Date of Award:

12-2026

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Committee Chair(s)

Juan J. Villalba

Committee

Juan J. Villalba

Committee

Eric Thacker

Committee

R. Douglas Ramsey

Committee

Stephan van Vliet

Committee

Jennifer W. MacAdam

Abstract

Beef cattle grazing systems in the western United States often depend on grass monocultures that decline in nutritional quality during summer. As pasture quality decreases, cattle have fewer opportunities for selective foraging, grazing efficiency declines, and producers face increased supplementation costs to maintain animal performance, welfare, and effective pasture use. This dissertation examined whether interventions that provide phytochemicals either as a supplement or through the establishment of taxonomically diverse “hot spots” in otherwise monotonous landscapes could improve cow-calf pair performance and enhance the sustainability of agroecosystems. The study tested two strategies with free-grazing cow–calf pairs: supplementation with tannin extract and establishing of small patches, or “islands,” of diverse, phytochemically rich forage species within bromegrass pastures. Using combined GPS–tri-axial accelerometer collars, pedometers, and machine-learning methods, the study identified cattle behavioral responses to these feeding strategies with high accuracy. The study developed a monitoring system that combined GPS collars, motion sensors, and direct animal observations to classify cattle behavior while grazing. These tools were able to identify important activities such as grazing, resting, rumination, walking, and posture with high accuracy. Moderate tannin supplementation led cattle to graze longer during the evening, drink more water, change between lying and standing postures less often, and use the pasture more evenly than cattle that did not receive tannins. These responses suggest that tannin supplementation can influence grazing distribution and welfare, and may help reduce concentrated grazing pressure in free-grazing systems. Biological measurements also indicated changes in antioxidant activity, rumen microbial processes, and nitrogen use, showing that tannins had an impact on cattle through both behavioral and physiological pathways. When cattle grazed diverse forages in patches embedded in grass, their preference and selection changed over the summer. They did not graze all plants equally; instead, they showed a preference for sainfoin and adjusted their diets over time by mixing different forages. These findings show that diverse forage “hotspots” can expand feeding choices in otherwise monotonous pasture systems. By linking cattle behavior with welfare, performance, and health indicators, this dissertation shows that phytochemical-based strategies offer a practical way to improve grass monocultures during summer as forage nutritive value decline. Rather than relying solely on protein supplementation, integrating moderate tannin supplementation or establishing small patches of plant diversity can help cattle make better use of pasture resources while supporting more resilient and sustainable beef production systems.

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