The Stage of Lactation as a Factor in the Variation of the Per Cent of Fat in Cow's Milk

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Abstract
It is in general known that there is a relation between the stage of lactation and the percentage of fat in milk. Pingree (1) concluded from a study of the advanced registry records of eighteen Guernsey cows that the percentage of butter fat showed, on the average, a tendency to increase throughout the entire lactation period but the increase was most marked during the first five months and during the last month. Van Slyke (2) found that the percentage of fat and protein dropped in the second month of lactation, as compared with the first, and then began to increase, continuing to increase from month to month during the entire period of lactation. In the tenth and eleventh months of lactation, the increase of fat and of proteins is more marked than dm~g'the preceding months. Eckles and Shaw (3) found in a study of eleven cows of four breeds that there is a decline in fat during the first three months, followed by a period of from four to five months with little change. From this period on to the end of the lactation period the fat increases rapidly reaching the maximum at the close. They also conclude that there is, in general, some relation between the amount of miltr and the per cent of fat. When there is a sudden decline in the amount of mille secreted for any reason, as, for example, during sickness the per cent of fat with few exceptions increases sba~ly. The same holds true in the rapid decline that occurs in the last portion of the lactation period. Thorudike (4) found that the stage of lactation period makes a cow tend to vary from the general average composition of her m ill~ as follows: First month 89.6, second month 90.3, third 92.4, fourth 96.5, fifth 97.9, sixth 101.2, seventh 103.2, eighth 103, n~th 104.3, tenth 104.9, eleventh 105.3, and twelfth 109.4. Grady (5) presents data on 10 Jersey

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