Survey to Determine the Incidence of Bang's Disease in Minnesota Cattle. ∗

Abstract

Estimates of the prevalence of Bang's disease (contagious abortion) have been based on the results of agglutination tests that are available from laboratories engaged in the control of this disease. Such data do not give a true picture because the serum samples are from herds that request service. Usually testing is carried out only in herds in which there is reason to suspect the presence of Bang's disease. Also, retests of negative herds (from which the disease has been eliminated) tend to invalidate such figures as an estimate of the prevalence of this disease.

Reliable data on the incidence of Bang's disease are needed, not alone for obvious economic reasons, but also to provide a basis of estimation of the dependability of the agglutination method as a control measure for this disease. It has been shown, 1 by adequate experiments, that the test-tube agglutination test is exceedingly accurate with serums having either no specific agglutinin content or high agglutinin content (titre 1:250 or above). It has also been shown, however, that serums having a low to medium agglutinin content (titre 1:25 to 1:100) frequently give variable agglutination titres in different laboratories and in duplicate tests in the same laboratory. Therefore, it is obvious that the dependability of the agglutination method as a control measure, is inversely proportional to the percentage of animals having serums with low to medium agglutinin content (suspicious diagnosis).

We are attempting to obtain a more reliable estimate of the incidence of Bang's disease based on the total cattle population. The Minnesota State Live Stock Sanitary Board is cooperating in this work. The township has been selected as a representative sample of an area. At least 85% of the herds in a township are included in the study. The test-tube agglutination test, along with the age and as complete breeding history of the individual animals as can be obtained, form the basis of diagnosis. The agglutination tests were conducted in accorndance with the standard adopted by the United States Live Stock Sanitary Association, 2 except that a wider range of dilutions was employed, namely: 1:25. 1:50. 1:100. 1:250. 1:500, and 1:1000. All the bovine animals in the herd are included in the study.