Which term describes a numeric value that combines multiple traits with weights to rank animals for selection?

• A. It weights multiple traits to rank animals for selection
• B. It measures only body weight
• C. It predicts disease risk
• D. It is a single trait measurement

Answer: (A)

A selection index combines several traits into one numeric value by assigning weights to each trait based on its importance to the breeding goal. This single score lets breeders rank animals for selection, balancing different traits (like growth, efficiency, fertility) even when they’re measured on different scales. The weights reflect economic value or desired genetic progress, and the index may also incorporate how traits interact and how heritable they are to optimize long-term gains. That’s why the best description is that it weights multiple traits to rank animals for selection. The other ideas describe focusing on a single trait, predicting disease risk, or measuring just one trait, which don’t capture the idea of integrating multiple traits into a single ranking score.