Angus-cross steers (n = 165; 295 +/- 16 kg of BW) were used evaluate the effect of low vitamin A diets with high-moisture corn (HMC) or dry corn (DC) on marbling and fatty acid composition. Steers were allotted to 24 pens (7 steers/pen), such that each pen had the same average initial BW. Treatments were randomly allotted to the pens. The experiment had a completely randomized design, with a 2 x 2 factorial arrangement of treatments: low vitamin A (Lo, no supplemental vitamin A) and HMC (LoHMC); LoDC; high vitamin A (Hi, supplemented with 2,200 IU of vitamin A/kg of DM) and HMC (HiHMC); and HiDC. Diets contained 76% corn, 10% corn silage, 11% protein supplement, and 3% soybean oil (DM basis). Samples of feed ingredients were collected for carotenoid analysis. Blood samples were collected for serum retinol determination. Steers were slaughtered after 145 d on feed. Carcass characteristics and LM composition were determined. Samples from the s.c. fat depot were analyzed for fatty acid composition. High-moisture corn had a greater vitamin A content, based on its carotenoid content, than DC (614 vs. 366 IU/kg of DM, P < 0.01). No vitamin A x corn type interactions were detected for feedlot performance, carcass characteristics, or serum, s.c. fat, or liver retinol concentration. Average daily gain, DMI, and G:F were not affected by vitamin A (P > 0.05). Marbling score and USDA quality grade were greater (P < 0.05) in Lo vs. Hi steers. Hot carcass weight, backfat, and yield grade were not affected by the treatments (P > 0.05). Vitamin A and corn type did not affect LM composition (DM, ash, CP, or ether-extractable fat, P > 0.05). Vitamin A supplementation increased (P < 0.06) serum retinol on d 112 and 145 and increased (P < 0.01) liver retinol at slaughter (Lo = 38.7 vs. Hi = 102.9 mug/g). The s.c. fat retinol concentrations were less (P < 0.01) for Lo (0.8 mug/g) than for Hi (1.4 mug/g) at slaughter. Cell diameter of adipocytes in the i.m. depot was not affected by dietary vitamin A (P > 0.05). A vitamin A x corn type interaction was observed (P < 0.05) for the s.c. fat cellularity. Feeding HMC increased the number of cells per square millimeter when Lo diets were fed (LoHMC = 128 vs. LoDC = 100 cells/mm(2), P < 0.05), but not when Hi diets were fed (HiHMC = 109 vs. HiDC = 111 cells/mm(2), P > 0.05). The CLA content of adipose tissue was not affected by the treatments. Regardless of the corn type used, feeding low vitamin A diets for 145 d to Angus-cross steers increased marbling and quality grade without affecting yield grade, animal health, or performance.

A feedlot trial was conducted to determine the effect of dietary vitamin A concentration and roasted soybean (SB) inclusion on carcass characteristics, adipose tissue cellularity, and muscle fatty acid composition. Angus-crossbred steers (n = 168; 295 +/- 1.8 kg) were allotted to 24 pens (7 steers each). Four treatments, in a 2 x 2 factorial arrangement, were investigated: no supplemental vitamin A, no roasted soybeans (NANS); no vitamin A, roasted SB (20% of the diet on a DM basis; NASB); with supplemental (2,700 IU/kg) vitamin A, no roasted SB (WANS); and with supplemental vitamin A, roasted SB (WASB). Diets included high moisture corn, 5% corn silage, 10 to 20% supplement, and 20% roasted SB in the SB treatments on a DM basis. The calculated vitamin A concentration in the basal diet was < 1,300 IU/kg of DM. Blood samples (2 steers/pen) were collected for serum vitamin A determination. Steers were slaughtered after 168 d on feed. Carcass characteristics and LM composition were determined. Fatty acid composition of LM was analyzed, and adipose cellularity in the i.m. and s.c. depots was determined. No vitamin A x SB interactions were detected (P > 0.10) for cattle performance, carcass composition, or muscle fatty acid composition. Low vitamin A diets (NA) did not affect (P > 0.05) ADG, DMI, or G:F. Quality grade tended (P = 0.07) to be greater in NA steers. Marbling scores and the percentage of carcasses grading > or = Choice(-) were 10% greater for NA steers, although these trends were not significant (P = 0.11 and 0.13, respectively). Backfat thickness and yield grade were not affected (P > 0.26) by vitamin A supplementation. Composition of the LM was not affected (P > 0.15) by vitamin A or SB supplementation. Serum retinol at slaughter was 44% lower (P < 0.01) for steers fed NA than for steers supplemented with vitamin A (23.0 vs. 41.1 microg/dL). A vitamin A x SB interaction occurred (P < 0.05) for adipose cellularity in the i.m. depot; when no SB was fed, vitamin A supplementation decreased cell density and increased cell size. However, when SB was fed, vitamin A supplementation did not affect adipose cellularity. Adipose cellularity at the s.c. depot was not affected (P > 0.18) by vitamin A or SB treatments. Fatty acid profile of the LM was not affected by vitamin A (P > 0.05), but SB increased (P < 0.05) PUFA (7.88 vs. 4.30 g/100 g). It was concluded that feeding NA tended to increase marbling without affecting back-fat and yield grade. It appeared that NA induced hyperplasia in the i.m. but not in the s.c. fat depot.

Three experiments were conducted to determine the effects of cattle age and dietary forage level on the utilization of corn fed whole or ground to feedlot cattle. In Exp. 1, 16 steers were used to investigate the effects of cattle age and corn processing on diet digestibility. Two cattle age categories were evaluated (weanling [254 +/- 20 kg BW] and yearling [477 +/- 29 kg BW]; eight steers per group), and corn was fed either ground or whole to each cattle age category. Cattle age and corn processing did not affect (P > 0.10) diet digestibility of DM, OM, starch, CP, NDF or ADF, and no interactions (P > 0.10) between these two factors were detected. In Exp. 2, the effects of forage level and corn processing on feedlot performance and carcass characteristics were evaluated. One hundred eighty steers (310 +/- 40 kg BW) were allotted to 24 pens, and were fed one of the following diets: high-forage (18.2% corn silage) cracked corn (HFCC); high-forage shifting corn (whole corn for the first half of the trial, then cracked corn until harvest; HFSC); high-forage whole corn (HFWC); low-forage (5.2% corn silage) cracked corn (LFCC); low-forage shifting corn (LFSC); and low-forage whole corn (LFWC). For the high-forage diets, steers fed cracked corn had 7% greater DMI than those fed whole corn, whereas for the low-forage diets, grain processing did not affect DMI (interaction; P = 0.02). No interactions (P > 0.10) between forage level and corn processing were found for ADG and G:F. Total trial ADG and G:F, and percentage of carcasses grading USDA Choice, and carcass yield grade were not affected (P > 0.10) by corn processing. Cattle with fewer days on feed grew faster and more efficiently when cracked corn was fed, whereas cattle with longer days on feed had greater ADG and G:F when corn was fed whole (interaction; P < 0.10). In Exp. 3, the effects of forage level and corn processing on diet digestibility were evaluated. The high-forage cracked corn, high-forage whole corn, low-forage cracked corn, and low-forage whole corn diets used in Exp. 2 were fed to 16 steers (350 +/- 27 kg BW) in a digestion trial. No interactions (P > 0.10) between forage level and corn processing were detected for starch digestibility. Forage level and corn processing (grinding) did not affect (P > 0.10) diet DM, OM, starch, CP, and NDF digestibility. Processing corn did not provide additional benefits to feedlot cattle performance under these experimental conditions.