Daughters’ Maternal Grandsires in Sire Evaluation

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Abstract
First lactation records of 808,796 artificially sired cows in the Northeast United States were used to compare sire evaluations with and without maternal grandsires in the model. Marternal grandsires were identified on 55.7% of the records. Including maternal grandsire increased percent filled subclasses in absorbed best linear unbiased prediction equations by 43% (Guernseys) to 95% (Holsteins). Rank correlations between sire evaluations for the 2 models ranged from 0.91 (Ayrshires) to 0.97 (Holsteins). Product moment correlations ranged from 0.92-0.98. Holstein sires changed an average of 52 kg of milk. Negative assortative mating (good sires and poor maternal grandsires) was observed in the Guernsey and Brown Swiss breeds. Positive assortative mating (good sires and good maternal grandsires) occurred in the Ayrshires, Holsteins and Jerseys. Including maternal grandsires of cows in the model is a step toward utilizing more genetic relationships in a practical sire evaluation system.