Dr. S.F. Bilgili, Graduate Program Officer, Department of Poultry Science, Auburn University
Dr. Joseph Hess, Extension Specialist and Associate Professor, Auburn University
Green Muscle Disease (or Deep Pectoral Myopathy, DPM) is a degenerative disease of the minor pectoral muscles (i.e. the tenders), which is characterized by atrophy and necrosis. The condition arises when the muscle fibers become deficient in oxygen and is associated with sudden and excessive wing flap. The development of the disease can be split into three categories. Category 1 is the acute inflammatory lesion in which the deep pectoral muscle is very red and hemorrhagic. Category 2 describes the stage at which the lesion in the inner fillet becomes well defined and is sometimes circumscribed by a hemorrhagic ring. Category 3 describes the progressive degeneration and greening of damaged tissue. Although the incidence of DPM is increased in heavy broilers, it can occur at any age or weight and is dependent upon the management and husbandry systems employed. Identifying and eliminating the management issues which contribute to wing flapping and the development of the condition is key to reducing the incidence of DPM.
Introduction
Green Muscle Disease is a hidden problem in modern-day broiler chickens. Green Muscle Disease (or Oregon Disease) is a common name given to a degenerative muscle disease known as Deep Pectoral Myopathy (DPM). The condition is characterized by necrosis and atrophy of the tenders (i.e. supracoracoideus or minor pectoral muscles). The lesions often affect both tenders and vary in color, progressing from a pinkish hemorrhagic appearance to a gray-greenish discoloration as illustrated in Figure 1.
Figure 1: Deep Pectoral Myopathy
DPM was first described in mature breeder turkeys and broiler breeders but is being seen more in meat-type chickens, especially those selected for breast muscle development. The affected muscles are discarded during de-boning, result ing in saleable yield losses. However, the major issue with DPM is that if the birds are marketed as whole carcasses or parts, the problem is rarely detected during processing, resulting in consumer complaints and making the cause of the problem difficult to identify.
The condition is not associated with any infectious agent and therefore has no public health significance other than by affecting the aesthetic appearance of the meat.
DPM is rarely detectable during processing if the birds are marketed as whole carcasses or parts.
Why Does DPM Target Broiler Breast Muscles?
- The pectoral muscles in avian species are associated with flight and the deep and superficial pectorals work in synergy, one to raise the wing and the other to lower it.
- The anatomy of these muscles is, however, intrinsically different in that the inner fillet has a tough outer sheath which is made up of dense fibrous tissue and is inelastic.
- The outer or major muscle is simply surrounded by loose connective tissue that moves easily over the muscle surface as the muscle profile changes.
Contraction of the major pectoral muscles (the breast fillet) and the minor pectoral muscles (the tender) are responsible for the up- and down-strokes of the wings. During contraction, these muscles expand with increased blood supply (i.e. muscle pumping). The expansion of the minor pectoral muscle, by as much as 25% in volume, is problematic because this muscle is confined in a ‘tight compartment’, sandwiched between bone (the sternum) and the large breast fillet. The minor pectoral muscle is also encased in a rigid fibrous sheath which restricts increases in muscle volume. Therefore, when intramuscular pressure increases to levels above circulating blood pressure, the blood supply flowing into the muscle stops and, with continued muscle activity, oxygen deficiency rapidly develops and lack of oxygen (ischaemic necrosis) of the muscle fibers occurs. There is also an additive effect as the muscle pH falls. Typically the middle third of the muscle is involved. In experimental studies, relatively short periods of wing flap are enough to induce these degenerative changes.
Recognition and Identification of the Development Stages in DPM
In response to complaints of DPM from the processing plant and/or customers, an investigation should be organized. This should include the identification of the category of DPM (fresh or old) at the processing plant. This information can then be correlated to husbandry management practices.
Category 1: The acute inflammatory lesion in which the deep pectoral muscle is very red and hemorrhagic. Hemorrhages also appear on the fibrous sheath (see Figure 2). There is an obvious suffusion of serous fluid in the area of the damage making it appear wet. This stage is likely to be associated with a handling event (e.g. catching) and will be present for about 48 hours.
Figure 2: Early Acute Pectoral Myopathy
Category 2: At this stage the lesion in the inner fillet has become well defined and is sometimes circumscribed by a hemorrhagic ring (see Figure 3). The affected areas are pale pink to plumb colored and there are clear changes consistent with early coagulative necrosis of the muscle, when the tissue texture becomes fibrous. This is sometimes described as ‘fish flesh’. This stage will continue for a few days after the initial event or incident.
Figure 3: Pectoral Myopathy – developing lesions
Category 3: This stage reveals the progressive degeneration and greening of the damaged tissue (see Figure 4). Often, only the middle part of the fillet is involved and the progressive greening is in parallel with the loss of cellular structure, so that a ‘putty like’ consistency develops within the lesion. This green, necrotic area will persist and through time will gradually reduce in size as it is reabsorbed so that the sym metry of the breast is lost in some older birds. The green color is produced by the breakdown of hemoglobin and my oglobin to bile salts.
Figure 4: Aged Pectoral Myopathy
Factors affecting the occurrence of DPM
The pectoral muscles make up nearly a quarter of the total liveweight in current-day meat chickens. Rearing broiler chickens to heavy market weights can increase the probability for occurrence of DPM. Incidence is dependant on management and husbandry systems and not simply bodyweight as birds at any age or weight can be affected.
DPM is associated with the following factors:
- Excessive wing flapping
- Heavy market bodyweight
- Sex: incidence can be higher in males compared to females
- High white meat yield
- Rapid growth rate
The desirable efficiency in growth and anatomy of today’s broiler brings with it the possibility of DPM development.
Commercially raised broiler chickens are kept relatively comfortable and inactive during the growing period. Consequently, the pectoral muscles are not exercised enough to increase efficiency of the circulatory supply to the muscles and to allow the expansion of the surrounding fibrous sheath. It is doubtful that even a subtle amount of wing activity would help improve circulation or develop the sheath adequately.
Few, if any, processing plants actually track or document the incidence of DPM on a regular basis. Detection of DPM on whole carcasses and parts is extremely difficult as lesions are not visible during carcass inspection or sorting. As birds also exhibit no symptoms, finding affected live birds in a flock and treating them is not possible.
The key to avoiding the DPM lies with preventative management. Controlling the incidence of DPM hinges upon identifying and eliminating certain flock management issues that contribute to the development of the condition.
The key to reducing the incidence of DPM lies in management of the broiler flock and minimizing wing flapping.
To avoid the occurrence of DPM, the following flock management guidelines (Table 1) are suggested as starting points to investigate and minimize any unnecessary wing activity.
Table 1: Flock Management Guidelines to Minimize Unnecessary Wing Activity
About the Authors
Dr S.F. Bilgili is Professor and Extension Scientist in the Department of Poultry Science at Auburn University, Alabama, USA. His current responsibilities include developing and implementing outreach and research programs in the areas of broiler processing technology, slaughter and processing efficiency, broiler carcass quality and meat yield, food safety and animal welfare. He has authored or co-authored numerous articles in scientific and trade journals and serves on several industry and academic committees. He is currently Chairman of the National Chicken Council Animal Welfare Scientific Advisory Committee.
Dr Joseph Hess is an Extension Specialist and Associate Professor in the Poultry Science Department at Auburn University, Alabama, USA. His research focuses on practical aspects of management and nutrition in broilers and broiler breeders and he engages in practical research projects that can provide immediate feedback to the industry in terms of poultry performance, product quality or feed technology. He is a member of the Poultry Science Association, the Southern Poultry Science Society, the Alabama Poultry & Egg Association and works closely with the Alabama Feed & Grain Association. Aviagen provides customers with detailed Product Performance Objectives, Management Manuals and Nutrition Specifications as the basis for managing their flocks. Successful production of day old chicks or grown broilers depends also on the understanding and attention to detail in the day-to-day management of stock. This document is produced by Aviagen’s Technical Transfer Depart ment as one of an ongoing series. These give background information on various topics to provide an understanding of the princi ples which are essential to successful management of both breeders and broilers. While the principles should have a broad rele vance to most regions and production strategies, certain aspects may be directed to more specific situations.