Early expression of hereditary deep pectoral myopathy in turkeys due to forced wing exercise

The occurrence of deep pectoral myopathy in broilers and associated changes in breast meat quality

1. Two experiments were conducted to determine the effect of slaughter weight on the incidence and intensity of deep pectoral myopathy (DPM) of M. pectoralis minor (p. minor muscle) in commercial conditions in Turkey and to evaluate the impact of DPM on meat quality traits of pectoralis major (p. major) muscle in broilers. 2. In Experiment 1, a total of 116 250 carcasses from 59 Ross-308 broiler flocks, classified according to slaughter weight as 2.0-2.2, 2.2-2.4, 2.4-2.6 and >2.6 kg, were evaluated for occurrence of DPM. In Experiment 2, p. major samples from unaffected broilers and each DPM stage were evaluated for meat quality, oxidant and antioxidant properties, nutritional value and fatty acid profile. DPM was characterised as 1: muscles with coagulative necrosis, 2: muscles with fibrous tissue texture and pink to plumb and 3: muscles with green necrotic area. 3. The average incidence of DPM was found to be 0.73% in Experiment 1 and independent of slaughter weight. 4. In Experiment 2, p. major muscle of broilers with DPM 1 and 2 had higher pH values with higher redness and drip loss. All DPM stages resulted in an increase in lipid content and malondialdehyde activity and lowered ash content of p. major muscle compared with unaffected birds. DPM 2 increased superoxide dismutase and glutathione peroxidase activities in M. p. major. The p. major of broilers with DPM had lower content of C18:2 conjugated linoleic and C20:3n-6 fatty acids than those of unaffected broilers. Lower Δ6 desaturase and thiosterase activities and 18:2n-6 to 18:3n-3 ratio were observed for all DPM stages compared to unaffected. 5. It was concluded that these changes obtained in p. major muscle of broilers with DPM might indicate biochemical characteristics of muscle degenerations.

Muscle growth and poultry meat quality issues

Over the past 50 years the worldwide growing demand of poultry meat has resulted in pressure on breeders, nutritionists and growers to increase the growth rate of birds, feed efficiency, size of breast muscle and reduction in abdominal fatness. Moreover, the shift toward further processed products has emphasized the necessity for higher standards in poultry meat to improve sensory characteristics and functional properties. It is believed that genetic progress has put more stress on the growing bird and it has resulted in histological and biochemical modifications of the muscle tissue by impairing some meat quality traits. The most current poultry meat quality concerns are associated with deep pectoral muscle disease and white striping which impair product appearance, and increased occurrence of problems related with the meat’s poor ability to hold water during processing and storage (PSE-like condition) as well as poor toughness and cohesiveness related to immaturity of intramuscular connective tissue. This paper is aimed at making a general statement of recent studies focusing on the relationship between muscle growth and meat quality issues in poultry.

The Occurrence of Deep Pectoral Myopathy in Roaster Chickens

A study was conducted to determine the incidence of deep pectoral myopathy (DPM) in male roaster chickens reared under intensive conditions, processed at different ages (from 47 to 65 d of age), and belonging to 2 commercial genotypes (Ross 508 and Cobb 500). The study was carried out in a major Italian processing plant on a total of 120,700 male roaster chickens chosen at random from 151 flocks during a 6-mo period. The evaluation of DPM was performed on pectoralis minor muscles and consisted of a visual assessment of the presence or absence of the myopathy as well as the scoring of muscle damage level as being in an "early" (hemorrhagic appearance) or "old" (gray or green discoloration) developing stage. The average incidence of carcasses affected by DPM was found to be 0.84% (0.62 and 0.22% in early and old stages, respectively). The range in the incidence of total DPM was fairly large and varied from 0 to 16.7%. Considerable variations were also observed for early (range: 0 to 12.0%) and old (range: 0 to 5.6%) developing stages. Considering the effect of genotype, Ross 508 exhibited a higher incidence of DPM in respect to Cobb 500 (1.27 vs. 0.35%; P < or = 0.01). This result was due to the higher incidence of carcasses affected by both early (0.94 vs. 0.26%; P < or = 0.01) and old (0.33 vs. 0.09%; P < or = 0.01) developing stages of DPM in Ross 508 birds.

Developmental dynamics of some blood biochemical parameters in the growing turkey (Meleagris gallopavo)

Blood serum clinical biochemical parameters of fasted BUT Big 8 male turkeys were determined at the ages of 3 days, 4, 8, 12, 16 and 20 weeks, for a follow-up of the developmental changes of some serum metabolites, enzymes and ions. The serum protein content (total protein, albumin, globulin) increased with age, indicating also the moulting-associated metabolic changes in the age interval from the 8th to the 12th weeks. Creatinine was shown to have a peak at 3 days of age (role of muscle activity in thermogenesis), while urate concentration sensitively reflected the dietary protein amount. Serum triglycerides peaked at the time of yolk catabolism, while cholesterol was shown to indicate the moulting, as was serum malondialdehyde. Serum sodium content increased throughout the study. Alanine aminotransferase and aspartate aminotransferase activities increased along the ontogeny, while alkaline phosphatase activity decreased in parallel with the growth. Serum creatine kinase activity showed an over one-magnitude increase. General metabolic and enzymatic alterations were characteristic and applicable for the description of the ontogenetic development of a precocial (post-hatch triglyceride peak), large bodied, meat-type (lactate dehydrogenase, continuously increasing creatine kinase) bird species.

Comparison of skeletal muscle characteristics in chicken bred for meat or egg production. I. Histopathological and electron microscopic examination

A comparative histopathological and electron microscopic study based on selected skeletal muscle in layer-type and meat-type chickens was carried out to detect possible effects of selection for rapid growth and increased muscularity on muscle health. Disseminated fibre degeneration and other myopathological changes occurred more frequently in muscles of meat-type chickens than in layer-type chickens of the same age. The breast region of meat-type chickens--highly developed as a breeding aim--was particularly affected. Experimental exertion demonstrated the limited adaptability of skeletal muscle to psychomotor stress in meat-type chickens. Meat-type chickens showed a higher increase of histopathological muscular lesions after repeated wing exercise than layer-type chickens. Ultrastructural lesions caused by experimental exertion were classified as adaptive-reversible in layer-type chickens. As opposed to this, irreversible destruction of myofibrillar architecture in meat-type chickens are an indication for muscle ischaemia after exertion. Significant changes of structural, metabolic and functional parameters of skeletal muscle related to breeding aims in meat type chickens contribute to finding an explanation for their increased susceptibility to pathological reactions.

Histopathological alterations of turkey skeletal muscle observed at the slaughterhouse

1. Six leg muscles (iliotibialis cranialis, iliotibialis lateralis, flexor cruris lateralis pars pelvica, gastrocnemius lateralis, gastrocnemius medialis and puboischiofemoralis medialis) were collected immediately after slaughter from each of 200 randomly selected male commercial turkeys. 2. Among these 1,200 samples processed for histology and examined in cross-sections, 9.4% exhibited fibre splitting and 9% intrafascicular adipose tissue infiltration. 3. Gastrocnemius medialis muscles were more often affected than other muscles (P < 0.05), with 33% showing isolated necrotic fibres. There were rarely more than 5 necrotic cells out of roughly 4000 cells per sample. 4. Twelve percent of samples showed a high incidence of hypercontracted fibres, 63% a medium incidence (less than 8% present) and 24% none. Hypercontraction was more frequent in puboischiofemoralis medialis muscles (P < 0.05).

Turkey muscle growth and focal myopathy

Muscle structure and blood enzyme activity were studied to 16 wk of age in lines of turkeys selected for rapid growth. The body and carcass weights were measured, frozen sections of breast and leg muscles examined, and plasma creatine kinase (CK) levels determined. Muscle weights were usually proportional to BW except for the relatively larger superficial pectoralis (SP) muscles in the most rapidly growing line. Damaged muscle fibers were found in all muscles examined, especially in the SP of the breast, the gastrocnemius (GA), and other muscles of the leg; these damages became more common from 10 to 16 wk of age. There were more degenerating muscle fibers and higher levels of plasma CK in the rapidly growing lines than in a slower growing unselected line. The findings support the idea that a focal myopathy, unrelated to deep pectoral myopathy or to inherited muscular dystrophy of the chicken, is associated with rapid growth of turkeys.

Divergent selection for incidence of degenerative myopathy of the Musculus supracoracoideus of meat-type chickens

The response to three generations of selection for incidence of degenerative myopathy of the Musculus supracoracoideus (DMS) in meat-type chickens was studied. From each of two genetic bases named E and F, which were derived from two commercial broiler stocks, a high incidence, low incidence, and a nonselected control strain were initiated. Selection of breeders to produce Generations 1 and 2 was based on the incidence of DMS in their parents after induced wing exercise; mass selection for plasma creatine kinase levels after induced wing exercise was used to produce Generation 3. Little genetic progress in selection occurred in Generations 1 and 2. There was a response in Generation 3, especially in Base E selected for low incidence. Heritability of incidence of DMS was estimated to be .48. Body weights at 8 weeks of age, 18 weeks of age, and breast angle at 18 weeks of age of Generation 3 were greater (P less than .05) for affected than nonaffected birds and positively correlated phenotypically with incidence of DMS. Genetic correlations were extremely variable. The higher incidence of DMS in birds with desirable traits suggests that the breeder must use a multitrait selection program to reduce incidence of DMS as well as improve production traits.