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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



winter and the remainder as rain during the 

 spring. The major plant species are Artemisia 

 tridentata Nutt., Agropyron spicatum, Festuca 

 idahoensis, and Poa secunda. Three range units 

 were grazed with cows under a 6-year rotation 

 system that included two consecutive years of 

 late spring use (May 1-June 20), followed by 1 

 year of early summer grazing (June 20- August 

 10), 2 years of late summer grazing (August 10- 

 October 1), and 1 year of early summer grazing. 

 The growing season usually begins April 1 and 

 ends June 30. A fourth range unit was grazed 

 with cows season-long, approximately May 1 to 

 October 1. The stocking rate was approximately 

 the same under both systems and each year. The 

 cows on the season-long range had an average an- 

 nal advantage in weight gain of 4.1 kg. over 

 those on the deferred-rotation range (19). 



Grazing was more evenly distributed under 

 deferred-rotation than under season-long graz- 

 ing. Even though the season-long range unit 

 was utilized more heavily than the units under 

 deferred-rotation, vegetation density increased 22 

 percent under season-long grazing and 20 percent 

 on the deferred-rotation units. The desirable 

 grasses increased more than twice as much under 

 season-long grazing as under deferred-rotation 

 grazing. However, most of this increase was in 

 the lightly grazed area in the season-long unit. 

 Hyder and Sawyer (19) concluded that concen- 

 trating the cattle on a single unit of the three- 

 unit, deferred-rotation system during the grow- 

 ing season for 2 consecutive years seriously re- 

 duced plant vigor. Hyder (18) recognized that 

 the heavy grazing pressure during the growing 

 season placed this deferred-rotation system at a 

 disadvantage. 



Northern Great Plains 



Deferred-rotation and season-long grazing 

 were compared at the Northern Great Plains 

 Field Station during the period 1918-45 (33). 

 The average annual precipitation during this pe- 

 riod was 39 cm. — about half occurred from May- 

 July and three-fourths from April-September. 

 The dominant plant species are Bouteloua gra- 

 cilis (H.B.K.) Lag. ex. Steud., Agropyron 

 smith! i Rydb., Carex fill folia Nutt,, and Stlpa 

 comata Trin. & Rupr. The experimental range 

 units were stocked with steers from May 16 to 



October 13. Each of the three divisions in the 

 deferred-rotation system was grazed approxi- 

 mately one-third of the season. The 6-year rota- 

 tion grazing included 2 consecutive years of 

 spring use, 1 year of summer use, 2 consecutive 

 years of late summer and early fall use, and 1 

 year of summer use. 



Rogler (33) reported that moderate stocking 

 was about the correct rate on a season-long basis. 

 At that rate, vegetation changes were influenced 

 primarily by differences in precipitation. The 

 vegetation in the heavily stocked unit was defi- 

 nitely overgrazed for the 1918-31 period. During 

 the wetter 1938-45 period, the heavily stocked 

 unit was not considered overgrazed in any year. 

 The vegetation in the rotation units did not 

 show the adverse effects of grazing during 1918- 

 34 as did the unit grazed season-long at the same 

 rate. There was no evidence that, the rotation 

 units benefitted from any natural seeding that 

 theoretically should have occurred in the fall 

 grazed units. 



The average increase in seasonal gain of steers 

 on rotation over season-long at the same intensity 

 was 16 kg. per head for 1918-34. The steers grazed 

 season-long at the moderate rate gained 20 kg. 

 per head more than those on rotation. During the 

 period of 1938-45 when there was no shortage 

 of forage in any of the range units, the steers in 

 the moderate season-long unit gained 13 kg. per 

 head per season more than those in the rotation 

 units. The steers in the heavily stocked season- 

 long unit gained 9 kg. per head more than those 

 in the rotation units (33). 



Rogler (33) concluded that steer gains could 

 not be increased by using a rotation system when 

 there was sufficient forage for season-long graz- 

 ing. There would seem to be some merit in a 

 rotation system for improving range that has 

 been damaged by overgrazing. Rogler suggested, 

 however, that complete deferment until the range 

 condition recovers would be a more rapid method 

 of improvement. A rotation system might be. 

 used when it is necessary to stock at a high rate 

 during occasional years and with older cattle. One 

 of the advantages of continuous grazing is that 

 cattle have access to all the plants in the range 

 unit when highest in nutritive value. Young 

 cattle are less likely to gain under a rotation S} r s- 

 tem because thev do not utilize the mature for- 



