646 
Journal of Agricultural Research 
Vol. XI, No. ia 
control centrifuge. When the results were compiled with regard to the 
age of the cows, it appeared that the percentage of fat in the milk was 
highest during the first three years of the cow’s lactation life and de¬ 
clined at the rate of about 0.1 per cent of cream at intervals of two to 
three years. A few very old animals—that is, 15 to 18 years old— 
showed cream percentage 0.6 to 0.9 per cent of cream lower than normal, 
which was that observed during the fifth and sixth years of the cow’s 
life. 
Haas (2) studied the data gathered at Allgaii from 1894 to 1898 from the 
standpoint of the influence of the age of the cow upon the percentage of 
fat in the milk. The conclusion drawn from the data was that the fat 
content increases up to the fifth calf, after which there is generally a 
gradual decline. Individual animals, however, showed exceptions to 
this rule. It is stated also that the specific gravity of the milk is highest 
with the first calf and lowest with the sixth. 
op 
Hogstrom (4) compared the percentage of fat in the milk of 393 
Ayrshire cows of different ages with the average percentage of fat of 799 
lactation periods of these cows. The conclusion drawn was that the fat 
content of the milk is highest at 3 years of age, is high at 4 years, and 
remains close to the average for the family during the full activity of the 
cow—that is, through the tenth year—after which the fat percentage 
again rises slightly. The difference between the highest fat percentage 
(at 3 years of age) and the average was 0.14 per cent of fat. 
Wing (8) reported the average fat percentage of individuals in a herd 
of 25 grade Jersey and Holstein cows from the second to the sixth year 
with the following results: 3.71, 3.71, 3.68, 3.60, and 3.49 per cent of 
fat. The data were based on the first 40 weeks’ production of each 
cow’s lactation period. 
Hills (3) has made a very careful study of the records of 99 cows at the 
Vermont Experiment Station with regard to the effect of advancing age 
on the quality of the milk. The records of this herd for a period of 10 
years were studied with this question in view both from the standpoint of 
separately following the same animals through their lives in the herd, 
making comparisons of groups composed strictly of the same individuals, 
and also from the standpoint of making comparison of groups according 
to age, regardless of the changing individuality of the animals. On 
account of the large number of animals considered, practically the same 
conclusion was reached in each of the methods of study. 
When the same animals were studied throughout their lives in the 
herd in «nly 3 out of 46 cases was the percentage of fat higher after the 
first lactation. Of the remaining 43 cases 29 showed a downward trend 
of the fat percentage from the first lactation and the remaining 14 
showed a stationary fat percentage throughout the period of greatest 
activity, after which a gradual decline occurred, owing to old age. Hills 
concludes that— 
