ANIMAL HUSBANDRY. I05 



albuminoids instead of fish meal. In each year the pen of pigs 

 receiving green food came out as well as the pen receiving only 

 mixed cereal meals, and the pigs were in excellent condition 

 throughout. 



An experiment has also been conducted to compare the 

 values of green food and undecorticated cotton cake for feeding 

 to dairy cows at grass. The results of this experiment were 

 somewhat inconclusive in the summer of 1920 when there was 

 plenty of grass, but it was clear from the results obtained in the 

 summer of 1921, when there was a scarcity of grass, that cotton 

 cake could be substituted by an equivalent amount of vetches 

 (5^ lb. of vetches for i lb. of cake) without any detrimental effect 

 an the yield or quality of the milk. 



Energy Requirements . The Calorimeter. 



Reverting to the work in progress at Cambridge, we may now 

 refer to an attempt to deal with another important question for 

 the stock feeder, namely, what is known as the " energy require- 

 ment " of different classes of livestock under varying conditions. 

 AU work done by an animal, whether in digesting food, or forming 

 flesh, or trotting, or pulling a cart, can be expressed in terms of 

 energy, and the food which an animal requires can be determined 

 in the first instance by its energy requirement. It is compara- 

 tively easy to determine how much energy a particular weight 

 of a given food will supply, and if we knew precisely the total 

 amount of energy needed by an animal for a certain class of work, 

 it would be possible to say beforehand just how it should be fed 

 most economically and efficiently. In experimental practice, 

 energy is measured in terms of heat. In the case of the animal, 

 this heat is produced by chemical changes taking place within the 

 body of the animal, and the amount of chemical change can be 

 calculated from the heat evolution, which can in turn be measured 

 by means of an instrument known as a calorimeter. After a 

 considerable period of experimental work, an apparatus for this 

 purpose, large enough to take a bullock and cheap enough to be 

 within the reach of any scientific institution, has been constructed 

 at Cambridge, and from preliminary trials there is reason to hope 

 that the apparatus will be found sufficiently accurate for all 

 practical purposes and will lead to the accumulation of extremely 

 important data regarding the feeding of stock. A brief descrip- 

 tion of the apparatus may be interesting. The calorimeter 

 consists of a cylindrical galvanised iron tank, 9 feet 6 inches 

 long and 5 feet 6 inches in diameter, round the outside of which 

 is soldered a spiral of lead pipe through which a constant stream 



