The primary goal of this study was to investigate statistical properties of a mixed inheritance model for the localization of quantitative trait loci (QTL). This is based on the analysis of phenotypic data for the amount of intramuscular fat (IMF) scored on 305 individuals originating from a cross between Duroc and Norwegian Landrace breeds. Marker genotype information is available for F1 and F2 generations. Statistical procedures compared involve i) the interval mapping, ii) the composite interval mapping, iii) a regression method, and iv) a mixed inheritance model accounting for a random animal additive genetic effect and relationships between individuals. The basic statistical properties of the latter approach are then assessed using Monte Carlo simulations showing slight unconservativeness as compared to and reasonable power to detect QTL of moderate effects. In the analysis of IMF data, the significant evidence for the existing QTL is detected on chromosome 6. A chromosomal region recommended for a second-step fine mapping analysis is identified between markers SW1823 and S0228, based on three types of confidence intervals derived by using: i) the Jackknife algorithm, ii) the numerical variance approximation, and iii) the LOD score approach. The Jackknife algorithm was additionally used to quantify each family?s contribution to the test statistic and to the estimate of QTL position.
Long-chain omega-3 fatty acids (n-3 FAs) influence meat tenderness, juiciness, and flavor, and are beneficial to human health. The percentage of long-chain n-3 FAs in total FAs is termed the omega-3 index (O3I). It is thus of great interest to favor rising this index in bovine skeletal muscle, to obtain healthier, tastier, and more nutritive meat. This study was aimed to detect transcriptomic variations related to O3I in muscles in 15-month-old males of 4 Spanish cattle breeds raised under the same conditions. Through the analysis of extreme O3I phenotypes, 3 genes of interest (AANAT, UCP2 and AHA1) were identified. AANAT and UCP2 were strongly up-regulated, while AHA1 was repressed in animals with a high O3I. Moreover, gene expression differed between GDF8-null animal muscles (tested for nt821del11 and Q204X mutations) and the wild-type muscles for genes GDH1, IGF2R, FADS1, ASPH, and AIM1, all showing down-regulation in Asturiana de los Valles calves with muscle hypertrophy (GDF8-null). This shows that in GDF8-null animals other pathways are used for FA synthesis.
To predict meat quality after slaughter, biopsy samples were taken from musculus longissimus lumborum et thoracis of live pigs at approximately 40 kg and 80 kg of weight. The obtained values from biopsies for pH1 and EC50 (electric conductivity) were compared with measurements after slaughter at a weight of approximately 110 kg. RYR1 genotypes were determined from blood samples using PCR-RFLP. Mating of Nn sows with two nn boars resulted in 72 Nn and 40 nn offspring. Significant differences between the two genotypes were found for pH1 and EC50 values for the three weights. The coefficients of correlation for the Nn genotype of the RYR1 gene between the values after slaughter and both the first and the second biopsy for pH1 and EC50 were very low (r = 0.06, r = 0.14, and r = 0.26, r = 0.26, P 0.05). For the nn genotype were r = ?0.23, r = ?0.15, and r = ?0.25, r = ?0.11 respectively. The values of pH1 and EC50 were highly correlated (r = ?0.52 to ?0.84, P 0.001) both within biopsies and after slaughter.
The contractile protein troponin I (TnI), a constituent protein of the troponin complex located on the thin filaments of striated muscle, is involved in inhibition of calcium-induced myosin ATPase activity (and thus contraction). TnI-slow (slow-twitch skeletal muscle isoform, named TNNI1) and TnI-fast (fast-twitch skeletal muscle isoform, named TNNI2) are muscle-fiber-type-specific proteins, and expression of their genes may affect the composition of muscle fiber, thereby influencing the meat quality traits. Thus, the TnI genes are potential candidate genes for traits related to meat quality in animals. Association of 2 SNPs (EU743939:g.5174T>C in intron 4, and EU743939:g.8350C>A in intron 7) of the TNNI1 gene and a SNP (EU696779:g.1167C>T in intron 3) of the TNNI2 gene with 11 meat quality traits were studied on 334 Large White x Meishan F2 pigs. In the TNNI1 gene, g.5174T>C and g.8350C>A were found to be significantly associated with intramuscular fat content and meat color value of biceps femoris. The g.5174T>C also showed significant effects on meat color value and marbling score of longissimus dorsi, as well as pH of longissimus dorsi and semispinalis capitis. The g.1167C>T polymorphism in the TNNI2 gene affected significantly the pH of longissimus dorsi, meat color value of longissimus dorsi and semispinalis capitis, marbling score of longissimus dorsi, and intramuscular fat.
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