Distribution of cysts and tachyzoites in calves and pregnant cows inoculated with Toxoplasma gondii oocysts.

Sixteen calves and 6 cows were each inoculated with 100 000 infective oocysts of the GT-1 strain of Toxoplasma gondii. Cattle were necropsied between 3 and 287 days post-inoculation (DPI) and their tissues were inoculated into mice or fed to Toxoplasma-free cats for the detection to Toxoplasma in bovine tissues. Ten to 10 000-fold more T. gondii were recovered from small intestine and mesenteric lymph nodes of calves at 3 and 6 DPI than from lungs and liver, and the number of T. gondii in bovine tissues was reduced 1000-fold between 6 and 8 DPI. By using the Pepsin digestion technique, or feeding tissues to Toxoplasmas-free cats, it was demonstrated that T. gondii encysted in bovine tissues as early as 11 DPI and persisted as late as 287 DPI. More Toxoplasma gondii cysts occurred in livers than in many other bovine tissue. Of the 6 cows inoculated at 95--155 days after breeding, 5 delivered normal calves and T. gondii was isolated from only one of these calves. One cow was barren. Toxoplasma gondii was not isolated either by mouse inoculation or by feeding cats tissues from 2 cows killed 132 and 190 DPI. Toxoplasma gondii was not isolated in mice inoculated with tissues of cows killed 98 and 109 DPI, but cats fed on bovine tissues shed T. gondii oocysts. The organism, however, was isolated in mice inoculated with the mesenteric lymph nodes of 1 of the 2 cows killed 162 and 168 DPI, and from the small intestine of the other. Cats fed tissues of these cows later shed T. gondii oocysts.