Using iophenoxic acid injections of prey to identify mammals that feed on them

Identifying species or individuals that feed upon other species of animals is an important aspect of some predation studies. We evaluated the effectiveness with which the biomark associated with iophenoxic acid (IA) injections was transferred from domestic goats to coyotes (Canis latrans) that fed on them. We injected doses of 100, 300, or 1,000 mg of IA into goats to raise serum iodine levels, fed meat from the injected goats to coyotes, and monitored serum iodine levels in both species for about 120 days. Within 3 days, mean serum iodine levels in goats increased from 5.33 mcg/100 ml to over 2,847, 10,233, and 11,567 mcg/100 ml, respectively, for the 100-, 300-, and 1,000-mg IA treatments. A gradual dissipation of serum iodine concentrations in the goats ensued, approaching mean levels of 943, 3,213, and 6,310 mcg/100 ml of serum by day 120. When we fed coyotes (2/treatment) 500 g of meat from IA-treated goats, mean serum iodine levels among the coyotes increased within 2 days from 8 mcg/100 ml to 194, 410, and 645 mcg/100 ml of serum respectively for the 3 treatments. Mean serum iodine concentrations among these coyotes then declined systematically to 30, 45, and 82 mcg/100 ml of serum 112 days after ingestion. When we fed coyotes 500 g of meat from goats slaughtered 120 days after they had been injected with IA, mean serum iodine levels increased from base levels (8 mcg/100 ml of serum) to 69, 242, and 526 mcg/100 ml respectively for the 100-, 300-, and 1,000-mg treatments. We concluded that we were able to detect coyotes that fed on marked goats any time during a 120-day period after the goats were treated. Nonlinear regression analysis suggested a relation between levels of serum iodine achieved and IA dose rate (mg/kg) received by the goats, with iodine levels reaching saturation with intramuscular injections of 25-30 mg/kg IA