Date of Award

9-2025

Degree Name

MS in Agriculture - Animal Science

Department/Program

Animal Science

College

College of Agriculture, Food, and Environmental Sciences

Advisor

Zachary McFarlane

Advisor Department

Animal Science

Advisor College

College of Agriculture, Food, and Environmental Sciences

Abstract

Efficient use of native rangelands and improved reproductive success are primary objectives in beef cattle production. Grazing behavior during the breeding season may be influenced by pasture characteristics, including size and water availability, as well as physiological differences due to reproductive status. This study aimed to evaluate the relationship between grazing activity and conception method in crossbred Angus cows over a 2-year period. The study was conducted during the winter months (December – February) on the Central Coast of California with a mean temperate of 53 degrees Fahrenheit. Cows (n = 76) were blocked by age and then randomly assigned to be fitted with a Knight GPS tracking collar. All cows, except first-calf heifers (n = 12), were synchronized for fixed-timed artificial insemination (FTAI) and bulls were turned out 7 d after for a 65 d breeding season. Cattle were managed in an intensive rotational grazing system (n = 36; mean size: 22.13 ± 13.53 ha). Cows were retrospectively classified into the following groups: conception to FTAI (AI; n = 23), natural service (Bull; n = 37), and non-pregnant (Open; n = 16). Average daily distance traveled (km/d) and elevation gain (m/d) were measured at 10 minutes intervals. Data were analyzed using the MIXED procedure in SAS 9.4, including the main effects of conception method, number of water sources, pasture size and their interactions. Pasture size was retroactively classified as Small (n = 11, mean = 26 acres), Medium (n = 15, mean = 51.60), or Large (n = 7, mean = 115.14). Daily distance traveled, and elevation gain exhibited a conception method × water source × pasture size interaction (P < 0.001). AI-bred cows traveled the greatest distance in large and small pastures with only one water source available (P < 0.001). In contrast, Open cows exhibited the greatest distance traveled when two water sources were available (P < 0.001). In medium pastures, regardless of water source availability, distance traveled was comparable across conception methods (P ≥ 0.697). Open cows in large pastures with two water sources gained the most elevation (P < 0.001). Elevation gain was more evenly distributed across conception methods in small pastures (P ≥ 0.998). Regardless of pasture size, AI cows exhibited greater elevation gain when only one water source was available (P < 0.001). Bull bred cows were generally intermediate in daily distance compared with AI and Open groups, tended to show fewer extreme daily values, and concentrated activity more in lower elevation, central areas near water. By strategically managing pasture resources in the context of conception method then producers can increase grazing distribution in native rangelands to ensure continued sustainability.

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