The effects of dietary virginiamycin level on performance and liver abscesses in feedlot cattle were evaluated in seven dose-response studies. Steers and heifers were fed finishing diets ranging in energy content from 1.34 to 1.51 Mcal of NEg/kg of DM. In all studies, virginiamycin added to the diet improved average daily gain and(or) feed conversion, with no substantial effect on dry matter intake. Pooled analyses of four studies providing virginiamycin at 11.0, 19.3, and 27.6 mg/kg of DM in the complete diet indicated that growth and feed conversion were linearly improved (P < .05); feeding 19.3 mg/kg improved these measurements by 3.0 and 3.8%, respectively. Overall incidence (score 0 vs score 1, 2, and 3) and severity (score 0, 1, and 2 vs score 3) of liver abscesses were reduced (P < .01) by feeding virginiamycin at either 19.3 or 27.6 mg/kg. Linear plateau modeling indicated that the effective dose range for virginiamycin in feedlot diets (DM basis) was 19.3 to 27.3 mg/kg for increasing average daily gain, 13.2 to 19.3 mg/kg for improving feed conversion, and 16.5 to 19.3 mg/kg for reducing liver abscess incidence.

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The effects of roughage level (10, 20, or 30% roughage equivalent [RE]), roughage source (alfalfa vs cottonseed hulls), roughage regimen (constant RE vs 2% RE during the mid-finishing period), tallow level (1.2 vs 4.6%), and steer type (British crossbred [BRITX] vs Bos indicus crosses [BRX]) were evaluated in three experiments with a common allotment and several overlapping treatments. Steers (n = 432; initial weight = 326 +/- 26 kg) were divided into three BW blocks and allotted randomly to 72 pens and 24 treatments. Steers were fed steam-flaked, sorghum grain-based finishing diets for 124 to 166 d. Diets with 20% RE decreased gain efficiency and 30% RE diets decreased both gain (linear, P < .07) and efficiency (linear, P < .001) compared with 10% RE diets. Reducing roughage level during the mid-finishing period improved overall gain efficiency 2, 7, and 24% (P > .2, < .05, and < .001, respectively) for the 10, 20, and 30% RE diets, respectively. Steers fed cottonseed hulls consumed more feed (9.6 vs 8.8 kg/d, P < .001) but tended to gain less (1.53 vs 1.58 kg/d, P = .11) than steers fed alfalfa, were leaner, and had fewer carcasses grading Choice (62 vs 77%, P < .05). Feeding 4.6% tallow decreased DMI (P < .05) and improved gain efficiency (P < .05) compared with 1.2% tallow. The BRITX steers consumed more feed (6%, P < .001) but were somewhat less efficient (3.5%, P < .05) than BRX steers. Carcasses from BRITX steers tended to be fatter than carcasses from BRX steers and more of them graded Choice (62 vs 37%, P < .01). Commercial BRX steers did not perform as well as BRITX steers on higher-energy-density diets (4.6% tallow or variable roughage regimen). Knowledge of the genetic background of feeder cattle can be important in the selection of dietary energy density and marketing expectations.

A modified enzymatic method to measure processing effects and starch availability in steam-flaked sorghum grain (SFSG) was developed. To establish the method, experiments were conducted to determine the required enzyme concentration, color reagents, precipitants, sample particle size, shaking frequency and buffer pH. Glucose release at different incubation times (0 to 48 h) from uncooked (UNC) or fully cooked (CK, 100% gelatinized) ground sorghum grain, a 50:50 mixture of UNC and CK (C50) and SFSG was determined. Glucose release from UNC, CK and SFSG was expressed as one-component equations with rate constant k and r2 of .119 and .98, 1.781 and .98, and .368 and .99, respectively; C50 was characterized by having two starch components, one with a fast rate constant, 2.624/h, and one with a slow rate constant, .066/h (R2 = .99). Different degrees of gelatinization were obtained by mixing different proportions of CK and UNC. Glucose release from these samples was highly correlated with starch gelatinization (r2 = .99). By adjusting the tension between mill rollers, five SFSG samples with bulk densities ranging from 476 to 283 g/liter (37 to 22 lb/bu) were produced; respective roller mill electrical load ranged from 21 to 51.5 amps. Enzymatic determination of glucose release resulted in values of 422, 512, 588, 618 and 678 mg/g, which were more closely related to bulk density than birefringence measurements. The modified method for starch availability determination was found to be relatively simple, fast and sensitive, and is recommended.

Steers (n = 156) finished on rhizoma peanut (Arachis glabrata Benth.)-tropical grass pasture in Florida and slaughtered at Central Packing, Center Hill were compared with steers (n = 152) finished on a concentrate diet in Texas and slaughtered at Excel, Plainview. Average daily gain during the growing and finishing periods was lower (P < .001) for forage-finished steers (.49 and .94 kg/d, respectively) than for concentrate-finished steers (.78 and 1.33 kg/d, respectively). Forage-finished steers had less fat over the ribeye (8.3 vs 11.4 mm; P < .01), lighter hot carcass weight (280 vs 346 kg; P < .001), and smaller longissimus muscle area (70.8 vs 86.6 cm2; P < .001) than concentrate-finished steers. Yield grade was not different (2.7 vs 2.6; P > .10), but quality grade was slightly better (low Select vs mid Select; P < .01) for concentrate-finished steers. Lean color of forage-finished steers was darker (P < .001) and fat of forage-finished steers had a creamier color (P < .001), but carcasses were not discounted due to yellow fat color. Shear force values were higher (6.8 vs 4.0 kg; P < .001) for forage-finished than for concentrate-finished steers. Off-flavors were detected by trained sensory panelists in 36% of forage-finished and 14% of concentrate-finished carcasses, but all at barely detectable levels. This research indicates that steers can be finished on rhizoma peanut-tropical grass pastures, but with some reduction in quality grade relative to concentrate-finished steers.(ABSTRACT TRUNCATED AT 250 WORDS)