Allen: Effect of Parents' Age on Quality of Dairy Cows 171 



46.9 



45.1 



Great Grand Sire 



49.5 



46.6 



Grand Sire 



47.1 



43.1 



Sire 



Grand Dam. 

 66.7 



66.7 



42.1 



43.6 



Grand Sire 



Dam 



61.9 

 63,1 



Grand Dam 

 61.0 



64.7 



Great Grand Dam 

 62 5 

 65.7 



AN AGE-PEDIGREE OF THE TWO CLASSES OF COWS 



FIGURE 12. This shows the average age of the ancestors of the superior cows (Bold-face type), 

 and of the inferior cows (Italics). It is evident that there are no significant differences in the age 

 )f the forebears of the two classes. (See text, p. 169.) 



he sires of the Superior Class average 

 ess than four years of age, 46 . 4 months 

 ;o be exact, and that the sires of the 

 inferior Class average somewhat 

 younger. The largest number of off- 

 spring were born when their sires were 

 rom two and one-half to three years 

 )f age. This means that these bulls 

 sired a larger percentage of their off- 

 spring between twenty-two and twenty- 

 seven months of age than at any 

 ther time. 



Table II shows very clearly just 

 how our purebred sires are used. It 

 ndicates that improvement has been 

 based on the selection of young sires 

 rather than on the use of tried sires. 



THE PROVEN SIRE 



A bull cannot be called a proven sire 

 until his first crop of heifers come in 

 milk and can hardly be so called 

 until these heifers have milked at 

 east one year. Thus a bull can hardly 



be called a proven sire until he is five 

 years of age. In general practice, the 

 percentage of cows sired by unproven 

 bulls is probably much higher than the 

 percentage shown for the animals in- 

 cluded in this study. This means that 

 even the breeders who are making 

 records use a tried sire for only a 

 small percentage of their cows. That 

 the tried sire is more valuable is indi- 

 cated by the fact that 21.1 percent of 

 the Superior cows are daughters of 

 tried sires, whereas only 15.9 percent 

 of the Inferior cows are daughters of 

 bulls of an equal age. This may seem 

 to conflict with the idea that the bull 

 when old is not more valuable, but 

 the paper referred to above shows that 

 he is not more valuable as a parent. 



FREQUENCY DISTRIBUTION ACCORD- 

 ING TO AGE OF DAM 



The frequency curve for the dams, 

 Figure 13, is very much more irregular 

 than the curve for the sires but on the 



