What role does genetics play with regard to meat quality and boar taint?

by Dr Danie Visser Genetic and non – genetic factors have an inherent influence on meat quality. Quality refers to those attributes of meat which the public like best and for which they are indeed prepared to pay more than average prices. Genetics do influence the quality attributes of pork that will eventually satisfy or dissatisfy the consumer. Hereditary factors (excluding the effect of major genes) account for approximately 30% of the variation in most pork meat quality characteristics such as pHu [pH 24 hours post mortem], tenderness, juiciness and flavour. Genetics is also expressed by major gene effects. Table 1 gives an indication of the effect of major genes across different pig breeds on meat quality. The Duroc breed as termianl sire plays a pivotal role in many breeding programs across the world, and hence the genetics of meat quality should be ingrained in the end product. It is also heartening to note that very recent research conducted by Soma (2015) on the prevalence of the IGF2 - allele on Large White and Landrace offspring representing three different genotypes (AA; A/G & GG) did not have any significant negative effect on the meat quality aspects of the carcasses. Traits that had been involved in the study include pH, drip loss, water holding capacity, protein solubility, fatty acid composition, muscle colour, Warner-Bratzler shear force on cooked meat, muscle fibre typing and myofibril fragmentation. Boar Taint The prevalence, chemical components, biochemistry, heritability of its components (androstenone, skatole and indole) had been researched comprehensively across the globe for many years now. Market surveys in various parts of the world indicate that consumers do experience boar taint when buying and preparing pork. To discuss boar taint and put all its components in perspective warrants more than one article in this magazine. This phenomenon should be addressed taking the non-genetic management factors as well as the genetic factors into consideration. Androstenone is a pheromonal steroid that is being synthesized in the testes and metabolised in the liver. Certain amounts of androstenone accumulate in adipose tissue that is causing the typical urine like odour. Skatole on the other hand is produced in the large intestines by bacterial degradation (through enzymes) of the amino acid tryptophan and metabolised by the hepatic cytochrome P450 enzymes and sulphotransferase. The un-metabolised part of this degradation process ultimately accumulates in adipose tissue causing the faecal like odour. The non-genetic factors that are being used to minimize boar taint are: chemical castration via Improvac vaccination, sex splitting, genotype selection, feeding (the inclusion of activated charcoal - as such will adsorb any harmful or undesirable substances that may be present in the gastro-intestinal tract) and clean housing, weight for age marketing strategies, fat biopsies on live animals, on-line detection in processing plants, etc. Genetic markers and genomic selection have opened up far reaching opportunities to produce intact males that are free of boar taint, yet grow just as well as normal boars. Boar taint however is a paradoxal trait in the sense that previous attempts to select for boars/lines with low boar taint threshold values and thus identifying those breeding animals with low heritabilities for androstenone and skatole resulted in reproductive problems in dam lines. Hence the challenge for researchers is indeed to select for those specific markers for boar taint that would simultaneously minimize the negative effects of reproduction. At the University of Guelph in Canada researchers have a few years ago already developed genetic markers for low boar taint based on SNP’s in candidate genes. This research is also conducted and intensified in Europe, the Netherlands, France, Denmark, etc. The ultimate objective is to utilize genomics along with marker assisted selection to select and produce homozygous pigs (especially boars for the AI stations) that have all the favourable low androstenone alleles and that would decrease the adipose (fat) skatole and androstenone concentrations between 35 – 45 % respectively. Nature has bestowed some mercy on us in the sense that the allele associated with a low androstenone concentration in fat is the dominant allele over the allele with a high androstenone concentration. As mentioned already, the influence of genetics on meat quality is in the region of 30%. However, an integrated approach to enhance the desired meat quality traits in all the links of the supply chain should be endeavoured. Producers are compensated on the percentage lean meat in the carcass and hence the drive over the last two decades especially had been to produce leaner pigs and currently to produce leaner and heavier carcasses. However genetic antagonisms (for instance the Halothane Paradox and the Marbling Paradox) are also imprinted in animal and pig breeding. To this effect an unenviable situation in pig breeding is the marginal genetic antagonism (- 0.25) between meat quality traits (juiciness, tenderness, flavour and overall acceptability) and carcass leanness. What will the biggest challenges be for pig breeding over the next five years? Bio-security and health on a national and international level The competition between animal and man for protein and energy Optimal utilization of our water resources from a farmers perspective, but also from a government, local government, municipal and individual citizen perspective Aligning yourself with the right and value adding partners in the supply chain International benchmarking – proving that genetic suppliers can play in the Super League Import restrictions pertaining to frozen semen and breeding animals Meat imports, the vulnerability of the rand and currently the drought that we are facing The quest for efficiency and quality and to find a trade – off between the two Finally: It seems as if animal welfare, human rights, consumerism, bio-security and corporate social responsibility must all be built into your current and future pig breeding philosophy. An excerpt of an article that appeared in PORCUS: December 2015 pp 17 - 20
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