Transmammary transfer of toxicity to nursing kids from Isocoma pluriflora (rayless goldenrod) dosed to lactating goats.

Rayless goldenrod (RG; Isocoma pluriflora) poisons livestock in the southwestern U.S., west Texas, and northern Mexico. The putative toxin(s) have historically been thought to be benzofuran ketones. Goats have been used successfully as a model of RG poisoning. The transmammary transfer of toxicity to offspring from lactating goats has not been studied, thus the objective of this study was to determine if nursing kids would become poisoned via mother's milk when the dams were dosed with RG. Twelve lactating goats (6 controls and 6 treated; all with twin kids) were dosed via oral gavage with alfalfa or rayless goldenrod at 2% of BW per day for 14 days. Two kids showed overt clinical signs near the end of the study; however, no dams showed clinical signs, and none developed exercise intolerance or muscle weakness. After day 11 of treatment, the RG kids showed increased (P < 0.05) serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and creatinine kinase (CK) activities until exposure to the plant via mothers' milk ended. Serum CK activity of kids declined rapidly over 7 days after transmammary exposure ended. Histopathology revealed that one kid had extensive myonecrosis that involved both myocardium and skeletal muscles. The other kids from RG-treated does had minimal myocyte degeneration and necrosis characterized by individual myofiber swelling, hypereosinophilia and loss of striation. Benzofuran ketones were not detected in the milk of lactating goats; further, dosing with RG did not alter milk composition. In summary, milk ingestion from does dosed with >300 mg/kg BW of benzofuran ketones from RG over 14 days increased mean CK concentrations in treated kids compared to controls; however kids rapidly recovered when exposure ended. Additional work is needed to better define benzofuran ketone metabolism, toxicity, and animal susceptibility.