Effects of Sire of Fetus upon Subsequent Production and Days Open of the Dam

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Abstract
To quantify effects of the fetal-placental unit upon postpartum performance of the dairy cow, [USA] Dairy Herd Improvement Association records from Florida, Georgia, North Carolina and South Carolina (27,200 lactations of 11,935 Holsteins and 3731 of 1788 Jerseys) were studied by method of least squares. The final model included herd-yr-season, sire of fetus and sire of cow. Sire of fetus accounted for 8.2 and 11.8% of the total variability in mature equivalent milk yield (Holsteins and Jerseys), 9.8 and 14.3% in fat yield and 1.9-3.2% in days open. Interactions of sire of fetus with sire of cow accounted for none of the variability in yields (negative estimates of variance) but 4.4 and 4.8% of the variability in days open. Correlations between effects of sire of fetus on milk and fat yields were .96; for yields and days open they were .02 and -.02 for Jerseys and -.12 and -.13 for Holsteins. Correlation between sire of fetus constants and estimated breeding values for milk yield in a sample of 50 Jersey sires was -.04. Future consideration of sire of fetus effects could lead to increased repeatability of sire proofs and rate of genetic change. Hypothesized mechanism is that effects of the fetal-placental unit, possibly hormonal and at least partly genetically determined, influence development of the dam''s mammary gland and its subsequent performance.