The effects of an implant of 140 mg of trenbolone acetate and 28 mg of estradiol (TBA + E2) on performance and carcass composition were evaluated with 72 individually fed steers. Holstein (n = 24), Angus (n = 24), and Angus x Simmental (n = 24) steer calves were allocated by breed and implant treatment to either an individual feeding pen (n = 36) or an electronic feeding door in a group pen (three pens with 12 animals per pen). Intake and refusal of the 85% concentrate diet were recorded daily. Animals were slaughtered when ultrasonic attenuation values of the longissimus muscle at the 12th rib reached .55, which is correlated with low Choice marbling. At slaughter, complete carcass measurements were taken and the right side of each carcass was separated into boneless wholesale cuts. Implanting with TBA + E2 improved (P less than .01) daily gain and feed efficiency. Daily gain was increased 17, 26, and 21% in Holstein, Angus, and crossbred steers, respectively. The implant increased overall daily protein and fat accretion 23%. Carcass conformation and dressing percentage were not affected (P greater than .05) by TBA + E2 treatment. Implantation with TBA + E2 had little effect on yield of wholesale boneless cuts when expressed as a percentage of carcass weight but increased absolute weight as a small degree of marbling by 6 to 40 kg.

A total of 192 feeder steers of five breed types and body sizes commonly found in the United States cattle population were fed high-energy diets to three endpoints (275-, 300-, and 360-kg carcass weights) to determine their carcass composition. Before slaughter, ultrasound was used to predict fat thickness, longissimus muscle area, and marbling. Individual steer data were used for developing prediction equations, which were validated with three independent data sets. These data were used to develop and validate equations to predict carcass composition and DM requirements for individuals fed in pens and varying in breed type, body weight and size, and ADG. Equations to predict carcass weight during growth accounted for 84, 83, and 88% of the variation in the three data sets with 0, 1, and 3% bias. An equation to predict percentage of carcass fat from fat thickness and equivalent shrunk weight accounted for 96% of the variation in the percentage of carcass fat. An equation to predict yield grade from longissimus muscle area per 100 kg, fat thickness, and equivalent shrunk weight accounted for 93% of the variation. Dry matter requirement predicted by the system for individuals accounted for 48% of the variation in actual DMI with a 3% overprediction bias. The equations allow the user to allocate feed to individual animals in group-feeding environments along with marketing cattle on an individual basis at optimum endpoints given cattle types, feeding costs, and market prices.

The Cornell Net Carbohydrate and Protein System (CNCPS) and NRC (1985) models were evaluated for accuracy in predicting metabolizable protein (MP) and essential amino acid (EAA) allowable ADG, using chemical body and feed composition data from feeding trials with Holstein steers. Nine Holstein steers (113 to 200 kg) were slaughtered and determined to have the following whole-body essential amino acid composition of (grams/100 grams of protein): arginine, 5.94; histidine, 2.07; isoleucine, 2.28; leucine, 5.72; lysine, 5.81; methionine, 1.99; phenylalanine, 3.04; threonine, 3.52; tryptophan, .57; and valine, 3.32. The NRC and CNCPS were then tested against data from 25 feeding periods, each representing the 56-d growth of 10 Holstein steers (mean BW of 162 kg), to determine their ability to predict the gain allowed by the supply of MP and the first-limiting EAA. The NRC (1985) system accounted for 46% of the variation in MP allowable gain, with an average bias of -30%. The CNCPS accounted for 87 and 73% of the variation in MP and EAA allowable gain, with a bias of 8 and 5%, respectively. The bias was reduced to 3% (R2 of .82) when ADG was predicted by the factor (ME, MP, or EAA) first-limiting ADG.

We conducted two growth trials to evaluate the effects of monensin on amino acid sparing. When Holstein steers were fed a 90% concentrate diet supplemented with soybean meal (13.5% CP), the DMI, ADG, and efficiencies of feed and nitrogen utilization were greater than with urea (P < .10). Monensin improved ADG with both nitrogen supplements (P < .01), but the positive effects of monensin on efficiencies of feed (P = .12) and nitrogen (P = .26) utilization were greater for soybean meal than for urea. Increasing amounts of monensin (0, 11, or 22 mg/kg of DM) caused a linear increase in DMI with urea. Diets with soybean had greater intakes than diets with urea (P < .01); the greatest intake was of a soybean diet with monensin at 11 mg/kg of DM. Holstein steers fed soybean meal at 13.5% CP had lower DMI and greater efficiencies of feed and nitrogen utilization than steers fed 16.7% CP (P < .10). Crude protein level had no effect on ADG (P > .10). Monensin always increased the efficiencies of feed and nitrogen utilization (P < .05), but these trends were greater for diets with 16.7 than for those with 13.5% CP. Overall, monensin decreased DMI (P < .01), but this effect was greater for 16.7% than for 13.5% CP. Because the positive effects of monensin on diet NEg (P = .16) and efficiency of nitrogen utilization (P = .26) were greater for soybean meal than for urea, it seemed that monensin was sparing amino acids.

The effects of roughage source and timing of inclusion in high-concentrate diets on feedlot performance were evaluated in each of 2 yr with 144 and 120 long-fed Holstein steers, respectively. Roughage, when included in the diet, was delivered in a built-in-roughage (BIR) pellet supplying 15 and 6% roughage (percentage of DM) or hay crop silage (HCS) supplying 7 and 10% roughage (percentage of DM) for the growing and finishing periods, respectively. The six dietary treatments (two pens each) investigated were continuous whole corn and pelleted supplement (no added roughage; WSC-PEL); BIR with cracked corn either in the growing (BIR-G) or finishing (BIR-F) period with whole corn being fed with pelleted supplement when BIR was not part of the diet; BIR and cracked corn fed continuously (BIR-CONT); and two HCS treatments in which the corn was fed either whole (HCS-WSC) or cracked (HCS-CSC) for the entire feeding period. Replicates were slaughtered 4 and 3 wk apart for yr 1 and 2, respectively. Pooled daily gains (yr 1 and 2) for the entire trial (1.39 to 1.45 kg/d) were not different (P > .05). Daily DM and concentrate intakes were lower (P < .001) and gain efficiency was higher (P < .001) for the WSC-PEL than for the other treatments. Carcass characteristics were similar among treatments except for an improved yield grade (P < .02) for the HCS treatments over the BIR treatments. The WSC-PEL treatment was the most profitable (+/steer) and the BIR-CONT diet was the least profitable. The HCS treatments were the most profitable of the roughage treatments. A newly proposed intake prediction equation for feedlot cattle performed similarly to the 1984 NRC equation with long-fed Holstein steer calves.