Relationships between bovine phenotype, production practices, muscle proteins and the incidence of dark cutting beef

• Author / Creator

  Mahmood, Shahid

• Most recent reports indicated that the prevalence of dark cutting beef has increased in Canada and that 0.5% reduction in the problem could save CAD$1.77 million per annum. Understanding the underlying factors associated with the persistence and recent escalation in the occurrence of dark-cutting is essential; therefore, a series of studies addressing various hypotheses to highlight the factors linked to dark cutting were executed. The initial study revealed a trend for increased dark cutting in heifers than in steers. Cattle with increased DMI and having carcass weight greater than 300 kg were less likely to produce dark cutting. Heifers at risk of dark cutting had reduced weaning weight, slaughter weight, and produced carcasses of less weight. Intramuscular fat had no significant association with the manifestation of cutting dark. However, cattle slaughtered at a live weight greater than 550 kg were less predisposed to cut dark. It was revealed that there is a potential to identify ultimate carcass grades and predisposition to cut dark in live cattle by weighing and ultrasonically measuring subcutaneous fat depth, intramuscular fat, and muscle score. Survey of feedlots in Alberta further substantiated that heifers especially those killed as calf-fed had increased susceptibility to dark cutting whereas steers were less predisposed to produce dark carcasses, irrespective of the rearing system. There was no effect of hormonal-growth implants on the incidence of dark cutting likely because their use was in compliance with manufacturer’s instructions. Similarly, beta-agonists that may influence intramuscular fat deposition and carcass grades did not affect the incidence of dark cutting. Slow growing cattle appeared to be at risk of cutting dark but frequent shipping and extended stay in lairage substantially increased the likelihood of dark beef. The occurrence of typical dark cutting (pH > 5.9) beef was associated with a reduced concentration of muscle glucidic potential. However, such beef was as tender as normal beef after storage at refrigerated temperature for 21 days. Conversely, the atypical dark cutting beef (pH < 5.9) had glucidic potential theoretically sufficient to produce normal-coloured beef, but this beef did not acquire tenderness to the level similar to that of normal beef even after 21 days of storage. Increased toughness of atypical dark beef was independent of cattle sex and carcass phenotype. Extended lairage and/or frequent shipping negatively influenced muscle glycogen essential for post-mortem glycolysis and lowering of carcass pH. Proteomics of the longissimus thoracic, using two-dimensional gel electrophoresis coupled with LC-MS/MS mass spectrometry, revealed reduced abundances of creatine kinase, glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase and glycerol-3-phosphate dehydrogenase [NAD(+)] in atypical beef, implying a compromised glycolytic capability in atypically dark muscles. The atypical dark beef had increased levels of phosphatidylethanolamine-binding protein 1 and small heat shock proteins that might have compromised proteolysis and beef tenderness. The study suggested a disparity in muscle proteins and post-mortem muscle metabolism between normal and dark cutting beef.

• Subjects / Keywords

  • Growth promotants
  • Phenotype
  • Glucidic potential
  • Glycolytic proteins
  • Carcass weight
  • Slaughter weight
  • Average daily gain
  • Lairage time
  • Dry matter intake
  • Yearling-fed
  • Beef tenderness
  • Production practices
  • Atypical dark cutting

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R36D5PR2V

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.