16 PRINCIPLES OF FEEDING FARM ANIMALS 



stems become coarse and tough; hence their digestibility decreases 

 during the latter stages of plant growth (p. 58). The following 

 approximate amounts of fiber are found in different classes of 

 feeding stuffs: 



Buckwheat hulls, buckwheat straw, and flax shives, 45 per cent; 

 straw of cereals, 40 per cent ; hay from different grasses or legumes, 

 20 to 35 per cent ; cereals, 0.2 per cent (rice) to 10.8 per cent (oats) ; 

 roots and tubers, 0.4 to 2.2 per cent; concentrated feeds, 0.9 to 30 

 per cent, generally, however, less than 20 per cent (Fig. 4). 



A high fiber content indicates that a feed is of relatively low 

 value for stock feeding, and vice versa. The figures for this com- 

 ponent, with those for protein and fat, are, therefore, of the great- 

 est assistance to feed buyers in judging the value of manufactured 

 and other feeds. 



Chemical Analyses of Feeding Stuffs. The following com- 

 ponents are determined by the chemist in the ordinary analysis of 

 feeding stuffs: Water (often called moisture), protein, fat, fiber, 

 and ash; the difference between 100 and the sum of percentages 

 of these various components obtained in the analysis is known as 

 nitrogen-free extract (starch, sugar, pentosans, organic acids, etc.). 



Methods of Chemical Analysis. The outline of the common method 

 adopted in chemical laboratories in the analysis of feeding stuffs given below 

 will be of value to students by enabling them to better understand data 

 and discussions relating to the chemical composition of feeding stuffs 

 (Fig. 5). 



a. Moisture (water) is determined by heating a small portion (gener- 

 ally 2 grams) 2 of the carefully-sampled and finely-divided feeding stuff 

 in a steam-bath or water oven at 100 C. for two to five hours, till it no 

 longer loses weight. After cooling in a desiccator, it is weighed carefully 

 on a chemical balance and the percentage loss calculated on the original 

 weight is taken to represent moisture. Volatile organic substances some- 

 times present in minute amounts in plant materials would also be in- 

 cluded in this loss. In the case of some feeding stuffs containing fats that 

 take up oxygen, as corn, flaxseed, and other oil-bearing seeds, the material 

 must be heated in a current of hydrogen or other inert gas, so as to 

 prevent oxidation and a resulting increase in weight during the drying, 

 which would give too low a moisture content. 



6. Fat. The residue from the preceding determination is extracted 

 with anhydrous sulfuric ether in a suitable apparatus for a considerable 

 period of time, generally 16 hours, till the fat has been completely dissolved. 

 The ether is distilled off and the residue dried at 100 C. and weighed. 

 As previously stated, the ether extract, in the case of roughage and some 

 other feeds, contains considerable impurities, as chlorophyl, wax, and 

 resins. 



c. Protein is obtained by multiplying the total nitrogen by 6.25 (see 

 p. 9), the nitrogen being determined by the Kjeldahl method, so called 

 after the inventor, a Danish chemist. In this method a small portion of 

 the feed (generally 1 gram) is heated with 20 c.c. sulfuric acid till the 



2 T 1 ? of an ounce. 1 ounce equals 28.35 grams. 



