16 MARKET DAIRYING 
milk from the same cow may vary a great deal in compo- 
sition. The causes of these variations may be assigned 
to two sets of conditions: I.—Those natural to the cow. 
II.—Those of an artificial nature. 
I. QUALITY OF MILK AS AFFECTED BY NATURAL CONDI- 
TIONS. 
1. The composition of the milk of all cows undergoes 
a change with the advance of the period of lactation. 
During the first five months the composition remains prac- 
tically the same. After this, however, the milk becomes 
gradually richer until the cow “dries up.” The following 
figures from Van Slyke illustrate this change: 
Month of Per cent of fat 
lactation. in milk. 
Tigsic erate iaiseces oes ek neh wanernee eee 4.54 
Que ha nama earins Sat ccaphe tc a eis eeu nie 4.33 
5 Ve dea eask tana ousaateaeens cue carer ayaneaavenece oie 4.28 
Bes esi lec tpeesessnesee rR HA oe Peo SE 4.39 
Garren eens cio mee eae meee ak 4.38 
One cr ena ache pee ana tees tamer 4.53 
EPRI Rt aR RY IA hg oe aU eA a 4.56 
Bor aihs Spe rara eka tetera na enmueri nae acer 4.66 
Qi es ein bats tapenuianadecav a aie, eleva cpmcicteuntedstacets eins 4.79 
TOsvasoucce mimemncia veraeeneenaese nets 5.00 
It will be noticed from these figures that the milk 
actually decreases somewhat in richness during the first 
three months of the period. But just before the cow dries 
up, it may test as high as 8%. 
2. The quality of milk also differs with different 
breeds. Yet breed differences are less marked than those 
of the individual cows of any particular breed. 
Some breeds produce rich milk, others relatively poor 
