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The effect of the Duroc breed on the genetics of meat quality

Danie Visser, ARC-AII, Nov. 2003
INTRODUCTION
Carcass quality and meat quality have become increasingly important in modern day pig production. Wierenga (1998) indicated certain important changes in consumer patterns pertaining to product quality:

  • the pursuit for quality and value is stronger than before.
  • the inherent convenience factor associated with modern consumers.
  • products with desired quality attributes must be conducive to better health and safety.
  • consumers want to know the origin and production process of the products they buy (traceability).
  • compliance with sound animal welfare standards.
  • Consumers make decisions based on their perception of a products value. A satisfied consumer is one who perceives quality at or above expectation(s) and is more likely to be retained as a consumer and more likely to be engaged in a positive word-of-mouth.

MEAT QUALITY: INHERENT COMPLEX AND MULTIFACTORIAL
Quality or perceived quality of a product is not a constant and never will be. It will continuously change as the product becomes more or less available, as new products are introduced, as the product ranges of new and established products are extended and as consumers become more sophisticated / informed. This quest for meat or pork quality is aggravated by factors such as

  • Taste and low confidence levels of pork.
  • The fact that the product is not always consumed as such, but cooked, processed and blended with other products.
  • The fact that fresh meat (pork, beef and mutton) is generally sold unbranded.
  • Not many quality cues exist for consumers to rely on.

THE GENETIC BASIS OF PORK AND MEAT QUALITY
Many genetic and non-genetic factors have an inherent influence on meat quality. Non-Genetic Factors can be classified in four categories:

  • MANAGEMENT – Health, Housing, Transport, Feeding etc.
  • THE SLAUGHTERING – Pre-slaughtering handling of pigs, Abattoir,
  • PROCESS Slaughter day, Slaughtering Facilities,
  • Slaughtering Methods etc.
  • CONSUMER RELATED – Consumers perception, behaviour,
  • consumers satisfaction and modern consumer trends. Quality attributes such as labelling and safety and the impact of the media on the behaviour / decisions of the consumer.
  • BIOCHEMICAL PROPERTIE OF THE MUSCLE – Fibre type and fibre area. – Lipid and glycogen content
  • GENETIC FACTORS CAN INFLUENCE MEAT

QUALITY THROUGH THE FOLLOWING FACTORS:

  • MAJOR GENES (MH : RN- : IMF).
  • PSS (Porcine Stress Syndrome linked to the presence of the
  • MH gene) and pre-slaughtering factors).
  • BREED OR GENOTYPE.
  • BOAR TAINT.
  • The HERITABILITY of meat quality traits, such as:
  • pHu; water holding capacity; meat colour, intra muscular fat and tenderness.
  • GENETIC CORRELATIONS.
  • Genetics hereditary (excluding the effects of major genes) account for approximately 30% of the variation in most pork meat quality traits (Andersen, 1999). Various studies have indicated that the heritabilities of the muscle quality traits range between 0.2 to 0.4. The heritability of marbling IMF ranges typically between 0.5 – 0.6 However, unfavourable genetic correlations between meat quality traits and carcass lean content exist.

THE EFFECT OF THE DUROC BREED ON MEAT QUALITY
The effect of breed or genotype can have a marked influence on carcass and meat quality (Huiskes, Binnendijk, Hoofs + Theissen, 1997).
To typify the Duroc breed as the ultimate terminal sire breed or the ultimate solution to the genetic basis of meat quality should be done with caution. However, sufficient scientific studies indicate that the Duroc breed has unusually high values for marbling fat in relation to carcass fat (Edwards, Wood, Moncrieff & Porter, 1992; Hovenier, 1993 and Wood & Cameron, 1994; Blanched, Warkup, Ellis, Willis, Avery, 1999; Hviid, Barton-Gade Oksama & Aaslyng, 2002).
This has resulted in improved juiciness and tenderness of this breed in comparison with the so-called white breeds.
The higher concentration of red oxidative muscle fibres is associated with higher eating quality scores – muscles with more red fibres and according to certain studies also contain higher lipid deposits (Wood & Cameron, 1994).
In a recent selection experiment in Japan by Suzuki and co-workers (2002) the Duroc breed was exposed to seven generations of selection (using the Selection Index and BLUP) for daily gain, eye muscle area, back fat and intra muscular fat. IMF content was increased to 5% over 7 generations, but was associated with an increase in dg, back fat and stagnation of the eye muscle area. Meat tenderness was improved but at the cost of back fat and eye muscle area.
In more recent studies, based on the principles and guidance of the MLC (1992) results, other researchers Enfalt, Lundstrom, Hansson, Lundeheim & Nyström (1997) and Blanchard, Warkup, Ellis, Willis & Avery (1999) indicate superior sensory quality of meat originating from Duroc in comparison to Yorkshire crosses and the correlation between eating quality and the percentage increase in Duroc genes, respectively. According to Hermesch (1997) a higher intra-muscular fat content is genetically related to a higher pH45 and subsequently a reduced drip loss percentage and a darker meat colour.
Blanchard and co-workers (1999) indicated that slaughter pigs, possessing 50 percent Duroc genes in comparison to 0 percent Duroc genes produced more tender meat, had improved pork flavour and a higher overall acceptability. The Presence of 25 percent Duroc genes in the slaughter pigs is reflected in limited impact on growth and carcass traits, minor tenderness advantages, a weaker pork odour and an equal overall acceptability in comparison to white skinned genotypes. Certain research studies have indicated no explicit advantage using the Duroc as terminal sire. Furthermore, dressing percentage and carcass back fat levels increased and lean content decreased as the proportion of Duroc genes increased. On the contrary intensive selection for improved feed conversion and reduced back fat thickness, at 105kg over five and more generations in a Duroc line on pigs in the USA, has resulted in an inferior end product and meat quality (Kuhlers, Jungst & Gamble, 1996).
A study in Denmark to ascertain the impact of sire breed on eating quality was conducted by Hviid, Barton-Gade, Oksama & Aaslyng (2002) involving 337 loin chops from offspring of the following three terminal sire lines: The stress negative Pietrain (PP), The Danish Duroc (DD) and the Danbred Hampshire & Duroc (HD). The Hampshire breed was free of the RN- gene. Results from this study, pertaining to sensory traits and chemical analyses for the three terminal sires, are contained in Table 2.
Meat from the PP genotype was on the same level as that of the HD genotype, but less tender and juicy than that of the DD genotype. Meat from the DD genotype was more tender and had a lower bite resistance than the HD genotype. Other researchers have reported the same tenderness from a pure Duroc sire line when compared to the pure Hampshire sire line, even where the pure Hampshire is a carrier of the RN-gene. In this study (comparing the three terminal sires), the DD-genotype had a significantly higher IMF% (2.0%) in comparison to the HD-genotype (1.6%) and the PP genotype (1,3%). Hence, differences in eating quality of pork chops originating from different sire lines do exist, even in the absence of a major gene for meat quality.
VI CONCLUSIONS
The real challenge for the producer is to ensure that the end product (commencing at the input or genetic level) exhibits high quality when purchased (expected quality) and equally good quality when consumed (experienced quality).
Genetics form the core layer of pork as the product. If meat quality is fixed at conception, or the genetic level (using the desired breed such as the Duroc), future efforts to add value further down the supply chain would simplify the quest for pork quality substantially.
Progress toward higher marbling fat levels is often counteracted by the mean values for crossbred progeny – often less than the average of the parental breeds.
Despite the Marbling Paradox, the Duroc breed has inherent potential to be exploited further. Selection for increased IMF levels and increased lean meat content can be done simultaneously, due to: j the relative low genetic correlation (-0.25 to –0.37) between the two traits and k the high heritability (≥ 0.5) of IMF. Direct selection or gene markers can accelerate this.
Extremes in animal breeding should be avoided. Selection for improved feed conversion and lean growth levels, even in the absence of the MH-gene, will impair pork quality in the long run.
Utilizing the Duroc as terminal sire can partly solve the genetics of meat quality. The foremost answer to the problem is an integrated approach. It would appear that, in order to bring about a worthwhile improvement in eating quality, at least 50% Duroc genes in the slaughter generation are required, implying use of the pure Duroc as terminal sire.
REFERENCES
Andersen, H.J., 1999. What is Pork Quality?
In : Quality of meat and fat affected by genetics and nutrition. Proceedings of the joint session of the EAAP commissions on pig production, animal genetics and animal nutrition. EAAP Publication No. 100. Zurich, Switzerland. 25 August 1999.
Blanchard, P.J., Warkup, C.C., Ellis, M., Willis, M.B. & Avery, P., 1999.
The influence of the proportion of Duroc genes on growth, carcass and pork eating quality characteristics. Animal Science 68 : 495-501.
Edwards, S.A., Wood, J.D., Moncrieff, C.B. & Porter, S.J., 1992. Comparison of the Duroc and Large White as terminal sire breeds and their effect on pig meat quality. Anim. Prod. 54 : 289-297.
Enfält, A.C., Lundström, K., Hansson, I., Lundeheim, N. & Nyström, P.E., 1997. Effects of Outdoor Rearing and Sire Breed (Duroc or Yorkshire) on Carcass Composition and Sensory and Technological Meat Quality. Meat Science 45 : (1) 1-15.
Hermesch, S., 1997. Genetic influences on pork quality. In : Manipulating Pig Production VI. Edited by: P.D. Cranwell, Dec. 1997. Australian Pig Science Association. Pp 82-90.
Hovenier, R., 1993 Breeding for Meat Quality in Pigs. PhD Thesis. Department of Animal Breeding, Wageningen Agricultural University, Wageningen, The Netherlands.
Huiskes, J.H., Binnendijk, G.P., Hoofs, A.I.J. & Theissen, H., 1997. Effects of two sire lines on growth performance, carcass and meat quality. Research Reports 1997. Research Institute for Pig Husbandry. Rosmalen. The Netherlands. pp 57.
Hviid, M., Barton-Gade, P., Oksama, M. & Aaslyng, M-D., 2002. Effect of using Piétrain, Duroc or Hampshire / Duroc as sire line on eating quality in pork loin chops. Proceedings of the 7th World Congress on Genetics Applied to Livestock Production, August 19-23, Montpellier, France.
Kuhler, D.L., Jungst, S.B. & Gamble, B.E., 1996. Indirect selection for lean feed conversion in Duroc swine. J. Anim. Sci. 74 (1) 119 (Abstr)
Meat and Livestock Commission, 1992. Stotfold Pig Development Unit. Second Trial Results. Meat and Livestock Commission, Milton Keynes, U.K.
Suzuki, K., Kadowaki, H., Shibata, T., Uchida, H. & Sato, Y., 2002. Selection for daily gain, loin-eye muscle area, back fat thickness and intramuscular fat in 7 generations of Duroc pigs. Proceedings of the 7th World Congress on Genetics Applied to Livestock Production, August 19-23, 2002, Montpelier, France.
Wierenga, B., 1998. Competing for the future in the agricultural and food channel. In : Agricultural Marketing and Consumer Behaviour in a Changing World. Edited by : Wierenga, B. Van Tilburg, A., Grunert, K., Steenkamp, J-B & Wedel, M. 1998. Kluwer Academic Publishers, Dordrecht.
Wood, J.D. & Camerson, N.D. 1994. Genetics of Meat Quality in Pigs. Proceedings of the 5th World Congress on Genetics Applied to Livestock Production, University of Guelph, Guelph, Ontario, Canada 7-12 August, 1994.

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