60 Milk and Its Products 
If we concede that it is not an entirely safe practice to 
base this selection upon the producing capacity of the 
dams, we must look for some other basis of selection. 
It is.a generally accepted principle of heredity that 
- an animal which shows a tendency toward variation 
is one that is not likely to be prepotent. We desire 
to raise calves from cows that are not prepotent, in 
order that the prepotent qualities of the bull may 
have full scope. Cows, then, that show tendency 
toward variation, particularly toward improvement, 
are logically the ones over which the male is most 
likely to be prepotent, and at the same time the calves 
show the greatest tendency toward improvement. It 
is comparatively easy to determine in any herd of 
cows those which show the greatest tendency toward 
variation, and more particularly those which show 
the greatest tendency toward improvement when their 
conditions are made more favorable. We can then 
determine the cows from which we are likely to get 
the best half-blood heifer calves by giving the herd 
more and better feed, and selecting calves from those 
animals which show the greatest improvement under 
such a change of treatment. 
Experience has shown that where the principles 
‘stated above have been carefully carried out a very 
satisfactory improvement has been secured in the first 
generation. It is not uncommon to find an increase 
of fully 50 per cent in the average production of half- 
blood cows over their common mothers. Experience 
has also shown that in the second generation the 
three-quarter - bloods are not nearly so uniform as 
