EFFECT OF CATTLE TICK OjST MILK PKODUCTION. 13 



infested. During the final 10-day period the cows of the tick-free 

 group averaged 763.4 pounds in weight, an increase of 6.1 per cent, 

 and those of the tick-infested 732.9 pounds, an increase of 3.6 per 

 cent from the initial weight. 



In making this comparison it should be remembered that during 

 the entire experimental period the two groups consumed practically 

 an equal amount of nutrients, and that toward the latter part of the 

 experimental period the milk production of the tick-infested group 

 was considerably decreased, so that this group was fed an amount 

 in excess of that required for milk production. Presumably this 

 excess of food would tend to make flesh and thus offset any detri- 

 mental effect that the ticks would have upon the body weights. 



COMPARISON OF TICK-FREE AND HEAVILY INFESTED GROUPS. 



Four cows in the tick-infested group were soon found to be more 

 easily infested than the remaining six. A gross infestation of these 

 four cows was obtained early in the experimental period and was 

 maintained throughout the test. At different times all four suffered 

 from attacks of fever, with an almost total loss of appetite and a 

 falling off in milk flow. One, which suffered from an attack of fever 

 at the end of the experimental period, died shortly after the close of 

 the work. 



By referring to Table 3 it will be noticed that there is a much 

 more pronounced decrease in milk production between this group 

 and the tick-free group than when the two entire groups are com- 

 pared, showing that the heavier degree of infestation results in a 

 proportionately increased injury. This is likewise proved to be true 

 when the body weights of the two groups are compared. 



COMPARISON OF TICK-FREE AND LIGHTLY INFESTED GROUPS. 



While four cows of the tick-infested group proved to be easily 

 infested, another four of the same group proved to be very resistant. 

 The immature ticks were applied to these four cows with the same 

 care and in as large numbers as they were to the heavily infested 

 animals; in fact, extra efforts were made to obtain a heavy infesta- 

 tion upon these resistant animals. However, at no time during the 

 experimental period were any of the four so heavily infested that the < 

 degree of infestation could be classed as gross, and for the greater 

 part of the period none of them was carrying mature ticks. The 

 decrease in milk production was more than in the tick-free cows, but 

 considerably less than in the heavily infested animals. 



COMPARISON OF LIGHTLY INFESTED AND HEAVILY INFESTED GROUPS. 



While the heavily infested cows produced more milk during the 

 initial period and through the greater part of the experiment, they 

 also consumed, more feed than those of the lightly infested group 



