NOV. 20, 19x6 
Size of Cannon Bone 
369 
(4) There seems to be some basis for the current opinion among breed¬ 
ers of Gudbrandsdal and other heavy breeds that young parents give 
better offspring than older parents. 
It is extremely difficult to connect the data obtained with current 
genetic hypotheses and conceptions. The history of the Gudbrandsdal 
heavy horses leads one to expect heterozygosis. That the heavy regis¬ 
tered mares and stallions should give a range of types is not surprising 
in itself, for such a recent breed can hardly be expected to breed true. 
However, in genetic investigations on size, segregation is supposed to be 
independent of age, and an increased proportion of large-sized offspring 
from the younger parents is hardly expected. It will naturally occur to 
the critical that circumstances entirely independent of heredity underlie 
these peculiar frequencies of the size classes. For example, one wonders 
whether more large offspring from young stallions and young mares are 
not registered in order to establish their reputation; or may not young 
stallions be mated to high-grade mares in order to make a better showing 
as sires, whereas this selection in mating would not be as rigorous after 
the sire had proven his worth? Many years of familiarity with this 
breed and with the methods of registration lead the writer to attach but 
little value to these considerations. The best mares and the best sires 
are those which are kept the longest for breeding purposes. The fact 
that measurements must accompany registration has prompted careful 
selection at all ages. 
Available measurements or investigations that throw light on the 
inheritance of size in horses are scarce. It is not known whether cannon- 
bone size in horses is due to multiple factors such as are postulated in 
recent investigations on size in poultry by Punnett and Bailey (10), in 
rabbits by MacDowell (5), in ducks by Phillips (8, 9), in guinea pigs 
by Detlefsen (1), in com by Emerson and East (2), and the like. The 
investigation of Landman (4) may throw some light on the inheritance 
of cannon-bone size in horses. East Prussian country mares, with rela¬ 
tively small cannon bones, were graded up by crossing them with Belgian 
stallions. Although the total numbers recorded are smaller than is 
desired as a basis for conclusions, they indicate the gradual rise in the 
hybrid animals approaching the average for Belgian mares (Table VI). 
Table VI .—Sizes of the cannon hone in the East Prussian country mares , Belgian mares t 
and three hybrid generations 
Animal. 
Number of horses having a cannon bone of a given size (cm.). 
Average 
size of 
cannon 
bone. 
17 
i 7 -S 
18 
18.5 
19 
* 9 - 5 
20 
20. s 
21 
21.5 
22 
22.5 
23 
23-S 
24 
24*5 
25 
East Prussian coun¬ 
try mares. 
3 
6 
1 
10 
2 
14 
6 
7 
6 
1 
6 
10 
2 
Cm. 
18. 83 
20. 17 
21. 38 
22 . IO 
23. 53 
F t generation. 
4 
6 
8 
6 
3 
7 
12 
1 
1 
1 
2 
1 
2 
F 2 back cross. 
F 3 back cross. 
6 
1 
1 
3 
2 
I 
I 
I 
4 
Belgian mares. 
1 
2 
3 
