Gowen: Transmission of Butter-fat Percentage 
performance test of the sires is not 
known. 
Dunne* quotes some Danish records 
to show that there are two types of 
cows in the red Danish breed. One of 
these types tests about 3.3'per cent. The 
other type tests about 4.00 with the 
cross between the two having a butter- 
fat percentage which is intermediate. 
These results are however open to con- 
siderable criticism when viewed as 
critical evidence. The results cannot 
therefore be accepted as proof. 
Castle’ records an experiment com- 
menced by Mr. Bowlker on crosses be- 
tween the Guernsey and Holstein-Frie- 
sian breeds. Unfortunately only a 
very limited number of tests on the 
original pure bred cows were made. It 
is necessary therefore to use the aver- 
age butter-fat percentages of the breeds 
as the parents test for butter-fat. Such 
a procedure is open to error in that the 
breeds’ average butter-fat concentra- 
tion may not represent the test of the 
parental animals used in these experi- 
ments. In fact the wide variation of 
either the Guernsey or Holstein-Frie- 
sian breeds in this respect make it en- 
tirely probable that such is the case. 
The experiments are interesting how- 
ever in that wide differences are repre- 
sented in butter-fat percentages of the 
two breeds. The average butter-fat 
percentage of the Holstein-Friesian 
parents was assumed to be 3.3 per cent. 
The average test of the Guernsey par- 
ents was 5.0 per cent. The F; cross- 
bred cows had an average butter-fat 
percentage of 4.08 or were interme- 
diate between the two parental breeds 
approaching the lower testing Holstein 
Friesian parents more closely than the 
higher testing Guernsey parents. The 
outcome of these experiments despite 
the many uncontrolled variables is in 
essential agreement with the experi- 
ments herein reported from the Maine 
Station. 
®* Dunne, J. J. 
1914. 
No. 15, pp. 553. 
7Castle, W. E. 
1919. 
Acad. Vol. 5, pp. 428-434. 
Hereditary Transmission of Fat Percentage. 
BUTTER-FAT PERCENTAGES COMPARED 
TO MILK YIELD 
It is of interest to examine the results 
of these experiments on butter-fat per- 
centage in the light of those for milk 
yield. It will be remembered that in 
the F; crossbreds milk yield was inter- 
mediate between that of the high and 
the low parents but approached most 
nearly that of the high parent. In the 
genetics of many economic characters 
as yield of grain, size of the animal etc. 
the explanation used to account for 
such a phenomena is the heterozygous 
nature of the factors contained in the 
F, animal ascompared with the homozy- 
gous nature of the factors in the par- 
ental breeds or strains. Without ques- 
tion there may be something to this 
hypothesis for certain crosses. The 
results for milk yield and butter-fat 
percentage do present a paradoxical 
position when this hypothesis is applied 
to them. Thus milk yield is increased 
over what the true intermediate should 
be. This follows the expectation gen- 
erally agreed upon and accounted for 
by heterosis. But on these identically 
same animals the butter-fat per- 
centage is decreased below the inter- 
mediate. This is not the expectation 
generally considered as due to heterosis 
although it is by no means impossible 
to assume that increased vigor may re- 
duce rather than increase a character. 
The double nature of such a position 
does not appeal to the author, however, 
as furnishing more than a verbal ex- 
planation of the results having little 
parallel in the rest of genetics. The 
explanation which really seems most 
likely is that we have in these two cases 
the resultant of partially dominant fac- 
tors. Numerous similar cases can be 
cited in genetic literature. Perhaps 
the best known case is that of black in 
Drosophila where the factor for this is 
normally classified as a recessive but 
where if occasion demands it may be 
Hoard’s Dairyman. Vol. XLVII. 
Inheritance of Quantity and Quality of Milk Production in Dairy Cattle. Proc. Nat. 
