14 BULLETIN 147, U. S. DEPABTMENT OF AGEICULTUBE. 



(see Table 3). At the beginning of the experimental period the four 

 heavily infested cows produced an average of 212.6 pounds of milk, 

 while the four lightly infested cows produced an average of 157.5 

 pounds during the same 10-day period. During the final 10-day period 

 the heavily infested cows produced an average of but 54.5 pounds of 

 milk 7 a decrease of 74.3 per cent from their production during the 

 initial period. During the same period the lightly infested cows pro- 

 duced an average of 68.6 pounds of milk, a decrease of 56.4 per cent 

 from their production during the first period. While the heavily 

 infested cows produced 35 per cent more milk than the lightly 

 infested during the initial period, they produced only 79.4 per cent 

 as much during the final period. When the two groups are com- 

 pared with the tick-free groups, it is seen that the lightly infested 

 group produced during the final period of the experiment 81.4 per 

 cent as much milk as the tick-free, while the heavily infested group 

 produced but 57.6 per cent as much. A comparison of the body 

 weights of the two groups shows the heavily infested with an average 

 weight per cow of 700.7 pounds during the initial 10-day period, 

 which decreased to 691.4 pounds per cow, or 1.3 per cent, while the 

 lightly infested cows, with an average weight of 694.4 pounds, in- 

 creased to 736 pounds per cow, or 6 per cent. 



No figures are given on cost of milk production, as the aim was 

 merely to measure the effect of tick infestation on yield of milk and 

 body weight. As the cows were kept in comparatively small inclo- 

 sures, the cost of milk production was higher than under ordinary 

 conditions when cows are on pasture. 



EFFECT OF SPRAYING OR DIPPING IN AN ARSENICAL SOLUTION UPON 



THE YIELD OF MILK. 



At four different times during the experimental period the cows of 

 the tick-free group were sprayed with tick dip B, an arsenical solu- 

 tion. This was done to keep the tick-free cows absolutely free from 

 ticks. Each spraying caused a temporary reduction in the milk 

 yield, as shown by the curves in figure 6. The average yield for the 

 first day after each spraying, when compared with the average of 

 three days preceding spraying, showed percentage reductions in each 

 'case as follows: 8.7, 27, 8.3, and 5.7 per cent. It will be noted that 

 the reduction was much the highest for the second spraying. On 

 the day prior to this spraying and for two days thereafter timothy 

 hay was fed, owing to a shortage of alfalfa. This, no doubt, had its 

 influence on the milk yield, as indicated in the 1 excessive shrinkage at 

 that time. From three to five days were required for the cows to 

 return to their normal production. The average of five days after 

 each spraying compared with the average of three days preceding 



