Complex genetic relationships exist between pig lean growth efficiency and pork quality
Chunyan Zhang, PhD
Research Associate, University of Alberta / Genesus Inc.
All pig producers will agree, feed is the largest cost of production, accounting for about 65% of the total cost. So improvement of feed efficiency has always been a priority in pig breeding and selection programs, as any effort aimed at increasing feed efficiency will significantly reduce production cost, and consequently increase total profitability. As a meat producing animal, feed efficiency is usually defined as lean growth efficiency. Growth performance, feed intake, loin depth and backfat depth are routinely used to evaluate lean growth efficiency. Lean growth efficiency does not focus on pork quality at all. Over the last 35 years, pork consumption has decreased about 4.8 kg per-capita in US and 11.6 kg per-capita in Canada (AAFC, 2015). Of course this decline is related to many factors, but one possible reason is that the focus on lean growth efficiency has produced leaner, lower quality pork. This resulted, it might be argued, in a decrease in the taste and flavour of pork. In recent years, the demand for better tasting pork has been increasing along with improved living standards and purchasing ability, more and more people are willing to pay extra for better quality pork. Therefore, simultaneous selection for lean growth efficiency and pork quality becomes more and more important if a pig breeding company is to meet market demands and assure its continued competitiveness and success.
However, it is not necessarily easy to improve lean growth efficiency and pork quality simultaneously due to the complex relationship between them that are also not well understood. Growth performance, feed intake, carcass composition and pork quality depend on multiple interactive effects of genetics, rearing conditions (feeding level, housing and environmental conditions, production system), pre-slaughter handling, and carcass and meat processing. Considering the genetic part, a few studies reported the genetic correlations between these economically important traits. Generally, selection for lean growth efficiency resulted in reduced feed intake and backfat depth, plus increased growth rate and loin depth, which is favorable for lean meat yield. However, selection for lean growth efficiency also resulted in less marbling, lower pH, lighter meat color and greater drip loss (Suzuki et al., 2005; Gilbert et al., 2006; Cai et al., 2008; Lefaucheur et al., 2011), which is not desired for good quality pork. These findings suggest that high emphasis on lean growth efficiency may improve feed efficiency, but will likely impair pork quality.
Therefore, new approaches for improving lean growth efficiency and pork quality are especially desirable, and the possible options include modification of the multi-trait selection index and the use of genomic assisted selection. Genesus Inc., as a global pig breeding company has a systematic breeding program for purebred sire lines which involves weekly EBV evaluation for important economic traits including feed intake, growth performance, lean yield and important pork quality traits. Genesus is integrating advanced genomic technologies into it’s breeding program with the aim of increasing the rate of genetic gain for lean growth efficiency, carcass lean yield and pork quality. In addition to the studies on separate traits (please see the details from http://www.genesus.com/global-tech-report/genomic-selection, http://www.genesus.com/global-tech-report/genetic-improvement-on-carcass-and-pork-quality), we also investigated some important genomic markers to see how they impacted both lean growth efficiency and pork quality. In summary, as expected complex genetic relationships exist between the genomic markers and the traits. Some genomic markers have significant effects for both: for example, pigs with favorable alleles for growth (higher ADG) usually eat more (larger feed intake), also have better quality of pork with greater marbling, tenderness and pH. These genomic markers would be very useful to aid in selection for lean growth and pork quality, although these markers are associated with larger feed intake. However, some genomic markers had antagonistic effects on the two categories of traits, and the favorable alleles for faster growth resulted in lower marbling and pH, and larger shear force and drip loss, which are undesirable for pork quality. So these markers are better to be avoided if we aim to select both lean growth and pork quality. For quite a few other genomic markers, they were significant for one type of trait, but had no significant effect for the other type of trait. These genomic markers could help to improve one type of traits without antagonistic effects on the others.
A better understanding of the relationships among the economically important traits, especially at the genetic level, is key to update the selection indexes that are used for selection in the Genesus system, and will consequently contribute significantly to increasing the profitability for Genesus customers.Reference:
AAFC 2015. http://www.agr.gc.ca/eng/industry-markets-and-trade/statistics-and-market-information/by-product-sector/poultry-and-eggs/poultry-and-egg-market-information/industry-indicators/per-capita-consumption/?id=1384971854413; access date Dec.18, 2015.
Cai et al., 2008. Selection response and genetic parameters for residual feed intake in Yorkshire swine. J. Anim. Sci. 86: 287-298.
Gilbert et al., 2007. Genetic parameters for residual feed intake in growing pigs with emphasis on genetic relationships with carcass and meat quality traits. J. Anim. Sci. 85: 3182-3188.
Lefaucheur et al., 2011. Muscle characteristics and meat quality traits are affected by divergent selection on residual feed intake in pigs. J. Anim. Sci. 89: 996-1010.
Suzuki et al., 2005. Genetic parameter estimates of meat quality traits in Duroc pigs selected for average daily gain, longissimus muscle area, backfat thickness, and intramuscular fat content. J. Anim. Sci. 83: 2058-2065.