318 SCIENTIFIC FEEDING OF ANIMALS 



three periods of equal length are taken, and the 

 results in the first and third periods, where the same 

 food is given, are recorded, the second period during 

 which the added food is given can be calculated. 



An example will best serve to make this clear 

 Let it be assumed that it is to be proved whether 

 the addition of 0-5 kg. of a certain feeding-stuff 

 to a ration causes the yield of milk to increase. 

 For the investigation twenty healthy cows are 

 chosen, and these are fed in the first and third 

 periods with the original ration, and in each case 

 for a month. If, now, the daily weighing and exam- 

 ination of the milk during the last twenty days of 

 each period show that in the first period 15-38 kg. 

 of milk with 3'05%=46o, g. fat were given daily by 

 each cow, and that in the third period only 14-65 kg. 

 milk with 3*i2%=457 g. fat were got from each 

 cow, the natural decrease in this time is 0-73 kg. 

 milk and 12 g. fat. As between the middle of the 

 first and the middle of the third period forty days 

 elapsed, the daily decrease is 18-25 g- milk and 0-30 g. 

 fat. The middle of the second period in which 

 the added food is given is seen to be separated 

 from the middle of the first and third periods by 

 twenty days, and 15-015 kg. milk with 463 g. fat 

 would, therefore, have been obtained if no addi- 

 tion had been made. As, however, the milk was 

 x 5"35 kg. and the fat 480 g., the daily increase of 

 production due to the addition was 0-335 kg. milk 



