BUTTERFAT PRODUCTION OF CATTLE 
21 
EFFECT OF PREGNANCY 
That pregnancy has a pronounced influence on the quantity of butter- 
fat produced during a year when the calf is carried for a period of 265 
days or longer is evidenced by the average of 408 pounds of butterf at 
for 711 class GG records as compared with an average of 418 pounds 
of butterfat for 4,794 class G records of the Guernsey breed. All 
these, of course, are initial records. The other classes of Guernseys 
were not studied. 
The register-of-merit rules specified that a Jersey cow carrying a 
calf for 155 days during the period of her test was entitled to entry 
in class AA. One feature about the class AA Jersey records which 
tends to nullify the value of any conclusion drawn therefrom, is the 
fact that in the past many breeders failed to apply for transfer of 
animals from class A to class AA after they had fulfilled the calving 
requirement, and consequently there is a certain proportion of the 
animals which rightly belong to class AA now listed in the other class. 
For this reason, and in order to enhance the value of the class 
averages by using greater numbers, it was thought best to deal with 
all Jersey records as a single class. However, classes A and AA were 
compiled separately, and it was found that even with the moderate 
demands of the former Jersey rules some influence of gestation is 
apparent in the records. It is well to remember that the group of 
class AA cows includes some animals that carried a calf full time 
during the test, and that they grade down to those which just met 
the specified 155-day period. It might be assumed that the average 
time that these class AA cows were pregnant during their test 
periods would be a somewhere near 200 days. 
For purposes of comparison, Table 26 lists the Jersey class A and 
class AA records in parallel columns. 
Table 26. — Initial butterfat records for class A and 
A A Jersey cows 
Class A 
Class AA 
Class A 
Class AA 
Dif- 
fer- 
Dif- 
fer- 
Pro- 
Pro- 
ence 
Pro- 
Pro- 
ence 
Age 
duc- 
duc- 
in 
Age 
duc- 
duc- 
in 
Rec- 
tion 
Rec- 
tion 
but- 
Rec- 
tion 
Rec- 
tion 
but- 
ords 
of 
ords 
of 
ter- 
ords 
of 
ords 
of 
ter- 
but- 
but- 
fet 
but- 
but- 
fet 
terfat 
terfat 
terfat 
terfat 
No. 
Lbs. 
No. 
Lbs. 
Lbs. 
No. 
Lbs. 
No. 
Lbs. 
Lbs. 
Under 2 years... 
461 
344 
776 
342 
2 
8 to 834 years 
105 
497 
162 
469 
28 
2 to 2^ years 
1,567 
368 
2,066 
368 

834to9years_.__ 
104 
465 
128 
460 
5 
234 to 3 years 
669 
386 
944 
387 
1 
9 to 934 years 
77 
485 
86 
454 
31 
3 to V/i years 
586 
409 
812 
400 
9 
934 to 10 years. . 
67 
483 
61 
467 
16 
V/i to 4 years 
385 
427 
626 
420 
7 
10 to 1034 years.. 
50 
487 
64 
468 
19 
4 to ^Yi years 
350 
446 
574 
437 
9 
10H to 11 years.. 
28 
459 
40 
459 

434 to 5 years 
283 
457 
422 
451 
6 
11 to 1134 years.. 
26 
468 
27 
440 
28 
5 to 534 years 
265 
465 
408 
453 
12 
1134 to 12years.- 
17 
499 
22 
461 
38 
5^2 to 6 years 
219 
476 
368 
465 
11 
12 to 123^ years. . 
16 
452 
24 
440 
12 
6 to 63^2 years 
209 
482 
300 
470 
12 
1234 to 13 vears.. 
13 
438 
3 
427 
11 
6>4to7years 
165 
478 
239 
462 
16 
13 to 13K years.. 
8 
472 
10 
424 
48 
7 to 7H years 
168 
482 
227 
458 
24 
1334 to 14 years.. 
6 
495 
5 
451 
44 
IVi to 8 years 
134 
480 
176 
463 
17 
"Where the groups contain a considerable number of animals the 
difference in pounds of butterfat is not large enough to be of much 
significance, though evidence of the effect of gestation is found in 
the fact that every group, with the exception of those 2 years old, 
