Dylemma of deep pectoral myopathy (DPM) in broiler chickens

Dylemma of deep pectoral myopathy (DPM) in broiler chickens J. KIJOWSKI and E. KUPINSKA Dept. of Food Quality Management, Poznan University of Life Sciences, 60-637 Poznan, Poland *Corresponding author: kijowski @ up.poznan.pl Deep Pectoral Myopathy of musculus pectoralis minor is an anomaly observed in gallinaceous poultry. To date its cases have been reported in adult pedigree turkeys and hens and in recent years also in broiler chickens. This degeneration is manifested in an abnormal appearance of breast muscles, with changes in colour from pink to green as well as changes in texture of the muscle tissue. The anomaly is found most frequently in genetic lines of chickens characterised by dynamic weigh increment as well as a considerable increase in the proportion of pectoral muscles. The mechanism for the development of myopathy is already well known. It is related with ischemic necrosis initiated by rapid physical activity of birds, which mobilizes pectoral muscles, normally relatively inactive in modern intensive animal management systems. Absence of symptoms manifested in vivo results in a situation when muscles affected by myopathy are identified only during carcass dissection. An increasing number of cases of this anomaly as well as the fact that necrotic lesions affect valuable carcass elements make this problem of great importance for chicken growers and abattoirs. In recent years DPM cases have been reported with increasing frequency in the USA, Italy, Greece, Bulgaria in commercial genetic lines. In Poland we have recorded a number of DPM cases in large populations in flocks of 5-7-week old chickens at 0.02 up to 1.9 %. Risk factors for the occurrence of DPM on farms were analysed. They are mainly factors leading to intensive wing flapping. Identification of these factors may result in better farm management and constitute the basis for the DPM prevention system. A radical solution to this dilemma is not available at the moment. Key words: chicken; myopathy; DPM; induction; prevention. Introduction In the last several decades significant effects of genetic selection have been observed in broiler chickens in terms of the reached breeding and performance parameters: feed conversion rates, weight gain rates of birds, the proportion of meat, particularly breast muscles. Leading companies in the production of nucleus herds and parent flocks intensively compete on the market, offering increasingly better economic standards of birds. However, this intensification has led to several evident cardiovascular diseases, as well as anomalies of the skeletal and muscular systems in fattened broiler chickens and turkeys. Following mainly economic indexes, disregarding natural anatomical, physiological and behavioral predispositions of birds, has led to several degenerations, particularly within pectoral muscles. In recent years a marked intensification has been observed in the incidence of m. pectoralis myopathy symptoms (DPM) in specialized highly producing, well-muscled chickens. Etiology of the disease The cause of the development of the green muscle disease in m. pectoralis minor has been explained to a considerable degree. It is known that necrosis occurs in case of oxygen deprivation in muscles during normal physical activity of birds (Siller, 1985; Pastuszczak and Uradziński, 2002; World s Poultry Science Journal, Volume 69, Supplement 1

Bilgili and Hess, 2008). We need to stress here the important role played in the development of the anomaly by the specific location of m. pectoralis minor in a closed space with limited capacity for relaxation. During physical activity of birds, a properly functioning pectoralis minor muscle relaxes, thus increasing its volume by 20% (Siller, 1985) and even 25% (Bilgili and Hess, 2008). However, due to the limited physical activity of birds during their rearing the fascia surrounding m. pectoralis minor does not acquire elasticity. Most probably the capacity of fascia to expand does not develop in proportion to the rapid increase in weight of the tender (Siller, 1985). In case of further physical activity of the pectoral muscle oxygen deficit develops and tissue hypoxia occurs. The contracted muscle prevents inflow of oxygenated blood and gets hypoxied (Bilgili and Hess 2002; Bilgili and Hess, 2008). The production of green colour in muscles has not been comprehensively clarified to date. It probably results from anaerobic changes of the muscle pigment, i.e. myoglobin to oxymyoglobin and its derivatives. The change of muscle colour from pinkish-red to green and greyishgreen is most probably a consequence of the transition of hemoglobin into choleomyoglobin, when iron of the haeme pigment being in the ionic state Fe 3+ under the influence of hydroperoxide is transformed or when haeme with hydrogen sulfide and oxygen it forms the pigment of sulfomyoglobin (Grabowski and Kijowski, 2009; Pisula and Pospiech, 2011). Macroscopic changes of DPM symptoms Deep pectoral myopathy is observed as a change in the appearance of the pectoral muscle. Symptoms in turkeys and chickens are similar. This disease is detected only at the dissection of the carcass into cuts. Symptoms affect mainly the pectoral minor muscle, less frequently and to a lesser extent the major superficial muscle. Changes are observed both in colour and texture of the tissue. Most typically the muscle anomaly is described as pink colouring, tissue hyperaemia or at the stage of advanced lesions - the occurrence of green and grey-green colour. This is accompanied by tissue hyperaemia, visible broken blood vessels, while at a more advanced stage of the disease it includes also muscle retraction. Necrosis may cover one or both tenders of the pectoral muscle and lesions cover an area from 1/3 to 3/5 the tender. Myopathy develops mainly in the central part of the muscle, frequently only the central region is affected by the disease (Wight et al., 1981a; Bilgili and Hess, 2002; Kijowski and Kupinska, 2012). Our proposal comprises 4 stages of changes in macroscopic characteristics in muscles of chickens (Kijowski and Kupińska, 2012, 2013). The 1st stage of DPM is characterised by the occurrence of blood extravasations and clotted blood in blood vessels. The 2 nd stage of myopathy is characterised by pale-pink colour of the minor muscle as well as necrotic changes in the tissue, which becomes fibrous. The 3 rd stage is distinguished by greening of the muscle tissue, first of all in the central section of the minor muscle. In turn, in the 4 th stage the minor muscle becomes grey-white-green and is necrosised. Specific characteristics, particularly concerning muscle colour, were used to develop a chart to identify all the 4 stages of DPM symptoms for potential use at poultry abattoirs (Kupińska, 2012). Incidence and intensity of DPM case Studies by Bilgilli and Hess published in 2002 and then investigations conducted by Bianchi et al. (2006) on heavier roaster chickens aged 7-9 weeks, a report by Kijowski et al. (2009) concerning 6- to 7-week chickens, Kijowski and Konstańczak (2009) on 5- to 6-week chickens as well as Dinev and Kanakov (2011) on 7-week chickens, and Kijowski and Kupinska (2012) revealed an increasing incidence of DPM cases in commercial broiler chicken flocks. In literature concerning the green muscle disease we may find different data concerning the frequency of myopathy. In Poland the incidence of DPM cases recorded in populations of several thousand birds of commercial slaughter chickens was recorded at 0.02 up to 1.9% (Kijowski et al., 2009, Kijowski and Konstanczak, 2009). Lien et al. (2011) reported that incidence of spontaneous DPM cases ranges from 3 to 17% and they seem greater in broiler chickens with a greater growth dynamics and occur more increasingly in roosters than in hens. Badger (2011) identified 4.4% DPM cases in chickens cut up for customers. World s Poultry Science Journal, Volume 69, Supplement 2

Risk factors for the incidence of DPM The frequency of the green muscle anomaly in broiler chickens depends on many factors. They include rearing conditions, age, weight, sex and genetic line. Welfare of these animals is a major factor affecting the incidence of the green muscle disease. Necrotic changes in pectoral muscles are initiated in the course of the rearing period in animals. They are formed at the time of sudden mobility of birds, which may be caused by stress factors during rearing. Polish solution is connected with the production of crosses of native hen breeds with meat-purpose cocks, e.g. a Greenleg Partridge with a cock from the fast-growing meat purpose strain Ross 308 or Hubbard ( Połtowicz, 2012). Crossbreds are characterised by a consistently greater body weight and better muscling. Studies confirmed that such crossbreds may provide birds for alternative breeding systems, from which chickens are not prone to develop DPM symptoms. Cases of pectoral muscle myopathy are recorded much more frequently in older birds. Greater weight of birds contributed to a more frequent occurrence of the disease. It needs to be stressed that not only weight alone, but also growth rate, influences the risk of the anomaly. In birds with rapid weight gain rates DMP was detected in 17% animals, while in case of a slow growth rate this index was as low as 2.8 % (Bilgili and Hess, 2002). Within the last 40 years the weight of both the whole carcass and pectoral muscles from 42- day old chickens have increased almost twofold, while rearing time has simultaneously decreased by almost a half. To a certain extent these changes are a consequence of improved feeding and management systems; however, genetic selection is the most important factor in this respect (Savory, 2002). Trends advantageous from the point of view of slaughter animal producers and the poultry industry turned out to be a factor increasing the risk of the green muscle disease. All the recorded cases of identified DPM symptoms were found in chickens from genetic lines selected for a high share and yield of pectoral muscles such as Ross 308 and 508, Cobb 500 or Flex Hubbard. Stimulation and induction of DPM symptoms In our study on the stimulation of DPM incidence in Polish farms chickens of the genetic lines Ross 308 and Hubbart Flex were subjected to forced and control wing flapping (FCWF) according to the method developed within this study in cooperation with prof. S. Bilgili from Auburn University, USA (Kijowski and Kupińska, 2012). Early symptoms of myopathy stages I and II were observed in chickens subjected to FCWF at days 1 and 3 before slaughter. Induced wing flapping in birds at 5, 7 and 14 days before slaughter caused the appearance of stages III and IV of the anomaly. No DPM changes were observed in the group of birds subjected to FCWF at 21 days before slaughter. Analysis of Pearson s correlation (r = 0.73) showed a statistically significant positive linear dependence between FCWF duration and the frequency of the anomaly. The linear regression coefficient was 0.99. This means that if the duration of intensive wing flapping increases by 1 s, it may be expected that the frequency of DPM in broiler chickens will increase by 0.99%. In case of the experiment with FCWF, in which 42-day Ross 308 chickens were slaughtered, the frequency of induced myopathy was 43% analysed population. In turn, in the experiment on 45-day chickens of the Hubart Flex lines symptoms of myopathy were found in 64% examined population. In Poland a questionnaire survey was conducted among managers of 10 broiler chicken farms. The most important risk factors for the incidence of DPM ranked in terms of their importance include (Kupińska, 2013): disturbed flock hierarchy, flock thinning and selection, handling by catching by wings, inappropriate handling by staff, violent actions, scaring, excessive amounts of light, noise and new sounds in the vicinity of the henhouse, the applied method of bird weighing, excessive stocking rates, particularly at drinkers and feeders, excessive intervals in water and feed administration (over 3-4 h), veterinary practices, and prophylactic vaccinations. World s Poultry Science Journal, Volume 69, Supplement 3

Economic losses for abattoirs and processing plants Annual economic losses due to DPM, incurred by poultry processing plants in Poland, were calculated. The following assumptions were adopted: annual production of broiler chickens at 1 550 000 tons in 2011 (KRD-IG, 2012), mean minimum frequency of DPM incidence at 0.2 % (Kijowski et al., 2009), mean body weight of live chickens at 2.4 [kg], mean weight of pectoralis minor muscles with DPM lesions at 85 [g], value of 1 kg fillets (tenders) (m. pectoralis minor) at 3.5 (EURO). Disposal of pectoralis minor muscles (tenders) with DPM changes in Poland causes annual losses of 411 718 411 thousand. Assuming DPM intensity at 1% losses will amount to 2 058 590 2 million. In pectoralis major muscles with lesions typical for the anomaly a statistically greater thermal drip was recorded in comparison to pectoral muscles with no myopathic changes. Moreover, it was found that the later the stage of deep pectoral myopathy, the significantly greater thermal drip from m. pectoralis major. Muscles were subjected to thermal processing in a foil bag. Mean values of sensory quality attributes of meat, i.e. taste, colour on the surface and overall desirability, were lower in case of muscles corresponding to tenders with symptoms of only the last stage (IV) of myopathy in comparison to the control. In case of these samples the sensory panel detected an extrinsic taste (haeme) and adverse changes in colour on the surface (hyperaemia). Moreover, samples were grilled. Mean scores for all analysed sensory quality attributes of meat were lower in case of pectoralis major muscles corresponding to m. pectoralis minor with symptoms of individual stages in comparison to control samples. Summing up, for overall desirability of meat with DPM symptoms it was found that it differs from the control in case of thermal processing in a plastic bag and on a grill. In turn, after more intensive processing procedures, i.e. curing and smoking, differences in quality of pectoralis major muscles accompanying minor muscles with DPM symptoms are eliminated and do not influence quality attributes evaluated by consumers (Kupińska, 2013). Conclusions and recommendations DPM is caused by a complex of factors primarily of genetic, but also physio-anatomical background of chickens as well as management systems on commercial farms. A factor, which may to a considerable degree reduce the incidence of deep pectoral myopathy, is connected with slowing down the growth rate of birds, particularly weight gain of pectoral muscles. Studies have shown that in wild turkeys DPM does not occur even in case of enforced physical activity. This confirms a close relationship between the incidence of the disease and intensified rearing of gallinaceous poultry. Since a major factor influencing the incidence of DPM is connected with rearing conditions, their appropriate selection may prove to be an effective prevention measure. In 64% cases of pectoralis minor muscles affected by the analysed anomaly changes concerned also the inner side of the superficial muscle. Disturbed symmetry and muscle shrinkage were observed in almost all examined pectoral muscles (96%). An important element in studies on the pectoral muscle anomaly is to keep detailed documentation for each case of myopathy. If necrotic changes concern a greater number of fillets coming from one batch from one supplier, then on the basis of advancement of changes we may approximately determine when the inducing factor occurred. Documentation kept at abattoirs may provide valuable information for chicken growers and effective communication between these two entities may help reduce the incidence of the anomaly. In reality the DPM dylemma, apart from the economic issues, is also a problem of sanitary and veterinary nature as well as procedures adopted in abattoirs. As it was already shown, calculated economic losses due to DPM are considerable. Myopathy of the deep pectoral muscle is a degeneration caused practically by human activity, which does not take into consideration the laws of biology and anatomy governing the nature of birds. Myopathy is thus a price we have to pay for successful selection towards a desirable increase in muscling in broiler chickens. World s Poultry Science Journal, Volume 69, Supplement 4

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