Åsa Josell

A second mutant allele (V199I) at the PRKAG3 (RN) locus - I. : Effect on technological meat quality of pork loin.

The effect of three alleles (RN(-), rn(+) and a second mutant allele V199I, denoted rn*) at the PRKAG3 (RN) locus on such meat quality traits as pH, internal reflectance (FOP), Warner-Bratzler shear force, water-holding capacity and cooking loss were studied. M. longissimus dorsi (LD) from a total of 334 crossbreed pigs, entire males and females, Hampshire (H) and Finnish Landrace (L) of three combinations H × LH, LH × H and LH × LH, were used. The PRKAG3 alleles were identified with a DNA test and all possible RN genotypes, RN(-)/RN(-) (23%), RN(-)/rn(+) (24%), RN(-)/rn* (33%), rn(+)/rn(+) (8%), rn(+)/rn* (9%) and rn*/rn* (2%), were found. Water, intramuscular fat, protein and glycogen contents were determined. All the three alleles at the RN locus affected the studied technological meat quality traits of pork loin, except for the internal reflectance 24 h post mortem and the shear force. The RN(-) allele was dominant over the other two alleles, rn(+) and rn*, in LD with regard to ultimate pH, water-holding capacity and cooking loss, giving lower ultimate pH and water-holding capacity and higher cooking loss. The rn* allele affected ultimate pH in LD of non-carriers of the RN(-) allele, giving higher ultimate pH. The RN(-) allele was also dominant over the other two alleles in residual glycogen content in entire male pigs, but not in female pigs, where the rn* allele had a glycogen-lowering effect. The water content was higher and the protein content lower in LD of all RN(-)/- animals compared with the other genotypes, while no significant differences were found with regard to IMF content. Water-holding capacity, cooking loss and shear force were higher in LD of entire males compared with females.

Genome-wide identification of quantitative trait loci in a cross between Hampshire and Landrace II: Meat quality traits

BackgroundMeat quality traits are important in pig breeding programs, but they are difficult to include in a traditional selection program. Marker assisted selection (MAS) of meat quality traits is therefore of interest in breeding programs and a Quantitative Trait Locus (QTL) analysis is the key to identifying markers that can be used in MAS. In this study, Landrace and Hampshire intercross and backcross families were used to investigate meat quality traits. Hampshire pigs are commonly used as the sire line in commercial pig breeding. This is the first time a pedigree including Hampshire pigs has been used for a QTL analysis of meat quality traits.ResultsIn total, we analyzed 39 meat quality traits and identified eight genome-wide significant QTL peaks in four regions: one on chromosome 3, two on chromosome 6 and one on chromosome 16. At least two of the QTLs do not appear to have been detected in previous studies. On chromosome 6 we identified QTLs for water content in M. longissimus dorsi (LD), drip loss in LD and post mortem pH decline in LD. On chromosomes 3 and 16 we identified previously undetected QTLs for protein content in LD and for freezing and cooking loss respectively.ConclusionWe identified at least two new meat quality trait QTLs at the genome-wide significance level. We detected two QTLs on chromosome 6 that possibly coincide with QTLs detected in other studies. We were also able to exclude the C1843T mutation in the ryanodine receptor (RYR1) as a causative mutation for one of the chromosome 6 QTLs in this cross.

Sensory quality and the incidence of PSE of pork in relation to crossbreed and RN phenotype

The effects of crossbreed and of RN phenotype on pork and its eating quality were evaluated in four different pig crossbreeds [involving Swedish Landrace (L) × Yorkshire (Y) sows and Hampshire (H), Duroc (D), Yorkshire (Y) or Hampshire × Yorkshire (HY) as the terminal sire]. Pigs from the LYH crossbreed were also classified as either carriers or non-carriers of the RN(-) allele. In the crossbreeds investigated, M. longissimus dorsi (LD) and M. semimembranosus (SM) from LYH were found to have the lowest pH as measured 24h post-mortem (pH(24h)). The low pH in the LYH crossbreed was due to the large proportion of RN(-) carriers it had (approximately 70%). The non-carriers of the RN(-) allele in the LYH crossbreed had a pH(24h) close to that of LYD, LYY and LYHY. In a selected group of pigs (N=50), the ultimate pH in the ham muscles M. biceps femoris (BF), M. quadriceps femoris (QF), M. gluteus medius (GM) and M. semitendinosus (ST) was also found to be lower in RN(-) carriers of LYH than in the other crossbreeds. As determined visually, LYD had the highest frequency (2%) of pale, soft and exudative meat (PSE), in LD. Ham from RN(-) carriers of LYH had the highest frequency (23%) of PSE meat around the femur, indicating that when the pH is low, the deep musculature, in which the chilling rate can be slow, is particularly sensitive to the development of PSE. According to assessments by members of a trained sensory panel, tenderness was significantly greater in LD from carriers of the RN(-) allele in LYH than in LD from LYD, LYHY and non-carriers of LYH. The tenderness of LD from LYY was rated as intermediate. The intramuscular fat content was found to be highest in LD from LYD, no relationship between intramuscular fat content and tenderness being found. The RN(-) carriers of LYH received the highest ratings in terms of juiciness. In conclusion, the sensory ratings demonstrated the great eating quality of LD from carriers of the RN(-) allele, indicating that abandoning the Hampshire crossbreed or eliminating the RN(-) allele from it, would result in the meat being less tender.

Determination of RN(-) phenotype in pigs at slaughter-line using visual and near-infrared spectroscopy.

The specific characteristics of meat from the Hampshire breed of pig, including high glycogen content and low ultimate pH and technological yield, have been associated with the dominant RN gene. In Sweden, purebred Hampshire or Hampshire x Yorkshire is often used as terminal sire in the three-way crosses used for pig meat production. For the industry producing cured and cooked hams there is a need to detect the RN(-) carriers of the pigs early post mortem in order to select non-carriers for ham production. In the present study, the possibility of separating RN(-) carriers from non-carriers using a combination of visual and near-infrared (NIR) spectroscopic measurements in reflectance mode through a fibre-optic probe has been studied on commercial pigs in a slaughterhouse. The NIR measurements were performed 30 min post-mortem. Sixty-three animals were considered to be carriers and 33 animals non-carriers based on their glycolytic potential in M. semimembranosus (above 200 μmol/g for RN(-)rn(+) and below 180 μmol/g for rn(+)rn(+)). By using NIR together with classification with neural networks, RN(-) carriers could be separated from non-carriers. None of the carriers and only four non-carriers of the RN gene were misclassified as carriers of the RN gene. The ultimate pH could be predicted using linear partial least squares regression with a correlation coefficient of 0.57 and an accuracy of 0.074 root mean square error of prediction.

The influence of RN genotype, including the new V199I allele, on the eating quality of pork loin

The eating quality of M. longissimus dorsi (LD) from RN(-) homozygotes, RN(-) heterozygotes and RN(-) non-carriers was investigated in a Swedish Hampshire×Finnish Landrace pig population. The recently identified new allele (V199I, here denoted rn*) at the RN locus was also detected among the pigs selected and included in the sensory evaluation. The number of animals varied from 10 to 15 in the five genotype groups; RN(-)/RN(-), RN(-)/rn+, RN(-)/rn*, rn+/rn+ and rn+/rn* (in total 59 pigs). In addition, one pig was determined to be rn*/rn* but was excluded from the analysis. The three genotypes in which the RN(-) allele was represented (RN(-)/RN(-), RN(-)/rn+ and RN(-)/rn*) had higher glycogen and lower protein contents as well as lower ultimate pH (measured 48 h post-mortem) in LD than the non-carriers (rn+/rn+ and rn+rn*). Of the sensory parameters evaluated (tenderness, chewing time, chewing residual, juiciness, meat flavour and acidity), the five RN genotypes only affected acidity significantly; the RN(-) allele contributing to a more acid taste in LD. The influence of the rn* allele resembled that of rn+ on the sensory parameters. When the material was divided into three groups (homozygous, heterozygous and non-carriers of the RN(-) allele) the juiciness was found to be significantly influenced by RN genotype, and LD from animals that were homozygous and heterozygous with respect to the RN(-) allele exhibited a higher juiciness than LD from non-carriers. The RN(-) allele also tended to contribute to greater tenderness, which was significantly higher in LD from heterozygous carriers than from non-carriers of the RN(-) allele. A more rapid decline in pH (measured as pH at 45 min and 3 h post-mortem) contributed to a greater tenderness in LD (according to a trained panel and Warner-Bratzler shear force). In addition to the RN genotype, the decline in pH was influenced by carcass weight, which varied between 71 and 97 kg, and by stunning procedure, which changed during the course of the study from individual to group stunning with CO(2). The individual stunning procedure contributed to a lower pH in the initial post-mortem phase (pH(45)), whereas a higher carcass weight and the RN(-) allele lowered the pH in the mid-post-mortem region (pH(3h) and pH(24h)), significantly (P⩽0.05). The pH continued to decline after 24 h post-mortem and the ultimate pH was not reached until 48 h post-mortem. The cooking loss, juiciness and acidity were related to the specific characteristics of the RN(-) carriers, such as higher glycogen content, lower protein content and lower ultimate pH (pH(48h)).

Possible mechanism for the effect of the RN-allele on pork tenderness.

The effect of the dominant RN(-) allele on rigor development, ageing and tenderness was studied in M. longissimus dorsi (LD) from 11 heterozygous carriers and five non-carriers of the RN(-) allele. Rigor development was followed by measurements of muscle shortening, isometric tension, pH and FOP. During ageing the myofibrillar length and Warner-Bratzler shear force were measured in the meat. Sensory analysis was performed at 4 days post-mortem using a trained expert panel. It was found that the decrease in pH was faster for RN(-) carriers than non-carriers during the first 5 h post-mortem, after which the pH-time slope was similar for the two groups. This resulted in a significantly lower mean ultimate pH in LD from RN(-) carriers than non-carriers. During rigor development the isometric tension was lower in RN(-) carriers than in non-carriers, while contraction (shortening and sarcomere length) did not differ significantly between the two genotypes. The myofibrillar length, which is an indirect measure of the proteolytic activity that has occurred in the meat, was shorter for the RN(-) carriers than for the non-carriers. The difference in myofibrillar lengths between the genotypes was significant at 1 and 4 days post-mortem but not at 7 days post-mortem, which indicates that the RN(-) carriers have a higher proteolytic activity earlier post-mortem. The results from the Warner-Bratzler shear force measurements showed that the meat from the RN(-) carriers was significantly more tender, 1 and 4 days post-mortem, than the meat from the non-carriers. The meat from non-carriers needed 7 days to reach the tenderness attained by that from the RN(-) carriers 4 days post-mortem. The greater tenderness in LD from RN(-) carriers than that from non-carriers was also confirmed by a sensory panel at 4 days post-mortem. In conclusion, differences observed in the course of rigor and ageing in muscle from carriers and non-carriers of the RN(-) allele suggest that proteolytic action, as initiated by a more rapid fall in pH, is the most important factor governing the variation in tenderness of the two genotypes.

Effect of stunning conditions on occurence of PSE defects in hams of rn+/RN− pigs

Pigs of the same genetic type at the RN and HAL loci, i.e. rn(+)RN(-)/NN were reared in similar conditions of feeding and housing. They were slaughtered in two abattoirs (referred to as A1 and A2) using a mixture of air (30%) and CO(2) (70%), at a rate of 300 pigs per hour per slaughterline. One hundred and thirty-two pigs from 11 farms were slaughtered in A1 using a corusinga restrainer and 127 pigs from 5 farms were slaughtered in A2 with the backloading technique. pH at 40 min, 2.5 h and 24 h after slaughter and colour (L*, a*, b*) at 24 h after slaughter were measured in the semimembranosus muscle. Meat quality of the ham was scored as follows: 1, no PSE-zone; 2, doubtful; 3, PSE-zones in the semimembranosus and sometimes on the internal flexor muscles; 4, PSE-zones in all the flexor muscles. The muscle pH value was higher in A2 than in A1 at 40 min post mortem (P<0.01), but not at 2.5 and 24 h. L* (P<0.001) and b* (P<0.05) were higher in A1 than in A2. There was a remarkable difference in meat quality scores, with 50% of the hams scoring 3 or 4 in A1, vs 13% in A2. Lairage time before slaughter affected (P<0.01) the pH value at 2.5 h (5.69 vs 5.93). The values of pH1 and pH2.5 decreased with increasing the meat quality score. The values of L* and b* increased markedly with the score. The results of the present study indicate that the method of bringing the slaughter pigs to the stunning device affects the frequency and importance of PSE meat in the ham. The automated driving of groups of animals to the stunning machine combined with the backloading of a nacelle, compared to a traditional system driving pigs in single file using electrical goads and a restrainer was beneficial with respect to both meat quality and animal welfare.