AGB 211: Livestock and Poultry Breeding (2+1)

MODIFIED CONTEMPORARY COMPARISON

• Since only contemporaries of first calvers are considered, the herds less than 20 to 30 cows might not have any contemporary for comparison. However, the comparison of progeny with contemporaries of all ages might improve the accuracy of sire evaluation. But comparing cows in first lactation with older cows that are survivors of culling for yield could be important sources of biases in dairy sire evaluation.

MCA = [n₁ X₁ + W (X_i – Bias)] / (n₁ + W)

where,

n₁ = number of contemporaries of first lactation

X₁ = average of the contemporaries of first lactation

X_i = average of the contemporaries of later lactation

W = weight given to later lactation herd-mates

Bias = adjustment for later lactation cows, being the survivors of culling

The bias is calculated as average within herd-year-season difference between first and later lactation cows, adjusted for genetic trend

S_I = A + {n / (n + k)} (D – MCA)