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Conflicts between Heritabiliy Estimates of Mature Equivalent and Herdmate-Deviation Milk and Fat

Animal Science Research Division, USDA, ARS, Beltsville, Maryland 20705

ABSTRACT

Intraherd heritability (h²) of milk or fat yield, estimated from a cross-classified random model including nerds and sires, is typically higher for mature equivalent yield than for mature equivalent yield deviated from herdmate average. Dairy Herd Improvement lactation records of 7,997 progeny of 576 Holstein sires in artificial insemination were used to investigate this problem. Cows were 26 to 28 months of age and calved in November and December 1964. Estimates of h² for mature equivalent milk, fat, and fat per cent were .66, .62, and .71; those for deviations milk, fat, and fat per cent were .31, .28, and .50. Adjusting records with regional age factors to a 27-month base rather than to maturity gave lower estimates of heritability for milk and fat (.52 and .46). Biases in h² for milk and fat yields arose because of correlations between herd effects and because of partial confounding between sires and herds. Discrepancies in h² between mature equivalent and deviation yields were eliminated by stratifying records into six levels of average herdmate milk (average h² for milk: mature equivalent, .41; 27-month, .42; and deviation, .40). Heritabilities for deviation milk increased with herdmate yields (low to high) : h² = .27, .35, .36, .44, .47, and .48.

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				C. D. Dechow, H. D. Norman, N. R. Zwald, C. M. Cowan, and O. M. Meland Relationship Between Individual Herd-Heritability Estimates and Sire Misidentification Rate J Dairy Sci, April 1, 2008; 91(4): 1640 - 1647. [Abstract] [Full Text] [PDF]