180 FARM ANIMALS 



cows. A striking illustration of this is seen in the 

 fact that a number of cows have yielded from 

 five hundred to eight hundred pounds of butter 

 per year and one Guernsey cow in Wisconsin 

 even one thousand pounds in a year, while the 

 average yield may be set down as two hundred and 

 fifty pounds of butter. It is apparent, therefore, 

 that one cow may produce four times as much as 

 another during one period of lactation. A cow 

 with a high milk yield does not necessarily eat much 

 more than an unprofitable cow. At any rate, the 

 difference in the amount eaten is so small as 

 scarcely to affect the relative profit from the cow. 

 Moreover, as already indicated, there are thousands 

 of cows kept for dairy purposes which do not pro- 

 duce more than one hundred pounds of butter per 

 year. Such poor milkers cannot be kept at a 

 profit and are less valuable for milk than for beef. 

 t)ifferent cows vary greatly, not only in the amount 

 of milk produced, but in the amount of food 

 required to produce a pound of milk. Those cows 

 which can transform feed into milk most economic- 

 ally are obviously the most profitable cows, since 

 the greatest expense in connection with dairying is 

 the providing of food. 



Reference has already been made to flies as a 

 source of annoyance to cows. There are many 

 species of flies which attack cows, but the horn fly 

 and the common stable fly are most injurious and 

 are distributed over the greater part of the dairy 

 region. In some localities it has been found 

 necessary during the worst part of the summer to 

 keep the cows in cool barns during the heat of the 

 day, with the windows carefully screened to keep 

 the flies out. The cows are then allowed to graze 

 on pasture at night. Numerous remedies have 



