432 
GENETICS: W. E. CASTLE 
This is 1061 pounds less than the average yield of the pure Holsteins, 
but is 1995 pounds more than the average yield of the pure Guernseys. 
In other words, the average yield of an Fi cow exceeds the half-way point 
between Holsteins and Guernseys by 467 pounds. 
As regards butter-fat content of the milk, several different tests have 
been made of the milk of each Fi cow and on the basis of these tests rest 
the estimated percentages given in the table. They indicate an average 
butter-fat content of 4.08%, which is slightly less than the intermediate 
between 3.4, the butter-fat percentage of pure Holsteins, and 5.0, the 
butter-fat percentage of pure Guernseys, for the exact intermediate is 
4.2%. But the high quantity production of the Fi cows more than 
makes up for the slight deficiency in the quality of their milk, so that 
TABLE 3 
Milk and Butter-Fat Production of Pure-Bred Registered Guernsey Cows 
FIRST LACTATION PERIOD 
SECOND 
LACTATION PERIOD 
cow 
Total 
Total 
Age 
Time 
pounds of 
Age 
Time 
pounds of 
milk 
milk 
months 
months 
Hailey All Fawn 
5,014 
4i 
11 
(5,558) 
9 
(3,825) 
31 
7,664 
H. D. Lady 
3 
8 
(2,897) 
31 
4,852 
H. H. Dairymaid 
21 
6,942 
4rV 
7,093 
2i 
lU 
(5,548) 
3tV 
lU 
(6,084) 
H. Modena Maid 
3 
(6,060) 
4 
8i 
(3,983) 
Rockbottom Keepsake 
9 
(4,529) 
^2 
10^ 
(4,209) 
Rockbottom Leading Lady 
2t% 
n 
(2,121) 
3| 
101 
(5,307) 
2.72 
10.0 
4,617 
3.79 
5,593 
the average total butter-fat production of each cow is 270.2 pounds, which 
is 9 pounds more than the average butter-fat production of the pure 
Holsteins, and 40 pounds more than the estimated butter-fat production 
of the pure Guernseys. Accordingly on the basis of the records for their 
first lactation period the Fi cows seem to surpass either pure breed in 
butter-fat production and to be better than an intermediate between 
the pure breeds as regards quantity of milk produced. 
A second lactation period has been completed by 13 of the 31 Fi cows 
listed in table 1 . They of course produce more milk in the second lacta- 
tion period than in the first, and so comparison should be made with the 
second lactation period of pure-bred Holsteins and Guernseys, data for 
which are given in tables 2 and 3. Roberts^ has shown that the butter- 
fat percentage of a cow's milk does not change materially with age, so 
