Genetic and phenotypic relationships between individual subcutaneous backfat layers and percentage of longissimus intramuscular fat in Duroc swine

Abstract

Progeny (n = 589) of randomly mated Duroc pigs were used to determine the genetic and phenotypic relationships between individual s.c. backfat layers and i.m. fat percent (IMF) of the longissimus. Five days before slaughter, cross-sectional ultrasound images were collected at the 10th rib by a National Swine Improvement Federation-certified ultrasound technician using an ultrasound machine (Aloka 500 SSD) fitted with a 12-cm linear array transducer. Off-midline backfat (SBF) and loin muscle area (SLMA) were measured. Individual s.c. backfat layers were measured at the same location: outer (OBF), middle (MBF), and inner (IBF). Off-midline backfat (CBF) and loin muscle area (CLMA) were measured on the carcass 24 h postmortem. A slice from the 10th rib of the loin muscle was obtained for determination of IMF. Heritability estimates and genetic correlations were calculated fitting all possible two-trait animal models in MATVEC (Wang et al., 2003). The heritabilities for OBF, MBF, IBF, CBF, SBF, and IMF were 0.63, 0.45, 0.53, 0.48, 0.44, and 0.69, respectively. The genetic correlations of OBF, MBF, and IBF with IMF were 0.36, 0.16, and 0.28, respectively, and the genetic correlations of CBF and SBF with IMF were 0.25 and 0.27, respectively. Genetic correlations between OBF and MBF, OBF and IBF, and MBF and IBF were 0.43, 0.45, and 0.67, respectively. Results demonstrate that individual backfat layers are highly heritable, of similar magnitude to total backfat, and have similar genetic correlations with IMF. Individual backfat layers could become candidate traits for implementation into a multiple-trait genetic evaluation to improve IMF, while minimizing the detrimental effect on total backfat depth.

Phenotypic Correlations of Backfat Thickness with Meatiness Traits, Intramuscular Fat, <i>Longissimus</i> Muscle Cholesterol and Fatty Acid Composition in Pigs

“…Bahelka et al (2007) found that the correlation between ABF and LMP was −0.50, which is substantially smaller than in our study (−0.69). Also, the phenotypic correlations between the three individual subcutaneous backfat layers and LMA reported by Newcom et al (2005) were considerably smaller (−0.18 to −0.23) than in the present study.…”

“…Correlations of five individual subcutaneous backfat thickness and ABF with IMF were 0.32 to 0.50 (P <0.01), respectively. Newcom et al (2005) and Yang et al (2010) reported smaller correlations between the individual subcutaneous backfat layers and IMF (0.26 to 0.34). The value for the correlation between ABF and IMF reported by Bahelka et al (2007) (0.33) is also substantially smaller than that observed in the present study (0.49).…”

“…Substantially greater correlations of individual backfat layers at the 10th rib (outer, middle, and inner) with IMF for Duroc-sired pigs (0.66, 0.76 and 0.71, respectively) were reported by Eggert (1998). Newcom et al (2005) suggested that the contradictory results may be because of differences in the populations of pigs that were studied (pure bred vs. cross bred pigs), measurement methods and the mean values of these traits.…”

“…The genetic and phenotypic correlations between subcutaneous backfat depth and IMF content show moderate positive values (Newcom et al, 2005). This indicates that reductions in carcass fatness are likely to be accompanied by lower intramuscular fat levels in meat.…”

Intramuscular fat content in meat-producing animals: development, genetic and nutritional control, and identification of putative markers

“…Genetic selection Heritability of IMF content is relatively high (h 2 5 0.26 to 0.86, mean of 0.50) in pigs (Sellier, 1998;Newcom et al, 2005) and cattle as well as in fish (0.2 to 0.5; Rye and Gjerde, 1996). IMF content shows a moderate but positive genetic correlation with carcass fatness (r G close to 0.30, Sellier, 1998).…”