J. Anim Sci. 2007. 85:802-811. doi:10.2527/jas.2006-427
© 2007 American Society of Animal Science
Effects of a dietary Aspergillus oryzae extract containing 
-amylase activity on performance and carcass characteristics of finishing beef cattle
J. M. Tricarico*,1,2,
M. D. Abney
,
M. L. Galyean,
J. D. Rivera,3,
K. C. Hanson
,4,
K. R. McLeod and
D. L. Harmon
* Alltech Biotechnology Inc., Nicholasville, KY 40356;
and
Department of Animal and Food Sciences, Texas Tech University, Lubbock 79409; and
and
Department of Animal and Food Sciences, University of Kentucky, Lexington 40546
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Abstract
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Three experiments were conducted to examine the effects of an Aspergillus oryzae extract containing 
-amylase activity on performance and carcass characteristics of finishing beef cattle. In Exp. 1, 120 crossbred steers were used in a randomized complete block design to evaluate the effects of roughage source (alfalfa hay vs. cottonseed hulls) and supplemental -amylase at 950 dextrinizing units (DU)/kg of DM. Significant roughage source x -amylase interactions (P < 0.05) were observed for performance. In steers fed cottonseed hulls, supplemental -amylase increased ADG through d 28 and 112 and tended (P < 0.15) to increase ADG in all other periods. The increases in ADG were related to increased DMI and efficiency of gain during the initial 28-d period but were primarily related to increased DMI as the feeding period progressed. Supplemental -amylase increased (P = 0.02) the LM area across both roughage sources. In Exp. 2, 96 crossbred heifers were used in a randomized complete block design with a 2 x 3 factorial arrangement of treatments to evaluate the effects of corn processing (dry cracked vs. high moisture) and supplemental -amylase concentration (0, 580, or 1,160 DU/kg of DM). Alpha-amylase supplementation increased DMI (P = 0.05) and ADG (P = 0.03) during the initial 28 d on feed and carcass-adjusted ADG (P = 0.04) across corn processing methods. Longissimus muscle area was greatest (quadratic effect, P = 0.04), and yield grade was least (quadratic effect, P = 0.02) in heifers fed 580 DU of -amylase/kg of DM across corn processing methods. In Exp. 3, 56 crossbred steers were used in a randomized complete block design to evaluate the effects of supplemental -amylase (930 DU/kg of DM) on performance when DMI was restricted to yield a programmed ADG. Alpha-amylase supplementation did not affect performance when DMI was restricted. We conclude that dietary -amylase supplementation of finishing beef diets may result in increased ADG through increased DMI under certain dietary conditions and that further research is warranted to explain its mode of action and interactions with dietary ingredients.
Key Words: -amylase • Aspergillus oryzae • beef cattle • feedlot
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INTRODUCTION
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Starch is a major component in diets fed to intensively raised cattle, especially in finishing beef cattle, where it provides the majority of the animal’s energy intake. In growing cattle, starch digestion is energetically more efficient in the small intestine than in the rumen (McLeod et al., 2001
); however, within the normal range of starch intakes for finishing beef cattle, starch digestion is limited in the small intestine but not in the rumen (Harmon et al., 2004). Extensive ruminal starch digestion is advantageous, but excessively rapid starch fermentation can result in ruminal acidosis and decreased performance (Owens et al., 1998). Consequently, maximizing ruminal starch fermentation and avoiding conditions leading to ruminal upset are desirable.
Feeding supplemental amylases to finishing beef cattle has not been extensively studied. Amylase activities were only minor components in primarily fibrolytic preparations used in recent studies by McAllister et al. (1999) and Hristov et al. (2000). More recently, Tricarico et al. (2005) reported increased milk production in lactating dairy cows, whereas DeFrain et al. (2005) noted improvements in energy balance in transition dairy cows as a result of feeding a defined supplemental -amylase. We hypothesized that -amylase supplementation may represent an alternative for manipulating ruminal starch fermentation and thereby improve performance in finishing beef cattle.
The specific objectives of each of the 3 experiments reported here were to examine 1) the effects of supplemental -amylase and roughage source on performance and carcass characteristics of finishing steers (Exp. 1), 2) the effects of 2 concentrations of supplemental -amylase and corn processing on performance and carcass characteristics of finishing heifers (Exp. 2), and 3) the effects of supplemental -amylase on ADG by finishing steers when DMI was restricted within the context of a programmed feeding (Exp. 3).
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MATERIALS AND METHODS
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Procedures used in Exp. 1 and 3 were approved by the Texas Tech University Institutional Animal Care and Use Committee, and procedures used in Exp. 2 were approved by the University of Kentucky Institutional Animal Care and Use Committee.
Experiment 1
Cattle and Treatment Assignment.
One hundred sixty-two steers (British and British x Continental; average initial BW = 363 ± 33 kg) were received at the Texas Tech University Burnett Center on 17 April 2002. Cattle had previously grazed winter wheat pasture at a location approximately 8 km from the Burnett Center. Steers were assigned randomly to 12 soil-surfaced pens (13 to 14 steers per pen) and offered a 70% concentrate diet on arrival. Steers were processed the following day, including (1) individual BW measurement, (2) individual identification by ear tag, (3) vaccination with clostridial 7-way and Haemophilus somnus vaccine (Vision 7/Somnus with Spur, Intervet, Millsboro, DE) and with Bovishield 4 + Lepto (Pfizer Animal Health, Exton, PA), and (4) treatment for internal and external parasites (Cydectin, Fort Dodge Animal Health, Overland Park, KS). Steers were returned to the soil-surfaced pens after processing and fed the 70% concentrate diet for 14 d. They were switched to an 80% concentrate diet on 2 May 2002 and to a 90% concentrate diet on 9 May 2002. All steers received a zeranol implant (Ralgro, Schering-Plough Animal Health, Union, NJ) and were sorted to their assigned pens 7 d before the experiment began.
Steers were weighed on 7 May 2002 to obtain BW for sorting into treatment groups. They were sorted by BW in ascending order and assigned to 6 blocks of 20 steers each. Four treatments were randomly assigned to individual steers within each block, beginning with the lightest 4 steers (block 1) and proceeding through the heaviest 4 steers (block 6). Blocks were then assigned to 4 contiguous pens (24 pens total), and treatments were assigned randomly to pens within each group of 4 contiguous pens in a block. Therefore, a total of 24 slotted-floor concrete pens (2.9 x 5.5 m, with 2.5 m of linear bunk space) were used in this experiment, with 6 weight blocks, 4 treatments, 6 pens per treatment, and 5 steers per pen. The 4 dietary treatments consisted of alfalfa hay or cottonseed hulls as the roughage source and the presence or absence of supplemental -amylase (Amaize, Alltech Inc., Nicholasville, KY) in a 2 x 2 factorial arrangement.
The -amylase preparation contained Aspergillus oryzae extract and Saccharomyces cerevisiae fermentation solubles. Alpha-amylase activity was determined according to the procedure described in the Food Chemicals Codex (1996). One -amylase dextrinizing unit (DU) was defined as the quantity of enzyme required to dextrinize soluble starch at the rate of 1 g/h at 30°C and pH 4.8. Final -amylase concentrations were 0 or 950 DU/kg of dietary DM. The enzyme concentrations selected were those recommended by the manufacturer and were based on the total amounts of dietary -amylase provided to dairy cattle in previous studies (De-Frain et al., 2005; Tricarico et al., 2005).
Experimental Diets, and Feeding and Weighing Procedures.
Experimental diets were formulated to provide 5.7% NDF from roughage (based on tabular NDF values for alfalfa and cottonseed hulls; NRC, 1996) and contained steam-flaked corn as the primary ingredient. The ingredient and nutrient compositions of the diets fed during Exp. 1 are presented in Table 1. Diets contained an intermediate premix, and supplemental -amylase was added as a second premix consisting of 46.07% ground corn and 53.93% Amaize (DM basis). Ingredient samples were collected every 2 wk for DM determinations and were used to calculate the DM content of each dietary ingredient for the experiment. Feed bunk samples were collected weekly for DM determinations. Feed sample DM values were used to compute average DMI for each pen. Feed samples were composited for each 28-d period, ground to pass a 2-mm screen in a Wiley mill, and analyzed for DM, ash, CP (Kjeldahl N), and ADF (AOAC, 1990). Samples of hay and cottonseed hulls fed during the study were analyzed for NDF (Goering and Van Soest, 1970).
The 4 experimental diets were mixed in a 1.27-m3 capacity paddle mixer. Mixed feed was delivered to the pens using a self-propelled mixing unit (Rotomix, Garden City, KS), with the quantity of feed allotted to each pen within treatment weighed to the nearest 0.45 kg. Clean-out of the mixing unit was monitored closely to avoid cross-contamination of diets. Feed bunks were visually evaluated at approximately 0700 to 0730 daily. The quantity of feed remaining in each bunk was estimated, and the suggested daily allotment of feed for each pen was recorded. The feeding process was designed to ensure ad libitum access to feed, with a target of no more than 0.2 kg of unconsumed feed/steer remaining in the feed bunk each morning.
Cattle were weighed on a pen basis using a platform scale after 28, 84, and 112 d on feed. Cattle were weighed individually on d 0, 56, when they were implanted with Revalor S (Intervet), and before shipment to slaughter using a single-animal scale (C & S Single-Animal Squeeze Chute set on 4 load cells; Cummings and Sons, Garden City, KS). In all instances, the scales were calibrated with 453.5 kg of certified weights (Texas Dept. of Agric.).
Carcass Evaluation.
Steers were visually examined by block after d 112 and were scheduled for slaughter (Excel Corp., Plainview, TX) when approximately 60% of steers within a weight block were judged by visual appraisal to have adequate finish to grade USDA Choice. Steers in blocks 5 and 6 were shipped for slaughter on d 133. Steers in blocks 3 and 4 were shipped to slaughter on d 154, whereas steers in blocks 1 and 2 were shipped to slaughter on d 168. Carcass data collected included HCW, fat thickness at the 12th rib, LM area, percentage of KPH, marbling score, and USDA quality and yield grades.
Experiment 2
Cattle and Treatment Assignment.
Ninety-six crossbred heifers (average initial BW = 364 ± 17 kg), housed at the University of Kentucky Agricultural Research Center Beef Unit, were used in the study. Heifers were processed immediately after arrival, including 1) individual identification by ear tag, 2) vaccination with ViraShield 5 + Somnus (Novartis Animal Vaccines Inc., Overland Park, KS), 3) body temperature monitoring, and 4) treatment with Nuflor and Banamine (Schering-Plough Animal Health, Union, NJ) when body temperatures exceeded 40°C. Heifers with persistent fevers (>39.4°C) were later dosed with Micotil (Elanco Animal Health, Greenfield, IN). Heifers were fed a receiving diet and adjusted to corn silage for approximately 4 wk after arrival. Beginning 1 d before the initiation of the study, animals were individually weighed, treated for internal parasites with fenbendazole (Safeguard, Hoechst-Roussel Pharmaceuticals Inc., Somerville, NJ), and implanted with Revalor-IH (Intervet).
Heifers were stratified by BW into 4 blocks. Heifers within a block were assigned randomly to 1 of 6 treatments in a randomized complete block design with a 2 x 3 factorial arrangement of treatments for a total of 4 pens per treatment and 4 heifers per pen. The 6 dietary treatments were the combinations of corn grain processing (dry cracked or high-moisture corn) and -amylase (Amaize, Alltech Inc.) supplementation at 0, 580, or 1,160 DU/kg of dietary DM. The enzyme concentrations were selected to provide a similar and an intermediate -amylase concentration relative to Exp 1.
The corn DM concentration was analyzed weekly throughout the study. The dry corn averaged 87.9% DM (range = 86.7 to 88.7%), and the high-moisture corn averaged 61.4% DM (range = 59.8 to 64.6% DM) over the entire study. Before feeding, the dry corn was coarsely cracked using a roller mill. The high-moisture corn was harvested whole and stored whole in an upright, concrete stave silo. With the extent of mechanical handling used in feed processing and delivery, the majority of the kernels were broken at feeding.
Experimental Diets, and Feeding and Weighing Procedures.
The ingredient and chemical compositions of the finishing diets fed during Exp. 2 are presented in Table 2. The diets were formulated to be isonitrogenous (12.0% CP, DM basis) and fed once daily as a completely mixed ration to achieve ad libitum intakes. Heifers were adjusted to the final finishing diets over a 3-wk period by varying the proportion of corn and corn silage in the diet. Heifers were fed (DM basis) 60% corn silage and 30% corn in wk 1, 45% corn silage and 45% corn in wk 2, and 30% corn silage and 60% corn in wk 3. All step-up diets contained the same ingredients in the 10% supplement as the finishing diets. Heifers were fed the final finishing diets containing (DM basis) 15% corn silage, 75% corn, and 10% supplement from d 21 until the end of the experiment. The supplemental -amylase preparation was mixed with ground corn as a carrier, 5% wet molasses, and 5% dry molasses to make 3 pre-mixes. The concentration of supplemental enzyme preparation in each premix was formulated to deliver the corresponding -amylase activities when 500 g of the premix was top-dressed per pen. The premix was top-dressed immediately after the feed was delivered to each feed bunk.
Total feed offered was measured daily. Supplement samples were collected for analysis after each new batch was mixed and composited. Feed refusals were collected from the feed bunks every Tuesday before the heifers were fed, and refusals from each bunk were weighed, and a sample was collected and composited within each treatment combination and analyzed for DM. Feed ingredients were analyzed for DM concentration, and diets were adjusted accordingly every Tuesday to correspond with weigh days and collection of refusals. Heifers were individually weighed on d 1, 28, 56, and the day before slaughter. Initial BW measurements were obtained over 2 d and averaged, whereas final BW was based on HCW adjusted for an average dressing percent of 57.69%.
Carcass Evaluation.
Due to the limited number of animals that the slaughter facility in Cincinnati, OH, could handle at one time, 24 heifers were shipped for slaughter on each slaughter day. We harvested the cattle in blocks 1 and 2 on d 63 and 70 and blocks 3 and 4 on d 91 and 98. The 2 heaviest heifers from each pen of blocks 1 and 2 were killed on d 63, and the remaining heifers were killed on d 70. The same procedure was followed for blocks 3 and 4 on d 91 and 98. Carcass data collected included HCW, fat thickness at the 12th rib, LM area, percentage of KPH, marbling score, and USDA quality and yield grades.
Experiment 3
Cattle and Treatment Assignment.
The objective of Exp. 3 was to examine the effects of supplemental -amylase (Amaize, Alltech Inc.) on growth performance of steers fed in a programmed-gain (restricted DMI) system for 56 d. Sixty-four crossbred steers (British x Continental; average initial BW = 365 ± 31.4 kg) were housed at the Texas Tech University Burnett Center. The steers were blocked by BW into 4 blocks and assigned randomly, within block, to 1 of 8 soil-surfaced pens (4 pens per treatment and 8 steers per pen). Treatments consisted of -amylase supplementation at 0 or 930 DU/kg of dietary DM.
Experimental Diets, Feeding and Weighing Procedures.
The ingredient and nutrient compositions of the diets fed during Exp. 3 are presented in Table 3. Diets contained an intermediate premix, and supplemental -amylase was added as described for Exp. 1. Feed sampling and analyses also were as described for Exp. 1. Feed was delivered daily in quantities sufficient to allow for an average daily shrunk BW gain of 1.52 kg/ d, with an assumed BW of 567 kg at a target end point of USDA Choice grade. The quantity of feed required to yield this shrunk ADG was calculated using the NRC (1996) NE equations. The steers were weighed individually and implanted with Revalor IS (Intervet) on d 0 of the study. Weighing procedures were as described for Exp. 1.
NE Calculations and Statistical Analyses
Dietary NEm and NEg concentrations for Exp. 1 and 2 were calculated from animal intake and performance using a generalized quadratic solution and the NRC (1996) equations, as described by Gleghorn et al. (2004). All calculations were done using pen means. A 4% adjustment of BW measurements was used to calculate initial and final shrunk BW. Data were analyzed separately for each experiment. Performance data in Exp. 1 and 2 included carcass-adjusted ADG and G:F that were determined using a calculated final BW obtained by dividing HCW by the average dressing percent in each experiment (62.84% for Exp. 1 and 57.69% for Exp. 2). Performance and carcass characteristics for Exp. 1 were analyzed as a randomized complete block design with a 2 x 2 factorial arrangement of treatments. The fixed effects of the model included roughage source, -amylase supplementation, and their interaction. Performance and carcass characteristics for Exp. 2 were analyzed as a randomized complete block design with a 2 x 3 factorial arrangement of treatments. The model included the fixed effects of corn processing method, -amylase supplementation, and their interaction. Orthogonal polynomials were used to partition linear and quadratic effects of -amylase supplementation in Exp. 2. Block was considered a random effect in both experiments. Data were analyzed with pen as the experimental unit using the MIXED procedure (SAS Inst. Inc., Cary, NC). The distribution of carcasses grading USDA Choice was analyzed as a binomial proportion using the GLIMMIX procedure of SAS, with the same fixed and random effects as for the performance data. Performance data for Exp. 3 were analyzed as a randomized complete block design using the MIXED procedure of SAS with pen as the experimental unit. As in Exp. 1, the fixed effects of the model included -amylase supplementation, and block was considered a random effect.
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RESULTS
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Experiment 1
Performance.
Roughage source did not affect performance when diets were balanced for the percentage of NDF supplied by alfalfa hay or cottonseed hulls. Although diets were formulated to supply 5.7% NDF from roughage based on tabular values for NDF, analyzed values of 52.1 (alfalfa) and 89.7% (cottonseed hulls) NDF resulted in NDF from roughage of 6.3 and 5.9% for alfalfa and cottonseed hull diets, respectively. There were no overall effects of -amylase supplementation on finishing cattle performance (Table 4); however, significant -amylase x roughage source interactions for ADG were observed through d 28 (P = 0.02) and 112 (P = 0.04). In addition, trends (P < 0.15) for the -amylase x roughage source interaction were observed for carcass-adjusted ADG, as well as ADG on all other weigh dates throughout the feeding period. In all cases, -amylase supplementation increased ADG by steers fed the diet containing cottonseed hulls but not in steers fed the diet containing alfalfa hay. An -amylase x roughage source interaction was observed for DMI (P = 0.05) through d 112, and trends (P < 0.15) were noted through d 56 and 84. Alpha-amylase supplementation increased DMI by steers fed the diet containing cottonseed hulls but not by steers fed the diet containing alfalfa hay. An -amylase x roughage source interaction was observed for G:F (P = 0.02) through d 28, and a trend (P < 0.15) was observed through d 112. Alpha-amylase addition increased G:F in steers fed the diet containing cottonseed hulls and decreased G:F in steers fed the diet containing alfalfa hay. Calculated dietary NE concentrations were greater than estimates from ingredient tabular values for both diets and were greater (P < 0.04) in the alfalfa hay than in the cottonseed hulls diet (Table 5). Supplemental -amylase had no effects on calculated dietary NE concentrations in either diet.
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Table 4. Effects of -amylase addition (950 DU/kg of DM) and roughage source on BW, ADG, DMI, and G:F of finishing beef steers in Exp. 1
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Table 5. Effects of -amylase addition (950 DU/kg of DM) and roughage source on dietary NE concentrations (Mcal/kg of DM) predicted from performance data in Exp. 11
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Carcass Characteristics.
The effects of -amylase supplementation and roughage source on carcass characteristics are presented in Table 6. Roughage source did not affect carcass characteristics of finishing steers, and -amylase supplementation increased LM area (P = 0.02) regardless of roughage source. In addition, steers fed supplemental -amylase had greater adjusted final BW and HCW when fed cottonseed hulls but not when fed alfalfa hay, with the -amylase x roughage source interaction approaching significance (P = 0.12) for both variables.
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Table 6. Effects of -amylase addition (950 DU/kg of DM) and roughage source on carcass characteristics of beef steers in Exp. 1
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Experiment 2
Performance.
Although the DMI by heifers fed high-moisture corn tended (P = 0.10) to be greater than that of heifers fed cracked corn during the initial 28 d on feed, there were no overall effects of corn processing on finishing heifer performance (Table 7). Alpha-amylase supplementation increased ADG (P = 0.03) and DMI (P = 0.05) during the initial 28-d period and overall carcass-adjusted ADG (P = 0.04) across both corn processing methods. The increases in ADG during the initial 28 d resulting from -amylase supplementation was linear for heifers fed cracked corn and quadratic for heifers fed high-moisture corn with the -amylase x corn processing interaction approaching significance (P = 0.11) and significant linear (P = 0.04) and quadratic (P = 0.05) effects for -amylase supplementation. The increase in carcass-adjusted ADG for the overall feeding period resulting from -amylase supplementation was, however, quadratic (P = 0.04) for both corn processing conditions. The increased DMI during the initial 28 d on feed seemed to be quadratic for both corn processing methods, with quadratic effects for -amylase supplementation approaching significance for the 28 d (P = 0.06), 56 d (P = 0.07), and overall (P = 0.07) feeding periods. The G:F did not differ across treatments throughout the study, but trends were noted for the quadratic effects of -amylase supplementation during the 56 d (P = 0.14) and overall (P = 0.07) feeding periods and for the -amylase x corn processing interaction during the overall (P = 0.14) feeding period. Calculated dietary NE concentrations were greater than estimates from ingredient tabular values in both diets (Table 8). Corn processing and -amylase supplementation had no effects on calculated dietary energy concentrations, although trends (P < 0.15) were observed for quadratic decreases as a result of -amylase supplementation.
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Table 7. Effects of -amylase addition and corn processing on BW, ADG, DMI, and G:F by finishing beef heifers in Exp. 2
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Table 8. Effects of -amylase addition and corn processing on dietary NE concentrations (Mcal/kg of DM) predicted from performance data in Exp. 21
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Carcass Characteristics.
The effects of -amylase supplementation and corn processing on carcass characteristics are presented in Table 9. Corn processing had no effects on carcass characteristics of finishing heifers. Supplemental -amylase resulted in a quadratic decrease in yield grade (P = 0.02) across both corn processing conditions. Quadratic increases resulting from -amylase supplementation also were observed for adjusted final BW (P = 0.03), HCW (P = 0.03), and LM area (P = 0.04) across both corn processing methods. Supplemental -amylase also altered fat thickness (P = 0.05), but these effects were not similar across corn processing methods, as the -amylase x corn processing interaction approached significance (P = 0.14). Alpha-amylase supplementation tended to linearly increase fat thickness in heifers fed high-moisture corn (P = 0.09) and quadratically decrease it in heifers fed cracked corn (P = 0.07).
Experiment 3
Performance.
Actual ADG for the 56-d experiment was slightly less than predicted (1.39 vs. 1.44 kg/d for -amylase and control, respectively, vs. 1.52 kg/d predicted gain). Thus, -amylase supplementation had no effects on ADG or G:F of finishing beef steers when the DMI of a finishing diet containing cottonseed hulls, similar to the diet fed in Exp. 1, was restricted to follow a programmed-gain system for 56 d (Table 10).
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Table 10. Effects of -amylase addition (930 DU/kg of DM) on BW, ADG, DMI, and G:F by finishing beef steers fed in a programmed-gain system in Exp. 3
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DISCUSSION
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The overall objective for the experiments reported herein was to evaluate effects of a supplemental -amylase on performance and carcass characteristics of finishing beef cattle under different dietary roughage sources or corn processing methods. Roughage source did not affect performance when diets were balanced for the percentage of NDF supplied by roughage. This observation agrees with previous findings reported by Defoor et al. (2002) and Galyean and Defoor (2003). Nonetheless, -amylase supplementation increased ADG through d 28 and 112 in steers fed cottonseed hulls but not in steers fed alfalfa hay. The reasons for the interaction between roughage source and supplemental -amylase observed in this study are unclear; however, these interactions might be attributable to differences in ingredient composition between the diets. Gleghorn et al. (2004) suggested that urea seems to be a more effective source of N than natural protein sources for steam-flaked corn diets. Therefore, one potential explanation for the interaction could be that a larger proportion of dietary CP was provided by urea in the cottonseed hull diet than in the alfalfa hay diet as a result of formulating the diets to be isonitrogenous and to provide similar amounts of degraded intake protein. A second factor potentially associated with the -amylase x roughage source interaction may be the different sources of dietary Ca in the 2 diets. A greater concentration of calcium carbonate was added to the cottonseed hull diet than to the alfalfa hay diet. Aspergillus oryzae -amylase, like other -amylases, contains one strongly bound Ca2+ ion that is essential for structural stability and enzyme activity and a secondary Ca2+-binding site that is responsible for Ca2+-mediated inhibition at Ca2+ concentrations of 20 mM or above (Boel et al., 1990). It is possible that a difference in readily available Ca2+ resulting from different Ca sources and differences in expected ruminal pH between the 2 roughage sources affected -amylase activity in the rumen. Finally, Bhatti and Firkins (1995) examined the kinetics of digestion, specific gravity, and hydration for several roughages, including alfalfa and cottonseed hulls. These authors reported that cottonseed hulls have a greater extent of digestion with a longer lag time and a slower rate of digestion than alfalfa. Consequently, potential differences in rates of passage and ruminal digestion between steers fed alfalfa hay or cottonseed hulls diets might also be related to the interaction between roughage source and supplemental -amylase observed in this study.
We hypothesized that amylase supplementation may be more efficacious in the dry rolled corn diet because of the predicted differences in starch availability. However, corn processing did not affect performance, even though the DM concentrations of cracked and high-moisture corn were markedly different over the entire study (87.9 vs. 61.4% DM, respectively). In the absence of supplemental -amylase, the heifers fed cracked corn seemed to consume more DM throughout the entire study and outperform the heifers fed high-moisture corn during the initial 28 d on feed. This observation may agree with the conclusion by Owens et al. (1997) that slight decreases in ADG resulting from reduced DMI may be attributed to subclinical acidosis when more extensively processed grain is fed to cattle. In addition, heifers fed high-moisture corn and -amylase at 580 DU/kg of DM consumed numerically more DM than heifers on any other treatment. It is possible that -amylase supplementation allowed the heifers on high-moisture corn to overcome a certain degree of subclinical ruminal acidosis. This also might explain why a response was noted for the cottonseed hulls diet in Exp. 1 because, with more total grain in the diet and equal intake, expected ruminal pH could be lower with the cottonseed hulls than with the alfalfa hay diet.
We hypothesized that if supplemental -amylase would stimulate ruminal starch degradation, the response would be greater with dry corn than with high-moisture corn because of a slower rate of digestion for dry corn (Philippeau et al., 1999). Nonetheless, -amylase supplementation increased carcass-adjusted ADG, carcass-adjusted BW, and HCW with both corn processing methods. In addition, -amylase effects on ADG were dose-dependent and predominantly quadratic in nature. This observation agrees with a quadratic response in milk production to -amylase supplementation by lactating dairy cattle (Tricarico et al., 2005); however, the reasons for this quadratic response remain unclear. The absence of an -amylase x corn processing interaction in this study and lack of increased ruminal in situ starch disappearance in lactating dairy cows and steers fed supplemental -amylase reported by Tricarico et al. (2005) suggest that the potential effects of -amylase on performance are not mediated through increased ruminal starch digestion. It is also unlikely that -amylase supplementation affects energy utilization in feedlot cattle, as evidenced by the absence of -amylase effects on our estimates of dietary NE concentrations predicted from performance data. Nonetheless, a trend for a quadratic decrease in calculated dietary NE concentrations was evident in Exp. 2, particularly with the high-moisture corn diet. This numerical decrease in dietary NE concentration was probably a consequence of the considerable increase in DMI (1.42 kg/d on average for d 0 to end) observed in the high-moisture corn diet supplemented with -amylase.
Supplemental -amylase increased LM area in both experiments. In Exp. 1, LM area increased to a greater extent in the cottonseed hulls diet without changes in fat thickness or yield grade. This effect on LM area is probably associated with the numerically greater ADG and carcass-adjusted BW observed for -amylase supplementation with cottonseed hulls. In Exp. 2, LM area increased in the cracked and high-moisture corn diets but only with -amylase supplementation at 580 DU/ kg of DM. Similar to cottonseed hulls, the greatest LM area was associated with the greatest carcass-adjusted ADG and BW under both corn processing conditions. In the high-moisture corn diet, fat thickness increased linearly with -amylase supplementation, resulting in the greatest yield grade with 1,160 DU of -amylase/ kg of DM. However, fat thickness was decreased with -amylase supplementation at 580 DU/kg of DM in the cracked corn diet, substantially improving yield grade and suggesting a potential change in the composition of gain for the combination of cracked corn and -amylase at 580 DU/kg.
The increases in ADG attributable to -amylase supplementation were primarily mediated through increased DMI and were consistently greater during the initial 28-d period in Exp. 1 and 2. Additional support for a DMI-mediated -amylase effect is provided by the lack of response to -amylase supplementation when DMI was restricted within the context of a programmed-gain system in Exp 3. The potential mechanisms for increased DMI resulting from -amylase supplementation were not addressed in these studies; however, Tricarico et al. (2005) reported that -amylase supplementation changed ruminal fermentation in lactating cows, steers, and rumen-simulating continuous cultures by increasing butyrate and decreasing propionate molar proportions. These changes in fermentation could be indicative of a lesser role for lactate as an intermediate when amylase was fed. These changes may support increases in feed intake. Oba and Allen (2003) reported negative effects of increasing ruminal propionate on DMI in dairy cattle. Therefore, the increases in DMI as a result of -amylase supplementation in beef cattle could possibly be related to the ability of this enzyme preparation to decrease the molar proportion of propionate in the rumen. The ruminal molar proportion of propionate was least for the intermediate level of supplemental -amylase in dairy cows (Tricarico et al., 2005); however, ruminal characteristics were not measured in the present studies, and information on VFA changes with -amylase supplementation in high-concentrate diets is lacking.
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IMPLICATIONS
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Although our results suggest that effects of -amylase supplementation are not predictable with different roughage sources or corn processing methods, there is potential for increased weight gain and improved carcass characteristics in finishing beef cattle fed this supplement. The effects on performance and carcass characteristics seem to be primarily a consequence of increased feed intake resulting from potential effects on the process of ruminal digestion without necessarily increasing ruminal starch disappearance. Additional research is warranted to further examine the mode of action of this supplement and its interactions with various dietary ingredients.
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Footnotes
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1 3031 Catnip Hill Pike (phone: 859-885-9613 ext. 3463; fax: 859-887-3233). 
3 Present address: Eli Lilly, Monterrey, Mexico.
4 Present address: USDA APHIS National Wildlife Research Center, Starkville, MS.
2 Corresponding author: jtricarico{at}alltech.com
Received for publication July 3, 2006.
Accepted for publication November 4, 2006.
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LITERATURE CITED
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Abstract
INTRODUCTION
