Endocrine associations with beef carcass quality and yield
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Serum concentrations of insulin, insulin-like growth factor I (IGF-I) and leptin were investigated relative to their association to beef carcass quality and yield grades at harvest. We observed that in a high quality, homogeneous population of beef steers, serum leptin levels correlated with USDA yield grades 1, 2, 3, and 4, but not 4 vs. 5. Serum leptin levels also discriminated (i.e. differed significantly) between the carcass quality grades of Select, Premium Choice, and Prime, while serum IGF-I levels discriminated the carcass quality grade of Prime from lower quality grades. We also determined that previously observed differences in average leptin levels, differing up to 2-fold, in previous studies were unlikely due to sample management differences such as blood collection type (serum versus plasma) or interval from blood sample collection to sample centrifugation (0, 24, or 48 hrs). We also found that Naturally managed cattle (i.e. raised without use of implants or antibiotics) had higher serum leptin levels than Traditionally managed cattle. Gender of cattle had a potent effect on serum levels of leptin and IGF-1, thus intriguing and warranting further study. Transport durations between 400 to 1100 km did not affect serum leptin or IGF-I levels in relation to quality and yield grades. A longer post slaughter chill time improved correlations between serum IGF-I levels and carcass characteristics. We also observed that in traditionally weaned cattle, leptin in blood collected 28 d prior to harvest and insulin levels in blood collected at the time of weaning were correlated with final carcass quality. Finally, we found that implanting cattle may prohibit significant correlations between serum hormone levels and carcass characteristics.
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