New York AGRICULTURAL EXPERIMENT STATION. pares 
only ‘when we have secured life records of a number of animals 
of each breed sufficient to overcome the variations of individuals 
and give us what may fairly represent the average of the breed. 
So far as we have gone, the results indicate generally that the 
larger the number of lactation periods recorded, the greater the 
results secured. Hence, to compare the first lactation period of 
one breed or animal will not indicate the same relation that a 
comparison of the same number of lactation periods would. It 
will, therefore, be well to keep in mind that the animals and 
breeds having the fewer number of lactation periods completed 
will probably improve in the future more than those that have 
completed a larger number of periods. 
V. COMPARISON OF DIFFERENT BREEDS OF DAIRY 
CATTLE WITH REFERENCE TO THE PRODUCTION 
OF MILK. | 
1. Cost or Foop Eaten. 
For the sake of uniformity in making our comparisons of the 
breeds, we have arbitrarily adopted ten months as the duration 
of a single period of lactation. In actual dairying, if a cow were 
productive ten months in each year, and non-productive during 
two months, the cost of keeping her twelve months would need 
to be considered in order to find the actual cost of keeping and 
production. The actual cost would be based, not upon the cost 
of her food for the ten productive months, but upon the cost of 
her food for the whole year, the non productive as well as the 
productive period. However, in this investigation, we are not so 
much concerned with actual cost as with relative cost of produc- 
tion. Therefore, calculating for all breeds alike, the cost of 
production from the food consumed during the same productive 
period, we secure values that show the true relative cost of 
production for the different breeds. 
The table immediately below gives the cost of food eaten by 
each animal for each period of lactation: 
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