Broom snakeweed extracts dosed to late-term pregnant cattle do not cause premature parturition

Authors: Gardner, Dale; Green, Benedict - Ben; Stegelmeier, Bryan; Welch, Kevin

Submitted to: Poisonous Plant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2022
Publication Date: 5/20/2022
Citation: Gardner, D.R., Green, B.T., Stegelmeier, B.L., Welch, K.D. 2022. Broom snakeweed extracts dosed to late-term pregnant cattle do not cause premature parturition. Poisonous Plant Research. 5:13-21. https://doi.org/10.26077/15eb-503b.
DOI: https://doi.org/10.26077/15eb-503b

Interpretive Summary: Broom snakeweeds are found on many rangelands in western North America. Snakeweeds are generally unpalatable; however, animals will graze them when other forage is not available and there are field reports that pregnant cows that graze snakeweeds may abort calves, however, this has not been demonstrated under experimental conditions and any suspected toxins are unknown. It has been evident from experimental studies that large doses of snakeweed are quite toxic and can quickly damage the rumen resulting in bloating, acidosis and death if not treated. Past experimental studies have found the dosing of fresh plant material to cattle physically difficult. As an alternate method of testing snakeweed, we report here an attempt to use extracts of the snakeweed mixed with ground alfalfa hay to test for abortifacient activity in late-term pregnant cattle. The solvent extracts from the two most common snakeweed populations were tested and again no abortions could be produced. We conclude that broom snakeweed plants are unlikely to be directly responsible for cattle abortions.

Technical Abstract: Broom snakeweed [Gutierrezia sarothrae (Pursh) Britton and Rusby] and threadleaf snakeweed [G. microcephala (DC.) A. Gray] are found on many rangelands in western North America. Snakeweeds are generally unpalatable; however, animals will graze them when other forage is not available and there are field reports that pregnant cows that graze snakeweeds may abort calves. Subsequent feeding studies using fresh cut snakeweed, ground and gavaged into pregnant cattle have failed to reproduce abortions, though it was evident that at high doses snakeweed quickly damaged the rumen microflora resulting in severe rumen atony, bloating and acidosis. We report here an attempt to solvent extract the snakeweeds, mix the extracts with ground alfalfa hay, and test the extracts for abortifacient activity in late-term pregnant cattle. The dosed extracts again appear to be unable to reproduce snakeweed induced abortions in cattle. Extracts from snakeweed chemotype 1 plant appear to be quite toxic to the rumen and caused complete rumen stasis after 2-3 days. In contrast, cattle receiving chemotype 2 extracts were able to tolerate over twice the dosage as that given for chemotype 1 extracts. We conclude that broom snakeweed plants are unlikely to be directly responsible for cattle abortions observed in cattle grazing snakeweed invested rangelands. It is more likely that cattle may be affected by rumen toxicity and/or might suffer from poor nutritional factors given the lack of quality forage that might be available on rangelands with high snakeweed infestation.