Genetic parameters of compositional traits of two fat depots (backfat and leaf fat) and Longissimus dorsi muscle in pigs

Genetic parameters of chemical composition traits of backfat (BF), leaf fat (LF) and Longissimus dorsi muscle (LD) were estimated in centrally-tested Large White and French Landrace pigs. Pigs were fed ad libitum with barley, wheat and soja regimes and slaughtered at around 100 kg liveweight.Samples of BF (both inner and outer layers) and LD were removed from the carcass at the 13th -14th rib level. Data were recorded on 948-959 pigs for compositional traits of BF and lipid and water content of LD, 209-215 pigs for compositional traits of LF and 297 pigs for fatty acid composition of LD lipids. Records on performance traits of 2483 contemporary pigs were also taken into account. Genetic parameters were estimated by means of a REML-animal model procedure. Heritability estimates for compositional traits of BF, LF and LD range from medium to high : e.g. 0.26 ± 0.10, 0.65 ± 0.14 and 0.46 ± 0.13 for the total lipid content of BF, LF and LD, respectively, 0.44 ± 0.11 and 0.68 ± 0.13 for the fat firmness index of BF and LF (ratio of the sum C16:0 + C18:0 over the sum C16:1 + C18:1 + C18:2), respectively, and 0.29 ± 0.10 for the coefficient of unsaturation of total lipids of LD (average number of double bonds in unsaturated fatty acids). A positive genetic correlation (rA = 0.54 ± 0.04) was found between the fat firmness indexes of BF and LF. The genetic correlations between average daily gain (ADG) and compositional traits of the three tissues are of small or very small magnitude. However, a trend toward a positive genetic correlation (rA = 0.20 ± 0.10) between ADG and the fat firmness index of BF is found. The phenotypic and genetic correlations of compositional traits of the three tissues with carcass lean percentage are much more pronounced, with absolute values generally ranging from 0.3 to 0.6. A higher carcass lean percentage is genetically associated with a lower lipid content of the three tissues (e.g., rA = -0.66 ± 0.14 and rA = -0.44 ± 0.08 for BF and LD, respectively) and with a higher coefficient of unsaturation of lipids (rA = 0.63 ± 0.06, rA = 0.50 ± 0.07 and rA = 0.27 ± 0.03 for BF, LF and LD, respectively). The expected correlated responses to the current selection for increasing both ADG and lean percentage are assessed through the estimated genetic correlations of the compositional traits of the three tissues studied with an approximate measurement of lean tissue growth rate.