Modified contemporary comparison sire evaluations from first, all, and later lactations

Area of Science:

• Animal Breeding and Genetics
• Dairy Science
• Quantitative Genetics

Background:

• Modified Contemporary Comparisons (MCC) are crucial for sire evaluation in dairy cattle.
• Published progeny evaluations utilize data from both first and later lactations.
• Understanding discrepancies between early and later evaluations is vital for accurate genetic assessments.

Purpose of the Study:

• To analyze the characteristics of MCC for Holstein sires based on first and later lactation data.
• To investigate the relationship between first lactation evaluations and subsequent lactation performance.
• To identify factors influencing the prediction of later lactation yields.

Main Methods:

• Statistical analysis of Predicted Differences for milk yield from first, all, and later lactations for 200 Holstein sires.
• Calculation of average differences, standard deviations, and correlations between different lactation evaluation types.
• Correlation analysis of progeny test results with sire's age and culling rates.

Main Results:

• Average milk yield difference between later and first lactations was 47 kg, with a high standard deviation (149 kg).
• Strong correlations were observed between first, all, and later lactation evaluations (0.84-0.97).
• First lactation evaluations alone explained 71% of the variation in later lactation yields, with sire's age and culling rate also being important predictors.

Conclusions:

• Bull rankings for daughter milk yield can change significantly between first and later lactation evaluations.
• Sire's age showed a negative correlation with evaluations, suggesting potential genetic trend differences.
• The study highlights the importance of considering later lactation data for more robust dairy sire evaluations.