FEEDS 407 



sources and chemical composition of some ot our more important 

 loods and feeds. 



GENERAL COMPOSITION 



When feeding stuffs are purchased on the market, pure food laws 

 require that such feeds be sold on the basis of chemical composition. 

 As a result it is customary to make the following chemical analyses 

 on all feeding stuffs: 



1. Moisture. 



2. Crude protein. 



3. Crude fat. 



4. Crude fiber. 



5. Ash. 



6. Nitrogen-free extract. 



Moisture 



It is necessary to determine the moisture content of foods and 

 feeding materials in order that we may compare the composition of 

 one feed with that of another. As a rule feeds are usually fed and 

 compared on what is known as a moisture-free basis in order that 

 comparisons may be made on the basis of dry matter or total solids. 

 Certain feeds deteriorate rapidly if the moisture content exceeds 

 specific limits, which vary for different feeds. For these reasons 

 knowledge of the water content is highly desirable. Furthermore a 

 feed buyer cannot afford to pay feed prices for water. As a result the 

 buyers of such commodities often prescribe the maximum water con- 

 tent. 



Crude Protein 



Since many proteins contain about the same amounts of nitrogen 

 (16 per cent), it has become the practice of laboratories to determine 

 the total nitrogen present in the feed and multiply this amount by 

 the factor 6.25. This general factor is used for most proteins, al- 

 though there are exceptions to this rule. For example, the factor 5.7 

 is used for the calculation of crude protein in wheat and its products, 

 since the proportion of nitrogen in wheat proteins is greater (about 

 17.5 per cent) than in most other proteins. The nitrogen is deter- 

 mined by the Kjeldahl method, oxidizing the feed completely by 

 boiling in sulfuric acid. This liberates the nitrogen in the form of 

 ammonium sulfate. By the addition of a strong alkali (NaOH) the 



