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Effects of different growing diets on performance, carcass characteristics, insulin sensitivity, and accretion of intramuscular and subcutaneous adipose tissue of feedlot cattle

J. T. Vasconcelos^*,,1,2, J. E. Sawyer, L. O. Tedeschi, F. T. McCollum^* and L. W. Greene^*,3

^* Texas AgriLife Research and Extension Center, Amarillo 79106; and Department of Animal Science, Texas A&M University, College Station 77843

¹ Corresponding author: jvasconcelos2{at}unl.edu

Forty-eight individually fed crossbred steers (British and British x Continental; BW = 296 ± 16.7 kg) were used to evaluate effects of different growing diets on changes in accretion of intramuscular (IMF) and subcutaneous (SCF) adipose tissues, insulin sensitivity, and carcass traits. Dietary treatments were AL-LC (a low-corn diet fed to allow cattle ad libitum access to feed), AL-HC (a high-corn diet fed to allow cattle ad libitum access to feed), LF-HC (a limit fed high-corn diet with the energy intake equal to that provided by AL-LC), and AL-IC (a diet with approximately the midpoint daily energy intake between AL-LC and AL-HC). Steers received treatments until d 56, after which all groups were fed AL-HC until d 140. Real-time ultrasound and BW measurements were taken every 28 d, and 3 glucose tolerance tests (GTT) were conducted on d 0, 28, and 56 of the growing period to assess insulin sensitivity. Based on ultrasound IMF and SCF readings during the growing phase, AL-HC and AL-IC increased accretion of IMF (P = 0.01), and AL-LC and LF-HC diets resulted in less accretion of SCF (P < 0.01) compared with other treatments. During the finishing period, accretion of IMF (P = 0.13) and SCF (P = 0.81) did not differ among treatments, which diluted differences in overall (d 0 to 140) accretion of IMF (P = 0.28) and SCF (P = 0.52), such that final real-time ultrasound measures of IMF and SCF did not differ (P 0.36) among treatments. Actual carcass marbling scores, however, were greater for the AL-HC and AL-IC treatments (P = 0.02), and 12th-rib fat thickness tended (P = 0.08) to be greater for AL-HC and AL-IC groups. Based on incremental area under the curve and area over the curve as indicators of insulin release and glucose uptake, respectively, no differences (P 0.10) in insulin sensitivity were observed among treatments. Our results suggest that high-corn diets increase growing phase accretion of IMF and SCF; however, these differences were not related to differences in glucose and insulin kinetics.

Key Words: beef cattle • growing diet • insulin sensitivity • marbling

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