Variations in the Blood Picture of Cattle Following an Induced Infection with Brucella Abortus

Changes in the number of red and white blood cells and in the proportions of the different types of leucocytes were noted in the same animals, before and following artificial infection with Brucella abortus. The following significant effects were presumably produced by the infection: The total number of erythrocytes and leucocytes per cmm decreased following the infection.* Of the different types of leucocytes, the mean percentage of polymorpho-nuclear cells, monocytes, and basophiles increased, while that of the lymphocytes and eosinophiles decreased after the infection. In a previous study, no significant changes in average proportions of either basophiles or eosinophiles were observed; otherwise, the results of the separate studies are in agreement. The animals were classified as to whether they were resistant or susceptible to infection with Brucella abortus, and the observations on these groups in the pre-infection and post-infection periods are given separately. A comparison of the pre-infection "resistants" and "susceptibles," and the post-infection "resistants" with the "susceptibles" reveals the following differences: 1. The mean total number of red blood cells per cmm was higher in the susceptible than in the resistant animals in the pre-infection period. (The erythrocyte counts were not continued throughout the post-infection period.) 2. The susceptible animals had a significantly higher average number of leucocytes per cmm both preceding and following infection. 3. Of the different types of leucocytes, the percentages of polymorphonuclears and monocytes were slightly higher in the resistant animals, in both the pre-infection and post-infection periods. The proportions of lymphocytes and eosinophiles were greater in the susceptible animals, both before and after infection with Brucella abortus. The observations in the post-infection period were further divided into (a) those made before, and (b) those made following calving or abortion. The average number of leucocytes increased in the post-parturient period over that observed before parturition, and the mean percentage of monocytes likewise was slightly higher after parturition than before. The other types of cells showed no statistically significant changes prior to and after calving or abortion.