12 



BULLETIN 147., U. S. DEPARTMENT OE AGRICULTURE. 



cows of the tick-infested group produced an average of 60.6 pounds 

 per cow, a decrease of 65.9 per cent when compared with their first 

 10-day period. It should be noted especially that while the tick- 

 infested cows produced 1 per cent more milk than the tick-free cows 

 in the beginning, they produced only 65.8 per cent as much during 

 the final period. The two groups consumed practically the same 



TEH -DAY PERIOD ENDING- 



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Fig. 



-Average milk production by 10-day periods of the tick-free and tick-infested groups and of 

 four heavily infested cows. 



amount of feed during the entire period. The percentage of fat in 

 the milk of each group increased toward the close of the experiment, 

 that of the infested group showing a slightly greater increase. 



At the beginning of the test the tick-free cows weighed on the 

 average 719.2 pounds and the tick-infested 707.2 pounds. During 

 the experimental period each group increased in body weight, but 

 the increase of the tick-free group was greater than that of the tick- 



