BULLETIN 1352, U. S. DEPARTMENT OF AGRICULTURE 
and the average is 472 pounds of butterfat. The Guernsey cows 
seem to reach mature producing ability at 5 years of age, and there 
is no marked decline in the average production until the age of 11 
years. As shown in Table 1, this 6-year period includes 2,009 initial 
records averaging 492 pounds of butterfat. The percentages shown 
in Tables 1 and 2 are based on these amounts as average mature 
production. 
Unless this age of mature or maximum producing capacity is spread 
over a period of years it is difficult to account for the performances 
of those cows which have completed two or more records of approxi- 
mately equal quantities of butterfat during mature life. 
The distribution of the initial records for the two breeds studied 
is shown in Tables 3 and 4. It is true, however, that the require- 
ments for entry of cows in the Register of Merit and Advanced Reg- 
ister exert a selective influence on the distribution of records by ex- 
cluding animals which produce less than the required quantity of 
butterfat; and in addition there is some selection by breeders be- 
cause of the practice of testing only certain animals in their herds. 
The distribution is not symmetrical; 56.4 per cent of all the 
Guernsey records and 58 per cent of all the Jersey records fall below 
the averages of their respective groups. 
On statistical analysis the 14,571 Jersey records show a mean of 
411.41 ±0.51 pounds of butterfat, with a standard deviation of 
90.68 ±0.36 pounds of fat, and a coefficient of variability of 22.04 ± 
0.09. 
The mean of the 8,602 Guernsey records was found to be 442.07 ± 
0.69 pounds of butterfat, standard deviation 94.54 ±0.49 pounds of 
butterfat, and coefficient of variability 21.39 ±0.11. 
Table 3. — Distribution of initial records of single-letter advanced-register Guernsey 
cows according to age 
Age 
Pounds of butterfat 
Under 
2 years 
2 
years 
3 
years 
4 
years 
5 
years 
6 
years 
7 
3 T ears 
8 
years 
9 
years 
10 years 
and 
older 
Total 
250to274 
19 
29 
44 
35 
31 
31 
30 
16 
17 
10 
7 
3 
1 
2 
GO 
1S7 
325 
383 
436 
415 
390 
336 
271 
210 
181 
135 
91 
52 
40 
24 
17 
6 
8 
2 
1 
1 
79 
275 to 299 
7 
85 
142 
170 
193 
179 
_ 145 
165 
120 
93 
105 
62 
44 
28 
25 
10 
8 
4 
3 
2 
1 
! 
223 
300 to 324 
1 
34 
95 
122 
114 
112 
129 
106 
88 
62 
61 
39 
31 
23 
8 
9 
5 
5 
5 
4 
3 
1 
.._ 
455 
325 to 349 
... .! 
594 
350 to 374 
34 
65 
77 
72 
76 
85 
62 
43 
49 
35 
30 
25 
7 
11 
10 
2 
2 
30 
55 
60 
66 
65 
61 
42 
28 
29 
28 
19 
12 
6 
4 
9 
1 
13 
23 
29 
46 
34 
36 
36 
35 
22 
17 
11 
8 
4 
5 
3 
1 
13 
26 
16 
30 
20 
19 
25 
13 
17 
15 
10 
4 
4 
4 
I 
9 
14 
20 
23 
26 
16 
16 
13 
6 
12 
4 
8 
6 
2 
1 
2 
14 
19 
19 
21 
21 
6 
16 
14 
14 
5 
6 
3 
_. 
1 
i 
845 
375 to 399 
963 
400 to 424 . 
934 
425 to 449 
867 
450 to 474 
824 
475 to 499 - 
669 
500 to 524 
566 
525 to 549 
451 
550 to 574 . 
352 
575 to 599 
249 
C00to624 
179 
625 to 649 
132 
650to674 
• 62 
675 to 699 - 
5? 
700to724 
43 
725 to 719 
22 
750 to 774 
13 
775 to 799 
1 
1 
1 
2 
2 
1 
12 
800 to 824 
7 
825 to 849 
3 
850 to 874 
1 
1 
J = 
3 
875 to 899 
1 
2 
900 to 924 
925 to 949 
1 
1 

Total 
275 
3,578 
1,592 
1,057 
686 
519 
327 
223 
1S2 
163 
8,602 
