Impact of Nutrition on Metabolism, Performance, Carcass Merit, and Nutrient Balance by Feedlot Cattle

NON-TECHNICAL SUMMARY: Efficient agricultural systems are essential for satisfying the high demands of human consumers. The quantity and quality of animal-derived food and non-food products rely on effective management decisions made in a livestock production system. Systems of management are largely influenced by the availability of resources and costs associated with utilizing those resources. Beef producers face many decisions associated with resource use that can affect animal performance and carcass characteristics. Management decisions that improve efficiency of production will continue to be important for beef to remain competitive with other meats. Research efforts to improve the market position of beef must focus on specific production and management practices that increase efficiency of production of beef that is safe to consume and has desirable eating qualities. The research proposed herein will focus on feed additives and ingredients to increase production efficiency through improved ruminal function, decreased metabolic disorders, increased animal performance and increased pre-harvest food safety. <P>

APPROACH: Objective A, Experiment 1. Two hundred forty steers will be used. Treatments will include: 1) Control (no corn WDGS and no direct-fed microbial; DFM); 2) Wet Control (30% corn WDGS and no DFM); 3) LA51 (30% corn WDGS and 1x109 DFM strain LA51); and 4) C28 (30% corn WDGS and 1x109 DFM strain C28). Diet samples will be collected, dried, ground, and analyzed for nutrients. Feed refused will be weighed on each weigh day. Steers will be harvested at a commercial abattoir and carcass data collected. Data will be analyzed as a randomized complete block design using the Proc Mixed procedure of SAS (SAS Institute Inc., Cary, NC). Pen will be the experimental unit. The model statement will include treatment, and the random statement will include block. <P>Objective A, Experiment 2. Sixteen ruminally-cannulated steers will be allotted to 1 of 2 treatments in a completely randomized design. Treatments will include: 1) control (no DFM), and 2) Lactobacillus acidophilus. Steers will be adapted to a 70% concentrate diet for a minimum of 14 days. Following the adaptation period, steers will be fasted for 16 h, and then allowed 2.5% of BW of a 90% concentrate diet for 1.5 h. Feed remaining after 1.5 h will be placed directly in the rumen via the ruminal cannula. Co-EDTA (100 mL) will be pulse-dosed two hours after the morning feeding (1000 h). Ruminal content samples will be collected before dosing (0 h) and at 3, 6, 9, 12, 15, 18, 21, and 24 h after dosing to determine ruminal fluid pH, cobalt, VFA, (D-)- and (L+)- lactate and ammonia N concentrations. Fifty mL of whole ruminal contents will be collected at the same times for microbial analysis. Data will be analyzed as a completely randomized design using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC). The model will include terms for steer (as a random effect) and the developmental DFM. Ruminal fluid data will be analyzed as repeated measures. The model will consist of DFM, time of collection, and the two way interaction. <P> Objective B, Experiment 1. The design of the experiment will be completely random and will use fifteen ruminally-cannulated steers. Steers will be fed a diet with 4% of the DM as supplemental fat. Treatments will include: 1) Control (no supplemental fat); 2) 4% supplemental fat (50% from yellow grease and 50% from linseed oil); and 3) 4% supplemental fat (100% from linseed oil). Steers will be adapted to a 70% concentrate diet for a minimum of 14 days. Following the adaptation period, steers will be fasted for 16 h, and then allowed 2.5% of BW of a 90% concentrate diet for 1.5 h. Feed remaining after 1.5 h will be placed directly in the rumen via the ruminal cannula. Procedures will be similar to Objective A, Experiment 2. In addition, 2 blood samples will be collected via jugular venipuncture at each sampling time. One blood sample will be analyzed immediately using a Blood Gas Analyzer. The second blood sample will be collected in a tube to harvest serum for haptoglobin concentration determination. Data will be analyzed as a completely randomized design using the MIXED procedure of SAS Release 8.02 (SAS Institute Inc., Cary, NC) as described for Objective A, Experiment 2.

<P>PROGRESS: 2006/10 TO 2007/09 <BR>
OUTPUTS: A total of four experiments were conducted for this project. Two experiments were conducted to determine the effects of growing program on subsequent feedlot performance, carcass traits, body composition, critical organ mass, and tissue oxygen consumption, and two experiments were conducted to determine the effects of roughage level and a fibrolytic enzyme on feedlot performance, carcass characteristics, ruminal metabolism and site and extent of digestion by beef steers fed a high-concentrate diet. These projects included the mentoring of two Ph.D. students who conducted the research and analyzed the data. One of these students has completed his Ph.D. and is working as a nutritional consultant for the feedlot industry in Australia. The second student is in the process of completing his Ph.D. while attending Law School. Students have presented results from this research at the National Meetings of the American Society of Animal Science, at the Plains Nutrition Council Meetings, and at the Annual Alltech Syposium. Both fundamental and applied knowledge have been gained from this research. Feedlot nutritionists and managers can use this information to make informed decisions regarding nutritional management practices that will improve their efficiency of production and decrease cost of gain. A portion of this research involved collaboration with a large commercial feedyard. The feedyard has used the information to better understand the economics of how various growing programs influence costs of production during the finishing phase. This data has also been disseminated through various presentations at scientific meetings, and through extension publications that are available on the web.<BR> PARTICIPANTS: Dr. Gerald Horn, Oklahoma State University; Dr. John Wagner, Colorado State University; Dr. Matt McCurdy, Nutrition Service Associates, Kenmore, Queensland; Mr. Jacob Cranston, Oklahoma State University; ContiBeef, LLC <BR> TARGET AUDIENCES: Readers of the Journal of Animal Science; Feedlot managers and consulting nutritionists; Stocker and Feedlot Cattle Industry personnel
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IMPACT: 2006/10 TO 2007/09<BR>
In Exp. 1 and 2, effects of winter growing program on performance, body composition, carcass merit, organ mass and oxygen consumption of beef steers were investigated. Steers (n = 260) were allotted to: 1) high-concentrate diet; 2) grazed on wheat pasture (WP); 3) sorghum silage-based growing diet (SF); or 4) program fed a high-concentrate diet (PF). Steers in the WP, SF, and PF groups were managed to achieve equal rates of gain. After 112 d, WP, SF, and PF steers were adapted to a high-concentrate diet for finishing. Results suggest that program feeding a high-concentrate diet during the growing period may result in greater gains and increased retained energy compared with forage-based growing programs. Feeding high-concentrate diets during the growing phase may result in greater, more efficient gains during the subsequent finishing period compared with forage-based diets due to less accretion of visceral organ mass and lower maintenance energy requirements during finishing. However, if greater visceral mass and increased GIT capacity leads to increased DMI during finishing, then gains may not be decreased. Changes in organ mass due to diet during the growing phase may contribute to differences in splanchnic organ mass during finishing. It does not appear that diet has a major effect on metabolism or oxidative capacity of tissues in the gastrointestinal tract or liver on a cellular level. Therefore differences in energy expenditure of visceral organs seem to be driven by differences in organ mass. Energy expenditure by splanchnic organs may result in altered maintenance energy requirements and consequently lead to differences in performance. In Exp. 3, 184 yearling steers were used in a randomized complete block design with a 2 x 2 factorial arrangement of treatments. Steers were fed dry rolled corn-based finishing diets (DM basis): 1) 9.0% alfalfa hay without Fibrozyme; 2) 9.0% alfalfa hay with Fibrozyme (10 g&#8729;steer-1&#8729;d-1); 3) 4.5% alfalfa hay without Fibrozyme; or 4) 4.5% alfalfa hay with Fibrozyme (10 g&#8729;steer-1&#8729;d-1). In Exp. 4, 8 ruminally and duodenally cannulated crossbred beef steers were randomly allotted to the same 4 treatments in a replicated 4 x 4 Latin square design. Results suggest that Fibrozyme supplementation may be more efficacious for steers fed finishing diets with lower roughage levels. Although Fibrozyme supplementation did not affect nutrient digestibility, supplementing Fibrozyme was more effective in the 4.5% alfalfa hay diets rather than the 9.0% alfalfa hay diets in the feeding trial. Although no roughage level effect was detected on ruminal pH, mastication has been implicated to play a role in ruminal buffering. Because roughage level did affect rumination time (measured in pens), it is possible that either additional rumination time did not influence ruminal pH or pH measurements taken in the metabolism crates were not indicative of actual ruminal pH within the production setting. It should also be considered that the diets used in the present study did not depress ruminal pH enough to justify supplementation with Fibrozyme, according to a simulation model.
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PROGRESS: 2005/10/01 TO 2006/09/30<BR>
The objective of Exp. 1 was to determine the acute (4 d) and long-term (3 wk) effects of a challenge with Mannheimia haemolytica on DMI and N balance in fed or fasted steers. Twenty two steers (initial BW = 320+/-24 kg) were utilized. A total of six animals were assigned to one of four treatments: 1) fed ad libitum and not challenged (Fed/Control); 2) fed ad libitum and challenged (d 0) with 10 mL of a solution containing 1x109 CFU/mL of M. haemolytica (Fed/Challenge); 3) fasted for 72 h and not challenged (Fasted/Control); 4) fasted for 72 h and challenged (d 0) with 10 mL of a solution containing 1x109 CFU/mL of M. haemolytica (Fasted/Challenge). Dry matter intake and total urine and fecal excretion were collected and used for analysis of N retention. Disease challenge increased (P bacteria and leukotoxin on day 15. In the acute model, DMI responded with a diet*day*disease interaction (P=.02). After the 72 h fasting period, the Fasted/Control steers consumed the same amount of DM as Fed/Control. However, an erratic pattern of intake was observed during the acute phase of the experimental period for this group. In the long-term analysis a diet*disease*week interaction was observed (P=.002). The Fed/Control steers generally had constant DMI compared with the Fasted/Control and Fed/Challenge. However, the only difference (P challenged with a bovine respiratory disease (BRD) pathogen have lower N retention for up to 4 d following the insult, and that loss of performance may not be compensated for within the first 2 wk following the insult. Experiment two was conducted to test the ability to measure exhaled nitric oxide (eNO) and carbon dioxide (eCO2) in the breath of healthy beef calves and calves showing clinical signs of BRD using tunable diode laser absorption spectroscopy. The experiment used 395 steer and bull calves (initial BW = 218.6+/-22.4 kg) received from auction markets for breath measurements during a 42 d receiving trial. Upon arrival, all steers had breath sampled for eNO and eCO2 analysis. Subsequently, all calves treated for signs of BRD were sampled as well as randomly selected clinically healthy control calves. Arrival mean eNO was 310+/-41.1 ppt and mean eCO2 was 2.64+/-0.94%. No differences in eNO were found between cattle subsequently treated for BRD. Steers eventually treated for BRD exhaled higher levels of CO2 than calves never treated (P due to lower (8.4%) carcass weight. Increased protein synthesis required by sick animals in the form of acute phase proteins and antibodies, decreased dry matter intake, and lower nitrogen balance associated with fasting and a BRD event indicate that following a BRD event, sick animals are at a metabolic disadvantage compared to healthy and unchallenged animals. Understanding why changes in tissue metabolism during a BRD challenge occurs, and lessening the impact of those changes has the potential to save the beef industry nearly one billion dollars annually. Detecting and treating BRD early in its onset may decrease the negative impact on animal performance. In Exp. 2, the fact that eNO values were near the lower detection limits of current instrumentation and occasional contamination by high ambient NO decreased the accuracy of the measurement. Further improvements in technology and more research are needed.
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PROGRESS: 2004/10/01 TO 2005/09/30<BR>
A study was conducted to investigate the effects of winter growing programs on subsequent feedlot performance of beef steers. A total of 260 steers were utilized for the experiment and were allotted to one of four treatment groups. One group was provided ad libitum access to a high-concentrate diet (CF), another grazed wheat pasture (WP), the third was fed a sorghum silage-based growing diet (SF), and the fourth group was program fed a high-concentrate diet (PF). Steers in the WP, SF, and PF groups were managed to achieve approximately equal rates of body weight gain. After the growing phase steers in the WP, SF, and PF treatments were adapted to a high-concentrate diet for finishing and then all steers were harvested at a common 12th-rib fat of 1.27 cm. During the finishing phase dry matter intake was greater for SF steers than PF and CF steers, with WP steers being intermediate. Steers in the SF group had the greatest ADG, PF steers were intermediate, and WP and CF steers were lowest. This resulted in less desirable feed efficiency during finishing for WP steers. At harvest, WP steers had greater USDA Yield Grades and lower marbling scores compared with SF and PF steers. In a companion experiment, percentages of moisture, fat, protein, and ash were determined in 46 Angus x Angus-Hereford steers by means of proximate analysis. Urea space, specific gravity, and 9-10-11 rib section proximate analysis were performed and values for moisture, fat and protein were estimated. The composition of the 9-10-11 rib section was determined by three methods: dissection, proximate analysis, and dual-energy x-ray absorptiometry (DXA). The equations relating specific gravity to chemical composition of the carcass accounted for 70% of the variation for fat and 33% of the variation for CP. Similar relationships were derived between proximate analysis of the 9-10-11 rib section and carcass composition (R2 = 0.65 for fat and R2 = 0.39 for CP). Urea space was not successful as an indirect method of empty body composition estimation. The DXA scan was able to accurately predict the composition of the rib section (R2 = 0.69 and R2 = 0.71 for lean and fat, respectively).
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IMPACT: 2004/10/01 TO 2005/09/30<BR>
Silage-fed and program-fed steers had higher gains and converted feed to gain more efficiently during the finishing phase compared with wheat-pasture steers. Dry-lot feeding programs can be used to grow cattle with similar or greater performance and carcass merit compared with grazing wheat pasture. Of the methods evaluated to estimate body composition, specific gravity produced the most precise comparison to actual chemical composition of the carcass. In addition, the DXA scan was able to accurately predict the composition of the rib section, and may be a useful tool for estimating carcass composition with minimal loss in carcass value.
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PROGRESS: 2003/10/01 TO 2004/09/30<BR>
Roughage can be difficult to handle and process and is one of the most costly ingredients in a high-concentrate diet. However, some inclusion of roughage is required in feedlot diets to maintain rumen function. Our objective was to evaluate the effects of a fibrolytic enzyme and roughage level on feedlot performance and carcass characteristics of steers. One hundred eighty four steers (avg initial BW = 343 kg) were selected for use in the trial. Steers selected were stratified by BW into four blocks consisting of 40 steers in the lightest block and 48 steers per block in the remaining three blocks. Four treatments were assigned randomly to two pens within each block. Treatments included: 1) no enzyme and 9% dietary roughage; 2) no enzyme and 4.5% dietary roughage; 3) fibrolytic enzyme (10 g/steer/d) and 9% dietary roughage; or 4) fibrolytic enzyme (10 g/steer/d) and 4.5% dietary roughage. Neither roughage level nor enzyme supplementation had an effect (P > 0.13) on initial BW, however, steers receiving enzyme weighed an average of 5.9 and 6.4 kg greater than steers receiving no enzyme on d 28 and 56, respectively. In contrast, BW was not affected by treatment (P > 0.18) on d 84 or d 112. Dry matter intake (DMI) was not affected (P > 0.31) by roughage level or enzyme supplementation during any period in the study. In addition, no forage level x enzyme interactions were detected (P > 0.66) for DMI. Average daily gain (ADG) was not affected (P = 0.95) by roughage level for the first 28 d of the study. In contrast, when measured from d 1 to 56, increasing roughage level numerically (P = 0.16) decreased gains as steers fed the diets greater in concentrates gained 3.43% more weight per d than steers receiving 9.0% alfalfa hay. However, roughage level had no effect (P > 0.41) on gains measured from d 1 to 84 or d 1 to 112. The main effect of enzyme supplementation on ADG was not statistically significant during any period in the study; however enzyme addition numerically (P = 0.16) increased ADG from d 0 to 28. Averaged over roughage levels, steers supplemented with enzyme gained 6.01% more weight per day than steers not fed enzyme. Feed conversion (F:G) was not affected (P > 0.22) by roughage level or enzyme supplementation from d 1 to 28. In addition, F:G was not affected (P > 0.47) by enzyme supplementation measured from d 1 to 84 or d 1 to 112. A roughage level x enzyme interaction effect was observed (P = 0.03) from d 1 to 84. Enzyme supplementation improved (P = 0.05) F:G by steers fed the diets containing 4.5% alfalfa hay, while having no effect (P = 0.25) on F:G by steers receiving the diets containing 9.0% alfalfa hay. Enzyme supplementation might have been more efficacious for steers receiving the diets lower in roughage content because of a decreased ruminal pH resulting in decreased fiber degradation for steers not fed enzyme. However, enzyme supplementation decreased (P = 0.01) ruminal pH in steers fed diets containing 4.5% alfalfa hay, while having no effect (P = 0.29) in steers fed diets containing 9.0% alfalfa hay.
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IMPACT: 2003/10/01 TO 2004/09/30<BR>
Enzyme supplementation might have caused a greater increase in ruminal fiber degradation in steers fed diets containing 4.5% alfalfa hay compared with those steers fed diets containing 9.0% alfalfa hay. This improvement in fiber degradation could have resulted in more VFA production, causing the observed decrease in the ruminal pH.
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PROGRESS: 2002/10/01 TO 2003/09/30<BR>
A winter grazing/feedlot performance experiment and a metabolism experiment were conducted to evaluate effects of grazing dormant native range (NR) or irrigated winter wheat (WW) pasture on intake, feedlot performance, carcass characteristics, total tract digestion, and ruminal digesta kinetics. Winter wheat steers had greater (P < 0.01) ADG while grazing compared with NR steers. Feedlot ADG and gain efficiency was greater (P < 0.02) for NR steers. Hot carcass weight, longissimus muscle area, and marbling score were greater (P < 0.01) for WW steers than NR steers, whereas 12th-rib fat depth (P < 0.64) and yield grade (P < 0.77) did not differ. In Exp. 2, eight ruminally cannulated steers that had previously grazed WW or NR were used to determine intake, digesta kinetics, and total tract digestion. Restricted growth of cannulated NR steers during the winter resulted in greater (P < 0.001) DMI (% of BW) and ADG (P < 0.04) during finishing compared with WW steers. Total tract OM digestibility (P < 0.02) was greater for NR than WW steers. Greater digestibilities by NR steers early in the finishing period might account for some of the compensatory gain response. Although greater performance was achieved by NR steers in the feedlot, grazing WW before finishing resulted in fewer days on feed, increased hot carcass weight, and improved carcass merit. An additional two experiments were conducted to examine the effect of previous BW gain during winter grazing on change in body composition during the feedlot finishing phase. Treatments were high rate of BW gain grazing WW (HGW); low rate of BW gain grazing WW (LGW); or NR. Winter grazing ADG (kg/d) for HGW, LGW, and NR steers were, respectively, 1.31, 0.54, 0.16 (Exp. 1) and 1.10, 0.68, 0.15 (Exp. 2). At the end of grazing, fat mass and proportion in carcass, offal, and empty body were greatest (P < 0.001) for HGW, intermediate for LGW, and lowest for NR steers. Live BW ADG and gain efficiency during the finishing phase did not differ (P = 0.24) among treatments, but DMI (% of mean BW) for NR and LGW was greater (P < 0.003) than HGW steers. Fat accretion in carcass, offal, and empty body was greater (P < 0.05) for LGW and NR than HGW steers in Exp. 2. Heat production by NR steers during finishing was greater (P < 0.02) than HGW steers. For both experiments, initial total gastro-intestinal tract (GIT; g/kg of EBW) proportional weight was greater (P < 0.05) in NR steers than LGW, and LGW steers had greater (P < 0.05) initial GIT proportional weight than HGW steers. Rate of decrease of GIT during finishing was greater in NR compared with HGW and LGW steers, but mesenteric fat increased for NR steers resulting in a similar increase in TST across the finishing period for all treatments. Similar rates of increase of TST across the finishing phase corresponded with similar rates of live and carcass weight gain among treatments. Our data support the hypothesis that increased visceral organ mass increases maintenance energy requirements of growing cattle. Maintenance energy requirements during finishing were increased for nutritionally restricted steers that were wintered on dormant NR.
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IMPACT: 2002/10/01 TO 2003/09/30<BR>
Similar feedlot gains by high gaining wheat pasture cattle may partially be due to lower maintenance energy requirements compared with lower gaining or nutritionally restricted cattle from other grazing programs. Ad libitum intake of low quality forages by growing cattle may increase maintenance energy requirements to an extent that potentially increased feed intake during feedlot finishing is negated. While mechanisms need to be elucidated, our data show that differences in initial body composition of cattle when placed on feed might be effectively mitigated if they are fed to the same compositional endpoint.
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PROGRESS: 2001/10/01 TO 2002/09/30<BR>
The effect of previous BW gain during winter grazing on carcass characteristics, body composition, visceral organ mass, endocrine, and metabolite response in beef steers was determined in two experiments. Three treatments were used: high (HGW) or low (LGW) rate of BW gain grazing winter wheat; or grazing native range (NR). Carcass characteristics, body chemical composition, and visceral organ mass were determined before placement into the feedlot and at final harvest. Final carcass characteristics and body composition were similar (P > 0.10) among treatments, but differences in chemical accretion existed. Initial gastro-intestinal tract (GIT) (g/kg of EBW) was greater (P < 0.05) in NR than HGW and LGW steers. The decrease of GIT (g/g EBW/d) during finishing was greater in NR than HGW and LGW steers. Initial concentrations of glucose and hormones were greater (P < 0.05) in HGW and LGW than NR steers. Concentrations of glucose and hormones increased in both exp during finishing. In a companion study the effect of previous high (HG) or low (LG) rate of BW gain grazing winter wheat on finishing performance, acid-base balance, blood flow, and net metabolite and hormone flux across total splanchnic tissues (TST) of steers surgically fitted with portal, hepatic, and arterial indwelling catheters was compared. In the study with multi-catheterized steers, feedlot ADG and ADG:DMI was greater (P < 0.01, d 0-28) for LG than HG steers. Portal and hepatic blood flow increased across days (P < 0.001). Oxygen consumption by TST was greater (P = 0.002) in LG than HG steers. Nitrogenous metabolite, glucose, and insulin TST flux were similar (P > 0.30) between treatments. Glucose and insulin TST flux increased across days (P< 0.001).
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IMPACT: 2001/10/01 TO 2002/09/30<BR>
Physiological modifiers of growth might include: different rates of accretion of visceral organ and empty body protein and fat, changes in basal metabolic rate and maintenance energy requirements, changes in blood flow across TST, and greater quantities of energetic metabolites for growth of peripheral tissues.
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PROGRESS: 2000/10/01 TO 2001/09/30<BR>
Three experiments were conducted to determine effects of limit feeding of the final finishing diet as a means of dietary adaptation compared with diets increasing in grain over a period of 20 to 25 d on overall cattle performance, carcass characteristics, digestibility, digesta kinetics and ruminal metabolism. The three experiments consisted of two feedlot experiments and one metabolism experiment. In Exp. 1, 84 Angus x Hereford yearling steers (initial BW = 418 kg) were fed for 70 d. Limit feeding during adaptation had no affect on overall daily gain and gain:feed (P > 0.05), but reduced DMI (P < 0.05) compared with ad libitum feeding of step-up diets. In Exp 2, 150 mixed crossbred steer calves (initial BW = 289 kg) were fed for an average of 173 d. Limit feeding decreased overall daily gain (1.51 vs 1.65 kg/d; P < 0.01) and DMI (8.68 vs 9.15 kg/d; P < 0.05) compared with ad libitum fed steers; however, gain:feed was not affected (P < 0.05) by step-up method. Experiment 3 used eight ruminally and duodenally cannulated steers (initial BW = 336 kg) in a completely random design. Steers were dosed with Co-EDTA and Yb-labeled dry rolled corn and sampled every 3 h for a 24-h period on the seventh day of each adaptation period. Steers were also evacuated at the end of each period 4 h after feeding to determine liquid and DM fill. Limit feeding reduced daily DMI variation (P < 0.10) throughout the entire experiment compared with ad libitum feeding of three adaptation diets. Limit-fed steers had reduced intakes and fecal excretions of ADF and had greater OM digestibilities on days 4 through 7, 11 through 14, and 18 through 21 (adaptation method x period interaction, P < 0.05). Limit feeding decreased variation in dry matter intake in yearling cattle, reduced daily gain and final weights in calves and improved OM digestibility. Adaptation using the final diet was successful in all experiments; however, it appears to have less negative effects when used in yearling cattle than calves.
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IMPACT: 2000/10/01 TO 2001/09/30<BR>
Limit feeding of the final diet as a means of dietary adaptation can be used in yearling cattle with few problems from acidosis or related intake variation. Care is needed to ensure that the length and degree of restriction is limited so that daily gains are not depressed to a point where increased days on feed are required. This method of adaptation is also efficacious in calves. However, care should be taken in order to avoid disruptions in intake during the adaptation period which might result in restriction for an extended period of time and ultimately increased days on feed and possibly reduced Choice carcasses. The effects of limit feeding during the initial 28 days of the feeding period on site and extent of digestion, digesta kinetics, and ruminal metabolism appear to be minimal, supporting few differences in performance across the finishing period.
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PROGRESS: 1999/10/01 TO 2000/09/30<BR>
An experiment was conducted to determine the effects of implant and diet adaptation strategy on finishing cattle performance and carcass characteristics. One hundred-fifty crossbred steer calves (initial weight = 289 kg) were blocked by weight and randomly allotted to 30 pens (10 pens/bock; 5 hd/pen) in a 180-day finishing study. Five pens/block were assigned to one of two treatments: 1) ad libitum feeding of four step-up diets over a 20-day period with levels of dry-rolled corn increasing from 52 to 80 percent (DM basis), or 2) limit feeding the final diet with predetermined increases in intake until ad libitum intake was achieved. Within each method of adaptation, steers were assigned to one of five implant treatments: 1) no implant (NC); 2) implant d 0; 3) two implants d 0; 4) implant d 0 and reimplant d 94; and 5) implant d 0, explant and reimplant d 94. All implants were a combination of estradiol (24 mg) and trenbolone acetate (120 mg). Overall daily gain was greater (P negative control steers, whereas no other differences were observed for carcass traits.
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IMPACT: 1999/10/01 TO 2000/09/30<BR>
Limit feeding the final diet compared with using decreasing roughage has been shown to improve feed efficiency and decrease the amount of roughage required during adaptation in yearling cattle. In our experiment, use of limit feeding as a method of adaptation reduced daily gain and carcass weight in finishing calves. Therefore, limit feeding the final diet might be more efficacious in yearlings compared with calves. Performance and carcass traits were similar in steers implanted twice on day 0 compared with steers implanted on day 0 and reimplanted later in the feeding period.