BUREAU OF ANIMAL, INDUSTRY. 237 



as follows : Subcutaneous method, 129,058 cattle, with 8,238 reactors, 

 or 6.4 per cent; intradermic method, 2,689,313 cattle, with 70,718 

 reactors, or 2.6 per cent; ophthalmic method, 1,593 cattle, with 59 

 reactors, or 3.7 per cent; combination tests, 572,883 cattle, with 

 32,598 reactors, or 5.7 per cent. The intradermic test has largely 

 superseded the others because of its economy and practicability for 

 area work. 



About 47 per cent of the tests were made by bureau inspectors and 

 about 53 per cent by the State and county men and the accredited 

 practitioners. 



Information regarding the occurrence of tuberculosis in calves 

 was obtained by compiling figures of results of the testing of calves 

 in herds subjected to the tuberculin test. Among 66,504 calves under 

 1 year of age there were 2,390 reactors, or 3.6 per cent. The percent- 

 age of reactors among calves under 6 months of age was 2.6, while 

 among those from 6 months to 1 year old it was 4.3. 



A study of delayed reactions (at and after the seventy-second 

 hour following injection of tuberculin) indicated that in the intra- 

 dermic test observations should be made in every case at the seventy- 

 second hour, and in nearly all cases where infection is disclosed in the 

 herd another observation should be made between the one hundred 

 and twentieth and the one hundred and fiftieth hours. 



Department Circular 249, The Tuberculin Testing of Livestock, 

 published during the year, was widely distributed among veteri- 

 narians and has helped to set a standard for the application of the 

 various tests and their combinations. 



Close supervision was again given to the slaughter of reacting cattle 

 with a view to investigating the cases in which no visible lesions of 

 tuberculosis were found on post-nr^'^rteni Oiaiiiination. It is signifi- 

 cant that nearly three-fourths of such cases were from herds in 

 which infectiori"^was found. Of 107,250 reactors slaughtered, 17.3 

 per cent were classified as undoubted spreaders of the disease, and 

 13.3 per cent of the carcasses were either condemned as unfit for food 

 or sterilized. 



An endeavor has been made to conserve funds by systematizing 

 the work and grouping the herds or confining the activities to cir- 

 cumscribed areas so as to reduce the cost of testing per head. The 

 average cost of testing by bureau inspectors, including salaries and 

 expenses of field veterinarians, but not office expenses or salaries of 

 supervising officers, was 35 cents a head, as compared with 46 cents 

 during the preceding year and 57 cents the year before. 



SEGREGATION NOT WIDELY USED. 



Information was collected through bureau stations as to the extent 

 to which cattle which have reacted to the tuberculin test are being 

 held as segregated herds in the United States. This system involves 

 retaining for breeding purposes tuberculous animals of high breed- 

 ing value instead of slaughtering them. By separating the calves 

 from their dams and pasteurizing the milk before feeding it to them 

 an effort is made to raise healthy offspring. The bureau was able to 

 learn of only 201 such herds, containing 2,461 cattle, which were being 

 permanently maintained for breeding purposes, and about two- 

 thirds of these herds were in six States in which tuberculosis in live- 

 stock exists rather extensively. In 18 States no quarantined diseased 

 herds were being maintained. It is evident that the more direct and 



