2010-Casellas_et_al_b - Bayes factor analyses of...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Bayes factor analyses of heritability for serum and muscle lipid traits in Duroc pigs J. Casellas, J. L. Noguera, J. Reixach, I. Díaz, M. Amills and R. Quintanilla J ANIM SCI 2010, 88:2246-2254. doi: 10.2527/jas.2009-2205 originally published online April 23, 2010 The online version of this article, along with updated information and services, is located on the World Wide Web at: http://jas.fass.org/content/88/7/2246 www.asas.org Downloaded from jas.fass.org by guest on July 16, 2011 Bayes factor analyses of heritability for serum and muscle lipid traits in Duroc pigs1 J. Casellas,*2 J. L. Noguera,* J. Reixach,† I. Díaz,‡ M. Amills,§ and R. Quintanilla* *Genètica i Millora Animal, Institut de Recerca i Tecnologia Agroalimentàries (IRTA)-Lleida, 25198 Lleida, Spain; †Selección Batallé S.A., 17421 Riudarenes, Spain; ‡Tecnologia dels Aliments, IRTA-Monells, 17121 Monells, Spain; and §Departament de Ciència Animal i dels Aliments, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain ABSTRACT: Concern about pork quality has increased during last decades. Given the influence of fat content and composition on sensorial, nutritional, and technological variables of pork meat, an accurate knowledge about genetic control of pig lipid metabolism is required. This study focused on providing a broad characterization for serum and meat lipid trait heritability estimates in pigs. Analyses were performed on a population of 370 Duroc barrows and measured the additive polygenic background for the serum concentrations of cholesterol, triglyceride, and low- and high-density lipoproteins at 45 and 190 d of age (at slaughter), as well as intramuscular fat, cholesterol content, and C:12 to C:22 fatty acid content in longissimus thoracis et lumborum and gluteus medius muscles at slaughter. These traits were analyzed under Bayesian univariate animal linear models, and the statistical relevance of heritability estimates was evaluated through Bayes factor (BF); the model with polygenic additive effects was favored when BF >1. All serum lipid traits showed relevant genetic determinism, but the BF reached greater values at 190 d of age. Serum lipid traits displayed moderate modal estimates for heritability that ranged from 0.18 to 0.30. On the other hand, the genetic determinism for meat quality traits showed a heterogeneous behavior with large and less-than-1 BF. In general, longissimus thoracis et lumborum and gluteus medius muscles showed a similar pattern, with strong evidence of polygenic additive effects for intramuscular fat and palmitic, stearic, and cis-vaccenic fatty acids content, whereas oleic and muscle cholesterol content showed moderate to weak BF with moderate heritabilities. Similarly, results regarding linoleic, arachidonic, n-3, and n-6 fatty acids suggested a moderate genetic determinism, but only in gluteus medius muscle. For the remaining traits (myristic and palmitoleic fatty acids in both muscles, along with linoleic, arachidonic, n-3, and n-6 fatty acids in the longissimus thoracis et lumborum muscle), no statistical evidence for genetic control was observed in this study. As a whole, these results confirm the complexity of lipid metabolism in pigs. Key words: Bayes factor, cholesterol, fatty acid, heritability, lipoprotein, meat quality ©2010 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2010. 88:2246–2254 doi:10.2527/jas.2009-2205 INTRODUCTION 1 This research has been funded by grants AGL2002-04271-C03 (Ministerio de Educación y Ciencia, Spain) and AGL2007-66707-C02 (Ministerio de Ciencia y Tecnología, Spain). The authors are indebted to Selección Batallé S.A. (Riudarenes, Spain) for providing the animal material and for their cooperation in the experimental protocol, and to D. Almuzara (Genètica i Millora Animal, IRTALleida, Lleida, Spain) for technical support. The research contract of J. Casellas was partially financed by Spain’s Ministerio de Ciencia e Innovación (programs Juan de la Cierva and José Castillejo). The authors acknowledge the anonymous referees for their helpful comments on the manuscript. 2 Corresponding author: Joaquim.Casellas@uab.cat Received June 8, 2009. Accepted March 24, 2010. Lipid metabolism in pigs is an area of relevance in genetics research because it is directly or indirectly involved in human nutrition and health (Jarratt and Mahaffie, 2002). The intramuscular fat (IMF) content and its fatty acid (FA) and cholesterol (CHOL) composition show an impact on various traits related with pork quality, such as technological attributes (i.e., firmness, storage stability), flavor, nutritive value, and palatability (Cameron and Enser, 1991; Fischer, 2005; Wood et al., 2008). Moreover, these meat quality traits are also linked with serum lipid concentrations (Averette Gatlin et al., 2003), highlighting the complexity of lipid metabolism. From a nutritional aspect, pork is an important source of oleic and essential n-6 and n-3 2246 Downloaded from jas.fass.org by guest on July 16, 2011 Heritability of lipid profile in pigs FA, with their well-known influences on human health (Tribole, 2006). The characteristics of fat associated to meat are key factors for the production of high-quality dry-cured hams, where IMF content and FA composition can affect the drying period, ripening, and flavor of final products (Chizzolini et al., 1998; López-Bote, 1998). In spite of the relevance of pig meat composition for humans, our knowledge about the genetic control of pig serum and muscle lipid traits remains limited. There are few estimates of the genetic parameters for FA in pigs, mainly restricted to the most abundant FA (Fernández et al., 2003; Suzuki et al., 2006). The aim of this research was to characterize the heritability of 2 groups of relevant lipid-related traits in pigs: the blood concentrations of CHOL, lipoproteins, and triglycerides of young pigs at 2 ages, and the lipid characteristics of the longissimus thoracis et lumborum and gluteus medius muscles focused on IMF, CHOL content, and FA profile at slaughter. These analyses were performed on a Duroc population through the simplified Bayes factor (BF) test developed by GarcíaCortés et al. (2001) and Varona et al. (2001). MATERIALS AND METHODS All experimental procedures were approved by the Animal Care and Use Committee of the Institut de Recerca i Tecnologia Agroalimentàries (http://www.irta. es). Animal Material Source This study was performed on a commercial Duroc line (Selección Batallé SA, Riudarenes, Spain), which is primarily used for producing dry-cured ham. Phenotypic data were collected from 370 castrated males generated between August, 2003 and May, 2005 in 4 contemporary batches (95, 114, 83, and 78 animals per batch), under an experimental design of half-sib families. More specifically, 370 purebred Duroc sows distributed in 3 farms were mated with 5 purebred Duroc boars, and 1 male offspring per litter was taken at random (49, 93, 81, 84, and 63 sons per sire). After weaning, castrated animals born on the 3 farms (150, 153, and 55 animals per farm) were moved to the test station (IRTA Pig Control Center, Monells, Spain), where they were initially (transition period) housed with other animals foreign to the experiment. Barrows from each contemporary batch were moved together to the fattening and control units at 2 to 3 mo of age and randomly distributed over 10 pens (5 pens at each side of a central corridor in the same barn) in groups of 8 to 12 animals. Pigs were all raised under the same standard intensive management conditions and fed ad libitum up to slaughter. During the first period of fattening (up to 90 kg of BW, around 150 d of age) barrows were fed a standard diet with 18% protein, 3.8% fiber, 7.0% fat, 1.0% lysine, and 0.3% methionine (2,450 kcal/kg; DM basis). In the second period of fattening (the last 30 to 2247 40 d before slaughter), animals were fed a standard diet with 15.9% protein, 4.5% fiber, 5.2% fat, 0.7% lysine, and 0.2% methionine (2,375 kcal/kg; DM basis). Pigs were slaughtered at 122.5 kg ± 0.7 kg of BW and 193.7 d ± 0.4 d of age. All relevant data were recorded (e.g., farm of origin, batch and pen of fattening, along with age, backfat thickness, and BW at blood collection and at slaughter). Lipid Profile in Blood and Meat Samples Blood samples (5 mL) were taken from a jugular vein (Framstad et al., 1988) of each barrow at 45.0 ± 0.4 and 190.4 ± 0.4 d of age and appropriately processed to measure total CHOL (CHOL45 and CHOL190), low-density lipoproteins (LDL45 and LDL190), highdensity lipoproteins (HDL45 and HDL190), and triglyceride (TG45 and TG190) serum concentrations as described by Gallardo et al. (2008). Venous blood was collected into EDTA-containing TapVal tubes (Aquisel, Barcelona, Spain). Blood samples were kept on ice until centrifugation (10 min at 1,560 × g at 4°C), after which serum was collected and stored at −80°C until analyzed. Serum CHOL was measured by a CHOL oxidase-based method employing CHOL esterase, CHOL oxidase, and peroxidase enzymes (Richmond, 1992). Serum HDL concentrations were determined by immune-inhibition (Rafai and Warnick, 1994), whereas serum triglyceride (TG) concentration was quantified by means of a glycerol kinase reaction with the method reported by Fossati and Prencipe (1982). Finally, serum LDL concentration was calculated according to the equation reported by Friedewald et al. (1972). Two 200-g samples were taken from the longissimus thoracis et lumborum and gluteus medius muscles during carcass operations in the slaughterhouse (approximately 30 min after slaughter). After appropriate processing, IMF content was determined by Near Infrared Transmittance (Infratec 1625, Tecator Hoganas, Sweden), FA (C:12 to C:22 interval) composition was analyzed by gas chromatography of methyl esters as described in Mach et al. (2006), and muscle CHOL content (CHOLmusc) was measured following Cayuela et al. (2003). All these quantifications were performed in the Centre de Tecnologia dels Aliments of IRTA (Monells, Spain). Statistical Analyses Linear mixed model analyses were performed on CHOL, HDL, LDL, and TG serum concentrations (Table 1), as well as CHOLmusc and the percentage of IMF and myristic, palmitic, palmitoleic, stearic, oleic, cis-vaccenic, linoleic, and arachidonic FA in gluteus medius and longissimus thoracis et lumborum (Table 2). Fatty acids with a less-than-1 average percentage in both muscles were not included in the analyses due to their biological relevance and because their small measures were close to the instrumentation error, but the Downloaded from jas.fass.org by guest on July 16, 2011 2248 Casellas et al. Table 1. Phenotypic summary of lipid serum traits recorded in Duroc pigs at 45 and 190 d of age Trait Abbreviation At 45 d Cholesterol, mg/dL HDL2-cholesterol, mg/dL LDL3-cholesterol, mg/dL Triglycerides, mg/dL At 190 d Cholesterol, mg/dL HDL-cholesterol, mg/dL LDL-cholesterol, mg/dL Triglycerides, mg/dL Mean1 n SE CHOL45 HDL45 LDL45 TG45 333 333 333 333 77.30 30.43 38.03 44.08 0.74 0.38 0.48 1.07 CHOL190 HDL190 LDL190 TG190 316 316 316 316 125.15 51.66 63.12 51.37 1.47 0.57 1.15 1.31 1 Raw means from phenotypic data. HDL = high-density lipoprotein. 3 LDL = low-density lipoprotein. 2 sum of n-3 and n-6 FA were also analyzed given their implications on human health (Table 2). Serum concentrations were log-transformed to correct departures from normality as in Gallardo et al. (2008), whereas the remaining traits did not show relevant departures from normality (Gallardo et al., 2008). Nongenetic sources of variation were preliminarily evaluated with the Generalized Linear Models procedure (SAS Institute Inc., Cary, NC), leading to the following models for Yij = Bi + IMFj + eij d) IMF, Yij = Bi + BTj + eij and e) CHOLmusc, Yij = Bi + eij , a) serum lipid concentration traits at 45 d of age, where Y was the phenotypic record, Bi was the fattening contemporary batch, Fj was the farm of origin, covj was a different covariate depending on the trait (BW for CHOL, HDL, and LDL, and age at blood collection for TG), and IMFj and BTj were continuous covariates with the percentage of IMF and backfat thickness (mm) fat at slaughter, respectively, and eij was the residual term. The statistical relevance of the heritability parameter was evaluated through the BF described by García- Yijk = Bi + Fj + eijk b) serum lipid concentrations at 190 d of age, Yij = Bi + cov j + eij c) FA, Table 2. Phenotypic summary of intramuscular fat and fatty acid (FA) composition in longissimus thoracis et lumborum and gluteus medius muscles of Duroc pigs Longissimus thoracis et lumborum Trait Abbreviation Intramuscular fat, % CHOL2 content, mg/g Myristic FA, % Palmitic FA, % Palmitoleic FA, % Stearic FA, % Oleic FA, % Cis-vaccenic FA, % Linoleic FA, % Arachidonic FA, % n-6 FA, % n-3 FA, % IMF CHOLmusc C14:0 C16:0 C16:1 C18:0 C18:1n-9 C18:1n-7 C18:2 C20:4 n-6 n-3 Gluteus medius n Mean1 SE Mean SE 321 321 321 321 321 321 321 321 321 321 321 321 3.84 58.60 1.36 23.42 2.95 11.68 34.61 4.30 14.44 3.62 19.13 0.92 0.08 0.52 0.02 0.09 0.03 0.07 0.29 0.02 0.29 0.10 0.40 0.02 5.17 64.65 1.38 23.25 0.29 11.19 34.85 4.07 15.11 3.25 19.51 1.11 0.11 0.61 0.01 0.07 0.001 0.06 0.25 0.02 0.23 0.09 0.33 0.02 1 Raw means from phenotypic data. CHOL = cholesterol. 2 Downloaded from jas.fass.org by guest on July 16, 2011 2249 Heritability of lipid profile in pigs Table 3. Bayes factor and heritability estimates for lipid serum traits in Duroc pigs at 45 and 190 d of age Heritability3 Bayes factor2 Trait1 45-d-old pigs CHOL45 HDL45 LDL45 TG45 190-d-old pigs CHOL190 HDL190 LDL190 TG190 Mean Mode PSD HPD95 3.1 2.2 1.3 8.7 0.38 0.47 0.27 0.42 0.29 0.30 0.18 0.31 0.22 0.26 0.18 0.19 0.06 0.01 0.001 0.07 to to to to 0.68 0.81 0.62 0.70 47.9 2.1 16.3 16.1 0.37 0.45 0.36 0.34 0.28 0.22 0.30 0.23 0.20 0.27 0.19 0.20 0.08 0.02 0.07 0.05 to to to to 0.62 0.80 0.60 0.58 1 Total cholesterol (CHOL), low-density lipoproteins (LDL), high-density lipoproteins (HDL), and triglyceride (TG) serum concentrations at 45 d (e.g., CHOL45) and 190 d of age (e.g., CHOL190). 2 Bayes factor of the model with additive polygenic effects against the same model without additive polygenic effects following García-Cortés et al. (2001). 3 The posterior distribution of heritability was characterized by several basic statistics: mean, mode, posterior SD (PSD), and highest posterior density region at 95% (HPD95). Cortés et al. (2001) and Varona et al. (2001; see Appendix for a comprehensive description of this BF approach). Note that BF is the ratio of the posterior probabilities of 2 competing models, taking any positive value between >0 and +¥. In this case, a linear mixed model with additive polygenic effects (numerator model) was compared against a model without additive polygenic effects (denominator model), where greater-than-1 BF favored the numerator model and less-than-1 BF favored the denominator model. In this report, the BF results were discussed within the context of the Jeffreys (1984) discrete scale of evidences. This scale classifies the BF according to 6 different levels of evidence for the numerator model, objectively classifying the BF as denominator model supported, not worth more than a bare mention, substantial evidence, strong evidence, very strong evidence, and decisive evidence (see Appendix). From now on, this terminology will be systematically used when referring to the BF. For each analysis, a unique chain with 25,000 iterations was launched, after discarding the first 5,000 elements as burn-in. Convergence was evaluated by visual inspection after plotting the Markov chain Monte Carlo sampled values for all variance components across iterations. Moreover, the Raftery and Lewis (1992) approach was used to objectively evaluate the convergence and length of the burn-in period on the variance component parameters. For all traits and variances, convergence was guaranteed with less than 500 iterations. RESULTS Phenotypic Estimates The average phenotypic values for CHOL, HDL, LDL, and TG in 45- and 190-d-old Duroc barrows are shown in Table 1. Note that TG190 concentrations were approximately 1.2 times greater than TG45 whereas CHOL190, HDL190, and LDL190 serum concentrations were approximately 1.7 times greater that their corresponding estimates at 45 d of age. Longissimus thoracis et lumborum and gluteus medius muscles showed relevant differences (P < 0.05) in terms of IMF and CHOLmusc, with values of 3.84 ± 0.08% vs. 5.17 ± 0.08%, and 58.60 ± 0.52 mg/g vs. 64.65 ± 0.61 mg/g, respectively (Table 2). As a whole, oleic (n-9; ~34%), palmitic (~23%), and linoleic (~15%) acids were the most abundant FA, accounting for almost 75% of the overall FA amount. Genetic Determinism for Serum Lipid and Meat Composition Traits Results based on the BF test for heritability estimation are shown in Tables 3 and 4. Bayes factors between models with and without a genetic component gave values greater than 1 for all analyzed serum lipid concentrations (Table 3), providing evidence that the model was more predictive when polygenic additive effects were included. The greatest BF were reached by serum lipid concentrations at 190 d, where LDL190 and TG190 showed strong evidence (BF >10) and CHOL190 showed very strong evidence (BF >31.62) of genetic determinism according to the Jeffreys (1984) scale. Posterior estimates of heritabilities (mean and mode) reflected medium values (from 0.18 to 0.48) for all traits analyzed (Table 3). However, it should be noted that the large SD associated to the limited sample size of our experimental population led to large highest posterior density regions at 95% (HPD95), which included values near to zero for HDL45, LDL45, and HDL190 heritabilities and lesser BF. Focusing on meat quality traits, BF estimates for the genetic background of the muscular fat content and composition showed a consistent pattern across muscles Downloaded from jas.fass.org by guest on July 16, 2011 2250 Casellas et al. Table 4. Bayes factor and heritability for the intramuscular fat and fatty acid (FA) composition of 2 muscles in Duroc pigs Heritability2 Bayes factor1 Mode PSD 0.55 0.30 0.25 0.47 0.30 0.45 0.30 0.41 0.25 0.26 0.24 0.28 0.65 0.20 0.09 0.30 0.12 0.33 0.15 0.32 0.14 0.12 0.14 0.14 0.18 0.20 0.21 0.26 0.19 0.22 0.21 0.21 0.20 0.22 0.19 0.21 0.18 0.01 0.00 0.08 0.00 0.09 0.00 0.05 0.00 0.00 0.001 0.001 to to to to to to to to to to to to 0.91 0.65 0.67 0.88 0.60 0.86 0.69 0.84 0.68 0.74 0.64 0.79 992.9 4.8 0.1 40.4 0.9 1,575.0 1.6 566.6 8.9 2.9 1.1 2.0 Longissimus thoracis et lumborum muscle Intramuscular fat, % CHOL3 content, mg/g Myristic FA, % Palmitic FA, % Palmitoleic FA, % Stearic FA, % Oleic FA, % Cis-vaccenic FA, % Linoleic FA, % Arachidonic FA, % n-6 FA, % n-3 FA, % Gluteus medius muscle Intramuscular fat, % CHOL content, mg/g Myristic FA, % Palmitic FA, % Palmitoleic FA, % Stearic FA, % Oleic FA, % Cis-vaccenic FA, % Linoleic FA, % Arachidonic FA, % n-6 FA, % n-3 FA, % Mean 1,152.3 3.9 0.2 15.6 0.8 883.0 1.3 37.1 0.6 0.3 0.6 0.4 Trait 0.47 0.35 0.16 0.44 0.27 0.43 0.32 0.38 0.37 0.36 0.24 0.22 0.58 0.22 0.08 0.30 0.12 0.53 0.21 0.29 0.29 0.31 0.14 0.16 0.17 0.21 0.16 0.24 0.18 0.22 0.21 0.20 0.21 0.23 0.13 0.14 0.18 0.02 0.00 0.06 0.01 0.09 0.00 0.04 0.01 0.01 0.001 0.002 to to to to to to to to to to to to 0.86 0.70 0.50 0.90 0.62 0.81 0.73 0.78 0.77 0.82 0.49 0.50 HPD95 1 Bayes factor of the model with additive polygenic effects against the same model without additive polygenic effects following García-Cortés et al. (2001). 2 The posterior distribution of heritability was characterized by several basic statistics: mean, mode, posterior SD (PSD), and highest posterior density region at 95% (HPD95). 3 CHOL = cholesterol. (Table 4). The additive genetic variability for the percentage of IMF was clearly demonstrated with a BF of 1,152.3 and 992.9 for longissimus thoracis et lumborum and gluteus medius muscles, respectively. Additionally, this trait reached the greatest heritability estimates, with modal values around 0.6 in both muscles. Although the small sample size led to wide HPD95, they were far apart from the null estimate, starting around 0.18 (Table 4). Also CHOLmusc showed inheritable patterns in both muscles, but BF values provided less relevant evidences of genetic determinism with modal heritabilities centered around approximately 0.20. The additive genetic background for the different FA was not homogeneous. The percentage of stearic FA was very heritable in both muscles (0.53 and 0.33 in gluteus medius and longissimus thoracis and lumborum, respectively), providing decisive evidence (BF >100) on the basis of the Jeffreys (1984) scale. Also the cis-vaccenic acid content provided decisive (BF = 566.6; h2 = 0.38) and very strong (BF = 37.1; h2 = 0.32) evidence of an additive genetic background in gluteus medius and longissimus thoracis et lumborum muscles, respectively. The palmitic FA revealed strong (longissimus thoracis et lumborum; h2 = 0.30) and very strong (gluteus me- dius; h2 = 0.30) evidence of additive genetic variance. Heritability estimates for those FA with relevant BF were moderate, with modal estimates ranging between 0.29 (cis-vaccenic) and 0.53 (stearic). For the oleic acid content a small but BF >1 was observed. In the light of these results, and despite the medium values (from 0.28 to 0.32) obtained for the posterior mode of the heritability, it is difficult to conclude about the genetic determinism of oleic content. Linoleic and arachidonic FA revealed moderate BF (BF <10) in gluteus medius, suggesting a certain level of genetic control. The remaining FA scored nonrelevant BF, failing to provide evidence about polygenic additive genetic effects (Table 4). Note that n-3 and n-6 FA in longissimus thoracis et lumborum were included in this last group of FA because BF failed to identify evidence of genetic control. DISCUSSION Phenotypic Pattern Pork is one of the most consumed meats in Western cultures, with 35 kg/(habitant/yr) in the European Union, 30 kg/(habitant/yr) in the United States, 27 Downloaded from jas.fass.org by guest on July 16, 2011 Heritability of lipid profile in pigs kg/(habitant/yr) in Canada and 21 kg/(habitant/yr) in Australia. Moreover, pork is also relevant for Eastern countries like China [35 kg/(habitant/yr)] or Japan [18 kg/(habitant/yr)], and has an average worldwide consumption of 15 kg per habitant and year (Food and Agriculture Organization of the United Nations; http://www.fao.org). Within this context, concern about pork quality increased during last decades (Tarrant, 1998) concerning sensorial, nutritional, and technological variables. In our sample of Duroc barrows, longissimus thoracis et lumborum and gluteus medius muscles showed substantial differences in terms of IMF and CHOLmusc, with gluteus medius being fatter and with a greater CHOL content, as previously reported by Fiedler et al. (2003) and Kim et al. (2008). Apart from their incidence on quality of fresh meat, IMF content becomes a variable of paramount importance in the production of dry-cured products, where an increased IMF content has a key role in flavor and slow dehydration during the curing process (Ruiz-Carrascal et al., 2000). Despite differences in fat content, longissimus thoracis et lumborum and gluteus medius muscles are a relevant source of oleic (34.61 and 34.85%, respectively), palmitic (23.42 and 23.25%, respectively), and linoleic (14.44 and 15.11%, respectively) FA, without significant departures across muscles in terms of percentage. Although some metabolic differences were described previously between longissimus thoracis et lumborum and gluteus medius muscles (Mora et al., 2008), fat composition differences between both muscles focused on less abundant FA. It is important to highlight the significant increase in n-3 FA found in gluteus medius. Given that FA profile is largely determined by genotype and diet, our estimates showed substantial differences when compared with those provided by other authors (e.g., Cameron and Enser, 1991; Suzuki et al., 2006; Zhang et al., 2007), although the most abundant FA yielded values that agreed with previous studies in pigs (Cameron et al., 2000; Tejeda et al., 2002). Heritabilities for Serum Lipid and Meat Composition Traits The heritability of serum CHOL in swine in the current study was medium-to-large and comparable with that in humans (Feitosa et al., 2005). This result agreed with estimates previously reported in other pig populations (Rothschild and Chapman, 1976; Pond et al., 1986; Pond and Mersmann, 1996) and also with swine selection experiments with effective changes on serum CHOL (Pond et al., 1993; Young et al., 1993). Conversely, heritabilities for TG concentrations at both ages were also large but less than those reported by Pond et al. (1986). Heritabilities for HDL and LDL are, to the best of our knowledge, the first reported for pigs, with moderate values agreeing with the previous values reported in humans (Kaess et al., 2008). Even in 2251 humans, little information exists about the inheritance aspects of HDL- and LDL-bound CHOL concentrations, although their genetic background at older ages is undoubted (Heller et al., 1993; Bosse et al., 2004; Kaess et al., 2008). As a whole, our heritability estimates and the corresponding BF provide evidence of the existence of genetic factors controlling serum lipid concentrations at 190 d of age, but these were somewhat weaker for HDL90. Similar conclusions might be reached for serum lipid concentrations at 45 d of age, although the smaller BF and the wide HPD95 advocate for a cautious interpretation of these results. In any case, this genetic component agreed well with previous results demonstrating that serum lipid QTL segregate in this population (Gallardo et al., 2008), thus corroborating that pigs are a good model for studying genetic pathways involved in lipid metabolism. As previously mentioned, the IMF content has an important impact on various features of the sensory (Fernandez et al., 2000) and technological quality of pork meat (Ruiz-Carrascal et al., 2000). Heritabilities of IMF for gluteus medius and longissimus thoracis et lumborum muscles were included in the wide range of estimates reported in the literature for commercial breeds (from 0.26 to 0.86; Sellier, 1998). More specifically, our estimates match up with those obtained by Solanes et al. (2009) in another sample of the same commercial Duroc line (h2 = 0.57). In any case, the genetic background for IMF was clearly demonstrated, providing enough genetic variability for selection programs focused on meat-quality traits, as demonstrated by Suzuki et al. (2005) and Schwab et al. (2009) in other swine populations. Fatty acid profile has profound effects on meat quality because it determines the nutritional value, shelf life, and processing characteristics of meat (Sheard et al., 2000). Fatty acid composition also influences the firmness/oiliness of adipose tissue and the oxidative stability of muscle, which in turn affects flavor and muscle color (Wood et al., 2008). Several authors (e.g., Cameron et al., 2000; Nguyen et al., 2003) pointed out that the influence of nutrition is stronger than genetic effects on the FA composition of adipose tissues and also IMF, but few reports have addressed genetic parameter estimates of FA profile of IMF to corroborate this point. In the present study, all animals were subjected to the same dietary conditions, so no differences in the FA deposition resulting from differences in dietary FA were expected. Under these circumstances, some FA showed strong and moderate evidences of genetic determinism, whereas the BF failed to provide statistical evidences of additive polygenic effects in the remaining FA. The existence of additive genetic variability for the main SFA present in IMF and palmitic and stearic acids was beyond any doubt in longissimus thoracis et lumborum and gluteus medius muscles. Heritability estimates obtained for these FA matched previous estimates by Suzuki et al. (2006) in another Duroc population. In close resemblance with our data, Fernández et Downloaded from jas.fass.org by guest on July 16, 2011 2252 Casellas et al. al. (2003) showed that the greatest heritability content of subcutaneous fat in the Iberian breed corresponded to stearic (0.41) and palmitic (0.38) FA. Sellier (1998) reported mean heritability estimates of 0.51 (0.42 to 0.57) for stearic FA of subcutaneous fat. On the other hand, genetic influences for the myristic FA were not observed in our study, disagreeing with the weak, but significant heritability reported by Suzuki et al. (2006). In nonruminant animals, dietary FA may be oxidized or deposited in fat tissues, but there is also de novo synthesis of FA from acetyl-CoA derived from carbohydrate or protein breakdown or both (Acheson et al., 1988). In that way, palmitic, stearic and oleic acids are present in the meat composition (Fischer, 2005). According with results obtained in this and in previous studies, the genetic determinism of palmitic and stearic acids content in IMF is largely demonstrated, but the evidence for oleic FA is far more elusive. Medium to high heritabilities had been obtained for the oleic content of several fat tissues (from 0.26 to 0.44) by Fernández et al. (2003) and Suzuki et al. (2006) in Iberian and Duroc populations, respectively. In the present study, similar but not conclusive results regarding heritability of IMF oleic content were obtained in both analyzed muscles. Concerning other relevant MUFA, the cis-vaccenic FA showed polygenic genetic control in longissimus thoracis et lumborum and gluteus medius muscles, with posterior mean and mode estimates ranging from 0.29 to 0.41, which are the first estimates obtained in pigs for these traits. Opposite to the previously mentioned FA, the n-3 and n-6 PUFA are labeled as essential FA because the biosynthetic pathway for n-3 and n-6 FA does not hold in mammalian cells and they cannot be synthesized de novo in pigs (El-Badry et al., 2007). These FA are involved in multiple metabolic routes with direct incidence on human and animal health (Van Oeckel et al., 1997; Trivedi, 2006). As they can be obtained only from diet, several authors (e.g., Nguyen et al., 2003) confirmed that the percentage of essential FA in the subcutaneous and intramuscular fat of pigs is directly related to the percentage of these FA in the dietary fat. According to this statement, we would not expect to find evidence of genetic variability on n-3 and n-6 FA content. Our results corroborated this hypothesis within the context of the longissimus thoracis et lumborum muscle, with less-than-1 BF for both groups of essential FA, as well as for the majority n-6 FA (linoleic and arachidonic FA), which were analyzed separately. Nevertheless, a relevant genetic determinism with moderate heritabilities was suggested for linoleic and arachidonic n-6 FA in the gluteus medius muscle. Besides, Suzuki et al. (2006) obtained a relevant heritability for the linoleic content in several fat tissues of pig including IMF, and previous works showed heritabilities from 0.47 to 0.70 for linoleic acid of subcutaneous fat (Sellier, 1998). Evidence of genetic determinism were also found for n-3 FA in the gluteus medius muscle. Note that these heritabilities for n-3 FA agreed with the one reported by Greeff et al. (2006). Given that n-3 FA cannot be synthesized de novo by pigs, this genetic determinism must be related to the genetic architecture of intestinal absorption from diet or organ-specific distribution of n-3 FA. Our results confirm the complex genetic control of FA and relevant influences of environmental factors. The existence of an important genetic determinism affecting nonessential FA deposition has been confirmed, and also a relevant heritability for some essential FA has been demonstrated in the gluteus medius muscle, suggesting that its content in pig hams could be genetically modified. Nevertheless, further studies are required to evaluate genetic relationships between the lipid traits studied in this research. LITERATURE CITED Acheson, K. J., Y. Schultz, T. Bessard, K. Ananatharaman, J. P. Flatt, and E. Jéquier. 1988. Glycogen storage capacity and de novo lipogenesis during massive carbohydrate overfeeding in man. Am. J. Clin. Nutr. 48:240–247. Averette Gatlin, L., M. T. See, J. A. Hansen, and J. Odle. 2003. Hydrogenated dietary fat improves pork quality of pigs from two lean genotypes. J. Anim. Sci. 81:1989–1997. Bosse, Y., L. Perusse, and M. C. Vohl. 2004. Genetics of LDL particle heterogeneity: From genetic epidemiology to DNA-based variations. J. Lipid Res. 45:1008–1026. Cameron, N. D., and M. Enser. 1991. Fatty acid composition of lipid in longissimus dorsi muscle of Duroc and British Landrace pigs and its relationship with eating quality. Meat Sci. 29:295–307. Cameron, N. D., M. Enser, G. R. Nute, F. M. Whittington, J. C. Penman, A. C. Fisken, A. M. Perry, and J. D. Wood. 2000. Genotype with nutrition interaction on fatty acid composition of intramuscular fat and the relationship with flavor of pig meat. Meat Sci. 55:187–195. Cayuela, J. M., M. D. Garrido, S. J. Banón, and J. M. Ros. 2003. Simultaneous HPLC analysis of α-tocopherol and cholesterol in fresh pig meat. J. Agric. Food Chem. 51:1120–1124. Chizzolini, R., E. Novelli, and E. Zanardi. 1998. Oxidation in traditional Mediterranean meat products. Meat Sci. 49:S87–S99. El-Badry, A. M., R. Graf, and P.-A. Clavien. 2007. Omega 3 - omega 6: What is right for the liver? J. Hepatol. 47:718–725. Feitosa, M. F., T. Rice, T. Rankinen, L. Almasy, A. S. Leon, J. S. Skinner, J. H. Wilmore, C. Bouchard, and D. C. Rao. 2005. Common genetic and environmental effects on lipid phenotypes: The HERITAGE family study. Hum. Hered. 59:34–40. Fernández, A., E. de Pedro, N. Núñez, L. Silió, J. García-Casco, and C. Rodríguez. 2003. Genetic parameters for meat and fat quality and carcass composition traits in Iberian pigs. Meat Sci. 64:405–410. Fernandez, X., J. Mourot, B. Lebret, S. Gilbert, and G. Monin. 2000. Influence of intramuscular fat content on lipid composition, sensory qualities and consumer acceptability of cured cooked ham. J. Sci. Food Agric. 80:705–710. Fiedler, I., K. Nürnberg, T. Hardge, G. Nürnberg, and K. Ender. 2003. Phenotypic variations of muscle fibre and intramuscular fat traits in Longissimus muscle of F2 population Duroc×Berlin Miniature pig and relationships to meat quality. Meat Sci. 63:131–139. Fischer, K. 2005. Consumer-relevant aspects of pork quality. Anim. Sci. Pap. Rep. 23:269–280. Downloaded from jas.fass.org by guest on July 16, 2011 Heritability of lipid profile in pigs Fossati, P., and L. Prencipe. 1982. Serum triglycerides determined colorimetrically with an enzyme that produces hydrogen peroxide. Clin. Chem. 28:2077–2080. Framstad, T., Ø. Sjaastad, and R. A. Aass. 1988. Blodprøvetaking på gris. Norsk Veterinærtidsskrift 100:265–272. Friedewald, W. T., R. I. Levy, and D. S. Fredrickson. 1972. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin. Chem. 18:499–502. Gallardo, D., R. N. Pena, M. Amills, L. Varona, O. Ramírez, J. Reixach, I. Díaz, J. Tibau, J. Soler, J. M. Prat-Cuffí, J. L. Noguera, and R. Quintanilla. 2008. Mapping of quantitative trait loci for colesterol, LDL, HDL and triglyceride serum concentrations in pigs. Physiol. Genomics 35:199–209. García-Cortés, L. A., C. Cabrillo, C. Moreno, and L. Varona. 2001. Hypothesis testing for the genetic background of quantitative traits. Genet. Sel. Evol. 33:3–16. Gelfand, A., and A. F. M. Smith. 1990. Sampling based approaches to calculating marginal densities. J. Am. Stat. Assoc. 85:398– 409. Good, I. J. 1979. Studies in the history of probability and statistics. XXXVII A. M. Turing’s statistical work in World War II. Biometrika 66:393–396. Greeff, J. C., P. Young, S. Kitessa, and M. Dowling. 2006. Preliminary heritability estimates of individual fatty acids in sheep meat. Page 36 in Proc. 26th Aust. Soc. Anim. Prod. Aust. Soc. Anim. Prod., Perth, Australia. Hastings, W. K. 1970. Monte Carlo sampling methods using Markov chains and their application. Biometrika 57:97–109. Heller, D. A., U. de Faire, N. L. Pedersen, G. Dahlen, and G. E. McClearn. 1993. Genetic and environmental influences on serum lipid levels in twins. N. Engl. J. Med. 328:1150–1156. Jarratt, J., and J. B. Mahaffie. 2002. Key trends affecting the dietetics profession and the American Dietetic Association. J. Am. Diet. Assoc. 102:S1821–SS1839. Jeffreys, H. 1984. Theory of Probability. Clarendon Press, Oxford, UK. Kaess, B., M. Fischer, A. Baessler, K. Stark, F. Huber, W. Kremer, H. R. Kalbitzer, H. Schunkert, G. Riegger, and C. Hengstenberg. 2008. The lipoprotein subfraction profile: Heritability and identification of quantitative trait loci. J. Lipid Res. 49:715– 723. Kass, R. E., and A. E. Raftery. 1995. Bayes factors. J. Am. Stat. Assoc. 90:773–795. Kim, J. H., P. N. Seong, S. H. Cho, B. Y. Park, K. H. Hah, L. H. Yu, D. G. Lim, I. H. Hwang, D. H. Kim, J. L. Lee, and C. N. Ahn. 2008. Characterization of nutritional value for twenty-one pork muscles. Asian-australas. J. Anim. Sci. 21:138–144. López-Bote, C. 1998. Sustained utilization of the Iberian pig breed. Meat Sci. 49(Suppl. 1):S17–S27. Mach, N., M. Devant, A. Bach, I. Díaz, M. Font, M. A. Oliver, and J. A. García. 2006. Increasing the amount of n-3 fatty acid in meat from young Holstein bulls through nutrition. J. Anim. Sci. 84:3039–3048. Mora, L., M. A. Sentandreu, and F. Toldrá. 2008. Contents of creatine, creatinine and carnosine in porcine muscles of different metabolic types. Meat Sci. 79:709–715. Nguyen, L. Q., M. C. G. A. Nuijens, H. Everts, N. Salden, and A. C. Beynen. 2003. Mathematical relationships between the intake of n-6 and n-3 polyunsaturated fatty acids and their contents in adipose tissue of growing pigs. Meat Sci. 65:1399–1406. Pond, W. G., and H. J. Mersmann. 1996. Genetically diverse pig models for neonatal cholesterol nutrition: A review. Nutr. Res. 16:707–721. Pond, W. G., H. J. Mersmann, P. D. Klein, L. L. Ferlic, W. W. Wong, D. L. Hachey, P. A. Schoknecht, and S. Zhang. 1993. Bodyweight gain is correlated with serum cholesterol at 8 weeks of age in pigs selected for four generations for low or high serum cholesterol. J. Anim. Sci. 71:2406–2411. 2253 Pond, W. G., H. J. Mersmann, and L. D. Young. 1986. Heritability of plasma cholesterol and triglyceride concentrations in swine. Proc. Soc. Exp. Med. 182:221–224. Rafai, N., and G. R. Warnick. 1994. Lipoproteins and Apolipoproteins. Pages 91–105 in Laboratory Measurement of Lipids. AACC Press, Washington, DC. Raftery, A. E., and S. M. Lewis. 1992. How many iterations in the Gibbs sampler? Pages 763–773 in Bayesian Statistics IV. J. M. Bernardo, J. O. Berger, A. P. Dawid, and A. F. M. Smith, ed. Oxford Univ. Press, Oxford, UK. Richmond, W. 1992. Analytical reviews in clinical biochemistry: The quantitative analysis of cholesterol. Ann. Clin. Biochem. 29:577–597. Rothschild, M., and A. B. Chapman. 1976. Factors influencing serum cholesterol levels in swine. J. Hered. 67:47–48. Ruiz-Carrascal, J., J. Ventanas, R. Cava, A. I. Andrés, and C. García. 2000. Texture and appearance of dry cured ham as affected by fat content and fatty acid composition. Food Res. Int. 33:91–95. Schwab, C. R., T. J. Baas, K. J. Stalder, and D. Nettleton. 2009. Results from six generations of selection for intramuscular fat in Duroc swine using real-time ultrasound. I. Direct and correlated phenotypic responses to selection. J. Anim. Sci. 87:27742780. Sellier, P. 1998. Genetics of meat and carcass traits. Pages 463–510 in The Genetics of the Pig. M. F. Rothschild, and A. Ruvinsky, ed. CAB Int., New York, NY. Sheard, P. R., M. Enser, J. D. Wood, G. R. Nute, B. P. Gill, and R. I. Richardson. 2000. Shelf life and quality of pork and pork products with raised n-3 PUFA. Meat Sci. 55:213–221. Solanes, F. X., J. Reixach, M. Tor, J. Tibau, and J. Estany. 2009. Genetic correlations and expected response for intramuscular fat content in a Duroc pig line. Livest. Sci. 123:63–69. Suzuki, K., M. Ishida, H. Kadowaki, T. Shibata, H. Uchida, and A. Nishida. 2006. Genetic correlations among fatty acid compositions in different sites of fat tissues, meat production, and meat quality traits in Duroc pigs. J. Anim. Sci. 84:2026–2034. Suzuki, K., H. Kadowaki, T. Shibata, H. Uchida, and A. Nishida. 2005. Selection for daily gain, loin-area, backfat thickness and intramuscular fat based on desired gains over seven generations of Duroc pigs. Livest. Prod. Sci. 97:193–202. Tarrant, P. V. 1998. Some recent advances and future priorities for the meat industry. Meat Sci. 49(Suppl. 1):S1–S16. Tejeda, J. F., G. Gandemer, T. Antequera, M. Viau, and C. García. 2002. Lipid traits of muscles as related to genotype and fattening diet in Iberian pigs: Total intramuscular lipids and triacylglycerols. Meat Sci. 60:357–363. Tribole, E. F. 2006. Excess omega-6 fats thwart health benefits from omega-3 fats. BMJ 332:752–760. Trivedi, B. 2006. The good, the fad, and the unhealthy. New Sci. 2570:42–49. Van Oeckel, M. J., M. Casteels, N. Warnants, and C. V. Boucqué. 1997. Omega-3 fatty acids in pig nutrition: Implications for zootechnical performances, carcass and fat quality. Arch. Tierernahr. 50:31–42. Varona, L., L. A. García-Cortés, and M. Pérez-Enciso. 2001. Bayes factor for the detection of quantitative trait loci. Genet. Sel. Evol. 33:133–152. Wood, J. D., M. Enser, A. V. Fisher, G. R. Nute, P. R. Sheard, R. I. Richardson, S. I. Hughes, and F. M. Whittington. 2008. Fat deposition, fatty acid composition and meat quality: A review. Meat Sci. 78:343–358. Young, L. D., W. G. Pond, and H. J. Mersmann. 1993. Direct and correlated responses to divergent selection for serum cholesterol concentration on day 56 in swine. J. Anim. Sci. 71:1742–1753. Zhang, S., T. J. Knight, K. J. Stalder, R. N. Goodwin, S. M. Lonergan, and D. C. Beitz. 2007. Effects of breed, sex, and halothane genotype on fatty acid composition of pork longissimus muscle. J. Anim. Sci. 85:583–591. Downloaded from jas.fass.org by guest on July 16, 2011 2254 Casellas et al. APPENDIX Bayes Factor for Testing the Additive Polygenic Background of Quantitative Traits Heritability was evaluated by calculating the Bayes factor (Kass and Raftery, 1995) of a model accounting for infinitesimal polygenic effects, y = Xb + Za + e, against a reduced model without genetic effects, Smith, 1990), with the exception of h2, which required a Metropolis-Hastings step (Hastings, 1970). The Bayes factor was calculated from the Markov chain Monte Carlo sampling by averaging the full conditional densities of each cycle at h2 = 0 (see Varona et al., 2001 for a detailed description of this methodology). The Bayes factor provides the ratio of posterior probabilities between the 2 tested models. A Bayes factor >1 suggests a relevant genetic background for the analyzed trait, whereas a Bayes factor <1 shows that the model without genetic effects is more probable. Jeffreys (1984) Scale of Evidence for Bayes Factors y = Xb + e, by applying the García-Cortés et al. (2001) and Varona et al. (2001) method. Note that y was the vector of phenotypic data, e was the vector of residuals, β was the vector storing the systematic effects described above, a was the vector of additive genetic effects, and X and Z were appropriate incidence matrices. Following Varona et al. (2001), only the analysis of the most complex model is required to calculate the Bayes factor, after reparameterizing it as The BF is the ratio of posterior probabilities between 2 competing models placed as numerator and denominator in the ratio. Following Jeffreys (1984), the BF can be classified according to 6 levels of evidence: BF < 1: denominator model supported (<0 deciban; dB); 1 < BF < 3.16: not worth more than a bare mention (0 to 5 dB); y = Xb + e*, where e* = Za + e is assumed to follow a multivariate normal distribution with mean 0 and variance 2 V = sp éê ZAZ ' h 2 + I(1 - h 2 )ùú . Note that A was the nuë û merator relationship matrix between individuals, I was an identity matrix with dimensions equal to the num2 2 ber of data, sp was the phenotypic variance, sa was 2 2 the additive genetic variance, and h 2 = sa sp . Under a standard Bayesian development, the posterior probability of all the parameters in model was proportional to p ( b, s , h y) µ p ( y 2 p ( 2 ) 2 2 b, sp , h 2 p (b ) p (sp ) p (h 2 ) , ) 2 where p y b, sp , h 2 ~ N (Xb, V ) and the remaining a priori distributions were assumed flat as in Varona et al. (2001). Random samples from all unknowns in model were obtained by Gibbs sampling (Gelfand and 3.16 < BF < 10: substantial evidence favoring the numerator model (5 to 10 dB); 10 < BF < 31.62: strong evidence favoring the numerator model (10 to 15 dB); 31.62 < BF < 100: very strong evidence favoring the numerator model (15 to 20 dB); and BF > 100: decisive evidence favoring the numerator model (>20 dB). Note that these specific cutoff values were defined on the basis of a 5-unit dB increase, a base-10 logarithmic unit that measures information and entropy (Good, 1979). The BF can be transformed to a dB value (d ) by applying d = 10 (d ). BF Downloaded from jas.fass.org by guest on July 16, 2011 10 , and inversely, BF = 10 × log10 References This article cites 50 articles, 17 of which you can access for free at: http://jas.fass.org/content/88/7/2246#BIBL Downloaded from jas.fass.org by guest on July 16, 2011 ...
View Full Document

Ask a homework question - tutors are online