Response to selection for decreased backfat thickness at restrained intramuscular fat content in Duroc pigs1

Abstract

Intramuscular fat (IMF) content is a relevant trait for the pig industry and consumers. However, selection for IMF has the undesired correlated effect of decreasing lean growth. A selection experiment was performed to investigate the effects of selection against backfat thickness (BT) at restrained IMF. Barrows from a purebred Duroc line were allocated into a selected (n = 165) or a control (n = 185) group based on their litter predicted EBV. Litters in the selected group were selected against BT at 180 d at restrained IMF in gluteus medius (GM) whereas those in the control group were chosen randomly. Realized selection intensities and genetic responses for BT, IMF in GM, and BW were estimated using a 3-trait multivariate animal mixed model under a Bayesian setting. Correlated responses for other traits were estimated similarly but using a 4-trait model, where other traits were added to the previous 3-trait model 1 at a time. Selected pigs had less BT than control pigs [-1.22 mm, with highest posterior density interval at 95% (HPD95; -2.47, -0.75)] with restrained decrease in IMF, both in GM [-0.16%; HPD95 (-0.36, +0.05)] and in LM [-0.15%; HPD95 (-0.37, +0.09)]. However, the realized selection intensity for IMF in GM denotes that the restriction on IMF was incomplete [-0.18; HPD95 (-0.36, +0.02)]. Selection decreased BW [-1.64 kg; HPD95 (-2.47, -0.75)] but increased carcass lean weight [+0.66 kg; HPD95 (+0.14, +1.22)], indicating that the response in BT offsets the unfavorable correlated response in BW. Selected pigs were shorter [-0.50 cm; HPD95 (-0.81, -0.20)] but with similar ham weight and loin depth. These results provide evidence that lean weight can be improved restraining the genetic change in IMF. However, they also stress that a complete restriction on IMF is difficult to achieve unless selection is practiced on a big population where IMF is accurately predicted.

Slaughter weight rather than sex affects carcass cuts and tissue composition of Bisaro pigs

“…Hence, larger maturing of Bisaro pigs does not seem to increase their intramuscular fat deposition. In some purebred Duroc lines following a strict breeding programme to improve marbling without hampering their subcutaneous fat content (Ros-Freixedes, Reixach, Bosch, Tor, & Estany, 2013), Álvarez-Rodríguez et al (2018 found that an increase in slaughter weight up to 139 kg increased their intramuscular fat content in loins. On the contrary, this was not observed in crossbreds, which did not increased their intramuscular fat content in loins by increasing their slaughter weight from 69 to 120 kg (Duroc sires mated to Large-White × Landrace dams) (D'Souza et al, 2004), or from 116 to 133 kg (Pietrain × Large White sires mated to Landrace × Large White dams) (Latorre, Lázaro, Valencia, Medel, & Mateos, 2004).…”

Divergent selection on intramuscular fat in rabbits: Responses to selection and genetic parameters1

“…Other experiments of selection for IMF also showed positive correlated responses in the fat content of the carcass (Schwab et al [2009], in pigs, and Zhao et al [2007], in chickens). A selection experiment for low backfat thickness restraining IMF was performed in pigs for 1 generation (Ros-Freixedes et al, 2013), reducing backfat thickness with a slight reduction in IMF. Reference carcass weight was slightly greater in the high-IMF line than in the low-IMF line, but the phenotypic difference between lines was not relevant (P R = 0.63; Table 2).…”

Genetic Marker Discovery in Complex Traits: A Field Example on Fat Content and Composition in Pigs

“…Results indicated that they were able to increase IMF while constraining, but not reducing, backfat thickness. The experiment in Ros-Freixedes et al [28] was designed to test the opposite, whether backfat thickness can be reduced at restrained IMF, thereby assuming that IMF was already at the optimum value. In this experiment, consisting of three one-generation selection rounds on the mid-parent predicted breeding value for backfat thickness and IMF, selected pigs had greater lean weight but less IMF, although the decrease in IMF was half of the expected if it had not been restricted.…”