TRANSMITTING ABILITY OF HOLSTEIN-FRIESIAN SIRES 31 
The fact that the percentage of fat and the milk yield are in- 
herited independently, at least within limits, and that both the sire 
and dam contribute to the inheritance of their daughters, governing 
both milk yield and percentage of fat, indicates that improvement in 
yield of butterfat can be brought about by selection for both milk 
yield and percentage of fat. 
SUMMARY 
A study of the transmitting ability for milk yield, percentage of 
butterfat, and butterfat yield, of 23 Holstein-Friesian sires each 
having six or more daughters with yearly records, out of dams with 
yearly records, brought out the following results: 
1. A remarkable variation between the records of the daughters 
of any sire and their dams is evidenced. Prepotency in a sire is not 
indicated by the size of the coefficient of variability of his daughters. 
2. No sire in the list shows a complete prepotency in raising or 
lowering both the milk yield and the percentage of butterfat of all his 
daughters. Some sires are capable of raising both the milk yield 
and the percentage of butterfat; some raise one and lower the other; 
and some lower both. Not so many sires are prepotent in increasing 
the percentage of butterfat as are prepotent in increasing the milk 
yield. 
3. The coefficient of correlation for butterfat yield between 
daughters and dams varies widely for the different sires, regardless of 
whether the daughters of the sires are better or poorer than their 
dams. For only three sires is there a marked correlation; one of these 
sires has daughters that made an average increase of some 15 per 
cent in both milk and butterfat production over their dams; another of 
these three sires had daughters that showed an average increase of 
14.6 per cent in milk, but owing to a decrease in percentage of butter- 
fat, there was only about half that average increase in total butterfat; 
the third sire's daughters varied little from their dams in the produc- 
tion of either milk or butterfat. 
The fact that there is a correlation between the daughters and 
their dams with respect to yield of milk and butterfat does not mean 
that the sire is not prepotent in either raising or lowering the yield. 
It only indicates that where a number of daughters and dams are 
considered, the record of the daughter will be of the same relative 
size as that of her dam, though it may be larger or smaller. For 
instance, if a sire is mated with a cow of 10,000 pounds capacity and 
to another cow of 20,000 pounds capacity, the daughter of the first 
cow is likely to be in the 10,000 class, though she may produce from 
8,000 to 12,000 pounds, depending upon the germinal make-up of the 
sire with reference to milk yield ; the daughter from the second cow is 
likely to be in the 20,000-pound class, though she may produce from 
16,000 to 24,000 pounds. 
4. When the records of a large number of daughters are compared 
with the records of their dams there is a limited correlation or a 
tendency for the high-record daughters to come from high-record 
dams. The breeding record of each individual sire indicates, how- 
ever, that a sire may be prepotent in increasing the milk yield and 
decreasing the percentage of butterfat of his daughters as compared 
with the production of their dams, or he may be prepotent in lowering 
