Strategic use of ivermectin during pregnancy to control toxocara canis in greyhound puppies.

Twenty-one greyhound bitches were bred (Day 0) and housed throughout their pregnancies on three greyhound breeding farms in Kansas. These dogs were assigned randomly to one of four treatment groups. Group A dogs (6) were given ivermectin subcutaneously (300 microg/kg) on Day 0 (the first day the dogs were bred), and Days 30 and 60 of gestation. Group B dogs (6) were given ivermectin (300 microg/kg SQ) on Day 42. Group C dogs (3) were given ivermectin (300 microg/kg SQ) on Days 0, 30, and 60 plus 10 days after whelping. Group D dogs (6) served as controls and received no anthelmintic. Bitches and puppies were moved to the university on the day after birth and were maintained inside for 28 days. Weekly quantitative fecal exams were done on the bitches during this time. The puppies were euthanized humanely at 28 days of age. Intestinal parasites were recovered, identified, counted, sexed, and preserved in either 10% formalin or frozen at -70 degrees C. The geometric mean numbers of adult Toxocara canis in the small intestines for Group A puppies (n = 40) were 2.8, 8.5 for Group B puppies (n = 39), and 29.7 for Group D puppies (n = 28). No adults were found in the Group C puppies (n = 15). The geometric mean eggs per gram of feces from the pups in group A, B, and D were 1.3, 704, and 27, 134, respectively. No eggs were recovered from the Group C pups. The strategic use of ivermectin at 300 microg/kg in greyhound bitches on Days 0, 30, and 60 of gestation reduced the worm burden carried by the puppies by 90% and the actual number of eggs passed into the environment by 99.8%. The same dose on day 42 reduced the worm burden by 71.4% and the number of eggs passed into the environment by 97.4%. This dose given on days 0, 30, and 60 plus 10 days postwhelping, reduced the worm burden by 100%, and no eggs were passed into the environment.