Hypocortisolaemia in a Labrador retriever

A four-year-old Labrador retriever was presented with lethargy and exercise intolerance. Clinical examination was unremarkable. A subnormal Cortisol response to adrenocorticotrophin hormone (ACTH) was demonstrated (plasma Cortisol concentrations before and after administration of ACTH were both below the detection limit of the assay) but plasma aldosterone concentrations were within the normal range. Endogenous plasma ACTH concentrations were high, indicating primary adrenocortical disease. Following glucocorticoid supplementation at a replacement dose (prednisolone 0.1 mg/kg) the dog made a full clinical recovery.     

Effect of post‐mortem temperature on chicken M. pectoralis major: Isometric tension and pH profiles

1. The relationship between isometric tension development and pH, as a function of storage temperature between 0° and 40°C, was examined in chicken M. pectoralis major (PM) muscle during the critical 24 h post‐mortem period.

2. The muscle strips incubated at 0°C developed a peak isometric tension of 53.3 g/cm². This occurred after only 17 min incubation when the pH was 7.02, demonstrating the potential of chicken PM muscle to cold shorten. Peak isometric tension at 5°C was considerably lower than that generated at 0°C. However, as this occurred when the muscle pH was still high (6.70), this also indicated some potential to cold shorten at 5°C.

3. At 10° to 30°C, the muscle strips developed mean peak isometric tensions of 18 g/cm² after 6 h incubation by which time the muscle pH had fallen to 6.00, demonstrating a limited potential to rigor shorten. In contrast, those incubated at 40°C developed a peak tension of 54.5 g cm² after 75 min when the muscle pH was also around 6.00, thus indicating the potential for intensive rigor shortening at this temperature. Incubation temperature and the resultant muscle pH therefore determine the potential of chicken PM muscle to either cold shorten or rigor shorten.

4. Despite the differences found in isometric tension profiles, cooked meat texture after isometric tension measurement was not significantly different at any of the temperatures studied primarily because the muscle strips were essentially prevented from shortening.     

Effect of post‐mortem temperature on chicken M. pectoralis major: Muscle shortening and cooked meat tenderness

1. Muscle shortening, sarcomere lengths and pH values were measured in strips of chicken M. pectoralis major (PM) muscle incubated at different time (0 to 24 h) and temperature (0° to 40°C) combinations immediately after slaughter; their effects on cooking loss and meat tenderness determined.

2. Maximum muscle shortening of 39% and 43% occurred at 0°C and 40°C respectively. At 0°C, most shortening occurred within 90 min postmortem when the pH of the muscle ranged from 7.13 to 6.52. In contrast, at 40°C, most shortening occurred during the development of rigor mortis, between 90 and 380 min post‐mortem, when the muscle pH ranged from 6.16 to 5.89. In a similar manner, minimum sarcomere lengths of 1.38 μm were reached after 90 min at 0°C while more severe sarcomere shortening, to 0.96 μm and 0.86 μm at 30°C and 40°C respectively, was not complete until after 380 min post‐mortem. Between 5°C and 20°C, muscle shortening ranged from 25 to 34% while minimum sarcomere lengths of 1.33 μm were recorded.

3. Cooking losses increased on average from 7 to 16% between 30 and 380 min post‐mortem, with maximum losses of 19% being achieved by the end of the 24‐h incubation period.

4. At 0°C, shear force values increased from 2.94 kg/cm² to 4.34 kg/cm² between 30 and 90 min post‐mortem while the muscle pH was > 6.5. At all other temperatures, increases in shear force values were not detected until 380 min post‐mortem when the muscle pH had fallen to 5.9 and rigor mortis had set in. At all times after 380 min, however, the muscle strips incubated at 0, 5 and 40°C had lower shear values (range 3.17 to 5.49 kg/cm²) than those incubated from 10°C to 30°C (range 5.06 to 7.22 kg/cm²).

5. A significant quadratic relationship was found between the degree of shortening and subsequent cooked meat tenderness, in which peak toughness occurred at 30% shortening. This would suggest that the actual extent of muscle shortening per se has an important role to play in determining the tenderness of chicken post‐mortem. Consequently, with unrestrained chicken muscle, where extensive shortening occurred at 0°C and 40°C (i.e cold‐ and rigor shortening) the cooked meat was more tender than that subjected to intermediate post‐mortem temperature regimens.     

The Global Ocean Biodiversity Initiative: Promoting scientific support for global ocean governance

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