Studies on the genetic mechanism of the marbling trait in carcasses of dairy steers.

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In the previous studies, an outstanding Holstein sire(A),Which was characterized with very high drgree of marbling in his progeny steer carcasses,was detected. In addition,semen of father's(B) and mother's sides(C) half-sib sires were obtained.These 3 sires were mated with Holstein cows to get their progeny. Of each sire, 3 steer calves were alloted to 3 fattening groups in the Exp. 1. All steers were slaughted at about constant body weight 650kg and at closely 21 months of age.The carcass weight of the 3 group were 360,376,379kg,respectively. the percentage of separable fat were 35.6,31.3 and 32.3 in average of 3 groups,showing higher percentage in the progeny group of sire A. The average marbling scores,calculated from scores recorded from the 5th thoracic to the 6th lumber vertebrae, i.e. 15 sections in total, were 2.5, 2.0, 2.0 respectively. It was also noticed on the degree of marbling that high degree of marbling at the fore section did not maintained at the rear sections,such as rear thoracic and lumber vertebrae sections.In the Exp.2., 4 steers of sire A were finished at 650 and 750kg body weight. Two steers slaughterd at 750kg B.W. spent about additional 8 months,with 5% increse in separable fat and without any level-up in the degree of marbling.It was estimated that the superiority of sire A must be brought about additive effect of father's and mother's sides.As the first step of objective evaluation on carcass traits,an image-analizer were applied for measurements on rib-eye area and the proportion of lean meat area at the surface of rib section. Considerably high correlations between two measurements were observed.