The following circumstances are of influence on lactation : 



Age of cow : "When a cow has its first calf, it does not pro- 

 duce the maximum quantity of milk, but the quantity increases 

 from year to year until a certain limit is reached, when, with fur- 

 ther increasing age, the quantity is reduced, at first slowly and 

 more quickly later on. 



The age to which it pays to keep cows for milking differs 

 according to individuality, race and treatment. It is generally 

 accepted that cows are the most profitable from their third to their 

 tenth year. 



Cows in heat : "We know but little of the changes which oc- 

 cur in milk at the return of the periods when cows get in heat. 



From the feeding experiments made by G. Kuehn and Fleischer, 

 a characteristic change of the milk, during these periods, cannot be 

 deduced. Such milk, it has been stated, will sometimes curdle on 

 boiling. A normal course of this process, which lasts but a few 

 days, should not influence normal lactation for any length of time. 



It may be remarked that also cows which have undergone the 

 process of castration, may produce milk. It is, however, not con- 

 sidered profitable to keep such cows longer than two years. They 

 fatten up rapidly, and their milk-producing qualities suffer in con- 

 sequence. 



S,ace and individuality: Good milk-producing qualities de- 

 pend principally on a strong and healthy development of the udder. 

 A defect in this can never be remedied by the best and most 

 nutritious food. The yield and quality of the milk depends directly 

 on individual properties of the animal and, therefore, also on its 

 race. 



Comparative investigations regarding the yield and quality of 

 the milk of different races have frequently been made, but they are 

 incomplete and little trustworthy. They have either been under- 

 taken with but few animals for a longer period, or if really on a 

 large scale, but for a short period. In some cases select stock has 

 been observed for longer periods. Average figures deduced from 

 such incomplete and heterogeneous observations are, therefore, of 

 little value. The yield and quality of the milk of various races and 

 breeds of cattle, cannot be determined without the collection of 

 copious and well selected statistics in the countries of which these 

 cattle are indigenous. Few investigations have been made to 

 which chemistry has contributed as largely as it should have done. 



