Implementing structural equation models to observational data from feedlot production systems.

Area of Science:

• Animal Science
• Agricultural Economics
• Statistical Modeling

Background:

• Bovine Respiratory Disease (BRD) significantly impacts feedlot morbidity and mortality, affecting production efficiency.
• Understanding the complex relationships between animal health and performance is crucial for optimizing feedlot operations.
• Traditional models may not fully capture the direct and indirect pathways influencing feedlot performance.

Purpose of the Study:

• To implement and illustrate a mixed-model-based structural equation modeling (SEM) approach for analyzing observational data in feedlot production systems.
• To assess the direct and indirect effects of arrival weight (AW) on average daily gain (ADG), mediated by Bovine Respiratory Disease (BRD) treatment costs (Trt$).
• To compare SEM-derived effect estimates with those from standard linear regression mixed models.

Main Methods:

• Utilized a dataset of 1430 lots (178,983 cattle) from 9 US Great Plains feedlot operations.
• Employed structural equation modeling (SEM) to analyze functional links between arrival weight (AW), BRD-related treatment costs (Trt$), and average daily gain (ADG).
• Accounted for fixed effects of sex and clustered correlations within feedlots using a mixed-model framework.

Main Results:

• The best-fitting SEM model indicated that AW had a direct positive effect on ADG (λˆ31=0.002±0.0001 kg/head/day).
• AW also had a direct negative effect on Trt$ (λˆ21=$0.08±0.006 USD/head), and increased Trt$ directly decreased ADG (λˆ32=0.004±0.0006 kg/head/day).
• SEM effectively distinguished direct and indirect pathways, providing a more nuanced understanding than standard regression models.

Conclusions:

• Mixed-model SEM provides a robust framework for dissecting complex causal interrelationships in feedlot production data.
• Arrival weight influences average daily gain both directly and indirectly through its impact on health-related treatment costs.
• Understanding these direct and indirect mechanisms is vital for improving feedlot health management and overall production efficiency.