The Relation of Food to Milk-Fat. 61 



Of the four experiments where tlie fat in the food increased the 

 proportion of milk-fat, one reports so great a reduction in the yield 

 as to make such feeding un])rofitable. The noted experiment of 

 Soxlilet whereby he increased the per cent of milk-fat by feeding 

 tlie cows oil emulsilied in the drinking water, has been repeated 

 many times by other experimenters, but none of them, so far as we 

 know, have reached a similar result. The protein foods which 

 increased the per cent' of fat were pahn-nut meal and sugar meal. 

 The molasses preparations may owe their power to increase the fat 

 content of milk to their rather abnormal character. 



Original Experiments. 



These experiments were conducted for the purpose of determin- 

 ing the comparative effect of rations liaving different nutritive ratios 

 upon milk production. This question has been the subject of experi- 

 mentation at various times and places as has been already noticed, 

 but further investigation along possibly different lines may throw 

 more light npon the problem. Much discussion has occurred over 

 the matter of the length of time during which a particular food 

 should be tested and as to the accuracy of conclusions drawn from 

 feeding trials where two or more foods were given during brief 

 alternating periods. Some contend that four or five weeks is sufii- 

 cient time in which to secure the true effect of a food, some think 

 that a shorter time, even ten days, is enough, while others hold 

 that the longer the period the more accurate and conclusive the 

 result. It is well known that, when a radical change is made in the 

 food of a cow, the secretion of milk is greatly affected. This is most 

 apparent in the fat content, which may either rise or fall, but is 

 more apt to rise. How long the fluctuation may continue depends 

 upon the al)ility of the cow to accustom herself to the new feed, 

 which time may be only a few days or it may be weeks. And when 

 the cow has become accustomed to the changed feed, her milk falls 

 back to its normal average composition. However, if the experi- 

 ment is concluded before this time, or if the feed is again changed, 

 then conclusions drawn therefrom must be more or less warped. 



In order that these sources of ei'ror might be obviated, we not 

 only continued the experiments for a long period, but also made no 



