22 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
or other very watery feed may cause a temporary de- 
crease of from 0.25 to 0.5 per cent. 
The time of milking will influence the composition of 
milk. When the intervals between the milkings are 
equal and the feed, amount of water, etc., are the same, 
there is no difference between the composition of the 
morning and evening milk; but in practice the periods 
are usually unequal, the shorter interval preceding the 
morning milking in the summer and the evening milking 
in winter. At the milking following the shorter interval 
the quantity of milk obtained is less and the fat per 
cent. is greater than at the other milking. Hence it fol- 
lows that in summer the morning’s milk is richer in fat 
but of lesser quantity than the evening’s milk, while in 
winter the reverse is true. The age of the cow has no 
appreciable effect on the composition of milk. Volun- 
tary ewercise in the open air increases the fat per cent. 
as well as the quantity of milk yielded; forced exercise 
decreases the water in the milk and consequently de- 
creases the volume of the milk flow, but the per cent. of 
fat is increased, while violent exercise reduces both the 
volume and the per cent. of solids. The effects of estrum 
are not uniform; the fat may be increased or decreased, 
the albumin may be increased to such an extent that the 
milk will curdle when boiled, or there may be no change 
in the composition. In one test of milk from a cow with 
nymphomania the proteids were increased to 5.72 per 
cent. Weaning, or removing the calf, when it causes the 
cow to become restless and fretful, is attended with a 
decrease in the fat per cent. The variations in quantity 
and composition caused by disease will be considered in 
the chapter on the “ Influence of Disease on Milk.” 
Market Milk varies less in composition than indi- 
