Genetic study of litter size and litter uniformity in Landrace pigs

ABSTRACT We aimed to estimate litter size and litter uniformity genetic parameters and genetic trends of Landrace pigs at birth and at three weeks by using multitrait analyses for 2,787 litters. The following litter traits were evaluated: number of piglets born alive (NBA), within-litter weight mean at birth (MBW), within-litter weight standard deviation at birth (SDB), within-litter weight coefficient of variation at birth (CVB), number of piglets at three weeks (NT), within-litter weight mean at three weeks (MT), within-litter weight standard deviation at three weeks (SDT), and within-litter weight coefficient of variation at three weeks (CVT). Heritability estimates for NBA, MBW, SDB, and CVB were 0.09±0.04, 0.31±0.08, 0.01±0.04, and 0.07±0.05, respectively, greater than those obtained at three weeks (0.06±0.04, 0.10±0.06, 0.01±0.04, and 0.02±0.04 for NT, MT, SDT, and CVT, respectively). The genetic correlations between NBA and MBW and between MBW and CVB (−0.73±0.20 and −0.93±0.21, respectively) were of moderate to high magnitudes, as well as the genetic correlations between CVT and SDT (0.85±0.39). Genetic correlations between MBW and MT, SDB and SDT, CVB and CVT, and NBA and NT were 0.73±0.16, 0.69±0.54, 0.36±0.80, and 0.95±0.06, respectively. The genetic trends were linear for NBA and CVB and quadratic for MBW and SDB, whereas for all traits at three weeks, they were close to zero. Within-litter weight coefficient of variation (CV) may be the most appropriate variation measure for application in breeding programs, especially at birth, due to its greater heritability estimate and high and negative genetic correlation with MBW. The genetic trends show that NT does not follow the increase in NBA, emphasizing the need to review the breeding goals.

摘要 本研究旨在基于2787窝长白猪（Landrace pigs）仔猪数据开展多性状分析，估算其分娩时及出生后3周的窝产仔数与窝产仔均匀度的遗传参数及遗传趋势。本次评估的窝产性状包括：活产仔猪数（number of piglets born alive, NBA）、出生时窝内平均体重（within-litter weight mean at birth, MBW）、出生时窝内体重标准差（within-litter weight standard deviation at birth, SDB）、出生时窝内体重变异系数（within-litter weight coefficient of variation at birth, CVB）、3周龄仔猪数（number of piglets at three weeks, NT）、3周龄时窝内平均体重（within-litter weight mean at three weeks, MT）、3周龄时窝内体重标准差（within-litter weight standard deviation at three weeks, SDT）以及3周龄时窝内体重变异系数（within-litter weight coefficient of variation at three weeks, CVT）。活产仔猪数、出生窝内平均体重、出生窝内体重标准差及出生窝内体重变异系数的遗传力估计值分别为0.09±0.04、0.31±0.08、0.01±0.04及0.07±0.05，均高于3周龄对应性状的遗传力估计值（3周龄仔猪数、3周龄窝内平均体重、3周龄窝内体重标准差及3周龄窝内体重变异系数的遗传力分别为0.06±0.04、0.10±0.06、0.01±0.04及0.02±0.04）。活产仔猪数与出生窝内平均体重、出生窝内平均体重与出生窝内体重变异系数间的遗传相关分别为−0.73±0.20与−0.93±0.21，属于中等到高强度的遗传相关；3周龄窝内体重变异系数与3周龄窝内体重标准差间的遗传相关为0.85±0.39，同样具有较高强度。此外，出生窝内平均体重与3周龄窝内平均体重、出生窝内体重标准差与3周龄窝内体重标准差、出生窝内体重变异系数与3周龄窝内体重变异系数以及活产仔猪数与3周龄仔猪数间的遗传相关分别为0.73±0.16、0.69±0.54、0.36±0.80及0.95±0.06。遗传趋势方面，活产仔猪数与出生窝内体重变异系数呈线性变化趋势，出生窝内平均体重与出生窝内体重标准差呈二次变化趋势；而3周龄所有性状的遗传趋势均接近零。窝内体重变异系数（coefficient of variation, CV）或是育种计划中最适宜的变异度衡量指标，尤其是在分娩阶段，这得益于其更高的遗传力估计值，以及与出生窝内平均体重间较强的负向遗传相关。本研究的遗传趋势结果显示，3周龄仔猪数并未随活产仔猪数同步增长，凸显出重新审视育种目标的必要性。