1988 Volume 59 Issue 2 Pages 130-135
The genetic improvement of average daily gain (DG) in the performance testing data of Japanese Shorthorn cattle was confirmed and field progeny testing which used steers from farms was carried out to increase the salable meat percentage in a carcass. The breeding values of DG for 13 sires were estimated from the data of 183 male progeny by HENDERSON'S BLUP including a relationship matrix. These progeny data were gathered from performance testing carried out from 1974 to 1985 under the same feeding and management conditions in a test station. The regression coefficient of DG breeding value for the sire's birth year was +10.6g/year (p⟨0.05) and that of the DG phenotypic value for the testing year was +30.1g/year (p⟨0.01).
Carcass data for field progeny testing were collected from 1, 009 steers slaughtered from September 1985 to January 1986. Subcutaneous fat thickness at three positions (FA1-FA3), rib eye area (REA) and marbling score (MBS) were measured at the section between 5th and 6th rib. Means and standard deviations were 25.7±6.5mm for FA1, 21.9±6.2mm for FA2, 16.3±4.9mm for FA3, 40.2±5.1cm2 for REA and 0.33±0.21 for MBS. Measurements of fat thickness and MBS showed positive asymmetrical distribution.
An equation of multiple regression was obtained with the carcass data of 17 steers in order to estimate salable meat weight (SMW) from carcass weight (CW), total fat thickness of FA 1, FA 2 and FA 3 (FATL) and REA.
SMW (kg)=0.492×CW(kg)-0.280×FATL(mm)+0.488×REA(cm2)+33.31 (R=0.95)
When individual values of FATL, REA and 340kg as CW were substituted into this equation, the mean for SMW was 202.6kg and the range was from 186.0 to 218.0kg.
Expected progeny difference (EPD) on the carcass traits of 26 sires was estimated from the data for 237 progeny carcasses by HENDERSON'S BLUP without a relationship matrix. The ranges of EPD were-6.0-+12.1mm for FATL, -3.0-+2.9cm2 for REA and-0.10-+0.21 for MBS. When EPD for the FAIL and REA of each sire and 340kg as CW were substituted into the equation, SMW ranged from 197.9 to 203.9kg.
High heritabilites on FATL, REA and MBS and desirable genetic correlations between them for simultaneous improvement were obtained. Since subcutaneous fat thickness follows positive asymmetrical distribution, a rapid decrease in mean fat thickness can be expected by culling the sires which produce carcasses with extremely thick subcutaneous fat in their progeny. The reduction of fat thickness also increase the salable meat percentage in a carcass.
