316 



THE ROTHAMSTED EXPERIMENTS. 



Varying 

 yields of 

 milk. 



Basis of 

 compari- 

 son. 



butter-fat, 4.60 sugar, and 0.75 of mineral matter. The 

 estimates of the constituents in the fattening increase of oxen 

 are founded on the determinations at liothamsted of such 

 increase as already described. 



Keferring to the very wide range of yield of milk per head 

 per day which the figures in the table assume, it may be 

 remarked that it is by no means impossible that the same 

 animal might yield the largest amount — namely, 20 quarts, 

 or 5 gallons, per day — near the beginning, and only 4 quarts, 

 or 1 gallon, or even less, towards the end of her period of 

 lactation. At the same time, an entire herd of, say, Short- 

 horns or Ayrshires, of fairly average quality, well fed, and 

 including animals at various periods of lactation, should not 

 yield an average of less than 8 quarts, or 2 gallons, and would 

 seldom exceed 10 quarts, or 2\ gallons, per head per day, the 

 year round. 



For the sake of illustration, then, let us assume an average 

 yield of milk of 10 quarts, equal 2\ gallons, or between 25 

 and 26 lb. per head per day ; and let us compare the amount 

 of constituents in the weekly yield at this rate with that in 

 the weekly increase of the fattening ox at the higher rate 

 assumed in the table — namely, 15 lb. per 1000 live-weight, 

 or 1.5 per cent per week. 



Thus, whilst of the nitrogenous substance of the food the 

 amount stored up in the fattening increase of an ox will be 

 only 1.13 lb., the amount carried off as such in the milk would 

 be 6.6 lb., or nearly six times as much. Of mineral matter, 

 again, whilst the fattening increase would only require about 

 0.22 lb., the milk would carry off 1.35 lb., or, again, about six 

 times as much. Of fat, however, whilst the fattening increase 

 would contain 9.53 lb., the milk would contain only 6.33 lb., 

 or only about two-thirds as much. On the other hand, whilst 

 the fattening increase contains no other non-nitrogenous sub- 

 stance than fat, the milk would carry off 8.32 lb. in the form 

 of milk-sugar. It may be observed that this amount of milk- 

 sugar reckoned as fat would correspond approximately to the 

 difference between the fat in the milk and that in the fatten- 

 ing increase. 



From the foregoing comparison, it is evident that the drain 

 fooofb UP ° U U P 0U * ne f 00 ^ ^ S vei T muc h greater for the production of milk 

 milk than than for that of meat. This is especially the case in the im- 

 portant item of nitrogenous substance ; and if, as is frequently 

 assumed, the butter-fat of the milk is, at any rate largely 

 derived from the nitrogenous substance of the food, so far as 

 it is so, at least about two parts of such substance would be 

 required to produce one of fat. On such an assumption, 

 therefore, the drain upon the nitrogenous substance of the 



Substances 

 carried off 

 in milk and 

 required 

 for fatten- 

 ing. 



Greater 



by meat 

 production. 



