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Title: Growth associated and stress-induced myopathies in the domestic chicken (Gallus domesticus)
Author: Cooke, Victoria Elizabeth
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2005
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Genetic selection of broiler chickens for growth related production traits may have led to an increased susceptibility to both growth and stress induced myopathies. A comparison of a broiler (B); broiler great-grandparent (GGP) and layer (L) line revealed that by 25 weeks of age, the mean body weights reached by B, GGP and L lines were 5.1 kg, 5.2 kg and 1.9 kg. Increased Pectroalis major (Pm) breast muscle yield through increased fibres sizes may contribute to the greater B and GGP body weights. At 25 weeks, the mean Pm breast muscle fibre size reached by the B and GGP lines (65.9μm and 59.8μm respectively) were 1.5 times greater than that of the L line (38.1μm). Furthermore, there was divergence in muscle fibre growth between the mean Pm and Biceps femoris (Bf) leg muscle fibres of the B and GGP lines, but not the L line during growth. Cores, rims and split fibres observed in the leg muscles from older B and GGP birds may result from metabolitic stress associated with larger fibre sizes and inadequate capillary support. Enzyme markers of muscle damage were indicative of a greater growth associated myopathy in the B and GGP lines compared to the L line. Histopathological assessments also revealed muscle damage. The type and incidence of structural changes were related to bird line (B>GGP?L), age (prominent at 5 and 18-23 weeks), muscle (Ps: necrotic and basophilic fibres; Bf: hyaline and basophilic fibres), and circulating steroid levels (regenerative rather than degenerative processes associated with estrogen secretion). A reduction in enzyme markers of muscle damage preceded egg yolk precursor production and increased calcium (Ca2+) uptake for egg-shells synthesis. Estrogen may induce increased satellite cell activity and fibre regeneration, protecting muscle from the potential threat of Ca2+-induced muscle damage due the increased Ca2+ uptake. The demonstration of the alpha and beta estrogen receptor mRNA in chicken skeletal muscle indicates that the myoprotective effect of estrogen may involve receptor mediated gene regulation. The profile of muscle damage during the 48 hour period following exposure to acute heat stress was determined in birds from the B line. All or a combination of catching, handling sampling and crating procedures induced a hypocapnic alkalosis in the blood, which was associated with subsequent muscle damage. The heat stress was not severe enough to exacerbate this response, with the body temperature of the birds rising to just 42.5°C during heat stress exposure. Enzyme markers of muscle damage peaked between 12 and 48 hours following exposure to heat stress/control conditions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available