Available at: https://digitalcommons.calpoly.edu/theses/2912
Date of Award
12-2022
Degree Name
MS in Agriculture - Animal Science
Department/Program
Animal Science
College
College of Agriculture, Food, and Environmental Sciences
Advisor
Zachary D. McFarlane
Advisor Department
Animal Science
Advisor College
College of Agriculture, Food, and Environmental Sciences
Abstract
California’s approximately 660,000 head of beef cattle are highly dependent on range bulls used to produce offspring that can perform across the state’s diverse ecological regions. While knowledge of bull breeding behavior and the technology used to monitor cattle movement and behavior is critical to maximize conception rates and the overall efficiency in natural service sires on rangelands. Bulls need to be functional on rugged coastal landscapes, rolling foothills, deserts, and in high-elevation terrain. Few data exist that indicate factors related to selection, maintenance, and longevity of bulls used in rangeland landscapes. Objectives herein, were to assess factors influencing bull purchasing, management, and culling decisions of California beef producers. Another objective was to examine the relationship between activity level and the number of offspring born from a breeding season. Surveys were mailed to the California Cattlemen’s Association membership (n = 1,410) with ~ 16% response rate (n = 227). Mean age and years of bull selection experience of respondents was 61 ± 1 years and 27 ± 1 years, respectively. Respondents managed cattle on a total of 694,949 ha of owned, private leased, and leased public rangelands in California and surrounding states. Cow-calf herd size was 333 ± 92 head and bull battery averaged 18 ± 2 head with average bull longevity of 5 ± 1.3 years. The average price paid for bulls in the last 2 years was $5007 ± 163.33, while the highest price paid in the last 5 years was $7291 ± 335.40. Survey responses were used to define current factors driving management after purchase and for subsequent breeding seasons. After bull purchase, 48% of producers turned bulls out directly with females, while 52% held bulls until the following breeding season. Additionally, most producers (70%) did not manage bulls to reduce condition after purchase. Semen quality analysis, a major component of a breeding soundness exam, was evaluated annually by 45% of respondents, while 20% of respondents never evaluated semen quality. Respondents indicated bull age (35%) and structural soundness (29%) as the most common factors for culling bulls. Global Positioning Systems (GPS) units were affixed to bulls prior to the start of the breeding season and distance traveled was determined. Additionally, calf tissue samples for DNA parentage were collected and DNA was processed by Neogen’s SireSeek program. Changes in carcass traits, such as intramuscular fat (IMF), marbling (MARB), ribeye area (REA), and rib fat (RIBFAT), were significant in the ranch*year interaction (P < 0.05). This highlights the fact that carcass traits were the most influenced by the ranch location they had per year. While the survey research shows that despite the variability in operation demographics, there were similarities in beef bull selection and management across the state. Additionally, these data suggest the need for additional research focused on bull selection and management to maximize producer investment in reproduction.