摘要
本研究以金华加华种猪有限公司核心群内的加系大约克为试验对象，按体重分为25、50、75公斤三个阶段，对各阶段的试验猪同时用A超(RenCo)和B超(Ami900)在倒数3-4肋间和腰荐结合处离背中线4-6厘米处，测定背膘厚(B超还在P1点测定眼肌厚)，测定时记录其实测体重和测定日期。对25公斤阶段的仔猪，每周称一次体重，直到体重达到50公斤，以绘制生长曲线。试验结束时，选19头上市阉猪先用A超和B超活体测定背膘厚，再用游标卡尺在相同位点测定实际膘厚。所得数据用SAS软件进行平均值计算、方差分析、回归分析及遗传参数的估计。结果表明：所测膘厚在不同测定位点、性别间存在差异，总体情况为P1点处膘厚薄于P2点膘厚；公猪背膘薄于母猪背膘。A超和B超在两个位点所测膘厚对各自的体重存在线性回归现象，并得出A超在P2点膘厚与用B超在N点所测膘厚的回归方程：
母猪：B超P1点膘厚=6.8503+0.6105A超P2点膘厚；公猪：B超P1点膘厚=2.3447+1.0497A超P2点膘厚，回归模型达到极显著水平(p＜0.01)。
相关分析表明：在25公斤阶段，两个位点的背膘厚的A超测定值之间的表型相关为0.574，B超所测的两个位点的背膘厚之间的表型相关为0.579，都达到极显著(p＜0.01)。50公斤阶段实测体重与用A超P2点膘厚的表型相关为0.5628(p＜0.01)，遗传相关为0.0994；与B超P1点膘厚的表型相关为0.2784(p＜0.01)，遗传相关为0.2302，75公斤阶段体重与B超P1点膘厚之间的表型相关为0.3239(p＜0.01)；A超P1点膘厚与B超在两个位点处背膘的表型相关为0.5957和0.335，遗传相关为0.4346和0.74。在50和75公斤阶段B超P1点膘厚之间的表型相关为0.1859，遗传相关为0.247。
屠宰分析表明：A超P1点膘厚的平均值为13.94±3.32mm，P2点膘厚为14.88±2.93mm；B超所测膘厚分别为15.59±3.02mm和20.79±2.57mm；胴体实际膘厚分别为21.35±2.93mm和24.29±5.01mm。A超P1点与胴体实际背膘厚间的表型相关为0.7007，达到极显著(p＜0.01)；B超P1点背膘与胴体实际背膘间的表型相关为0.8316达到极显著(p＜0.01)。B超的准确性高于A超。
在50公斤体重阶段，A超在两个位点所测膘厚的遗传力分别为0.366和0.691，B超分别为0.634和0.549；在75公斤阶段，A超在两个位点所测膘厚的h~2分别为0.381和0.695，B超分别为0.641和0.564。
Probing test in Jinhua nucleus herd of Canadian Yorkshire with A mode (Renco, American)and B mode (Ami900,Canada) ultrasonic instrument simultaneity on last 3/4 rib (PI) and the joint-point of the thoracic vertebra and lumber vertebra (P2) off the mid-line 4-6cm when the pigs in their 25,50,75Kg body weight. The loin depth on the last 3/4 rib off the mid-line 4-6cm also was probed by B mode . When the pig's body weight between 25-50 kg , weighted them every week. To probe the 19 barrows (at 95.18 Kg body weight) with A mode and B mode on the two sites and after slaughter, using the caliper testing the backfat thickness on the same sites. SAS program was applied to analyze all the data to get the regression equations and to estimate the genetic parameters.
The results indicated that the probe site and sex had significant effect on the backfat thickness . The PI backfat thickness thinner than P2's, the boar's thinner than the gilt's.
The backfat probed by A mode and B mode existed significant linear regression. The regression equation was: the backfat thickness on PI by B mode =6.1657+1.0497 (the backfat thickness on P2 by A mode-4.07) (for the boars); the backfat thickness on Plby B mode =9.0723+0.6105 (the backfat thickness on P2by A mode -3.64) (for the gilts).
The analyze of correlation shows that in the period of 25Kg live weight ,the phenotype correlation for the two sites by A mode and B mode were 0.574 and 0.579,respectively. The phenotype and genetic correlation between the 50Kg live weight and the backfat on P2 by A mode were 0.5628 and 0.0984, respectively; the phenotype and genetic correlation between the 50Kg live weight and the backfat on PI by B mode were 0.2784 and 0.2302, respectively. The phenotype and genetic correlation between the 75Kg live weight and the backfat on PI by B mode were 0.3239 and -0.3265, respectively. The phenotype and genetic correlation between the backfat on Plby A mode and the backfat on site land P2 by B mode were 0.5957and 0.335, 0.4346 and 0.74, respectively. The phenotype and genetic correlation between the backfat on Plby B mode in 50Kg live weight and in 75Kg live weight were 0.1859 and 0.247, respectively.
The analyze of carcass shows that the means of the backfat on Plby A mode was 13.94?.32mm,on P2was 14.88?.93mm; the means of the backfat on Plby B mode was
43
15.59?.02mm, on P2were 20.79?.57mm; the means of the carcass backfat on the two sites were 21.35?.93mm and 24.29?.01mm, respectively. The phenotype correlation between the backfat on PI by A mode and the carcass's actual backfat was 0.7007, the phenotype correlation between the backfat on Plby B mode and the carcass's actual backfat was 0.8316.The accuracy of B mode is higher than A mode's.
The heritability of the backfat on the two sites by A mode in 50Kg live weight were 0.366 and 0.691,respectively, for the B mode were 0.634 and 0.549, respectively. In the period of the 75Kg live weight, the heritability of the backfat on the two sites by A mode were 0.381 and 0.695, for the B mode were 0.641 and 0.564, respectively.
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