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,2
USDA, ARS, Roman L. Hruska US Meat Animal Research Center, Lincoln, NE 68583-0908 and
and
Clay Center, NE 68933
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: beef cattle • breed • carcass expected progeny difference • genetic evaluation
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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developed a method to compare EPD for birth weight, weaning weight, and yearling weight from different breed associations having different base years for use on cows from different breeds. The common base when used with breed association EPD allows a herd owner to compare bulls of many breeds. The original method (Cundiff, 1993) has undergone relatively minor statistical changes. Barkhouse et al. (1994, 1995, 1998) added random sire and dam effects to obtain more appropriate standard errors for breed of sire solutions. In the 1996 analysis, a mixed model, including dam effects, was used to estimate regression of progeny records at USMARC on breed association EPD (Van Vleck and Cundiff, 1996). Van Vleck and Cundiff (2001) used estimates of heterosis from a Hereford by Angus diallel experiment to adjust all progeny records to the basis of 100% heterozygosity because the purpose of the evaluation is to compare sires of different breeds to produce crossbred calves. Annual updates of across-breed adjustment factors for birth weight, weaning weight, yearling weight, and maternal milk have been available since 1993 (Van Vleck and Cundiff, 2005). The purpose of this paper is to develop a similar procedure for adjusting breed association EPD to a comparable base for marbling score (MAR), fat thickness (FAT), ribeye area (RIB), and retail product percentage (RPP). The regressions of carcass traits from USMARC steers on breed association EPD were of special interest.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Data for these analyses were from steers produced in the Germplasm Evaluation (GPE) Program at the US Meat Animal Research Center whose sires had EPD for carcass traits in recent genetic evaluations of 11 different breeds. The number of sires represented in each breed and the number of progeny they produced in each cycle of the GPE Program are shown in Table 1. The GPE Program has been conducted in 8 cycles to compare topcross performance of 37 sire breeds. Eleven of these breeds have EPD for MAR, FAT, and RIB. The steers were F1 crosses produced from matings to Angus (cycles I to VIII), Hereford (cycles I to VII), and Composite MARC III (cycles V to VIII) dams. Composite MARC III is 25% each of Angus, Hereford, Red Poll, and Pinzgauer. In cycles I, II, IV, and VII, Hereford and Angus straightbreds, and reciprocal crosses were produced to provide estimates of heterosis.
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Estimates of heterosis were needed to adjust records to the equivalent of 100% heterozygosity expected in F1 crosses because offspring from some matings to Hereford, Angus, and Red Angus sires resulted in straightbred Hereford, straightbred Angus, and Red Angus x Angus progeny with 0% heterozygosity. Some progeny of Angus, Red Angus, or Hereford sires produced by MARC III composite dams had less than 100% heterozygosity, as did matings with Brangus (3/8 Brahman, 5/8 Angus) sires. To include more carcass records for estimation of heterosis and to improve ties over the various cycles, the progeny in the Hereford-Angus diallel analysis were not required to have sires with carcass EPD. For example, no estimates of heterosis would have been possible for RPP because no Hereford sires had EPD for RPP. Table 2 describes the analyses for estimating heterosis effects for the 4 traits. Unfortunately, no diallel information was available for breeds other than Hereford and Angus. Estimates from that diallel, however, should be better than no estimates or estimates that confound heterosis and maternal effects.
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summarizes the available records.
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lists the average accuracy for EPD (BIF, 2002) by breed of sire. As expected for carcass traits, these average accuracies were not large and were variable by breed, which contributed to variation in estimates of regression coefficients and of breed of sire effects. Table 5 includes the nonparent (animals born in year 2003) average EPD for the breeds and the average EPD (weighted by number of progeny) for sires of USMARC progeny. The differences in the average EPD were used in a later step.
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. Even with the weight traits, regression coefficients, which were estimated from many more records, were pooled across breeds. Pooled regression coefficients are shown in Table 7. With the carcass data, pooling was also by type of measurement used for the breed association EPD. Hereford and Brangus EPD were based on ultrasound measurements. The other EPD, except for Angus, were based on traditional carcass measurements. The American Angus Association furnished separate EPD based on ultrasound and traditional carcass measurements as indicated in Table 7. Because of the relatively large number of Angus progeny, the pooled regression coefficients chosen for later use included those from analyses of Angus progeny at USMARC with the traditional or ultrasound EPD of their sires.
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For example, let MARC(i) be the solution for breed of sire i from records of USMARC progeny. Let 
yyi be the mean EPD for the nonparent year (yy) for breed i and i be the mean EPD for sires of progeny with records at USMARC weighted by number of progeny. The regression coefficient used to adjust the MARC solution depends on whether the corresponding EPD was based on traditional carcass measurements (bc) or ultrasound measurements (bu).
For breed A with ultrasound EPD, the adjusted breed of sire solution is
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For breed B with traditional carcass EPD, the adjusted breed of sire solution is
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For sire m of breed A, the difference from EPDyyA can be represented as
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As a difference on the USMARC scale of measurement and to the common base year, the adjusted difference in EPD from EPDyyA is
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For sire n of breed B, the adjusted difference in EPD is
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Thus, MARC(A,m,adj) and MARC(B,n,adj) can be compared on the USMARC scale of measurement and to a common base year (yy).
For the weight traits, a regression coefficient of unity was assumed for the last step for all breeds. To construct a table of adjustment factors, 1 breed was usually chosen as a base. For example, the adjusted EPD for sire p of breed X would be
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with bx either bc or bu.
The constant parts of the differences in EPD of sires of breeds A, B, and X determine the across-breed adjustment factors with breed X chosen as the base breed. The difference between adjusted EPD for sire m of breed A and sire p of base breed X is
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Rearrangement from combining the constant parts and EPD of individual sires of the difference results in
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The sum of the 2 square brackets will be the constant adjustment factor to compare sires of breed A and sires of breed X. Let that sum be ADJ(A-X).
In contrast to adjustment factors for the weight traits, each of the 
yy was multiplied by the regression coefficient, which converted the units for yyto the units used for measuring the USMARC progeny.
When comparing EPD of individual sires of breed A and breed X, the EPD was also converted to the USM-ARC scale of measurement by the corresponding regression coefficient.
Similarly, the constant adjustment factor to compare sires of breed B with sires of breed X was
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Comparison of EPD for sire n of breed B with sire p of breed X was
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Comparison of EPD for sire m of breed A and EPD of sire n of breed B yields
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Comparison of EPD for pairs of sires, s and t, for the same breed (e.g., breed A) yields
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The first 2 terms (adjustment factors) cancel. The regression coefficient, bu, is not necessary for the comparison, but does convert the EPD for breed A to the USMARC scale of measurement.
To make a table of adjustment factors, the appropriate regression coefficient (bu or bc) was needed for each breed, including the base breed.
Conversion of adjusted EPD to a measurement scale other than that used at USMARC would be easy. Perhaps the easiest way is to make the comparisons as described above and then divide by bu if adjusted EPD on the ultrasound scale are desired or by bc for adjusted EPD on the traditional carcass scale.
Derivation of an equivalent set of adjustment factors does not require the mean breed association EPD for year yy. For example, examining the terms in the comparison of EPD for breeds A and X by expanding the parts of MARC(A,adj) and MARC(X,adj) yields
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The yyA and yyX terms cancel so that the remaining terms are
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Thus, the adjustment factor, ADJ(A-X) for comparing EPD of breeds A and X is the sum of the terms in the first 2 brackets:
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Similarly, the adjustment factor for breeds B and X is
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This derivation shows that the average EPD for non-parents (year yy) is not needed, but the logic of the adjustment is not as clear.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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are variable and have large standard errors. The estimates for the 2 analyses that included progeny of Angus sires with EPD based on ultrasound or traditional carcass measurement are generally similar, as would be expected, given that the same source of measurement was used for most breeds. What is distinctive is the difference in regression coefficients within the Angus breed of sire. The coefficients for regression of progeny on EPD were similar for MAR (0.90 and 0.82) for the 2 analyses, but were quite different for the other 3 traits, with differences in coefficients of regression exceeding even the large SE (2.89 vs. 1.53 for FAT; 0.95 vs. 1.93 for RIB; and 2.35 vs. 1.98 for retail product).
Pooled estimates of regression coefficients for all breeds with EPD based on traditional carcass measurements and with EPD based on ultrasound measurements are shown in Table 7. The estimates for the 2 analyses including Angus with other breeds having ultrasound EPD and with other breeds having EPD based on traditional carcass measures show similarity for MAR (1.0743 vs. 0.9206), considerable difference for FAT (2.8162 vs. 1.6694) and for RIB (0.8791 vs. 1.6527), and less difference with large SE for RPP (2.3468 vs. 2.0596). Thus, use of different coefficients of regression with EPD based on ultrasound measurements and with EPD based on traditional carcass measurements seems appropriate, especially for FAT and RIB, although for consistency in this project, regression coefficients used for MAR and RPP also were based on type of measurement used for EPD. The regression coefficients indicate that selection based on EPD for carcass traits can be effective in changing carcass traits in steers produced in commercial production systems. The fact that regression coefficients for FAT and RPP were significantly greater than 1.0 was not surprising because bulls and replacement heifers are not fed and finished to the same degree of fatness as steers fed for slaughter. Under these circumstances, the regression coefficients of approximate unity for MAR may suggest a need to improve estimation of breeding values for MAR. Nevertheless, the regression coefficients of near unity for MAR indicate that selection based on EPD calculated primarily from ultrasound measurements on live yearling bulls and heifers developed for breeding can impact profitability of beef production by increasing marbling, which is an important determinant of beef carcass value in domestic and export markets.
Thus far, differences between mean EPD for sires with USMARC progeny and mean nonparent EPD for a given base year (e.g., yy) and regression coefficients for adjusting breed differences at USMARC to a year yy basis have been described and estimated. The last link in the path to across-breed adjustment factors is estimation of breed of sire differences from carcass measurements of progeny at USMARC having sires with breed association EPD. Table 8 lists breed of sire solutions for the 4 carcass traits as differences from Angus for the 2 sets of analyses (differing only by which Angus progeny are included: those with sires having EPD based on ultrasound measurements or those with sires having EPD based on traditional carcass measurements). The model used for the analyses is given as a footnote. The F-statistics for testing whether all breeds of sire are equal are also given, computed from breed of sire solutions after adjusting for all other factors in the model. Differences in estimates are considerable for some pairs of breeds. These differences, however, are not really comparable because samples of sires come from different periods of time and samples of sires among breeds differ even for the same time period.
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where the regression coefficient b (for ultrasound or traditional carcass EPD) adjusts the change to conditions at USMARC.
The steps described earlier to create adjustment factors to allow comparison of EPD of different breeds were followed to obtain Table 9. The adjustment factors are relative to the Angus breed. Because, for this study, Angus EPD were available based on ultrasound or traditional carcass measurements, 2 sets of factors are shown. The 2 sets of factors are somewhat different because of 1) the difference in the source of Angus information (e.g., there were some differences in Angus sired progeny measured at USMARC, which makes across-breed comparisons at USMARC somewhat different), 2) different information included in the Angus EPD (ultrasound and carcass), and 3) the different coefficients of regression for Angus EPD depending on whether the EPD were based on ultrasound or traditional carcass measurements. Generally, the across-breed adjustment factors are similar to the breed of sire solutions because the differences in mean EPD between sires of progeny at USMARC and the mean nonparent EPD for the breed associations were small with few exceptions.
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contains estimates of variance components for carcass measures from the same analyses used to estimate breed of sire effects. The within-breed estimates of sire components for MAR, FAT, RIB, and RPP correspond to heritability estimates of 0.40, 0.57, 0.47, and 0.62, respectively, which indicate selection for these traits should be effective when EPD become generally available. Standard errors for estimates of heritability were 0.08, except 0.16 for RPP.
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Footnotes |
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2 Corresponding author: lvanvleck{at}unlnotes.unl.edu
Received for publication September 26, 2006. Accepted for publication February 24, 2007.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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