28 BULLETIN 790, TJ. S. DEPARTMENT OF AGRICULTURE. 



for an average grazing period of 72 days. The figures do not 

 include lands of no value for grazing. 



The ranges studied include sheep allotments on choice summer 

 range of Montana, inferior timber and brush ranges of Idaho and 

 Utah, and ranges of about average value in these States and in 

 Oregon and Wyoming. 



The sheep under observation were all ewe and lamb bands. Two 

 lambs were considered the equivalent of one mature sheep. The 

 bands contain an average of 58 per cent of lambs. The ratio of two 

 lambs to one mature sheep is an arbitrary one, since no data are 

 available to show the relative forage consumption by lambs and by 

 their mothers on summer ranges. To use this ratio, however, and 

 include the lambs is better than to disregard the lambs, because the 

 percentage of lambs may vary greatly. 



The average lamb crop for the far western range States as given 

 by the United States Tariff Board x is 70.3 per cent, with Washington 

 the highest at 92.5 per cent and Arizona lowest at 59.3 per cent. 

 The general average has probably been increased slightly since this 

 report was issued, so that to figure on a 75 per cent average lamb 

 crop in using the grazing-capacity figures given will be within the 

 general margin of accuracy and uniformity of grazing estimates and 

 methods. 



If such a thing as a uniform measure of grazing capacity can be 

 used, it would appear from close study of the tests conducted, and 

 from similar figures deduced from range reconnaissance surveys, that 

 0.01 forage acres per head per day is about right for range suited 

 to sheep grazing. This would be equivalent to about 0.03 surface 

 acres per head per day, exclusive of range having no value for graz- 

 ing, or about 3 surface acres for a grazing period of 100 days. 



ACREACE FOB CATTLE. 



A high, open, rolling range on the Lewis and Clark Xational Forest 

 in Montana supported one cow to every 7.37 surface acres, furnishing 

 2.65 forage acres per cow for a period of 100 days. This is at the 

 rate of 27 surface acres, or 9.69 forage acres per year. 



On cattle ranges of southern Idaho 10 surface acres, furnishing ap- 

 proximately 1 forage acres, was found to be the minimum required 

 for one cow over a period of five and one-half months. This range 

 is well watered and was closely utilized. 



Good grass foothill pasture of the Santa Eita Range Reserve in 

 southern Arizona has furnished an average of 365 cow-days' feed 

 annually over a period of years on an average of about 11 acres. 

 Each year during the main growing season the number of stock was 



l U. S. Tariff Board, Wool and Manufactures of Wool, Vol. IT fpt 2). H. Doc. No. 342, 

 C2d Cong., 2d sess., 1912. 



