No abstract

Two trials were conducted to evaluate roughage levels in whole shelled-corn finishing diets and to compare use of self-feeders to a total mixed ration in a whole corn program. In trial 1, steers were fed whole corn diets alone or with 4 or 8% roughage or a rolled corn diet with 8% roughage. Increasing the roughage level increased dry matter in take, feed required per unit of gain, and carcass weight and finish, and reduced the incidence of liver abscesses. Despite better feed efficiency and lower costs of gain, reducing the dietary roughage level reduced profitability because of lighter slaughter weights. In trial 2, feeding 4% vs no roughage in a whole-corn finishing program increased dry matter intake and tended to increase rate of gain by finishing heifers. No performance benefit resulted from feeding a total mixed ration vs using self-feeders and providing chopped hay in a feed bunk. Feeding very little or no roughage in whole corn diets can improve feed efficiency and reduce cost of gain. However, these advantages can be outweighed by potentially lower slaughter weights and increased metabolic problems (acidosis, bloat, liver abscesses).

Thirty-three Hereford x Angus first-calf heifers were used to determine the relationship between production efficiency (PE = calf weaning weight/[12-mo dam+calf ME intake]) and nonlactating dam maintenance ME requirement/BW.75 (MEm) and its components, the efficiency of ME use for maintenance (km), and fasting heat production/BW.75 (FHP). Each heifer was kept in drylot from 19 mo of age until weaning of its first calf, during which time individual feed intakes were measured. After the PE phase, heifers were moved to the metabolism facility and indirect respiration calorimetry was used to determine maintenance energy metabolism. Maintenance metabolism of the dam, determined in controlled conditions, contributed little to explaining PE variation (r2 < or = .04). This may have been due to the high plane of nutrition provided and (or) to the physiological state of the heifers during metabolism measurements. Selection for lower MEm, as determined by the procedures used in this study, is unlikely to improve heifer PE if nutrition is not limited relative to requirements. Additionally, MEm was closely related to FHP (r2 = .73), suggesting that it could be used as an indicator of fed maintenance requirements when determined within defined conditions.

The nature of gold (Au) ore deposits plays an essential role in determining the best gold recovery method as an alternative to cyanidation, considering environmental concerns. Thiourea (Tu) leaching of gold is an alternative lixiviant for treating sulfide gold ores and concentrates. The present study investigated the leaching behavior of Au from sulfide gold ore concentrates obtained from the Cripple Creek site (Newmont operated mine) using acidified thiourea solution. The concentrates containing pyrite, K-feldspar, quartz, and gypsum as major minerals were roasted before leaching to break down complex sulfides and improve the gold’s leachability. Parameters investigated include the leaching time (1–7 h), temperature (20–60 °C), pulp density (20–60 g/L), and thiourea concentration (20–60 g/L) to determine optimum conditions for Au dissolution. Hydrogen peroxide (H2O2) was used as an oxidizing agent and sulfuric acid (H2SO4) to maintain an acidic environment during the leaching process. The highest Au dissolution percentage of 96.2 was obtained after 6 h of leaching with 40 g/L thiourea at 60 °C, pH 1, and pulp density of 20 g/L. Based on the results presented in this work, the dissolution of gold with thiourea in an acidic solution would be a potential alternative to the traditional cyanide process, with the increase in understanding of the green leaching of Au from sulfide gold ores.

Roughage level and method of corn processing were evaluated for the propensity to cause subacute acidosis in a controlled acidosis challenge model. Four ruminally fistulated steers were adapted to a high grain diet, randomly allocated within a 4 x 4 Latin square, and fed a corn-based finishing ration at 2% of BW/day (dry basis) in two equal feedings. Chopped alfalfa hay was used as the roughage source and added at 8% of the diet dry matter or not added. Corn was fed either whole (WSC) or dry rolled (DRC). Roughage level and grain processing had no effect on postchallenge molar percentage of acetate or total volatile fatty acid production. An interaction (P<.05) was seen in both percent propionate and acetate:propionate ratio. Eliminating roughage in the WSC diet resulted in increased production of propionate and a lower acetate:propionate ratio. Ruminal pH at 3 hours postchallenge and intake during the recovery period were lower (P<.05) for 0 vs 8% roughage. Ruminal pH at 3 and 6 hours postchallenge was lower (P<.05) for DRC than for WSC. Intake during the recovery period did not differ between DRC and WSC. Hours below pH 5.6 were greater (P<.05) for DRC vs WSC and for 0 vs 8% roughage. Though statistically higher (P<.05), no biologically significant levels of lactate were found for either DRC or WSC. This study indicates that adding roughage or feeding WSC vs DRC reduces the propensity for subacute acidosis.