54 ’ Milk and Its Products 
will produce a_ seven-eighths-blood, and so on ad 
infinitum. Since only the offspring of pure-bred 
parents on both sides are eligible to registry in the 
herd books of any of our dairy breeds, it follows that 
no matter how far the process of grading up by the 
use of pure-bred sires on grade females is carried, 
pure breds, in the technical sense, can never be pro- 
duced. Since pure-bred animals are sought after for 
breeding purposes, the offspring of pure-bred animals 
are, therefore, more valuable, and command a higher 
price than do the offspring of grades. Hence, if the 
value of the calves is taken into consideration, a pure- 
bred herd is a more productive one, other things being 
equal, than a grade herd. ‘On the other hand, by the 
grading-up process above referred to, continually 
selecting the cows that are the best producers, it is 
entirely possible, and by no means difficult, to estab- 
lish a herd of grade cows that will equal, in the pro- 
duction of milk, any herd of pure-bred animals. 
Hence, if the main product alone is sought after, a 
grade herd may produce as largely as a pure-bred 
one; but if the by-product in calves is to be taken 
into consideration,-a pure-bred herd certainly has an 
advantage over a grade herd of equal productive 
capacity. 
Maintenance of the dairy herd.—A dairy herd may 
be maintained in two ways: First, by continued pur- 
chase of mature animals to replace those whose period 
of usefulness has passed. There are many conditions 
under which this may be a wise practice. If it is 
desirable to have the whole herd composed of cows 
