Johnson Z B, Nugent R A
Department of Animal Science, University of Arkansas, Fayetteville 72701, USA.
J Anim Sci. 2003 Aug;81(8):1943-9. doi: 10.2527/2003.8181943x.
The objective of this study was to estimate heritability for body length (LEN) at the end of performance testing and to estimate genetic correlations with backfat (BF) thickness and loin muscle area (LMA) in Landrace, Yorkshire, Duroc, and Hampshire breeds of swine. Also examined were two measures of body density involving body length and weight and their relationships to backfat and loin muscle area. Data consisted of performance test records collected in a commercial swine operation from 1992 to 1999. Boars from 60% of the litters were culled at weaning based on a maternal breeding value of the dam. Remaining boars and all females were grown to 100 d of age (15,594, 55,497, 12,267, and 9,782 Landrace, Yorkshire, Duroc, and Hampshire pigs, respectively). At this time, all pigs were weighed (WT100) and selected for performance testing based on a combination of maternal and performance indexes, which differed by breed. All pigs were weighed at the end of the 77 d performance test (WT177) when BF, LMA, and LEN were measured. Two measures of body density involving length were calculated: Body mass index (BMI) = WT177/LEN2 and body density (DENSITY) = WT177/LEN. For each breed, genetic parameters were estimated using an animal model with random litter effects and multiple-trait REML procedures. A series of three-trait models including WT100 and combinations of two other traits in each analysis was conducted. Fixed effects included contemporary group and age as a covariate. Average estimates of heritability were 0.16 to 0.32 for LEN (unadjusted for WT177), 0.12 to 0.26 for LEN (adjusted for WT177), 0.23 to 0.33 for DENSITY, and 0.16 to 0.25 for BMI. Genetic correlations between LEN and LMA were low. Genetic correlations between LEN (unadjusted for WT177) and BF were 0.10 to 0.41. Adjusting LEN for WT177 gave correlations of 0.11 for Landrace and Hampshire and negative correlations (-0.06 and -0.19, respectively) for Yorkshire and Duroc. Genetic correlations between LMA and DENSITY and between LMA and BMI were comparable and ranged from 0.44 to 0.54. Genetic correlations between BF and DENSITY were slightly higher (0.53 to 0.68) than those between BF and BMI (0.37 to 0.67). In these data, not much relationship between BF and body length at a constant weight and age was found. There was a negative relationship between LMA and LEN at a constant weight and age, implying that longer pigs had smaller LMA.
本研究的目的是估计长白猪、大白猪、杜洛克猪和汉普夏猪在性能测试结束时体长（LEN）的遗传力，并估计其与背膘（BF）厚度和腰肌面积（LMA）的遗传相关性。还研究了涉及体长和体重的两种体密度测量方法及其与背膘和腰肌面积的关系。数据包括1992年至1999年在一家商业养猪场收集的性能测试记录。60%窝中的公猪在断奶时根据母猪的母本育种值被淘汰。其余公猪和所有母猪饲养至100日龄（分别为15594头长白猪、55497头大白猪、12267头杜洛克猪和9782头汉普夏猪）。此时，所有猪均称重（WT100），并根据母本和性能指标的组合进行性能测试选择，不同品种的指标有所不同。所有猪在77天性能测试结束时称重（WT177），同时测量BF、LMA和LEN。计算了两种涉及体长的体密度测量值：体重指数（BMI）=WT177/LEN²，体密度（DENSITY）=WT177/LEN。对于每个品种，使用具有随机窝效应的动物模型和多性状REML程序估计遗传参数。进行了一系列三性状模型分析，每次分析包括WT100以及其他两个性状的组合。固定效应包括当代组和作为协变量的年龄。LEN的遗传力平均估计值（未根据WT177调整）为0.16至0.32，（根据WT177调整）为0.12至0.26，DENSITY为0.23至0.33，BMI为0.16至0.25。LEN与LMA之间的遗传相关性较低。LEN（未根据WT177调整）与BF之间的遗传相关性为0.10至0.41。根据WT177调整LEN后，长白猪和汉普夏猪的相关性为0.11，大白猪和杜洛克猪的相关性为负（分别为-0.06和-0.19）。LMA与DENSITY之间以及LMA与BMI之间的遗传相关性相当，范围为0.44至0.54。BF与DENSITY之间的遗传相关性略高于BF与BMI之间的遗传相关性（0.53至0.68比0.37至0.67）。在这些数据中，未发现恒定体重和年龄下BF与体长之间有太多关系。在恒定体重和年龄下，LMA与LEN之间存在负相关，这意味着体长较长的猪LMA较小。
