Variations in Quality. 27 
“ 
or fourth week of lactation the percentage of fat 
in the milk remains nearly constant until the seventh 
or eighth month, or until the quantity of milk begins 
to rapidly diminish; but while the percentage of fat 
does not markedly change, the character of the fat 
undergoes several marked and characteristic changes. 
The butter globules are largest in size early in the 
period of lactation, and constantly diminish as lac- 
tation progresses, at the same time that they in- 
crease in number, so that the total amount of fat 
is not greatly changed. Early in the period of lac- 
tation there is a larger proportion of olein. In 
some cases it may amount to 50 per cent of the 
total fat. As the lactation progresses the propor- 
tion of olein decreases and stearin’ and palmitin in- 
crease, until the proportion of olein may fall as low 
as 20 per cent. This change is more marked when 
the animal changes from fresh to dry food, as the 
period of lactation progresses. The hardening of 
the fat and the shrinking in the size of the glob- 
ules are also more marked when the animal again 
becomes pregnant. In the case of cows that are 
milked for a prolonged period, as sometimes hap- 
pens with farrow and spayed cows, the milk often 
becomes abnormally rich, not only in fat, but in 
casein; and in such cases the fat is usually made 
up of very minute globules. 
It is usually observed that milks drawn at 
night and morning differ quite widely in the per- 
centage of fat. This is not because there is any 
difference in the milk secreted by night or by day, 
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