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Chick-News.com Poultry Industry News, Comments and more by Simon M. Shane

Industry Concern over Myodystrophy Goes Public

03/11/2019

The Wall Street Journal on March 11th commented on the impact of myodystrophy in heavy broilers in an article authored by their agricultural correspondent Jacob Bunge. What he conveyed in principle is correct but his numbers were wrong. The following computation is an attempt to place an approximate dollar value on the problem from the perspective of the industry in 2018:-

 

  • Mass of broiler meat produced on a wog basis = 42.0 billion lbs.
  • Total breast meat available, assuming 33 percent carcass yield = 13.8 billion lbs.
  • Total breast meat from the proportion of heavy birds (+7.0 lbs. live) susceptible to myodystrophy, assuming 25 percent of total production is in this weight range= 3.5 billion lbs.
  • Downgraded and “lost” product assuming a 20% prevalence of obvious myodystrophy = 700 million lbs.
  • Average annual loss in wholesale value of breast meat, averaging values for  fillets and line-run at  $1.50 per lb. = $1billion.

 

Obviously in some complexes producing exceptionally heavy live mass the proportional impact will be greater. This may be implied from the quarterly reports of the public companies, indicating their respective gross margins. The projection of cost does not take into account labor involved in segregating and processing affected breasts or their salvage value as ground meat.

 

Switching from economics to pathology, a consensus regarding causation focuses on a disparity between the development of the vascular supply and the rate of accretion of pectoral musculature. This reality gives rise to myodystrophy, first manifested as “white striping” as fat replaces degenerated muscle tissue.  Subsequently with increasing age or weight and severity “wooden breast” is evident as connective tissue replaces muscle in the pathogenesis of the syndrome.

 

Myodystrophy is evidently genetic in origin and parallels deep pectoral necrosis in turkeys. This condition was successfully suppressed by genetic selection and is no longer a financial burden to this segment of the industry.

Primary breeders have inadvertently created problems in their justifiably relevant selection programs emphasizing growth rate and breast muscle deposition. To their credit, breeders have managed to maintain skeletal conformation in high-yield strains but the deficiencies in vascularization of pectoral musculature were initially subtle. It is only with programs that “push the envelope” that serious losses occur.

 

The primary breeders have previously encountered undesirable phenotypic effects that have been resolved by adjusting components of their index selection. These include tibial dyschondroplasia in the 1970s, eliminated by application of screening of pure lines and elimination of families with a predisposition to the defect. The emergence of ascites syndrome at high altitude in the 1980s and the right-heart failure counterpart termed “flip-over” in the 1990s were caused by a relative disparity in cardio-pulmonary development and growth rate. These conditions were addressed in the short term by changes in management involving brooding systems, temperature control, duration of lighting and ventilation management. Over a few generations of intensive selection the underlying genetic-factors were resolved although high-yield broiler strains subjected to a generous plane of nutrition may still be vulnerable to right-heart failure.

 

Given the current state of knowledge of the pathogenesis of pectoral myodystrophy a short-term solution seems self-evident. High yield broilers should be harvested at a lower live weight as denoted by monitoring the prevalence of the defect in individual complexes. Since there is evidence of pathology induced by hypovascularity at an early age, “slowing” the inherent growth rate in the brooding and post-brooding period may be more beneficial than attempting an intervention from mid-cycle onwards.

 

Although claims have been made for beneficial effects from feed additives the return in terms of improvement in breast quality is difficult to measure under field conditions.  It is evident that there will be no “simple fix” to the problem. The primary breeders (both of them!) are all too conscious of the magnitude of the problem and will incorporate selection against what may be a characteristic of low heritability into their index selection. Fortunately there are alternatives to “high –yield” strains available to suit the product-market scope of specific complexes.

 

As an indirect observation, the WSJ article correctly presents the problem of myodystrophy as a quality-related financial and marketing issue. To date, opposition to high-yield and ultra-heavy broilers has been based on welfare considerations involving locomotory dysfunction and sentiment.  

 

Certainly over the intermediate term integrators will have to throttle back on their preoccupation with breast yield that has inappropriately driven genetic selection. Companies will have to develop programs that optimize return over production cost. It is not a matter of absolutely eliminating the condition on the line, the objective should be to maximize return by achieving a level of the defect that can be tolerated in terms of production cost, value of product and acceptable quality standards. A headlong retreat to “slow-growing” strains would be counterproductive in terms of sustainability and profitability.


 
Copyright 2019 Simon M. Shane