38 MILK HYGIENE 



To be sure, there are many reports in print of 

 other results, but upon examination these are found to 

 extend over so short a period that the temporary 

 changes had not yet disappeared, or they refer to inves- 

 tigations with different cows whose milk was not suf- 

 ficiently examined, or to cows that did not receive the 

 same food in the beginning of the experiment, or, finally, 

 sufficient allowance was not made for the daily varia- 

 tions and for those that occur at different stages of the 

 lactation period. 



The temporary changes in the composition of milk 

 which occur after a change in the food, may be consid- 

 erable, but here, too, the question of individual peculiari- 

 ties enters, so that the changes shown by two cows under 

 the same conditions may differ materially. 



It is of an old belief, that the change from dry food 

 to green causes an increase in the fat content of the milk. 

 The investigations in the Danish experimental labora- 

 tory have proven this ; they show that the fat percent- 

 age under these conditions may increase 0.5 per cent., 

 with some cows it increased even 1.0 per cent., but this 

 increase lasted only a few weeks. Also, when changing 

 the ration to include some of the oil cakes, a similar 

 increase in the percentage of fat has been observed, but 

 seldom more than about 0.5 per cent. On the other 

 hand, as stated before, there are observations of tem- 

 porary falling of the fat from 0.25 per cent, to 0.5 per 

 cent, when a change of food is made to distillery slops 

 or similar rations. 



It is, then, possible to show that the udder reacts 

 rather characteristically to certain changes in the ration 

 and especially to some food stuffs ; but this reaction is 

 lost when the cow has become accustomed to the new 

 food. Under such conditions, simultaneously with the 

 increase of the fat percentage there frequently occurs a 



