178 FOODS [chap. 



yet if carbohydrates are added to a hay or straw diet the 

 digestibility of the proteins in the original diet is reduced 

 when the added carbohydrates amount to more than lo 

 per cent, of the fodder. Thus, roots should not be added 

 to a hay and straw diet in greater proportion than 15 

 per cent, (reckoning both as dry matter), unless some 

 concentrated protein food be given at the same time in 

 order to maintain the ratio between nitrogenous and 

 non-nitrogenous constituents of the food at a higher 

 level than i to 8. 



Table XVII. (page 179), which is copied from a table 

 compiled by Dr Crowther, of Leeds University, sets out 

 the average composition of a number of the foods most 

 commonly in use, together with the percentages of the 

 same constituents that are in a digestible condition and 

 one or two other factors which will be explained later. 



The most concentrated of all foods are the meals and 

 cakes, the latter being the residues left after crushing 

 various oil-bearing seeds in order to extract as much oil 

 as will come out by pressure alone. The composition of 

 such cakes will vary with the nature of the seed and its 

 origin, but the amount of oil in the cake can also be 

 greatly modified by the extent of pressure put on and 

 the temperature at which the crushing is conducted. 

 With linseed cake in particular it is customary not to 

 extract the oil as fully as would be possible, whereby 

 the cake is enriched and at the same time rendered 

 softer and easier of digestion. In some cases the oil is 

 extracted by chemical means, but the seed residue is 

 then generally used for manure ; as a rule, rape seed 

 is treated in this fashion because it is rarely pure 

 enough to be used afterwards as cattle food, being often 

 mixed with a considerable proportion of mustard seed. 

 In the United Kingdom few cakes are used beyond 

 those derived from linseed and cotton seed, and of 



