1907.] 



Variations i.\ Milk. 



39 



3-75 per cent, of fat, but rapidly decreased and reached its 

 minimum (3*50 per cent.) in the third month, it then rose 

 steadily till the close of the lactation period (4*14 per cent, in 

 the eleventh month), being above the average from towards 

 the middle of the sixth month. The variation, in Herr 

 Hogstrom's opinion, undoubtedly represents a natural adjust- 

 ment, both as regards quantity of milk and its fat-content, to 

 the needs of the growing calf. 



Effect of Season of Year. — In order to trace the influence of 

 the season of the year on the variations in the milk, a number 

 of records from cows calving in each successive month of the 

 year was taken, in such a way as to eliminate the variations 

 due to the progress of the lactation period, with the result 

 that a very marked fall was shown to take place from April 

 (372 per cent.) to June (3-45 per cent.) from which date it 

 rose to a maximum in October (3*96 per cent.), when it again 

 declined. 



These two factors, viz., the variation in the lactation period and 

 the seasonal fluctuation, are considered to have a great influence 

 on the quality of the milk. For instance, in the case of a cow 

 calving in March, the third and fourth months after calving, 

 when the milk has the smallest proportion of fat over the whole 

 lactation period, coincide with the period May- June- July, 

 when the seasonal influence also causes the milk to be the 

 poorest. On the other hand, in the case of a cow calving in 

 August these two factors work in opposite directions. The 

 minimum point in the lactation period then occurs in October, 

 when the seasonal influences tending to raise the fat-content 

 are at their maximum. 



It is regarded as improbable, however, that the monthly 

 variations are due merely to t he external influence of the seasons 

 or changes of temperature, and still less to changes in food. 

 Herr Hogstrom considers it far more likely that the cause is 

 to be found in the organism of the animal itself, ami suggests 

 ih.it it is related to the natural tendency of cows to calve in 

 .March or April, the quality of the milk being adapted to the 

 requirements of the call and the season ol the year. When 

 :ows calve at other times of the year there is still a tendency 

 to produce milk of tin- quality related to the time of year. 



A large number of records of cows were examined with refer- 



