An evaluation of porcine longissimus myoglobin concentration was conducted to determine breed and gender differences for myoglobin content, estimate genetic parameters for myoglobin concentration, and determine the relationship between myoglobin content and objective measures of muscle color. Data from centrally tested (n = 255), purebred Yorkshire (42), Duroc (61), Hampshire (17), Chester White (28), Berkshire (67), Poland China (28), and Landrace (12) barrows and gilts from the 1999 National Barrow Show Sire Progeny Test were used. Ultimate pH and Hunter L were measured on the 10th-rib face 24 h postmortem. A section of bone-in loin containing the 10th rib was taken to the Iowa State University Meats Laboratory. At 48 h postmortem, Hunter L, CIE L*, a*, and b*, Japanese color score, and water-holding capacity were measured on the face of the 10th-rib loin chop. A slice from the 10th-rib loin section was evaluated for percentage of i.m. fat. The resulting loin chop was used for the determination of soluble myoglobin concentration (mg/g, wet basis). Chester White, Hampshire, and Duroc pigs had the highest (P < 0.05) myoglobin concentration (0.92, 0.95, and 0.85 mg/g, respectively), whereas Landrace had the lowest (0.62 mg/g; P < 0.05). No gender differences were detected for myoglobin concentration. The heritability estimate for soluble myoglobin concentration was 0.27. Residual correlations between soluble myoglobin and CIE L*, a*, b*, Hunter L (24 h), Hunter L (48 h), and Japanese color score were -0.17, 0.23, -0.15, -0.16, -0.13, and 0.13, respectively. These correlations are low but in the desired direction. The residual correlation between soluble myoglobin and intramuscular fat percent was 0.18. Results show that myoglobin concentration has a moderate heritability and could be used in a selection program to make pork loins darker in color.

Purebred Durocs (n = 207) were used to develop a model to predict loin intramuscular fat percentage (PIMF) of the longissimus muscle in live pigs. A minimum of four longitudinal, real-time ultrasound images were collected 7 cm off-midline across the 10th to the 13th ribs on the live animal. A trained technician used texture analysis software to interpret the images and produce 10 image parameters. Backfat and loin muscle area were measured from a cross-sectional image at the 10th rib. After harvest, a slice from the 10th to the 11h rib loin interface was used to determine carcass loin intramuscular fat percentage (CIMF). The model to predict loin intramuscular fat percentage was developed using linear regression analysis with CIMF as the dependent variable. Initial independent variables were off-test weight, live animal ultrasonic 10th rib backfat and loin muscle area, and the 10 image parameters. Independent variables were removed individually until all variables remaining were significant (P < 0.05). The final prediction model included live animal ultrasound backfat and five image parameters. The multiple coefficient of determination and root mean square error for the prediction model were 0.32 and 1.02%, respectively. An independent data set of Duroc (n = 331) and Yorkshire (n = 288) pigs from two replications of the National Pork Board's Genetics of Lean Efficiency Project were used for model validation. Results showed the Duroc pigs provided the beat validation of the model. The product moment correlation and rank correlation coefficients between PIMF and CIMF were 0.60 and 0.56, respectively, in the Duroc population. Results show real-time ultrasound image analysis can be used to predict intramuscular fat percentage in live swine.

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.

The objective was to estimate correlations of gilt estrus, puberty, growth, composition, and structural conformation traits with first-litter reproductive measures. Four groups of gilts (n = 1,225; Genetic Improvement Services of NC, Newton Grove, NC) entered the NC Swine Evaluation Station (Clayton, NC) averaging 162 d of age and were observed daily for symptoms of estrus. Once symptoms of first estrus were observed in 70% of gilts, recording of symptoms of estrus in all gilts occurred every 12 h for 30 d, utilizing fence-line boar contact. Subjective estrous traits were maximum and total strength of standing reflex, as observed with and without the presence of a boar, and strength of vulva reddening and swelling. Objective estrous traits consisted of vulva redness, vulva width, length of estrus, and age at puberty. Growth and composition traits included BW at puberty, days to 114 kg, and 10th rib backfat and LM area at 114 kg and at puberty. Subjective structural conformation traits were muscle mass, rib width, front leg side view, rear leg side view, front legs front view, rear legs rear view, and locomotion. First-litter sow traits included if gilt farrowed (Stay), age at first farrowing (AFF), total number of piglets born (TNB), and weaning to conception interval (WCI). Variance components were estimated using an animal model with AIREMLF90 for linear traits and THRGIBBS1F90 for categorical traits. Heritability estimates for Stay, AFF, and TNB were 0.14, 0.22, and 0.02, respectively. Genetic correlations between length of estrus, the standing reflex traits, and age at puberty with Stay were 0.34, 0.34 to 0.74, and -0.27, respectively, and with AFF were -0.11, -0.04 to -0.41, and 0.76, respectively. Days to 114 kg had genetic associations with Stay, AFF, and TNB of 0.52, -0.25, and -0.08, respectively. Backfat at 114 kg had genetic correlations with Stay, AFF, and TNB of -0.29, 0.14, and 0.47, respectively. Vulva redness and TNB were negatively correlated phenotypically (r = -0.14) and genetically (r = -0.53). Associations between structural conformation traits with Stay, AFF, TNB, and WCI were generally low to moderate and favorable. Selection for longer length of estrus, stronger standing reflex, or younger age at puberty would increase the proportion of gilts that farrow and reduce age at first farrowing.

Data from 456 homozygous halothane normal purebred Yorkshire, Duroc, and Other-breed pigs from two national progeny testing and genetic evaluation programs were utilized to estimate genetic parameters for carcass components in pigs. Carcass components were cut and weighed according to Institutional Meat Purchase Specifications. Primal cut weights evaluated included 401 Ham (HAM), 410 Loin (LOIN), 405 Picnic shoulder (PIC), 406 Boston Butt (BB), and 409 Belly (BELLY). Individual muscle weights included the inside (INS), outside (OUT), and knuckle (KNU) muscles of the ham, the longissimus dorsi (LD) and psoas major (TEND) of the loin, and the boneless components of both the Boston Butt (BBUTT) and picnic (BPIC). Muscle weights from each primal were summed to yield a boneless subprimal weight (BHAM, BLOIN, BSHLDR), and all boneless subprimals were summed to yield total primal boneless lean (LEAN). Heritability estimates for HAM, LOIN, and BELLY were 0.57, 0.51, and 0.51, respectively. Heritability estimates for BB and PIC were 0.09 and 0.21, respectively. Heritability estimates for the boneless components of each primal were higher than those for the intact primals. Genetic correlations for HAM, LOIN, and PIC with loin muscle area (LMA) were 0.53, 0.78, and 0.70, respectively, and-0.62, -0.51, and -0.60, respectively, with 10th rib off-midline backfat (BF10). Boneless subprimal components were highly correlated with LEAN. Gilts had heavier weights (P < 0.01) than barrows for all boneless subprimals, individual muscles, LEAN, and for all primal cuts except BELLY. Gilts also had less BF10 and more LMA (P < 0.01) than barrows. Duroc pigs had a heavier (P < 0.01) weight for HAM and PIC when compared to Yorkshires. Yorkshire pigs had more (P < 0.01) LOIN weight than did the Durocs. Results suggest primal, boneless subprimal, and individual muscle weights in pigs should respond favorably to selection.