﻿TRAISrSMITTIIsrG ABILITY OF HOLSTEIN-FKIESIAN SIRES 31 



The fact that the percentage of fat and the milk yield are in- 

 herited independently, at least within limits, and that hoih 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 coefhcient of variability of his daughters. 



2. No sire in the list show^s 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 darns there is a limited correlation or a 

 tendency for the high-recoid daughters to come from liigh-record 

 dams. The brc^eding record of each individual sire indicates, iiow- 

 ever, that a sire may be prepotent in increasing tlie milk yield and 

 decreasing the percentage of butterfat of his daughters as compared 

 with the production of their dams, or he may bo prepotent in lowering 



