Technical note: Toxic plants in sheep diets grazing extensive landscapes: Insights from fecal DNA metabarcoding

Authors: SCASTA, DEREK - University Of Wyoming; JORNS, TAMARAH - University Of Wyoming; Derner, Justin; STAM, BARTON - University Of Wyoming; MCCLAREN, M - University Of Wyoming; CALKINS, CRAIG - University Of Wyoming; STEWARD, WHIT - University Of Wyoming

Submitted to: Livestock Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2020
Publication Date: 3/9/2020
Citation: Scasta, D.J., Jorns, T., Derner, J.D., Stam, B., McClaren, M., Calkins, C., Steward, W. 2020. Technical note: Toxic plants in sheep diets grazing extensive landscapes: Insights from fecal DNA metabarcoding. Livestock Science. 236. Article e104002. https://doi.org/10.1016/j.livsci.2020.104002.
DOI: https://doi.org/10.1016/j.livsci.2020.104002

Interpretive Summary: Toxic plants negatively affect livestock production but detection is difficult. Fecal DNA (fDNA) metabarcoding technology is an emerging but untested method. We quantified diets for 2 Rambouillet flocks in western Wyoming, USA with fDNA. Three toxic plants and 6 lichens were identified and there were multiple species in diets for each sampling date. fDNA challenges include discerning between species and georeferencing is required to increase the utility of this methodology for ranchers and land managers.

Technical Abstract: Toxic plants can negatively affect livestock production due to acute or chronic toxicosis. Detecting toxic plants in free-ranging animal diets has been a persistent challenge as toxicosis may only be noted with acute toxicity and subsequent mortality – but not necessarily when signs are sub-clinical. New fecal DNA (fDNA) metabarcoding technology can quantify diet composition of free-ranging livestock without the need for gathering/handling animals or the use of invasive procedures to determine hepatotoxicity and could inform more proactive toxic plant management. We quantified sheep diet composition in extensive rangeland environments with the specific aim of estimating toxic plant consumption using fDNA technology. Diets for 2 Rambouillet flocks in western Wyoming, USA [HSC flock: 1,800 ewes (+ lambs), 3,328 ha allotment, 1,829-2,438 m elevation; SBT flock: 1,010 ewes (+ lambs), a 4,262 ha allotment, 2,438-3,048m elevation] were quantified with fDNA in the 2017 summer months. A total of 93 plant species were identified. HSC diets were dominated by grasses (51%) and forbs (31%) but SBT diets were dominated by forbs (42%) with minor contributions from shrubs (14%) and grasses (13%). Three toxic species were identified: Short’s milkvetch (Astragalus shortianus), chokecherry (Prunus virginiana), and Geyer’s larkspur (Delphinium geyeri). In addition, one Operational Taxonomic Unit (OTU) related to either selenium accumulating plant species or the toxic plant deathcamas (Zigadenus venenosus var. gramineus), was also detected. Six genera of lichens were also identified in diets. Challenges with fDNA technology include (1) an OTU might be shared by several plant species, and (2) reconciling fDNA laboratory data with georeferenced plant data is necessary to ensure correct interpretations. Finally, fDNA could be used for adaptive grazing management to enhance livestock nutrition and as a proactive tool to increase awareness of potential toxicosis problems before clinical signs or mortalities occur.