Differences in modified contemporary comparison sire evaluations from first and later lactations by breed

Area of Science:

• Animal Genetics
• Dairy Science
• Quantitative Genetics

Background:

• Accurate sire evaluation is crucial for genetic improvement in dairy cattle.
• Differences in lactation records can affect the reliability of sire genetic merit predictions.
• Understanding breed-specific variations in evaluation accuracy is important for breeding programs.

Purpose of the Study:

• To investigate differences in sire milk production evaluations between first and later lactation records.
• To assess the impact of culling and sire age on these evaluation differences across multiple dairy breeds.
• To determine the correlation between first and later lactation evaluations.

Main Methods:

• Utilized Modified Contemporary Comparison procedures on daughter records from Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss bulls.
• Analyzed three sets of records: first lactation only, later lactations, and all records.
• Calculated average differences and standard deviations between first and later lactation evaluations.

Main Results:

• Significant differences in sire evaluations between first and later lactation records were observed across all breeds, with notable variation.
• Culling of first lactations positively correlated with larger differences favoring later evaluations.
• Sire age improved prediction accuracy for later records in Guernsey, Holstein, and Jersey breeds, with younger sires showing higher evaluations.

Conclusions:

• Important discrepancies exist between sire evaluations derived from first versus later lactation records for all studied breeds.
• Culling practices and sire age are significant factors influencing the accuracy and direction of sire genetic evaluations.
• Breed-specific analyses are essential for optimizing dairy cattle breeding strategies based on lactation performance data.