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 exercise 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 cestrum 

 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 

 nympliomania 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- 



