Impacts of Genetic Improvement on Meat Quality

Meat lines are being genetically selected for rapid growth, high feed conversion efficiency and large muscle mass. The effects this has on meat quality are beginning to emerge, and it is now recognized that they depend partly on the genotype that is chosen at the outset. Each species, and sometimes each breed, needs to be considered separately.

Some of the improvements in growth performance and conformation have had unwanted effects on meat quality. Animals with large muscles often have poor marbling in their meat and this is leading to problems with meat dryness. This has been a feature in beef, pigs and turkeys, but an additional problem in turkeys is the high cooking loss of its breast meat.

Selection for growth rate in cattle, pigs and broiler chickens is resulting in paler meat. In the case of pigs, this is linked to the PSE condition, where selection is being directed towards stress-susceptible genotypes. Turkey sire lines are being selected inadvertently for stress-induced glycogen depletion in their muscle and DFD meat.

Some of the traditional European beef breed societies claim that meat quality is superior in their genetically improved pedigree stock. However, the differences are not as pronounced as some of them might hope. When two African breeds (Afrikaner and Nguni) were compared with a range of temperate cattle breeds under comparable conditions, their meat had less marbling but when ovenroasted it had similar eating quality (Strydom et al ., 2000). At the other extreme, genetic selection for double muscling is leading to less marbling and paler, less red meat and, because of the lower level of marbling, there is a risk that the meat has less succulence and flavour. In temperate cattle breeds not expressing double muscling, selection against fatness could be leading to tougher meat, as in some breeds the genetic correlation between the two traits is strong (Table 12.7). However, simultaneous selection for growth rate should counteract the trend towards toughness. In subtropical beef breeds selection against fatness may be less closely linked to meat toughness, whilst selection for growth rate could be leading to paler meat (Reverter et al ., 2003). In addition, the heritability of meat quality traits is slightly higher in subtropical compared with temperate breeds (Johnston et al., 2003).

It should be possible to improve marbling genetically when an appropriate marker is discovered. Marbling score can be highly heritable in beef, but this depends to some extent on breed ( h 2 = 0.71; Splan et al ., 1998). The h 2 for tenderness is not as strong (0.26 to 0.35), and meat flavour and juiciness are not heritable.

In pigs, intramuscular fat content and meat tenderness have a high heritability ( h 2 = 0.4 to 0.6), as does meat redness ( h 2 = 0.72; Oksbjerg et al., 2004). It might be hoped that insufficient redness could be corrected genetically by influencing the fibre types in the muscles. However, genetic selection for a high proportion of slow-twitch type I fibres in the longissimus dorsi muscle did not influence the rate of post-mortem muscle glycolysis in that muscle or subsequent meat colour in the biceps femoris (Lefaucheur et al ., 2000).