LACTATION PERIODS. 39 



that obtained in experiments carried out on a small scale, will take place. 

 Undoubtedly, in the case of single cows, the expansion of the milk cavity 

 in the udder, and the multitude of gland-baskets and their physiological 

 activity, accommodate themselves to the times of milking. According to 

 the degree in which this takes place, the differences, at first noticeable in 

 the yield, necessarily diminish, and it is highly probable that in most cases 

 they eventually entirely disappear. In large dairies, in the case of pastur- 

 ing animals, or where the milk is utilized in large factories, the three- 

 times-a-day milking system is practically inadmissible. If the system of 

 milking three times a day really gives an increase, which has not been 

 definitely proved, its adoption in small dairies may not always be found 

 to pay, when the increased expense, as well as the waste of time and the 

 inconvenience incidental to such a system, are taken into account. Of 

 course, in the case of heavy milking and newly-calved cows, the milking 

 must be done three times a day, or even oftener. 



14. Lactation Periods. The time during which a cow gives a 

 continuous supply of milk, that is, the time intervening between 

 calving and becoming dry, is called the lactation period. This may 

 be taken, on an average, under ordinary circumstances, to be 300 days; 

 and the cows remain dry for the following six or eight weeks. In 

 most cases the milking capacity of the cow reaches its highest point 

 in the course of the first two months after calving, and diminishes 

 from then till the time when it becomes dry. The yield of the cow 

 may become reduced pretty gradually, or perhaps intermittently, 

 and in the latter case frequently occurs in three unequally long 

 intervals, more or less distinctly marked. This natural process is 

 influenced by suitable treatment and management, and especially by 

 an intelligent regulation of the calving-time suitable to the local 

 conditions of feeding. 



In the case of richly-fed and well-tended milk cows of average age, 

 the percentage of total solids in the milk almost always increases with the 

 advancement of the period of lactation. At the same time, not only is the 

 percentage of fat in the milk increased, but also the percentage of fat in 

 the dry total solids, so that the milk becomes absolutely, as well as rela- 

 tively, richer in fat. With regard to the behaviour of the other constituents 

 during lactation, we have up till now few reliable observations. G. Kiihn 

 found in the case of cows with which he experimented that generally the 

 percentage of protein, especially the caseous matter, increased with the 

 period of lactation, while the albumin and the milk-sugar showed a 

 decrease. 



