are used in determining yield or utilization by counting the num- 

 ber of stems that have been grazed on small plots and then 

 estimating for each species the weight of the forage that has been 

 eaten. Considerable training is required for using this method, 

 but one advantage is that the actual weight of the yield of each 

 species can be used in training and in checking the estimates. In 

 grazing studies estimates of weight deserve wider use and may 

 be more valuable than those of cover, for the percentage com- 

 position of species in an area usually varies with the characteris- 

 tic that is measured. For example, in the same meter-square 

 quadrat in northern Colorado, western wheatgrass comprised 9 

 per cent of the total basal area of all species but 31 per cent of the 

 total actual weight of all species, and the corresponding figures for 

 buffalograss were 45 and 8, respectively. i°^ While the area of the 

 latter was much greater, the grazing value of the former, as 

 shown by the dry weight, was considerably higher. 



The use of animals as instruments for measuring the grazing 

 value of plants includes methods such as the weights of cattle or 

 sheep, carrying capacity in numbers of animals, production of 

 milk or beef, total digestible nutrients, digestion trials, palatability 

 trials, and biological assays with small animals. Periodic weighing 

 of animals, especially beef cattle, dairy heifers, or sheep, is less 

 complicated than measuring the production of milk from dairy 

 cows, but precautions must be taken to select highly similar 

 animals. Special devices such as movable pens and tethering 

 have been developed for using sheep in evaluating pastures. 

 Some objections to the live-weight method are (1) the difficulty 

 of control, (2) the relatively small areas grazed, and (3) the in- 

 exactness of comparing a grassland under a short-term experi- 

 ment to one grazed for a long period under field conditions. The 

 total digestible nutrient method is considered by many to be the 

 best for evaluating pasturage when milk-producing cows are 

 used. The nutrients supplied in the herbage and in supplemen- 

 tary feeds are considered in relation to the requirements of 

 digestible nutrients for the milk production, maintenance of the 

 animals, and for increases in live weight. ^^ 



The nature of the chemical components of plants is important 



llO • THe Conrnmnunifty 



