Skeletal muscle fibre growth and growth associated myopathy in the domestic chicken (Gallus domesticus)

Abstract

1. Genetic selection of broilers may have pushed muscle fibres to their maximum functional size constraints. Broiler (B), female great-grandparent (GGP) and layer (L) lines were weighed, blood sampled and killed from 5 to 25 weeks of age. 2. At 25 weeks, Pectoralis major (Pm) fibre size reached by the B (65.9 microm) and GGP (59.8 microm) were 1.5 times greater than the L (38.1 microm). In the B and GGP lines, fibre growth of the Pm markedly exceeded that of the Biceps femoris (Bf) muscle. However, in the L line, fibre growth of the Pm and Bf muscle was comparable. Connective tissue content was generally higher in the Bf than in the Pm of all lines. 3. Centralised nuclei were observed predominantly in Pm, and may regulate fibre size. Both large muscle fibres and inadequate capillary supply may induce metabolic stress in B and GGP lines due to the large diffusion distances for oxygen, metabolites and waste products. 4. Enzyme markers of muscle damage (creatine kinase (CK), lactate dehydrogenase (LDH) and aspartate aminotransaminase (AST)) and histopathological analysis of Pm and Bf indicated greater myopathy in B and GGP vs L. 5. Regenerative processes were associated with oestrogen secretion. Reduced CK and LDH preceded egg yolk precursor production and increased calcium uptake for eggshell synthesis in all three lines. Oestrogen may stimulate muscle fibre regeneration and recovery as a myo-protective adaptation to potentially detrimental changes in calcium economy during egg production.

Evaluation of Physiological Parameters of Broilers with Dorsal Cranial Myopathy

“…In addition to the increase in enzyme activities, those authors reported microscopic lesions, such as necrosis and basophilia, in the pectoris major and biceps muscles of 5-weekold broilers with myopathies. However, in the present study, except for the ALD, no other muscles were macroscopically or microscopically evaluated, and therefore, no comparisons with the study of MacRae et al (2006) can be made. …”

“…Zimermann (2008) observed histologic lesions, such as degeneration, necrosis, and lympho-histiocytic infiltrate, in normal anterior latissimus dorsi muscle and in other grossly normal muscle groups of broilers; however, the authors did not analyze CK and AST levels. MacRae et al (2006) reported levels of 955 IU/L for CK and 35.1 IU/L for AST in broilers with skeletal muscle fiber growth and growth associated myopathies. In addition to the increase in enzyme activities, those authors reported microscopic lesions, such as necrosis and basophilia, in the pectoris major and biceps muscles of 5-weekold broilers with myopathies.…”

Egg yolk environment differentially influences physiological and morphological development of broiler and layer chicken embryos

“…Interestingly, the phenotypic differences between the two chicken breeds arise as early as the first few days of embryonic development (Clum et al, 1995;Burggren et al, 2004;Boerjan, 2004), potentially setting the stage for the breed-specific differences observed in latestage embryonic (Sato et al, 2006;Everaert et al, 2008), juvenile (Martinez-Lemus et al, 1999;Latimer and Brisbin, 1987;Odom et al, 2004) and adult (Martinez-Lemus et al, 1998;Koenen et al, 2002;Schreurs et al, 1995;McRae et al, 2006) phenotypes. Broiler embryos have faster overall development rates than layer embryos, which is first evident at 48h of development (Boerjan, 2004;Everaert et al, 2008).…”

Scientific Opinion Concerning the Welfare of Animals during Transport

“…These pathologies are attributable to alterations in intracellular calcium homeostasis (Sandercock and Mitchell 2003;Sandercock et al, 2006) and consequent changes in sarcolemmal integrity and may result from excessive myofibre hypertrophy and inadequate development of support tissues and vascular supply (MacRae et al, 2006(MacRae et al, , 2007. These myopathies may have, in turn, a range of implications for both product quality and bird welfare (Mitchell, 1999).…”

“…The genetic selection of broiler chickens for improved production traits has resulted in both growthassociated and stress-induced muscle pathologies or myopathies (MacRae et al, 2006;Sandercock and Mitchell, 2003;Sandercock et al, 2006;, which are coupled to an impaired thermoregulatory capacity and consequent susceptibility to thermal stress in transport. These are important factors, since the risk of hyperthermia in commercial lines of birds is increased compared to their genetic predecessors and thus the induction of pathology and distress may be greater in the current broiler strains.…”