TH6 JOORNAIs 



OP 



Tfie department of ^gricufture 



OF 



VICTORIA. 



Vol. XIV. Part 9. 11th September, 1916. 



FOOD VALUES AND RATIONS. 



By B. A. Barr, Senior Dairy Supervisor. 



The total amount of essential constituents in cattle food determined 

 by chemical analysis does not give any definite information of their 

 respective food values. It serves to show in what proportions the consti- 

 tuents are present, but it does not reveal whether they are in a condition 

 to be readily digested, nor does a scrutiny of the figures convey any 

 knowledge of that amount of nourishment available for animal nutrition. 



ISTevertheless, a chemical analysis is the first step to a comparison of 

 relative food values, and the average obtained frojn a large number of 

 samples is taken to represent the average composition of any particular 

 variety of foodstuif. As a result of feeding trials, the percentages of 

 digested protein, carbohydrates, and fat — called digestible nutrients — are 

 found. This data furnishes coefficients of digestion, whicli find applica- 

 tion in general practice. In addition to a knowledge of the amounts of 

 digestible nutrients in any food, it is important to know the cost of 

 digestion, i.e., the amount of energy expended in rendering the digestive 

 matter to an assimilable state, as shoAvn in Table I. The energy expended 

 in digestion reduces the value of the digested materials by the amount 

 used, and the difference between the total energy of the digestible food- 

 stuff and that used in digestion is net gain to the animal, which may be 

 used for milk production. The cost of digestion varies according to 

 class of foodstuff. Green grass is more easily digested than dry grass. 

 Hay cut on green side is more easily digested tlian hay cut almost ripe. 

 Pollard is more easily digested than bran. Crushed oats are more easily 

 digested than whole oats. 



Some of the factors which influence the cost of digestion are, the 

 variety of food, its chemical and physical condition. A food in a finely- 

 divided state is digested at a lower cost than some of the same variety 

 in a coarse state. The stage of growtli at which hays are cut influences 

 both the digestibility and cost of digestion; as the ]>l;iiit ripens the 



10372. 



