62 Bulletin 173. 



changes in the kinds of foods given during tlie whole thne. Tlie 

 feeding trials lasted through two successive Avinters and for a period 

 of twenty-two weeks during each winter. The effect of the differ- 

 ent rations was studied by comparing tlie influence of each upon the 

 average milk production of the cows used. We think this method 

 to be satisfactory because, in the first place, the cows were so selected 

 as to make the different lots fairly equal as to age, breed and gen- 

 eral characteristics ; and in the second place, if a given ration will 

 produce any particular effect upon milk production, then this ration 

 will show its influence on the average composition of the milk 

 from the lot of cows to which it is fed when compared with the 

 average composition of milk from other cows on other rations. 



Our study is confined to the yield of milk and its quality so far 

 as represented by the percentage of butter-fat. The determinations 

 of fat were made by the Babcock test from samples of milk taken 

 from each cow during tlie last three days of each week. These 

 daily samples were tested separately and their average taken for the 

 average per cent of fat in the week's milk. Each cow's milk was 

 weighed as soon as drawn and the weekly yield of milk multi})lied 

 by the average per cent of fat gives the total fat produced during 

 the week. 



The rations fed were of three kinds, one with a narrow, one with 

 a medium, and the third with a wide nutritive ratio. No analyses 

 of foods were made except of the oat chop which was fed during 

 the first year. The amount of dry substance and the nutritive ratio 

 were calculated largely from the average composition of feeding 

 stuffs given in Bulletin No. 11 of the office of Experiment Stations' 



With one exception the same cows were used throughout the two 

 years of experiment. Moreover the same cows were fed rations 

 having practically the same nutritive ratio, though made up of dif- 

 ferent foods dnring both years, /. e. tlie cows receiving a narrow 

 ration the first year also received a narrow ration the second year 

 likewise with the cows on other rations. None of the rations are 

 what would l)e called unusual for similar ones may be found in use 

 oJi dairy farms in various ])arts of the country. During the whole 

 length of both experiments it was the aim to give the cows all the 

 food they could readily consume. 



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