THE FEEDING OF MILCH CATTLE 329 



carbohydrate material, maintain the milk yield at 

 the same level as do digestible proteins. Probably 

 these substances are converted by the help of 

 bacteria in the partly digested food into protein. 

 Before it is possible to satisfactorily answer the 

 questions which arise out of the above-mentioned 

 observation, it will be necessary to test the effect 

 of a large number of substances rich in amides in 

 the same way as has been done with ammonia. 



(e) The effect of non-nitrogenous nutrients. 



It has been previously stated that with a food 

 rich in nitrogen-free substances and poor in protein 

 all the proteins that are not required for the main- 

 tenance of the animal can be transformed into milk 

 proteins. As milk contains in addition to the 

 protein large quantities of fat and milk sugar, these 

 constituents must be formed from the digested 

 fat and carbohydrates. Milk fat, like body fat, 

 can be made from the carbohydrates of the food, 

 as many experiments with cows to which a ration 

 artificially freed from fat was given, have proved. 

 In one case, for example, during an experimental 

 period of fourteen days, the quantity of digested 

 fat was 2- 18 kg., and that portion of fat which could 

 arise from the decomposed protein (p. 65) was at 

 most 1778 kg., so that in all a maximum of 19-96 kg. 

 fat was available for the milk. As 37-65 kg. fat 



