Investigation on an Equation for Converting Marbling Score Used in the Old Beef Carcass Grading Standards into Beef Marbling Standard

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  • 旧牛枝肉取引規格における脂肪交雑評点のBMSへの変換式に関する検討
  • キュウ ウシ エダニク トリヒキ キカク ニ オケル シボウ コウザツ ヒョウ

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Abstract

This study was conducted to convert marbling score used in the Old Beef Carcass Grading Standards before 1987 into beef marbling standard (BMS) used in the New Standards which have been adopted since 1988, in order to be added as BMS records for the genetic evaluation of sires and cows. [Analysis-1] Such conversion equations were searched using records of 4, 386 fattened Japanese Black steers obtained from 1988 to 1990. Each steer had two scores, i. e., BMS which was evaluated by the official grader of Japan Meat Grading Association, and marbling score evaluated by a technician who skilled in the old system. Polynomial regression analysis was done to obtain a conversion equation every year. The mean of BMS was significantly higher than that of marbling score (P<0.01). The variance of BMS did not show significant difference among years, but that of the marbling score showed significant difference (P<0.01) between 1988 and 1990. BMS and marbling score did not seem to show linear relationship, but BMS was highly evaluated as compared to marbling score. When the 1988's conversion equation was used, the variance of the converted score became closer to that of BMS, but not significant. [Analysis-2] Marbling score records of 6, 848 fattened Japanese Black steers collected from 1981 to 1987 were converted by the conversion equations obtained. BMS records of 1, 784 steers of the same breed were also collected from 1988 to 1992. Sires were evaluated by BLUP with a maternal grandsire model, using the data for BMS, marbling score, and the converted score. The correlation coefficient obtained between expected progeny differences (EPDs) for BMS and the converted score by 1988's conversion equation was higher than the other converted scores, but not significant. Therefore these results suggest that the 1988's conversion equation is the best, but the effect of conversion from marbling score into BMS by the equation on sire evaluation seem to be small.

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