116 Agricultural Chemistry. 



Influence of age and kind of animal. If a mature animal, as 

 a steer, for example, is confined in such a manner that all the 

 excrement, both liquid and solid, can be preserved, it will be 

 found that all the nitrogen, phosphoric acid and potash of the 

 food will be contained in the excreta. This is when the animal 

 is not gaining in weight. None of these constituents will be stored 

 in the tissues, but all are voided in the dung and urine. On the 

 other hand, only about half of the total dry matter of the ration 

 will be voided in the excrement, a large part of the other half 

 having been given off from the lungs as carbon dioxide. While 

 the excreta, therefore, contain only about half of the total dry 

 matter which was present in the ration, they contain all the con- 

 stituents that are generally considered of fertilizing value. 



With young growing animals, gaining in weight, the above 

 statement is incorrect. They retain a certain proportion of the 

 nitrogen, potash and phosphoric acid for use in building up their 

 bodies. The amount retained depends upon the age of the animal 

 and its rate of growth. Experiments indicate that calves retain 

 during the first three months of their Jives about one-third of the 

 fertilizing value of the food consumed, while the other two-thirds 

 would be found in the excrement. For the first year of their 

 existence they use in growth about one-fifth of the nitrogen, 

 phosphoric acid and potash present in the food and as the animal 

 ages, the amount gradually diminishes until practically none of 

 these materials are retained. When a mature animal is fatten- 

 ing there is practically no drain on the fertilizing value of the 

 feed, provided the gain is all fat. This is due to the fact that 

 fat contains only carbon, hydrogen and oxygen, and consequently 

 its production does not remove any of the fertilizing constituents. 



The above deductions are equally applicable to the other classes 

 of farm animals, such as swine, sheep and horses, and the age of 

 the animal has the same effect on the value of the manure. 



Influence of milk production. In the case of the cow another 

 factor is introduced, as a certain proportion of the nitrogen, 

 phosphoric acid and potash is removed in the milk. One hundred 



