Genome-wide identification of quantitative trait loci in a cross between Hampshire and Landrace I: carcass traits.

We report the identification of quantitative trait loci (QTL) affecting carcass composition, carcass length, fat deposition and lean meat content using a genome scan across 462 animals from a combined intercross and backcross between Hampshire and Landrace pigs. Data were analysed using multiple linear regression fitting additive and dominance effects. This model was compared with a model including a parent-of-origin effect to spot evidence of imprinting. Several precisely defined muscle phenotypes were measured in order to dissect body composition in more detail. Three significant QTL were detected in the study at the 1% genome-wide level, and twelve significant QTL were detected at the 5% genome-wide level. These QTL comprise loci affecting fat deposition and lean meat content on SSC1, 4, 9, 10, 13 and 16, a locus on SSC2 affecting the ratio between weight of meat and bone in back and weight of meat and bone in ham and two loci affecting carcass length on SSC12 and 17. The well-defined phenotypes in this study enabled us to detect QTL for sizes of individual muscles and to obtain information of relevance for the description of the complexity underlying other carcass traits.

Free range rearing of pigs with access to pasture grazing - effect on fatty acid composition and lipid oxidation products.

The influence of free-range rearing, RN genotype and sex on different pig meat quality traits, including intramuscular fatty acid composition and levels of lipid oxidation products, were studied. A total of 60 Hampshire crossbred pigs were reared outdoors for two months with access to green feed, while 60 others were kept indoors, in a 120-m(2)-large pen, throughout the rearing period. From these 120 animals a subsample of 44 animals was chosen for meat quality analysis. Of the three factors studied, the RN genotype had the largest influence on basic technological meat quality traits, whereas the rearing conditions and sex had limited effects. However, outdoor rearing resulted in higher levels of polyunsaturated fatty acids in the intramuscular fat (P=0.026) and in an increased level of vitamin E (P=0.030) compared with the pigs that had been reared indoors. The sex and RN genotype of the animals also had an effect on the fatty acid profile: females had higher levels of unsaturated fatty acids (P=0.003) as well as lower levels of saturated fatty acids (P=0.011) than castrated males. Carriers of the RN(-) allele expressed a higher sum of omega-3 fatty acids (P=0.047) and C22:5 (P=0.012) than did the non-carriers. In a storage study where meat from free-range and indoor reared pigs was stored for 3 months at-20°C, it was shown that the lipid oxidation product malondialdehyde was formed at increased levels in animals that had a higher lean meat percentage than others, i.e. females that were carriers of the RN(-) gene and that were reared outdoors.

Sensory and technological meat quality in carriers and non-carriers of the RN(-) allele in Hampshire crosses and in purebred Yorkshire pigs.

The effect of the dominant RN(-) allele on technological and sensory meat quality of loin and ham from pigs, crossbred from Landrace × Yorkshire sows and one Hampshire sire heterozygous for the RN(-) allele was studied. The non-carriers of the RN(-) allele and the purebred Yorkshire pigs were similar regarding most of the technological traits. In comparison with the RN(-) carriers, they had higher values for pH(u), Napole yield, dry matter and protein content, but lower values for drip loss, filter paper wetness, cooking loss, internal reflectance, residual glycogen and glycolytic potential. The three groups did not differ concerning lactate content, intramuscular fat or ash content. Shear-force values did not differ between the two RN genotypes, but both genotypes had lower shear-force values than the purebred Yorkshire pigs. Non-carriers had higher processing yield for cured cooked ham than RN(-) carriers. The RN(-) allele had little effect on the sensory attributes, as assessed by a trained panel using a descriptive test, but there was a tendency to lower chewing time for meat from the crossbreds compared to the purebred Swedish Yorkshire. RN(-) carriers produced more acidic fresh loin than non-carriers and purebred Yorkshire pigs, and juicier cured cooked ham than non-carriers.

Estimated frequency of the RN- allele in Swedish Hampshire pigs and comparison of glycolytic potential, carcass composition, and technological meat quality among Swedish Hampshire, Landrace, and Yorkshire pigs.

The frequency of the dominant RN- allele (Rendement Napole) was estimated in purebred Swedish Hampshire pigs (n = 208) by using the estimated glycogen content in the longissimus muscle at slaughter (glycolytic potential; GP). Carriers (n = 177) and noncarriers (n = 31) of the RN- allele were compared with purebred Swedish Yorkshire (Y, n = 208) and Swedish Landrace (L, n = 114) pigs with respect to GP and carcass composition. Technological meat quality was compared between the RN phenotypes from the Hampshire breed and Yorkshire pigs. The distribution of GP deviated from a normal distribution in all three breeds. Hampshire pigs with GP > or = 183 micromol lactate equivalents per gram wet weight were regarded as carriers of the RN- allele (RN-/RN-, or RN-/rn+), and those constituted 85% of all Hampshire pigs evaluated, giving a frequency of .61 for the dominant allele (RN-). The RN- carriers had higher GP than noncarriers, Landrace, and Yorkshire pigs, but noncarriers and Landrace did not differ regarding GP. The two RN phenotypes did not differ in carcass composition, but the carriers were leaner than Landrace and Yorkshire, with larger proportions of meat plus bone in ham and back. Noncarriers and Yorkshire did not differ in leanness, but both these groups were leaner than Landrace. The RN- carriers had lower Napole yield (cured cooked muscle) and higher drip loss than noncarriers and Yorkshire, but in comparison with noncarriers they also had lower shear force values. In conclusion, the frequency of the RN- allele is high in purebred Swedish Hampshire. Most of the effects of the allele on technological meat quality (i.e., ultimate pH, water-holding capacity, and technological yield) found in crossbred pigs seem also to be consistent for purebred pigs. However, the RN- allele exerted less influence on meat content in purebred pigs.

Effects of outdoor rearing and sire breed (Duroc or Yorkshire) on carcass composition and sensory and technological meat quality.

The effects of outdoor rearing and sire breed on carcass composition and technological and sensory meat quality in pigs were studied in a trial with 102 crossbred slaughter pigs (Yorkshire, or Yorkshire × Landrace sows and Duroc or Yorkshire as terminal sire). Half of each litter were reared conventionally indoors, while the remainder were reared outdoors in a 50 000 m(2) area, as a single group. All pigs were fed ad libitum. Yorkshire sired pigs had significantly leaner carcasses and meat with lower IMF content and marbling scores, and higher shear force and water content. The sire breeds did not differ regarding pH(u), water-holding capacity, or colour. Meat from the Yorkshire crosses was more acid, less tender and gained lower overall acceptance scores in the sensory test. The outdoor-reared pigs had lower daily gain values and leaner carcasses. They produced meat with lower pH(u), higher drip loss, higher shear force values and higher internal reflectances. Their meat contained more lactate and crude protein and had a higher glycolytic potential, less IMF and less water. Regarding the sensory qualities, outdoor rearing impaired tenderness, juiciness and overall acceptance.

Rapid prediction of RN phenotype in pigs by means of meat juice.

The dominant RN(-) allele occuring in the Hampshire pig breed is associated with a high glycogen content in glycolytic muscles. To determine the RN phenotype in meat, certain alternative rapid methods were studied. Instead of using whole muscle, meat juice released from post-mortem longissimus dorsi muscle was used in the analyses. Carriers of the RN(-) allele were distinguished from non-carriers on the basis of the concentration of glucose + glucose-6-phosphate (spectrophotometrically determined), glucose only (determined with a rapid assay for blood glucose in diabetic patients) or the osmolality of meat juice. These results were compared with a classification based on the glycolytic potential or the residual glycogen (sum of [glycogen], [glucose] and [glucose-6-phosphate]) in muscle. Higher levels of glucose, of the sum of glucose and glucose-6-phosphate, and of osmolality were found in meat juice from animals of the RN phenotype. The sum of glucose and glucose-6-phosphate in meat juice seems to be a reliable marker for the determination of the RN phenotype in meat. Glucose or the osmolality of meat juice can also be used, but more as a preliminary method.

A major locus (RN) affecting muscle glycogen content is located on pig chromosome 15.

The RN locus in pigs has a major effect on the amount of stored glycogen in white muscle and affects meat quality. The fully dominant RN- allele, associated with high glycogen content, occurs in the Hampshire breed. We have mapped the RN locus using a large half-sib family comprising one heterozygous RN-/rn+ Hampshire boar mated to homozygous rn+/rn+ Swedish Landrace x Swedish Yorkshire sows. The segregation at the RN locus was inferred from data on glycolytic potential and residual glycogen in white muscle which both showed clear bimodal distributions. Highly significant evidence for genetic linkage was obtained against microsatellite markers on Chromosome (Chr) 15. Multipoint analysis revealed the order Sw1111-8.0-S0088-10.6-RN-4.8-Sw936,Sw906 (recombination estimates are given as Kosambi cM). Comparative mapping data imply that the human homolog of RN is located on Chr 2q.

Intramuscular fat and muscle fibre lipid contents in halothane-gene-free pigs fed high or low protein diets and its relation to meat quality.

Immediately after exsanguination, samples were taken from M. longissimus dorsi (LD) and M. biceps fermorsi (BF) of halothane-gene-free Swedish Yorkshire pigs (entire males and gilts) fed a high-protein (18·5% crude protein, 0·96% lysine; n = 20) or a low-protein diet (13·1% crude protein, 0·64% lysine; n = 20). The lipid content, measured as triglyceride (TG), was analysed after the samples had been freeze-dried and dissected free from blood, fat and connective tissue. Fibre type composition (type I, IIA, IIB, IIC) was analysed by histochemical staining on all samples. In 14 samples of LD, representing the entire variation of the intramuscular fat content (IMF) among the 40 animals, fibre areas, lipid content and oxidative capacity within the fibre types were evaluated. IMF, meat colour and drip loss were measured in both muscles. Shear force was measured on cooked meat samples from LD. IMF was higher in both LD (2·5%) and BF (2·0%) from pigs on the low-protein diet compared with LD (1·5%) and BF (1·3%) from pigs on the high-protein diet. TG content did not differ between diets in BF but was higher in LD from pigs on low- vis-à-vis high protein diet. A significant correlation was seen in LD between IMF and TG content (r = 0·57; P < 0·001). Fibre type composition did not differ between pigs on the two diets. BF had a higher proportion of type I and IIA fibres and a lower proportion of IIB fibres, compared with LD. TG content in muscle was not correlated with fibre type composition or staining intensity for lipids and oxidative capacity. High staining intensity for lipid in LD was seen in all type I fibres and in some type IIA fibres. Meat quality parameters did not differ between groups except shear force, which was higher in pigs fed the high- vis-à-vis low-protein diet (4·7 and 4·0 kg/cm(2), respectively). Shear force was correlated significantly with TG content (r = -0·42; P < 0·01) and IMF (r = -0·43; P < 0·01) in LD. The results of this study show that lipids are stored mainly in type I fibres and in some type IIA fibres. Intracellular triglycerides account for only a small fraction of IMF. The results indicate that IMF and TG content in muscle fibres may be related to shear force.

Muscle histochemical and biochemical properties in relation to meat quality during selection for increased lean tissue growth rate in pigs.

The relationship between the histochemical and biochemical properties of muscle and the quality of meat during selection to improving the lean tissue growth rate was studied. Pigs (n = 82) from Generations 2 and 4 were randomly sampled in a selection experiment in which the genotype x protein interaction was studied. Comparisons were made of longissimus muscle (LM) and quadriceps femoris (QF) from Generations 2 and 4, and biceps femoris (BF) in the fourth generation from pigs fed a low- or high-protein diet. A higher total growth rate, lean tissue growth rate, and lean percentage were found in pigs fed the high-protein diet than in pigs fed the low-protein diet. Pigs fed the high-protein diet had a higher glycolytic capacity in all muscles than pigs fed the low-protein diet. When the meat quality traits were compared, pigs fed the high-protein diet had a lower intramuscular fat content, higher shear force value, higher protein extractability, lower light reflectance, and somewhat higher water-holding capacity. With selection, pigs became fatter on both diets. In Generation 4, glycolytic and oxidative capacity was somewhat higher in muscle tissue than in Generation 2. Muscle metabolic profile and meat quality traits differed among muscles (LM, BF, QF) but no pronounced differences were found between generations. No marked changes were observed in Type I, IIA, or IIB fibers, either between diets or between generations. The Type IIC fibers could only be identified in Generation 4.

Early Post Mortem pH decrease in porcine M. longissimus dorsi of PSE, Normal and DFD quality.

The purpose of this investigation was to compare the muscle pH at exsanguination and the rate of pH changes in porcine M. longissimus dorsi (LD) of normal, DFD (Dark, Firm, Dry) and PSE (Pale, Soft, Exudative) quality. The pH was continuously measured in the LD in 116 carcasses during the first 50 min post mortem. Calculations were made both on measured pH-values and on pH-values transformed to hydrogen ion concentrations. A regression of pH or hydrogen ion concentration on time was made for each animal. These individual regressions were then combined, using a multivariate analysis to estimate regression curves for each meat quality class. The two methods for expressing pH gave somewhat different results. The relationship between the hydrogen ion concentration and time was found to be linear for normal and DFD muscles and quadratic for PSE muscles. As a consequence of the mathematical properties of pH, the relationship between pH and time was found to be quadratic for the normal and DFD qualities, and linear for the PSE quality. For both methods of calculations the slopes for the regression curves were significantly different between PSE and the other two quality classes with both calculating methods, while the slopes did not differ between normal and DFD muscle qualities. The intercepts of the regression curves differed significantly between PSE and the other two quality classes only when the calculations were made on measured pH-values without transformation. A temporary increase in pH was seen in some normal and PSE carcasses during the measured time period. Development of muscles with PSE characteristics thus seems to be initiated by a combination of a lower muscle-pH already at exsanguination and a faster pH decrease. It is also of importance to consider the special mathematical properties of the pH-value.