.01  

71.5

1.09

$12.60  

47.4

2001  

*

 

2.09

$48.68  

98.0

1.09

$28.35  

56.7

2002

0.31

($1.49)

17.8

2.09

($43.88)

-37.4

1.09

 ($9.67)

40.1

2003  

*

 

2.09

$92.60  

67.9

1.09

$53.25  

43.3

2004

3.04

$121.71

94.8

2.09

$108.69  

112.1

1.09

$66.56  

76.9

2005

1.97

$19.76

60.8

2.09

$19.66  

62.6

1.09

$14.00  

38.1

2006

1.67

$48.66

5.6

2.09

$44.99  

-19.9

1.09

$41.75  

20.6

2007  

*

 

2.09

$65.60  

97.6

1.09

$36.58  

54.3

2008

1.73

$52.63

81.5

2.09

 $50.16 

81.4

1.09

$45.09  

67.0

18-year avg.

1.79

$38.24

70.3

2.09

$36.10  

74.5

1.09

$27.25  

55.1

* The regressions for 2001, 2003, and 2007 were not suitable to project the peak in returns to land, labor, and management.

 


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