Genetic improvement of meat quality traits in pigs

In order to make genetic progress for an economically important trait, the trait (or a closely related trait) must be measurable, heritable, and have sufficient additive genetic variation. Genetic parameters must be estimated to determine the amount of additive genetic variation and heritability for use in a genetic evaluation and selection program. Superior individuals for the trait of interest must be identified and retained for breeding purposes to effectively implement a successful breeding program. Finally, the selected individuals must be mated in a way to produce the maximum response while limiting any negative impact selection for the trait of interest may have on other economically important correlated traits. In this thesis, four projects were conducted to investigate intramuscular fat percentage, an important pork quality trait, its measurement in live swine, estimation of genetic parameters, and determination of its relationship with carcass, meat, and eating quality traits, and implementation of this trait into a selection experiment to improve the trait.;In the first project, purebred Durocs (n = 207) were used to develop a model using real-time ultrasound technology to predict loin intramuscular fat percentage of the longissimus muscle in live pigs. In the second project, data from two national progeny testing programs were used to compare the relationships of intramuscular fat percentage of the longissimus predicted using real-time ultrasound and chemical intramuscular fat percentage with meat quality traits in pigs. In the third project, data from a selection project designed to increase intramuscular fat percentage (IMF) in a Duroc swine population were utilized to compare three different models used to estimate breeding values for IMF. In the final study, data from randomly mated and selected Duroc pigs (n = 589) were used to determine the genetic and phenotypic relationships between individual subcutaneous backfat layers and intramuscular fat percentage of the loin. Results of the first project showed real-time ultrasound image analysis can be used to predict intramuscular fat percentage in live swine.;Results from the second project demonstrated that selection for intramuscular fat percentage estimated from chemical analysis or by real-time ultrasound should yield similar genetic changes in other meat quality traits in pigs. Results from the third project indicated that selection based on a combination of ultrasonically predicted IMF and sib carcass IMF produced the greatest selection differentials and should lead to the greatest genetic change when compared to selection based on ultrasound estimates of IMF alone. Results from the final project demonstrated that individual backfat layers are highly heritable and of similar magnitude as total backfat, and have similar genetic correlations with IMF. The outer or inner backfat layers could be implemented into a multiple-trait genetic evaluation, instead of total backfat, to improve IMF.;Overall, the results from the four projects contained in this thesis indicate measuring intramuscular fat percentage of the porcine longissimus can be accurately performed utilizing real-time ultrasound, the genetic parameters and relationships with other meat and eating quality traits for IMF predicted from real-time ultrasound are similar to those of IMF estimated from the carcass, and substantial genetic progress can be made when implementing this technology into a selection program. In addition, inclusion of a single backfat layer into the genetic evaluation for intramuscular fat percentage could increase in the amount of genetic progress realized through selection

Relationship Between Backfat Depth and its Individual Layers and Intramuscular Fat Percentage in Swine

Results show the correlations between IMF and different measures of total fat thickness are of similar magnitude, regardless of the measure being a single measure of total subcutaneous fat or a sum of the individual layers. Results also show that the correlation between the inner and outer backfat layers is less than the correlation between the middle layer and the inner and outer layers

Genetic parameters of pork carcass components

Data from 456 halothane normal purebred Yorkshire, Duroc, and Other breeds 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 sub-primal weight (BHAM, BLOIN, BSHLDR), and all boneless sub-primals were summed to yield total primal boneless lean (LEAN). Heritability estimates for HAM, LOIN, and BELLY were 0.60,0.61, and 0.67, respectively. Heritability estimates for BB and PIC were 0.10 and 0.18, 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 LMA were 0.57, 0.79, and 0.83, respectively, and -0.66 with BF10. Boneless sub-primal components were highly correlated with LEAN. Gilts had heavier weights (P \u3c 0.01) for all primal cuts (with the exception of BELLY) and boneless sub-primals, individual muscles, and LEAN. Gilts also had less BF10 and more LMA (P \u3c 0.01). Duroc pigs had a heavier (P \u3c 0.01) weight for HAM when compared to Yorkshires, but were not different (P \u3e 0.05) from the Other breed. Yorkshire pigs had more (P \u3c 0.01) LOIN weight than did the Duroc or the Other breed. No breed differences (P \u3e 0.05) were found for BLOIN, BSHLDR, LEAN, or BPIC. Results suggest primal and boneless sub-primal and individual muscle weights in pigs should respond favorably to selection

Effect of Technician, Machine, and Animal Body Composition on Accuracy of Ultrasonic Measures of Backfat and Loin Muscle Area in Swine

Records (n = 11,305) from the 1998 to 2003 National Swine Improvement Federation (NSIF) ultrasound certification programs were used to determine the effect of technician, machine (A-mode and B-mode: Aloka 500, Classic Scanner 200), and level of animal fat depth and loin muscle area on the accuracy of tenth rib off-midline backfat (BF10) and loin muscle area (LMA) measured on live pigs

The Effects of Long Term Selection for Reduced Backfat and Increased Loin Muscle Area on Meat and Eating Quality Traits in Duroc Swine

A study was conducted to evaluate differences in performance, carcass composition, and eating quality characteristics of pigs sired by purebred Duroc boars currently available and pigs sired by purebred Duroc boars from the mid 1980’s. Two lines were developed by splitting and randomly allocating littermate and ½ sib pairs of females to matings by current (CTP) or old (OTP) time period boars. Subsequent boar, barrow, and gilt progeny from two replications were weighed on test at a group mean live weight of 140 lbs. Off-test ultrasonic LMA, BF10, and IMF measurements were collected on 789 pigs at a mean live weight of 240 lb. Records on pigs sired by CTP boars, from both replications (n=556), represented 23 sires while pigs sired by OTP boars (n=231) consisted of 15 sire groups. All available barrows and randomly selected gilts (n=277) were sent to a commercial abattoir and measurements of tenth-rib backfat (CBF10), last rib backfat (CLRBF), last lumbar backfat (CLLBF), and loin muscle area (CLMA) were collected. Chemical intramuscular fat percentage was determined by lab analysis of a loin sample from the 10th rib face of the longissimus muscle. Additional meat and eating quality traits measured were: Minolta reflectance and Hunter L (24 and 48 h); pH (24 h and 7 d); water holding capacity; subjective visual scores for color, marbling, and firmness (48 h); Instron tenderness, cooking loss, and trained sensory panel evaluations (7 d). Six serial ultrasonic measurements of 10th rib loin muscle area (LMA), off-midline backfat (BF10), and intramuscular fat percentage (IMF) from the first replication were collected every two weeks and used to assess deposition rate and growth pattern differences. There was no significant difference in average daily gain of pigs sired by boars from the two time periods. Pigs sired by CTP boars had larger (P \u3c 0.05) LMA measurements and less BF10, while pigs sired by OTP had significantly more IMF. Carcass evaluation revealed larger CLMA measurements, and significantly less CBF10, CLRBF, and CLLBF measurements for pigs sired by CTP boars. Pigs sired by OTP boars had a higher intramuscular fat percentage, lower Instron tenderness values, and higher subjective marbling and color scores than pigs sired by CTP boars (P \u3c 0.05). There were no significant differences between time periods for Minolta reflectance, Hunter L (24 and 48 h), water holding capacity, pH (24 h and 7 d), and subjective firmness scores. Trained sensory evaluations revealed higher (P \u3c 0.05) flavor scores and lower off-flavor scores for OTP sired pigs; however, no significant differences in tenderness score, juiciness score, chewiness score, and cooking loss were found between lines. Progeny of OTP boars began the test period at heavier weights and begin to decrease in daily body weight gain toward the conclusion of the test period, finishing with no advantage in body weight when compared to progeny of CTP boars. The analysis of serial backfat measurements revealed a linear pattern of backfat deposition between 150 and 270 lbs. Pigs sired by OTP boars deposited more backfat (

Effect of Removing Market Ready Pigs on Performance of Their Pen Mates

Results of this study suggest removing 25% or 50% of market ready pigs two weeks prior to the final marketing date does not affect test performance of pen mates. This study does not support the commonly held producer belief that removal of a percentage of market weight pigs will improve overall pen performance. If pigs are provided the space per animal utilized in this study, producers could reduce the labor associated with marketing by selling all of the pigs as a single group

Selection for Intramuscular Fat in Duroc Swine

Today’s U.S. pork industry is experiencing phenomenal growth as it continues to meet consumer demand and pork is the most widely eaten meat worldwide. Pork has proven to be a valuable protein source as Americans consume 66 lbs/person/year on a carcass disappearance basis (USDA, 2002 Agricultural Statistics). Pork production in the United States is also a vital part of the economy. Nearly 19 billion pounds of pork, with a retail value of $38 billion, was processed from about 97 million hogs in 2001. The U.S. pork industry is responsible for over$72 billion in total domestic economic activity. In addition, the pork industry adds over $27 billion of value to basic production inputs such as corn and soybeans (NPPC, 2003)