MILK PRODUCTION 475 



Table 124 shows, this difference is accompanied by a rela- 

 tively smaller secretion of water, so that the percentage of total 

 solids in the resulting milk is greater. 



Cooke, 1 in 1890, drew the same conclusion from a study of 

 over 2400 analyses of milk reported by the experiment sta- 

 tions of the United States up to that date, and more recently 

 Haecker 2 has reached substantially the same result from 

 analyses of 544 individual samples of milk from the Minnesota 

 Station herd. 



566. Variability of composition in same animal. It should 

 be noted that the foregoing conclusions are drawn from 

 the average composition of the milk of the same individuals 

 for comparatively long periods. The composition of the milk 

 of the same cow, however, may and frequently does vary quite 

 widely from one milking to another without affecting its average 

 composition as computed from analyses of a number of milkings. 



This has been observed especially in the case of the fat be- 

 cause far more determinations have been made of this con- 

 stituent than of any other, the fat being both the most valuable 

 and the most easily determinable ingredient. Variations as 

 great as i per cent in the fat content of successive milkings of 

 the same cow are not uncommon and differences of 2 and even 

 3 per cent not very rare. Whether there is a correlated varia- 

 tion in the proportion of lactose, as in the averages compared 

 in the previous paragraph, does not appear. It is presumed 

 that these variations are due largely to external influences but 

 no definite connection with any specific factors of environment 

 has been traced with certainty, although Spier 3 believes them 

 to be due to incomplete milking (575) . It is evident that correct 

 comparisons of the yields of different animals, or of the same 

 animal at different times, can be made only on the basis of the 

 average yield and composition for a number of days. 



The extent of this variability in the composition of milk from 

 one milking to another appears to be an individual peculiarity, 

 the milk of some cows being much more uniform in daily com- 

 position than that of others. An interesting example of this 

 has been reported by Farrington. 4 



1 Vt. Expt. Sta., Rpt. 1890, pp. 97-100. 



2 Minn. Expt. Sta., Bui. 140 (1914), p. 51. 



3 Jour. Highland and Agr. Soc., 1909, p. 287. 



4 Ills. Expt. Sta., Bui. 17 (1891), p. Q. 



