Protozoal abortion in a herd of cattle concurrently infected with Hammondia pardalis

Protozoal infection was diagnosed as the cause of abortion in a large drylot dairy herd located in northeastern Mexico. Diagnosis was made on the basis of finding encephalitis, myocarditis, protozoal cysts, and protozoal tachyzoites in aborted fetuses. The blended ration fed to the cows had been contaminated by the feces of a large resident population of feral domestic cats that used components of the blended ration for den sites (stored hay) or as a latrine (grain). The cows that aborted contained tissue phases of a protozoan infective for domestic cats. The morphologic features of the oocyst and biologic features of the protozoan were identical to those of Hammondia pardalis.