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

在以往的研究中，发现了一种优良的荷斯坦种公牛（A），其后代胴体大理石花纹程度很高。另外，还获得了父亲（B）和母亲（C）的半同胞B种公牛的精液，并将这3种公牛与荷斯坦母牛交配，获得它们的后代。每头公牛犊3头，随机分为3个育肥组，每组10头。1.试验牛均在650kg左右恒重、21月龄左右进行屠宰，胴体重分别为360、376、379kg。3个组的平均可分离脂肪率分别为35.6、31.3和32.3，其中A组的后代可分离脂肪率较高。从第5胸椎到第6腰椎共15个切片的大理石纹评分平均值分别为2.5、2.0、2.0。在大理石纹程度上还注意到，在前部的高度大理石纹在后部，例如后部胸椎和腰椎部分没有保持。在实验2中，公畜A的4头阉牛在650和750 kg体重时完成。750 kg B.W.用图像分析仪测定肋眼面积和肋切面表面瘦肉面积比例，作为客观评定胴体性状的第一步。观察到两个测量值之间具有相当高的相关性。

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.