Sheep dietary preferences in targeted grazing: Demographic, management, and weather effects in northern mixed-grass prairie

Authors: KERSH, AARON - University Of Wyoming; FRALEY, HANNAH - University Of Wyoming; SCASTA, J - University Of Wyoming; Derner, Justin; DE MELLO TAVERES LIM, PAULO - University Of Wyoming; STEWART, WHIT - University Of Wyoming

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2024
Publication Date: 11/28/2024
Citation: Kersh, A.J., Fraley, H.M., Scasta, J.D., Derner, J.D., De Mello Taveres Lim, P., Stewart, W.C. 2024. Sheep dietary preferences in targeted grazing: Demographic, management, and weather effects in northern mixed-grass prairie. Frontiers in Veterinary Science. Article 11:1502948. https://doi.org/10.3389/fvets.2024.1502948.
DOI: https://doi.org/10.3389/fvets.2024.1502948

Interpretive Summary: The poisonous plant plains larkspur (Delphinium geyeri Greene) in northern mixed-grass prairie presents challenges for late spring/early summer grazing by cattle. Sheep, however, could be used to target graze this species before cattle grazing occurs to reduce potential losses of cattle. We evaluated target grazing of sheep in a dry (2022) and a wet (2023) year. Across the targeted grazing season (mid-May to mid-June), sheep consumed less than one percent of plains larkspur in their diet. Age of sheep nor breed of sheep affected diet proportions. Sheep did successfully reduce the abundance of plants of plains larkspur to prevent negative effects on subsequent cattle grazing, although forage biomass available for cattle was reduced.

Technical Abstract: Diet selection and composition of sheep target grazing plains larkspur (Delphinium geyeri Greene) in northern mixed-grass prairie were evaluated during a drought year (2022). Thirteen Rambouillet ewes (3- to 6-year-old, body weight (BW) 76 kg ± 2.9), 14 Dorper ewes (3- to 6-year-old, BW 47 kg ± 1.8), and 123 Dorper ram lambs (<1 year-old, BW 25 kg ± 0.4) were used for targeted grazing. Over the 20-day first phase (mid-May to early June), sheep were subjected to three stock density treatments: 1) high, 40 animal units (AU)/ha, 2) moderate, 20 AU/ha, and 3) light, 13 AU/ha. In the second phase (21 d, early- to late-June), the same sheep grazed four 1.5 ha paddocks sequentially at a very light stock density of 7 AU/ha. Dietary composition was assessed through focal bite count observations at the plant functional group level for phase one only, and dietary composition was estimated through fecal DNA metabarcoding (f.DNA) at the plant species level for both phases. Results indicated a uniformly low preference for larkspur (< 1% in diets). There were no significant effects of breed or age on focal bite count observations of plant functional groups (grasses, forbs, and larkspur), nor were there significant effects of breed or age on f.DNA diet proportions of plant functional groups (P > 0.05). Stock density did influence focal bite count observations, with higher forb intake (P = 0.0004) and lower grass intake (P = 0.009) observed at the moderate density compared to the high density. In phase two, grass and larkspur intake decreased while forb intake increased according to f.DNA (P < 0.01). These findings suggest that moderate stock density, combined with an understanding of plant phenology, precipitation variability, and animal forage preferences can optimize vegetation and animal performance in adaptive targeted grazing management within this ecosystem.