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138 Report oF THE DIRECTOR OF THE | 
Composition of Milk in Successive Periods of Lactation. 
The following tables present the changes in the yield and com- 
position of milk, the first table during the first and second, and the 
second table during the first, second and third periods of lactation. 
Thus far the number of cows to be compared for the three 
periods is perhaps too limited to more than indicate the probable 
changes which will be shown by subsequent investigation, and 
should such changes be found in accord with a general rule it 
will prove of great practical importance to the dairymen. 
In comparing the first and second periods, iti will be seen that 
during the first months of the second period of lactation the milk 
yield is very considerably in excess of the yield for the same 
months of the first period and that gradually this excess dis- 
appears, so that after the seventh month the average yield of 
milk becomes much less even than it was during the latter months 
of the first period. The same is true as to the amount of total solids © 
while the per cent. of total solids during the entire second period 
is a little more than during the first period but remains aes 
constant during the entire period. 
The per cent. of fat in the milk of the second period is at first 
4 or 5 per cent. less than during the first period but during the 
fourth, fifth and sixth months equals the per cent. for the saine 
months of the first period, but again falls off in the latter months ‘ 
of the second period. 
The total amount of fat and of caseine of the second period fol- 
lows closely the changes in milk yield, while the per cent. of © 
easeine, at the first about 95 per cent of what it was during the 
first parts of the first period gradually increased until during 
the ninth and tenth months it is ten per cent. above what it was 
ati the same time in the first period. 
The per cent. of sugar is 10 to 12 per sent. greater during the | ? 
early months of the second period than during these early months 
of the first but diminishes slowly during lactation, while the total 
amount of sugar begins 40 per cent or more above what it was — 4 
at the beginning of the first period but diminishes constantly until | 
during the ninth month it is one-third less than it was the ninth: a 
month of the first period of lactation. 
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