14 CITY MILK SUPPLY 



fat, 20 to 25 per cent, a range of 1.1 to 2 per cent, of butterfat; 5 per cent, 

 a range of 2.1 to 3 per cent, of butterfat and the rest still wider variation. 



Individuality of the Cow and the Production of Butterfat. The indi- 

 viduality of the cow has a determining influence on the quality of milk. 

 The percentage of fat in the milk of one cow may be high, and that of 

 another one low, for no other reason than that it is the nature of the beasts. 

 The tendency to produce rich milk is hereditary and does not always 

 come from the female line ; the influence of a bull of good milking ancestry 

 in raising the fat test of the herd is well recognized and is taken advan- 

 tage of by wide-awake dairymen in building up their herds. In the 

 Dairy Record Center at Farmers Union, Ontario, there were 14 herds, 

 seven of which had been improved by the use of purebred sires and the 

 other seven of which had always used grade sires. The former group 

 with 82 cows, had an average production of 7,901 Ib. of milk a year, 

 while the latter group with 84 cows had one of only 4,712 Ib. The dif- 

 ference in production per cow of 3,187 Ib. of milk divided a profit of 

 $2,646.87 among the owners or $378.12 additional to each man. 



Effect of the Condition of the Cow at Calving. Eckles has shown that 

 a cow that is fat at calving, will yield milk for 20 to 30 days, and 

 in some cases, for as long as 4 months, that will test higher than 

 her milk does, when she calves in poor condition. This is so, because 

 the cow in fat, converts her body fat to butterfat. The practical signifi- 

 cance of this is, that it pays a dairyman to bring a cow to calving in 

 good condition, that he may reap extra profits from her high-testing milk. 

 Another point is that it is possible to deceive the unwary by selling a 

 cow on a butterfat test that is considerably higher than her average for 

 the year, because it was made soon after calving. 



Changes in the Character of Milk during the Lactation Period. 

 Besides the variations in the milk of the individual cow there are those 

 of a more general character that arise from the regimen of the milk 

 flow, the seasonal changes and the breed of the cows. 



Eckles and Shaw have shown that in the course of a lactation period 

 there are three stages. 



"The first covers a period of 3 to 6 weeks and runs from the time milk secre- 

 tion begins until it reaches normal. The period is characterized by high protein 

 and ash content of the milk for 4 to 5 days, a decline in protein and fat for 3 to 

 6 weeks and by very large fat globules which grow small rapidly. 



"The second stage begins with the close of the first, when the milk becomes 

 normal and extends over a variable period, usually 6^ months, to the time 

 when the milk yield begins to fall off rapidly, which usually occurs 6 to 8 weeks 

 before the close of the lactation period. During this period the composition of 

 the milk is uniform. 



"The third stage is sometimes sharply defined and sometimes the change is 

 gradual. It begins 6 to 8 weeks before the close of the lactation period. The 



