34 Journal of Agriculture, Victoria. [10 Jan., 1916. 



THE DAIRY COW AS A MACHINE. 



By B. A. Barr, Senior Dairy Supervisor. 



A macliine is a contrivauce which, if supplied with sufficient power, 

 is able to perform work. By its use some of the potential energy of the 

 fuel is transformed into work. The work performed by a milking 

 coAV is in the form of milk production. 



To enable a machine to do work, it is necessary to supply it with 

 sufficient motive power, such as steam, gas, petrol, electricity, &c., all 

 of which possess varying capacities for work. 



The dairy cow requires food as fuel, and just as the different fuels 

 used to drive machines vary in value, so do the different foods available 

 to the cow vary in their value for milk production. 



Under similar conditions 1 ton of coal will perform a greater amount 

 of work than 1 ton of wood, and similarly 1 cwt. of green oats will 

 produce a larger quantity of milk than 1 cwt. of green maize, or 1 cwt. 

 of bran will give a much greater return than 1 cwt. of lucerne hay. 

 All the energy of the fuel which is burned in the furnace of a boiler 

 or directed to the combustion chamber of a gas engine is not trans- 

 formed into work. Some of the fuel is not completely burned, and 

 some of the products of combustion escape in the air. This represents 

 a considerable loss. In the most efficient internal combustion engine 

 only 40 per cent, of the total energy of the fuel is transformed into 

 work, and in many steam-driven plants not more than 10 per cent, is 

 recovered. A similar loss results in feeding cows, when, according to 

 the capacity of the individual animal, from 20 per cent, to 45 per cent, 

 of the total energy of the fuel is transformed into milk. A portion of 

 the food is not digested, and from this no milk can be secreted. Portion 

 of the digested food is required to repair wastage and to maintain the 

 body temperature. When wet cold food is given during cold weather 

 a considerable amount of food is burned to raise up to body temperature 

 the cold contents of the stomach. What is left after these demands is 

 available for milk production. 



The fuel supplied to a machine is used only for the production of 

 work. When any part wears, either it is replaced by a duplicate or 

 taken out, turned, and re-fitted; but in the case of the cow the food is 

 converted into work and also keeps the machine in repair; in other 

 words, whilst supplying the secretory cells of the udder with digested 

 food-material for conversion into milk it also maintains the bodily 

 condition and health of the animal. 



The value of a fuel for driving a machine is determined by chemical 

 mean? and by the rapidity and completeness of its combustion. The 

 food value of a fodder may be somewhat similarly determined by its 

 chemical constitution and its digestibility. Just as certain fuels give 

 best results when directed to particular classes of Avork, so certain foods 

 give best results for milk production. The dairy cow requires not only 

 a larger amount of food, but also a diiferent kind of food from that 

 of the dry or fattening animal. The larger amount is required because 

 the Avork" ])erformed is greater ; the different kind is required because 

 a different class of work is done. 



