Dec. 17,1917 
Influence of Age of Cow on Milk and Milk Fat 
647 
heifers practically “strike their gait/' so far as the quality of the milk flow is con¬ 
cerned, in their first lactation; and whatever the effect of advancing years upon milk 
quality may be, it is not profound enough to be of importance until old age becomes 
imminent. 
Hooper (5) has recently studied data showing the records of 634 Hol¬ 
stein cows on official test. When the data were classified according to 
the age of the cows, the percentage of fat in the milk was practically con¬ 
stant from the second through the seventh year. The author concluded 
that the heifers gave richer milk than the mature cows, but the differ¬ 
ences do not appear to be sufficiently great to justify this conclusion* 
The percentage of fat beginning at 2 years 2 months of age and ending 
with 7 years 2 months of age was as follows: 3.51, 3.55, 3.54, 3.78, 351, 
3.50, and 3.52. 
With regard to the question of whether aged cows give normal milk, 
Klein and Kirsten (6) studied the composition of the milk fat of cows of 
different ages, the oldest of which was 13 years of age. All the younger 
cows gave milk fat of normal composition throughout the lactation 
period, the characteristic changes due to advanced lactation, as mani¬ 
fested in the decline in the saponification value and Reichert-Meissl 
number and the increase in the iodin value, occurring in each case. The 
old cow in the group, however, failed to show these changes at the close 
of the lactation period. The milk fat was also abnormal at the begin¬ 
ning of lactation, showing a Reichert-Meissl number of 43.5 and an iodin 
value of 31.7. The authors attributed the abnormalities in the case of 
this cow to individuality rather than to the age of the animal. At the 
same time they express the view, based on practical experience, that 
very old cows no longer produce good butter. 
INFLUENCE OF AGE ON PERCENTAGE OF FAT IN MILK 
The records from which the data presented in this paper are drawn 
consisted of the true average percentage of fat for the entire lactation 
period of each cow. This figure has been calculated from the total milk 
and fat production for the period, the milk production being based on 
the actual amount of milk produced at each milking for the entire period, 
and the fat production being based on the percentage of fat in a composite 
sample of five days' duration taken at the middle of each month. It 
should also be stated in connection with the lactation periods considered 
for each animal that whenever this exceeded 12 months the milk and 
fat production for the 12 months were considered that of the lactation 
period. This, coupled with the not infrequent failure for periods of 
parturition to be 12 months apart, results in it being impossible to make 
the number of lactation periods of an individual animal a criterion of 
its age. This means, for example, that the 20 Jerseys who completed 
six lactation periods were not necessarily of the same age at the end 
of the sixth period. Our data should, therefore, be interpreted more 
