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

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, 2,438–3,048 m 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 potentially toxic species were identified: Short's milkvetch (Astragalus shortianus), chokecherry (Prunus virginiana), and larkspur (Delphinium species). In addition and problematically, one Operational Taxonomic Unit (OTU) could be attributed to either 3 different selenium accumulating plant species in the Asteraceae family or the toxic plant deathcamas (Zigadenus venenosus var. gramineus) in the Liliaceae family, 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.