Document Type

Thesis - Open Access

Award Date

2026

Degree Name

Master of Science (MS)

Department / School

Animal Science

First Advisor

Ira Parsons

Abstract

Replacement beef heifer development in extensive grazing systems is challenged by variation in forage quality, supplement intake, and animal behavior, all of which influence the ability to achieve targeted growth prior to breeding. Precision livestock technologies (PLT) enable continuous monitoring of individual animal performance, while energy-based nutritional models support individualized supplementation. However, their application under extensive grazing conditions remains poorly understood. Therefore, the objectives of this thesis were to (1) evaluate heifer utilization of multiple precision livestock technologies and their relationship with animal performance and (2) evaluate the accuracy of an individualized energy-based supplementation model by comparing predicted supplement allotments and growth trajectories with observed intake, growth, energy balance, and movement behavior. Angus heifers (n = 47; initial BW = 191 ± 30.2 kg) grazed dormant native rangeland from November 26, 2024, to May 1, 2025. During P1, heifers received Low (75%; n = 16), Constant (100%; n = 15), or High (125%; n = 16) proportions of model-predicted supplement requirements. During P2, all heifers received individualized supplement allotments targeting a body weight of 326 kg (60% of mature body weight). Supplement intake, body weight, methane emissions, and movement were monitored using precision livestock technologies. Precision scale visitation did not differ among supplementation strategies (p = 0.16) but decreased from P1 to P2 (p < 0.01). Precision feeder visitation varied among individuals but was not associated with average daily gain (R² = 0.026, p = 0.28). OCGQS utilization was sufficient during P1 but limited during P2 because of equipment downtime. During P1, methane production differed among supplementation strategies (p = 0.03), with Low and High heifers producing more methane than Constant heifers. The energy-based supplementation model generated distinct projected growth trajectories, but observed average daily gain remained below projected values during P1. Only 15.2% of heifers achieved projected growth targets within ±10% of model predictions. Final body weight averaged 314 ± 52 kg, and 60.9% of heifers remained below the target body weight of 326 kg. Growth strategy did not influence daily distance traveled, pasture area utilized, or site fidelity (p > 0.05). These findings demonstrate that precision livestock technologies can quantify individual animal behavior and performance under extensive grazing conditions, although data quality varied among technologies because of differences in animal utilization and system reliability. Although the energy-based supplementation model generated individualized supplementation strategies, observed intake, energy availability, and growth frequently differed from predictions, indicating that additional biological and behavioral factors should be incorporated into precision nutritional management of grazing beef heifers.

Publisher

South Dakota State University

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Rights Statement

In Copyright