The association of IGF2 with productive traits of pigs of Large White breed in the aspect of sexual differentiation

Marker-assisted selection is an attractive way to improve the economically important traits in domestic animals and particularly in pigs. Insulin-like growth factor 2 (IGF2) is one of the potentially important genetic marker for growth and carcass traits of pigs. The objective of our work was to study G3072A polymorphism of IGF2 gene in different pig breeds and to evaluate the effect of boar genotypes on productive traits of their offspring of different sexes. IGF2 polymorphism was studied in seven pig breeds including large white and their close related breeds Yorkshire and Edelswine (LW, n = 1247), Landrace (L, n = 934), Duroc (D, n = 642), Pietrain (P, n = 87), Belorussian meat (BM, n = 37), Liven (LIV, n = 54), Estonian beckon (EB, n = 10), one synthetic line Body (BD, n = 138) and one terminal cross (TM, n = 66). Association studies were performed using data records of 5908 offspring (including 5015 gilts and 893 young boars) produced from twenty LW boars with known genotype for IGF2. The following productive traits were evaluated: body weight at the end of growing period (BW, kg), daily gain during entire growing period (DG, g), daily gain during early period from birth to 76.41±0.04 days (DG1, g), daily gain during late period from 76.41±0.04 to 170.23±0.05 (DG2, g); the age at 100 kg (AGE100kg, days), average actual back fat thickness measured in four points at the end of growing period (BF, mm) and average back fat thickness calculated for the 100 kg body weight (BF100kg, mm). Significantly higher frequencies of the potentially «desired» A allele and AA genotype were observed in BD (0.986 and 0.971, respectively), ТМ (0.977 and 0.955), P (0.966 and 0.931) and D (0.960 and 0.921). LW pigs were characterized by the intermediate values of allele A (0.664) and genotype AA frequencies (0.532). In EB, BM and L the frequencies of A allele and AA genotype varied from 0.250 to 0.363 and from 0.100 to 0.243, respectively. We did not identify A allele in local Russian LIV pig breed. Association studies showed high-significant tendency to increase of BW, DG1, DG2, DG, BF and BF100kg values and to decrease of AGE100kg values of both gilts and boars at the order of genotypes GG → AG → AA. Calculations performed with additive-dominance model and two-way analysis of variance (ANOVA) showed the faster increasing (decreasing) above-mentioned traits in order of genotypes GG → AG → AA in young boars comparing to gilts. Principal component (PC) analysis showed that first two PCs (PC1 and PC2) determine 76.23 % of variability of the initial matrix for young boars and 82.49 % for gilts. PC1 is highly associated with daily gains during the late growing period (for DG2: r = 0.501 for young boars and 0.896 for gilts) and for the entire growing period (for DG: r = 0.923 and 0.929), whereas PC2 is associated with the daily gains during early growing period (for DG1: r = 0.709 and 0.769). The additive (A) and dominant (D) components of the variability and effects of allele substitution calculated for PC1 were similar for both sexes: А = 0.290, p < 0.001; D = 0.064 — in gilts and А = 0.351, p < 0.001; D = 0.040 — in young boars. We received significant values for PC2 in young boars only for dominant component (А = 0.085; D = 0.177, p < 0.05), whereas in gilts it was only for additive component (А = 0.094, p < 0.001; D = 0.031). The quantitative effects of IGF2 genotypes growing performance on the growth and carcass traits of pigs, and sex-dependent effect of marker genotypes on growing performance of pigs among growing periods should be taken in a point for development of programs of markerassisted selection utilizing IGF2.