Embryonic mortality in Sprague-Dawley rats induced by snakeweed (Gutierrezia microcephala)

Three experiments were conducted to determine the effects of ingested snakeweed foliage (SW) on gestating rat embryos. Mature female Sprague-Dawley rats were paired with male rats and after breeding were randomly allotted to diets containing up to 15% SW. Feeding SW caused a decrease (P < .01) in the percentage of live embryos and markedly increased (P < .01) the percentage of dead or resorbed embryos. Snakeweed decreased (P < .01) feed intake in a dose-dependent manner and caused BW loss (P < .01) compared with control animals. However, decreased feed intake had no effect on gestating embryos. Rats fed the control diet, with intakes restricted to equal the average intake of rats fed SW, and those with ad libitum access to the control diet had similar percentages of live and dead embryos (P > .10). Serum clinical profiles reflected undernutrition (decreased triglycerides and cholesterol; P < .01) and mild toxicosis (elevated blood urea nitrogen, creatinine, and bilirubin; P < .01). Because fluid accumulation was noted in the uterus of several rats fed SW, a uterine weight bioassay was conducted. Snakeweed, fed as 10% of the total diet, decreased (P < .01) uterine weight of immature Sprague-Dawley rats. Ingestion of SW during early gestation caused embryonic mortality that could not be attributed to undernutrition or estrogenicity.