Effect of large-scale family selection on body weight of Litopenaeus vannamei by computer simulation

To test change of genetic gain for body weight, we designed selection schemes which included 10 levels of family number (100–1 000) and 11 levels of family size (100–5 000). By using computer simulation technology, breeding values and inbreeding coefficients of the nucleus breeding and multiplication populations from different simulation schemes were compared after performing between-family (percentage retained: 50%) and within-family selections (1 male and 2 females selected per family) of 19 generations. The mean and standard deviation for body weight were set at 18.41 g and 3.24 g, respectively. Three levels of heritability (0.1, 0.35, 0.6) were included in the simulation. This study will provide basic parameters to optimize the selective breeding program based on large-scale families. Compared with the control scheme with parameters including 100 families, 100 individuals tested per family, and heritability of 0.35, breeding values of body weight for the nucleus population increased by 48% (62.75–92.87 g) with the increase of family size (100 to 5 000) due to higher selection intensity, but increasing extent presented downward trend (100–2 500: 40.60%; 2 500–5 000: 7.40%); standard deviation of breeding values decreased by 2.90% (1.38–1.34 g) when family size increased. Breeding values of body weight for the nucleus breeding population increased by 1.88% (62.75–63.93 g) and the standard deviation of breeding value increased by 4.35% when increasing family number due to low selection intensity. Breeding values of harvest weight for the multiplication population had the same increase trend with those of the nucleus population, but increasing extent was more than that in the nucleus population on family level (63.63–65.48 g, 2.91%). Inbreeding coefficients of the nucleus breeding population decreased by 90.32% (0.093–0.009) with increase of family number, but decline rate presented downward trend (100–500: 79.57%; 500–1 000: 10.75%). It did not affect inbreeding level of the nucleus population when increasing family size. In summary, it will further improve the genetic gain for body weight of nucleus breeding population and multiplication population if there is increase of family size. The inbreeding level (inbreeding rate 0.25%) is below the safety threshold (<0.5%) when the breeding population consists of more than 200 families. Therefore, the main purpose of increasing the number of family is to reserve more genetic variation and establish multiple breeding lines for different traits.