EFFECT OF CATTLE TICK ON MILK PRODUCTION. 



15 



spraying showed reductions, respectively, of 6.2, 21.7, 4.5, and 7.6 

 per cent. Disregarding the second spraying, the average reduction 

 for five days was 6.1 per cent. 



These results with spraying are similar to those obtained with dip- 

 ping during the 165-day test conducted by J. H. McClain. of the Dairy 

 Division, Bureau of Animal Industry, at Summerville, S. C, in 

 1912. In this experiment 10 cows were dipped seven times with a 

 solution of tick dip B, the dippings coming at intervals oi about 21 

 days, with an average decline in milk production, for two days, of 

 10.6 per cent after each of the seven dippings. But apparently the 

 cows became accus- 

 tomed to the dipping- 

 process, for there was 

 no appreciable de- 

 crease in the milk 

 flow after the first 

 four dippings except 

 the natural decrease 

 due to the advance 

 in the lactation 

 period. The average 

 decline in production 

 was approximately 

 as follows: After 

 each of the first four 

 dippings, milk 14.8 

 per cent; fat 8.9 per 

 cent; after each of 

 the last three dip- 

 pings, milk 1.9 per 

 cent, but an increase 

 of 10.6 per cent in 

 yield of fat. 



Fig. 6.— Effect of spraying on milk production, showing the average 

 amount of milk produced by the tick-free group for three days before 

 and seven days after each of four sprayings. The unusual decline 

 at the second spraying was probably due to a change in feed. 



That the heavily infested cattle in our experiments yielded fully 

 40 per cent less milk than the check animals at the close of the 

 experiments, and that even those lightly infested gave less by 25 per 

 cent, has been heretofore recorded. Conversely, we may infer that 

 the check cows in this experiment and those regularly dipped in the 

 Summerville experiment gave this additional quantity of milk on 

 account of being kept free from ticks. Had this freedom been 

 obtained without the use of arsenical dips, it is quite certain that an 

 amount of milk equal to 10.6 per cent during one-tenth of the time 

 in the Summerville experiment, and to 6.1 per cent during one- 

 seventh of the time in our experiments, would also have been saved 



