84 THIRTIETH ANNUAL REPORT OF THE 



why there should be variation. The general tendency of the 

 herd will be as the cows go along- in lactation to give rather rich- 

 er milk. While there are many exceptions, the general rule is 

 that cows coming in in the spring will give a fairly even 

 grade of milk for the first five months in their lactation, and 

 then increase in quality until they grow dry. If they are far- 

 row cows quality changes but little as time goes on. If an all- 

 the-year-round dairy is used there should be less change on 

 this account. 



WEATHER. 



Stress of weather is another cause of variation. We have 

 given much time at the Vermont station to the study of the 

 effect of temperature upon the milk-flow. Our results indi- 

 cate that the quality of a cow's milk alters inversely to tem- 

 perature change. When the temperature rises the tendency 

 is for the quality of the milk to fall; when the temperature 

 falls the tendency is for the quality of the milk to rise. 

 There are, however, many exceptions to this rule. No attempt 

 has been made to test this matter in long periods but only as 

 to daily or weekly fluctuations. 



SURROUNDINGS. 



The environmental differences, the nervous excitement of the 

 cow already mentioned, as they vary from time to time, may 

 cause fluctuation in t;he quality of the cow's milk. The 

 change from barn to pasture, or the reverse, lack of water, 

 poor water, drying pastures, new milkers and the like, may 

 and often do have influence. Then, too, it must be confessed 

 that there sometimes occur fluctuations in the quality of 

 the milk of a cow, and, occasionally, of a herd for a week or 

 more for which no rational explanation can be offered, 

 changes which, because of care in sampling and testing 

 and the conditions surrounding the operation, are removed 

 beyond all likelihood of being due to error rather than to fact. 

 There is much that we do not know about cow nature and 

 cow doings in milk-making. And here, as ever, those who 

 know the most are those who impute the least, while those- 

 less well informed are the more suspicious of wrong doing. 



An editorial in a recent number of Hoard's Dairyman is 

 very much to the point in this connection. It says: 



"The cow is not a machine that will turn out the same 

 quantity or quality of milk from day to day, and consequently 

 the milk varies according to the physical and perhaps mental 

 condition of the animal. The physical comfort or discomfort 

 of the animal is reflected in the milk pail, and if the great 



