P. Le Roy

Stress hormones, carcass composition and meat quality in Large White×Duroc pigs.

The levels of stress hormones, cortisol and catecholamines (adrenaline and noradrenaline), were measured in urine collected after slaughter from the bladder, in 309 pigs (females and castrated males) from an F2 intercross between the Large White and Duroc breeds to analyze the relationships between stress-responsive neuroendocrine systems, carcass composition and meat quality. Intramuscular fat content was measured from a biopsy sample taken at a live weight of 70 kg from the longissimus lumborum muscle, and carcass and meat quality traits were also collected. Carcass fat content was higher and estimated carcass lean meat content was lower with increasing urinary levels of cortisol and adrenaline (that are highly correlated with each other), but was not related to the levels of noradrenaline, showing that adrenal hormones favor the accretion of fat at the expense of muscle proteins, a typical physiological effect of cortisol. On the contrary, intramuscular fat levels were unrelated to either hormone level. Finally, muscle pH measured 24 h after death was positively correlated with catecholamine levels, an effect related to the catabolism of muscle glycogen by catecholamines released by preslaughter stress, which impairs post-mortem acidification of meat. These results show the importance of a control over stress neuroendocrine systems to increase pork production and product quality, and the value of the genetic approach to reach this goal.

Accurate mapping of the “acid meat” RN gene on genetic and physical maps of pig Chromosome 15

It has been shown that a major gene, called RN, is responsible for the RTN technological yield, a meat quality porcine trait. Experimental families informative for the segregation of RN gene were constituted from animals belonging to the Laconie composite line. We have previously mapped the RN gene to Chromosome (Chr) 15 (Milan et al. Genet. Sel. Evol. 27, 195-199, 1995). A Chr 15 map was established with 16 markers. The RN gene was found to be located between markers Sw120 and Sw936, at 2 cM from Sw936 (LOD = 38.1). In addition, by localizing Sw936 at 15q21–22 using DISC-PCR, we also located RN on the physical map.

A muscle transcriptome analysis identifies positional candidate genes for a complex trait in pig

Muscle tenderness is an important complex trait for meat quality and thus for genetic improvement through animal breeding. However, the physiological or genetic control of tenderness development in muscle is still poorly understood. In this work, using transcriptome analysis, we found a relationship between gene expression variability and tenderness. Muscle (longissimus dorsi) samples from 30 F(2) pigs were characterized by Warner-Bratzler Shear Force (WBSF) on cooked meat as a measurement of muscle tenderness. Gene expression levels were measured using microarrays for 17 muscle samples selected to represent a range of WBSF values. Using a linear regression model, we determined that samples with WBSF values above 30 N could be effectively analysed for genes exhibiting a significant association of their expression level on shear force (false discovery rate <0.05). These genes were shown to be involved in three functional networks: cell cycle, energy metabolism and muscle development. Twenty-two genes were mapped on the pig genome and 12 were found to be located in regions previously reported to contain quantitative trait loci (QTL) affecting pig meat tenderness (chromosomes 2, 6 and 13). Some genes appear therefore as positional candidate genes for QTL.

Numerical comparison between powers of maximum likelihood and analysis of variance methods for QTL detection in progeny test designs: the case of monogenic inheritance

Simulations are used to compare four statistics for the detection of a quantitative trait locus (QTL) in daughter and grand-daughter designs as defined by Soller and Genizi (1978) and Weller et al. (1990): (1) the Fisher test of a linear model including a marker effect within sire or grand-sire effect; (2) the likelihood ratio test of a segregation analysis without the information given by the marker; (3) the likelihood ratio test of a segregation analysis considering the information from the marker; and (4) the lod score which is the likelihood ratio test of absence of linkage between the marker and the QTL. In all cases the two segregation analyses are more powerful for QTL detection than are either the linear method or the lod score. The differences in power are generally limited but may be significant (in a ratio of 1 to 3 or 4) when the QTL has a small effect (0.2 standard deviations) and is not closely linked to the marker (recombination rate of 20% or more).

Genetic variability of transcript abundance in pig skeletal muscle at slaughter: Relationships with meat quality traits

A family structured population of 325 pigs (females and barrows) was produced as an intercross between 2 commercial sire lines and was subjected to a systematic transcriptome analysis of LM samples obtained shortly after slaughter. Additionally, measurements of meat quality traits of fresh and cooked loin were gathered from the same animals. The transcriptome analysis was achieved by microarray hybridization, using a custom repertoire of 15,000 6mer DNA probes targeting transcripts expressed in growing pig skeletal muscle. These data allowed us to estimate the heritability of expression abundance for each of the quantified RNA species. The abundance of 9,765 RNA was estimated as heritable with a false discovery rate of 5%, from which 1,174 were deemed as highly heritable (h(2) > 0.50). We also observed a large number of transcripts whose LM expression abundance is genetically correlated with 4 meat quality traits: the loin pH measured at 45 min postmortem (pH45), 253 transcripts; the loin cooking loss (CL), 134 transcripts; the cooked loin shear force (SFc), 184 transcripts; and the loin color redness (a*) value, 190 transcripts. Heritable and meat quality genetically correlated transcripts showed an over-representation of biological processes involved in the induction of apoptosis (genetically correlated with CL), complement activation (genetically correlated with SFc), glucose metabolism (genetically correlated with a*), and cation channel activity (genetically correlated with pH45). Overall, the biological functions highlighted in the highly heritable transcripts and the lack of transcript that would be genetically correlated with LM glycolytic potential suggest that the genetic variability of the LM postmortem transcriptome is focused on muscle tissue response to postmortem ischemia and reflects more distantly the antemortem muscle physiology. Because of the contrasting distributions of the genetic correlations between LM RNA concentrations and the different meat quality traits studied, indirect selection strategies of meat quality traits based on measurements of selected LM RNA species could be only proposed for a subset of the analyzed meat characteristics (pH45, SFc, a*, CL). A substantial improvement in the efficiency of selection for these meat quality traits could result from measuring muscle RNA concentrations on selection candidates, if the same genetic parameters can be verified using in vivo-sampled muscles.

Updated estimates of HAL n and RN— effects on pork quality: Fresh and processed loin and ham

A 1000-pig F2 intercross QTL detection experimental population was generated using two commercial sire lines. Independent carriers of HAL n and RN- mutations (10% and 14%, respectively) were included in this population as control genotypes. The effects of HAL n and RN- heterozygous genotypes on fresh and transformed loins and hams were estimated using a mixed model methodology. The results document the unfavorable effects of both mutations on meat quality. Smaller effects of HAL Nn genotype compared to HAL nn or RN-rn+ genotypes were estimated. Interestingly, effects of HAL Nn genotype on meat pH and loin color could be insignificant at 24-h postmortem, but translate into higher water losses on storage and cooking, and result in tougher cooked loin. Using the same methodology, significant effects of the PRKAG3 (RN) I199 allele on ultimate pH values but not on glycolytic potential were observed.

Comparison between some approximate maximum-likelihood methods for quantitative trait locus detection in progeny test designs

Abstract The power and efficiency of parameter estimation of four approximate maximum-likelihood segregation-analysis methods for QTL detection were numerically compared using Monte Carlo simulation. The approximations were designed to avoid the long computation required by exact maximum-likelihood segregation analysis for populations composed of large, independent half-sib families, as found in forest-tree and animal-breeding programs. The methods were compared both when information from a marker closely linked to the QTL was available and when it was not. Three of the approximations were from the literature: the Modal-Estimation method initially developed by Le Roy et al., an approximate Regressive Model from Demenais and Bonney, and the Within-Sire method used by Boichard et al. The fourth method was derived from this Within-Sire method by ignoring between-male-parent information and segregation within families due to the alleles inherited from the female parents. The relative advantages of the criteria are compared for various hypotheses concerning the characteristics of the QTL and the size of the population. No one method was clearly superior over all situations studied. The fourth, and simplest, method, however, performed sufficiently well when marker data were available, particularly in terms of power, for it to provide a tool for rapid preliminary screening of data from QTL mapping studies.