title: Effects of different growing diets on performance, carcass characteristics, insulin sensitivity, and accretion of intramuscular and subcutaneous adipose tissue of feedlot cattle.
abstract: 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 >or= 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 >or= 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.
authors.affiliation: Texas AgriLife Research and Extension Center, Amarillo 79106, USA. jvasconcelos2@unl.edu
authors.forename: J T
authors.initials: JT
authors.lastname: Vasconcelos
authors.forename: J E
authors.initials: JE
authors.lastname: Sawyer
authors.forename: L O
authors.initials: LO
authors.lastname: Tedeschi
authors.forename: F T
authors.initials: FT
authors.lastname: McCollum
authors.forename: L W
authors.initials: LW
authors.lastname: Greene
mesh_terms: D000273:Adipose Tissue / Q000000981:diagnostic imaging / Q000254:growth & development*; D000821:Animal Feed; D000818:Animals; D001823:Body Composition / Q000502:physiology*; D002417:Cattle / Q000254:growth & development* / Q000378:metabolism*; D004032:Diet / Q000662:veterinary*; D005947:Glucose / Q000378:metabolism; D005951:Glucose Tolerance Test / Q000662:veterinary; D007328:Insulin / Q000378:metabolism*; D008297:Male; D011897:Random Allocation; D050151:Subcutaneous Fat / Q000000981:diagnostic imaging / Q000254:growth & development*; D014463:Ultrasonography
chemical_list: D007328:Insulin; D005947:Glucose