Fluctuating asymmetry in broiler chickens: a decision protocol for trait selection in seven measuring methods

Area of Science:

• Animal Science
• Developmental Biology
• Quantitative Genetics

Background:

• Fluctuating asymmetry (FA) is a proposed indicator of animal fitness and welfare.
• Existing research shows inconsistent links between FA and animal performance or welfare.
• Methodological issues in measurement and statistical analysis may explain these inconsistencies.

Purpose of the Study:

• To review problems in interpreting FA results in poultry.
• To provide guidelines for accurate measurement and analysis of FA in broilers.
• To evaluate the applicability of various measurement techniques for FA estimation.

Main Methods:

• Measured a range of morphological traits in broilers using 7 different techniques.
• Evaluated measurement techniques based on criteria: significant FA, absence of directional asymmetry/antisymmetry, no between-trait correlation, and high signal-to-noise ratio.
• Assessed the accuracy of FA estimates in relation to method complexity and time investment.

Main Results:

• 3 to 14 measurements per method were suitable for FA estimation based on selection criteria.
• FA estimate accuracy positively correlated with measurement method complexity and time.
• Repeatability analyses highlighted the need for larger sample sizes and more repeated measurements than commonly used.

Conclusions:

• Accurate FA measurement and statistical analysis are crucial for reliable interpretation of animal welfare and performance.
• Specific measurement techniques and robust statistical power are recommended for FA studies in poultry.
• Future FA research should adopt standardized protocols and sufficient sample sizes to enhance study validity.