130 FEEDS AND FEEDING 



has been pointed out (63, 92), when the protein supply in the ration is 

 already adequate, any additional amount of this nutrient is broken down 

 in the body, the nitrogenous portion being excreted in the urine, and only 

 the remainder utilized for the formation of the fat and carbohydrates in 

 flesh or milk, for body fuel, or for the production of work. In all such 

 cases protein will have a value corresponding only to the amount of net 

 energy it furnishes. Over large sections of our country protein-rich 

 feeds are cheaper than those high in carbohydrates. In the West with 

 its abundant and cheap alfalfa hay, and in the South with its low-priced 

 cottonseed meal, it is often necessary to add carbonaceous feeds rather 

 than protein-rich concentrates to balance the usual rations. Thus the 

 feed-unit system does not furnish a safe guide by which the farmer can 

 determine the value of feeds under all conditions. The worth of a given 

 feed to him will depend on the other feeding-stuffs with which it is to be 

 combined. In some instances protein-rich feeds will be worth the most, 

 and in others, those which are high in carbohydrates. The feed-unit 

 system has been evolved in a comparatively small region, where similar 

 crops are grown on the different farms and the price of purchased feeds 

 does not vary widely thruout the entire district, hence this difficulty 

 has not arisen there. No arbitrary values for feeding-stuffs, expressed 

 in terms of money or other fixed units, can be devised which will hold 

 good under widely differing conditions. 



179. Measuring economy of production in feed units. The chief value 

 of the feed-unit system for dairymen in any given region is that it fur- 

 nishes a simple means of comparing the feed consumption and the milk 

 and fat production of different cows, as, is shown in the following: 



If during a month a cow has consumed 240 Ibs. of hay, 750 Ibs. of 



"silage, 60 Ibs. each of barley and ground corn, and 90 Ibs. of linseed oil 



meal, the calculation based on the valuation table would be as follows: 



Feed consumed ' Lbs. for 1 unit Feed units 



240 Ibs. hay... -* 2.5 = 96 



750 Ibs. silage -J- 6.0 = 125 



120 Ibs. corn and barley -J- 1.0 = 120 



90 Ibs. oil meal -f- 0.9 = 100 



Total feed units = 441 



It is shown that the cow consumed 441 feed units during the month. 

 If in that time she yielded 850 Ibs. of milk, containing 30.6 Ibs. of fat, 

 each 100 feed units produced |^ = 193 Ibs. of milk, containing f| = 

 6.9 Ibs. butter fat. If the fat brought 30 cents per lb., 100 feed units 

 would return 6.9x$0.30=$2.07. 



180. The Swedish cow testing associations. The method of using the 

 feed-unit system to compare the relative efficiency of different herds is 

 illustrated by data secured in the Swedish cow testing associations. 

 During the year 1906-7, the cows in 96 associations consumed on the 

 average 5,280 feed-units, made up of the following : oil cakes, 856 units ; 



