The compounds of the present invention are described in the A. S. Tomcufcik et al. U.S. Pat. Nos. 3,725,407 issued Apr. 3, 1973; 3,828,041 issued Aug. 6, 1974 and 3,905,974 issued Sept. 16, 1975. The patentees describe methods for synthesizing 6-substituted 3-nitroimidazo[1,2-b]pyridazines and indicate that the compounds can be used to control amoebic and trichomonal infections in warm-blooded animals. No suggestion is made and it is not obvious from the disclosure that the stated compounds would be effective for the control of foot rot and liver abscesses in ruminant animals.