GENERAL CHEMISTRY OP MILK 111 



RECORDS OF THE DAUGHTERS OF THE SAME SIRE 



If the total milk production of cows having the same number 

 of lactation periods in the table is compared it will be seen that 

 there is a great difference. The variation in fat is also con- 

 siderable, a fact which is illustrated in the last column. All 

 these cows were of the same sire, and the differences must be 

 ascribed to individual differences in character. 



In regard to the differences in quantity of milk constituents 

 contained in the milk of individuals of the same breed, the general 

 rule seems to be that the individual follows closely the average 

 milk composition of her breed. Still there are variations even in 

 this respect. The total sohds, fat, and protein vary to some 

 extent, while the milk-sugar — according to Eckles and Shaw — 

 shows greater variation in milk from individual cows than the 

 average of the breed. The ash, as might be expected, shows 

 practically no variation. Usually the greater the fat and pro- 

 tein in the milk of a breed, the greater also is the individual 

 variation. Therefore in Jersey milk individual variations are 

 more marked than in the milk of other breeds. 



3. Difference in Milk from the Same Individual. — A variation in 

 the composition of milk from an individual cow exists: 1, between 

 milk from different milkings; 2, between morning and evening 

 milk; 3, between fore-milk, middle milk, and strippings. 



It is usually thought that the difference in composition under 

 the three conditions mentioned is confined to the fat content. 

 Fat unquestionably is the most variable factor, but other con- 

 stituents vary also. In comparing analyses of morning and 

 evening milk Eckles and Shaw give the extremes of fat variation 

 in a series of tests as follows: 56 per cent, came within 0.3 per cent, 

 of the average; 27.7 per cent, between 0.3 and 0.6 per cent.; 11.7 

 per cent, varied between 0.6 and 0.9 per cent, of the average, and 

 4.6 per cent, varied 0.9 per cent, from the average. 



