J. Anim Sci. 2008. 86:882-889. doi:10.2527/jas.2006-717
© 2008 American Society of Animal Science
Effect of method of applying fibrolytic enzymes or ammonia to Bermudagrass hay on feed intake, digestion, and growth of beef steers1
N. A. Krueger*,
A. T. Adesogan*,2,
C. R. Staples*,
W. K. Krueger*,
S. C. Kim*,
R. C. Littell
and
L. E. Sollenberger
* Department of Animal Sciences,
and
Department of Statistics, and and
Department of Agronomy, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611
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Abstract
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This study examined how different methods of applying a fibrolytic enzyme or ammonia affect the nutritive value of Bermudagrass hay and the performance of beef cattle. Fifty Angus x Brangus crossbred steers (mean initial BW 244 ± 26 kg) were individually fed for ad libitum intake of a 5-wk regrowth of a mixture of Florakirk and Tifton 44 Bermudagrass [Cynodon dactylon (L.) Pers] hay for 84 d with a concentrate supplement (77% soybean hull pellets, 23% cottonseed meal (DM basis) fed at 1% of BW daily. The Bermudagrass was conserved as hay without treatment (control), with NH3 (30 g/kg of DM), or with a fibrolytic enzyme (16.5 g/t, air-dry basis) that was applied immediately after cutting (Ec), at baling (Eb), or at feeding. Chromic oxide was dosed to steers for 10 consecutive days, and fecal Cr concentrations from the last 5 d were used to estimate apparent total tract digestibility. In situ ruminal DM degradability was measured by incubating ground (4-mm) hay samples in duplicate in each of 2 ruminally cannulated cows having ad libitum access to Bermudagrass hay and 500 g/d of soybean meal. Unlike the enzyme treatment, ammoniation increased (P < 0.001) the CP concentration and reduced (P < 0.001) NDF, hemicellulose, and lignin concentrations of hay. Total DMI was greater (P < 0.05) for steers fed hays treated with Ec or NH3 than for those fed control hays. All additive treatments increased (P < 0.05) DM digestibility, and NH3, Ec, and Eb treatments also increased (P < 0.01) NDF digestibility. The initial and final BW, ADG, BCS, G:F, and hip height of the steers were not affected (P > 0.05) by treatment. The wash loss fractions in hays treated with Ec and Eb were lower than that in the control hay, but the potentially degradable fraction, total degradable fraction, and the effective degradability were increased (P < 0.01) by NH3 treatment. Application at cutting was the most promising method of enzyme treatment, and this treatment was almost as effective as ammonia for enhancing forage quality.
Key Words: ammonia • beef cattle • Bermudagrass • fibrolytic enzyme • forage
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INTRODUCTION
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Most ruminant livestock production systems rely heavily on forage-based diets. During the winter, the quality and quantity of the perennial warm-season grasses available for grazing in the southern United States may limit cattle productivity. One method of enhancing the productivity of cattle in the winter is to improve the quality of the forage being fed. Ammonia treatment has been used successfully to improve the quality of warm-season grass hays (Klopfenstein, 1978
; Kunkle et al., 1983, 1984; Brown, 1988; Rasby et al., 1989; Brown and Adjei, 1995; Brown and Pate, 1997). However, the caustic nature of ammonia requires the use of special handling procedures and equipment. In recent years, the use of exogenous fibrolytic enzymes to improve feed digestion and utilization has been the focus of considerable research (Beauchemin et al., 2003). Studies have reported increases in DM digestion in situ and in vivo (Feng et al., 1996; Yang et al., 1999) and in voluntary intake (Feng et al., 1996; Yang et al., 1999; Pinos-Rodriguez et al., 2002) when enzymes were added to beef and dairy cattle diets. Although some studies reported improved animal performance resulting from enzyme treatment of diets (Feng et al., 1996; Beauchemin et al., 1999), others have not (ZoBell et al., 2000). These inconsistencies may be attributable to differences in enzyme type, preparation, activity, application rate (Bowman et al., 2002; Beauchemin et al., 2003), mode of application, and portion of the diet to which the enzyme was applied (Feng et al., 1996; Lewis et al., 1996; ZoBell et al., 2000). The majority of the research conducted with fibrolytic enzyme treatment of feeds has used temperate forage species and diets. Thus, little is known about the potential for improving the quality of warm-season grass hays with enzymes.
The objective of this study was to examine the effects of various methods of applying a commercial fibrolytic enzyme mixture or ammonia to Bermudagrass hay on feed intake, digestion kinetics, and growth performance of beef steers.
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MATERIALS AND METHODS
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Forage Treatments
Five-week-old fall regrowth of a mixed sward of Florakirk and Tifton 44 Bermudagrass [Cynodon dactylon (L.) Pers] was harvested as hay from a 40-ha field owned by a local hay producer in Alachua County, FL. The predominant soil was Fort Meade fine sand, and the pasture was fertilized 4 wk before harvest with 74 kg/ha of 20-5-15 (N-P2O5-K2O). There was no rainfall during the 5-wk regrowth period. Harvesting occurred over 2 consecutive days, on each of which 2 ha of forage were made into 18- to 20-kg square hay bales. The forage was stored without treatment (control) or after treatment with either a fibrolytic enzyme mixture (Biocellulase A20, Loders Croklaan, Channahon, IL) or anhydrous ammonia. The fibrolytic enzyme had shown promise for improving the digestibility of warm-season grasses in preliminary research (Dean et al., 2003). The manufacturer-stipulated enzyme activity was 1,400 units/g, where 1 unit of activity is the amount of enzyme required to release 1 µmol of glucose-reducing sugar equivalents/min at pH 4.5 and 40°C. Cellulase activity was also determined to be 51.3 units/g by using the filter paper method (Wood and Bhat, 1988), where 1 unit of activity is the amount of enzyme that releases 2 mg of glucose from 50 g of filter paper in 60 min at 39°C and pH 5.5. Xylanase activity was determined to be 3,530 µmol of xylose released/min per mL at 39°C and pH 5.5 by using the dinitrosalicylic acid procedure (Bailey et al., 1992).
The enzyme was either sprayed (16.5 g/t, air-dry basis) on the forage immediately after it was cut (Ec) with a New Holland 617 mower conditioner (New Holland North America, New Holland, PA), after a 72-h wilt just before it was baled (Eb) with a New Holland 385 square baler, or just before it was fed (Ef). For the Ec and Eb treatments, the enzyme was applied at a flow rate of 2.7 L/min by using a tractor-mounted, 57-L, continuous-flow sprayer (FIMCO, North Sioux City, SD) fitted with a 3-nozzle boom. The height of the nozzle from the ground was set to 406 mm, which allowed the spray from the boom to cover the entire windrow. The Ef treatment was applied with a 0.5-L handheld garden pump sprayer immediately after weighing the daily forage allocation for each steer. The ambient temperature ranged from 20 to 22°C when the enzyme was applied in the Ec and Eb treatments, whereas it ranged from 4 to 20°C when the enzyme was applied in the Ef treatment. For the ammonia treatment, square bales were stacked on wooden pallets, covered with 6-mil plastic, and treated with anhydrous ammonia (3% of DM) as described by Brown and Kunkle (1992). The forage was allowed to react with the ammonia for 6 wk and was then vented to release the ammonia gas.
Cattle and Diets
The Institutional Animal Care and Use Committee of the University of Florida approved the animal protocol for this experiment. Fifty 12-mo old Angus x Brangus crossbred steers (mean BW 244 ± 26 kg) were stratified by BW and assigned randomly within each BW group to the 5 forage treatments. Steers were dewormed with doramectin (Dectomax, Pfizer Animal Health, New York, NY) for internal and external parasite control 5 d before the trial began. No other dewormer or insecticide was used. The steers within each treatment were assigned randomly to 1 of 7 pens such that there were 7 steers in each of 6 pens and 8 steers in 1 pen. Within each pen, the steers were assigned randomly to 1 of 8 Calan gates (American Calan Inc., Northwood, NH) for individual animal feeding. Steers had ad libitum (110% of intake on the previous day) access to the hays and were supplemented with a basal concentrate at a constant rate of 1% of BW daily. The concentrate portion of the diet and half of the daily allotment of hay was provided at 0900 h and the remaining half of the hay was provided at 1500 h. The concentrate allowance was adjusted weekly as BW changed. This rate of supplementation represents the typical feeding regimen for weaned calves in north and central Florida. The trial consisted of a 14-d adaptation period and an 84-d measurement period.
Diets were formulated to meet the NRC (2000) requirements for steers with a BW of 250 kg gaining 1 kg/d. The chemical composition of the concentrate ingredients and hays is shown in Table 1. Each forage was chopped to 15-cm lengths by using a tub hay grinder (Roto Grind, model 760, Burrows Enterprises, Greeley, CO) after the second week of the measurement period to reduce sorting. The ingredients in the concentrate included 23% solvent-extracted cottonseed meal and 77% soybean hull pellets (DM basis). A mineral-vitamin mix (UF University special Hi-CU mineral mix, Lakeland Animal Nutrition, Lakeland, FL) was offered free choice, and the cattle had ad libitum access to drinking water. The mineral mix contained 21% NaCl, 13% Ca, 6% P, 0.8% K, 1% Mg, 0.95% Zn, 0.4% S, 0.4% Fe, 0.22% Mn, 0.2% Cu, 800 mg/kg of Fe, 200 mg/kg of Co, 175 mg/kg of I, 48 mg/kg of Se, 45,454 IU/kg of vitamin A, and 9,091 IU/kg of vitamin D3. The concentrate portion of the diet was offered in a separate container to each steer before the morning feeding of the hay, and it was consumed immediately. Before feeding, dietary refusals from the previous day’s offering were collected and weighed.
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Table 1. Chemical composition of the concentrate ingredients and hays that were untreated (control), ammonia-treated (NH3), or enzyme-treated at cutting (Ec), baling (Eb), or feeding (Ef)
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Sampling and Analysis
Duplicate samples of each feedstuff were collected weekly and composited monthly. Subsamples from each month were dried in a forced-air oven at 50°C for 72 h and analyzed in triplicate for DM, ash, NDF, ADF, lignin, and CP. Concentrations of NDF and ADF were measured in the forage samples by using the method of Van Soest et al. (1991) in an Ankom 200 Fiber Analyzer (Ankom Technologies, Macedon, NY). Lignin concentration was also measured with the ADL method of Van Soest et al. (1991). Crude protein concentration was calculated as N x 6.25 after N concentration was determined by using an adaptation of the procedure of Noel and Hambleton (1976) for an Alpkem Autoanalyzer (Alpkem Corporation, Clackamas, OR). Daily samples of the hay refusals were collected and composited on a weekly basis. Refusal subsamples from each month were dried in a forced-air oven at 50°C for 72 h and analyzed for DM. Shrunk BW was measured for 2 consecutive days before (d –1 and 0) and after (d 85 and 86) the measurement period. Full BW was measured weekly, and hip height was measured on d 0, 42, and 84 of the measurement period. Body condition score (on a scale of 1 to 9) was visually evaluated. Blood samples were collected by jugular venipuncture into Vacutainer tubes containing sodium heparin anticoagulant (Fisher Scientific, Pittsburgh, PA) on d 0, 28, 56, and 84 of the measurement period. The blood was centrifuged at 2,000 x g for 20 min at 4°C and the plasma was frozen (–20°C). A Technicon Autoanalyzer (Technicon Instruments Corp., Chauncey, NY) was used to determine the concentrations of plasma urea-N and glucose, with the modifications of Coulombe and Favreau (1963) and Gochman and Schmitz (1972), respectively. Ultrasound measurements of back, rump, and intramuscular fat depths and rib eye area were taken on d 6 and 84 of the measurement period by using real-time ultrasound, with an Aloka 500V system equipped with a 3.5-MHz, 17-cm transducer and superflab (Aloka US Inc., Wallingford, CT) to ensure proper fit of the transducer to the curvature of the animal.
In vivo apparent digestibility was estimated by using chromic oxide as a marker. Steers were brought through working chutes and restrained with a head catch, and a gelatin capsule (no. 10, Torpac Inc., Fair-field, NJ) containing 10 g of chromic oxide powder was dosed twice daily via a balling gun at 0700 and 1900 h into each steer for 10 consecutive days (d 67 to 77). Fecal samples were collected at 0630 and 1830 h during the last 5 d of dosing for digestibility determination, such that 10 samples were collected for each steer. Daily fecal samples (350 ± 50 g) were collected from the floor of the pen immediately after each steer defecated. For the few steers that did not defecate, fecal grab samples were taken while they were restrained in the head catch for chromium dosing. Feces were dried to a constant weight at 50°C in a forced-air oven, ground to pass through a 1-mm screen in a Wiley mill (Arthur H. Thomas Company, Philadelphia, PA), and a composite sample was made from all 10 fecal samples collected for each steer. Chromium concentration in the feces was determined by using a PerkinElmer 5000 atomic absorption spectrometer (PerkinElmer, Wellesley, MA), according to the procedure described by Williams et al. (1962). Crude protein and NDF concentration were measured in feces by using the previously described methods, and digestibilities of CP and NDF were calculated.
In Situ Rumen Degradability
Representative subsamples taken from the monthly hay samples for each treatment were mixed and composited to yield a single sample for in situ degradability analysis. The composited samples were ground to pass a 4-mm screen with a Wiley mill and weighed (5 g, as-is) into 10 x 23-cm nylon bags (pore size of 50 µm, Bar Diamond Inc., Parma, ID). Duplicate samples of forage from each treatment were incubated in each of 2 ruminally fistulated, nonlactating Holstein dairy cow rumens for 0, 3, 6, 9, 12, 24, 48, 72, 96, and 120 h. The cows were fed 9 kg/d of bahiagrass hay supplemented with 0.4 kg/d of soybean meal. After incubation, the bags were removed from the cow, rinsed with cool water, and frozen. At the end of the measurement period, all bags were thawed and washed in a Kenmore heavy-duty series 80 washing machine (Sears, Roebuck & Co., Hoffman Estates, IL) by using a cool-wash cycle without detergent. The bags were dried for 24 h at 60°C, and the residue weights were determined. A model (McDonald, 1981) was fitted to the in situ degradation data by using the nonlinear regression procedure of SAS, version 8 (SAS Inst. Inc., Cary, NC). This model was of the form
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where D is the DM disappearing at time t, A is the wash loss, B is the potentially degradable fraction, A + B is the total degradability, c is the rate at which B is degraded, t is the time incubated in the rumen, and L is the lag time.
Statistical Analysis
A randomized complete block design was used to examine the effects of the 5 forage treatments on the performance of the steers. The data were analyzed by using PROC MIXED of SAS. To evaluate the effects of the treatments on steer BW and DMI, pretrial BW and DMI values were used as respective covariates. The model used to analyze individual treatment effects was Yijk = µ + Ti + Sk(i) + Wj + TWij + Eijkl, where µ is the general mean, Ti is the effect of treatment i, Sk(i) is the effect of the kth steer in treatment i, Wj is the effect of week of feeding, TWij is the effect of treatment across weeks of feeding, and Eijkl is the experimental error. A repeated measures statement was used for the analysis of DMI, BW, BCS, and plasma glucose and urea. Contrast statements were used to compare each forage treatment against the control forage treatment. Where appropriate, the SAS slice command was used to examine treatment differences at each week for each dependent variable. The in situ degradability data were analyzed by using PROC GLM of SAS. Contrast statements were used to compare each treatment with the control. The model used to analyze individual treatment effects was Yijk = µ + Ti + Cj + Eijk, where µ is the general mean, Ti is the effect of treatment i, Cj is the effect of cow, and Eijk is the experimental error. Significance was declared at P < 0.05 and tendencies were declared at 0.05 < P 
0.10.
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RESULTS
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Diet and Forage Composition
Ammoniation reduced (P < 0.001) concentrations of NDF, hemicellulose, and lignin and increased (P < 0.001) CP concentration in the hays. Application of Eb increased (P < 0.01) NDF and lignin concentrations, whereas Ef application increased (P < 0.01) NDF and hemicellulose concentrations, but slightly reduced (P = 0.01) lignin concentration.
Animal Performance
Steers fed NH3- and Ec-treated hay had greater (P < 0.05) intakes of total and hay DM and total NDF than steers fed the control hay (Table 2). Steers fed NH3 and Ec also had greater (P 0.02) hay NDF, total CP, and hay CP intakes than steers fed the control hay. Intakes of total or hay DM or NDF were unaffected by Eb treatment, but intakes of total and hay NDF tended to be increased (P < 0.10) by Ef treatment. Figure 1 shows that the DMI of the steers fed Ec- and NH3-treated hay was generally greater than that of steers fed the control hay. The erratic DMI during wk 1 and 2 largely resulted from sorting, and it was stabilized for most treatments when chopped hay was fed in subsequent weeks. The decrease in DMI across treatments in wk 10 to 12 may have resulted from dosing with chromic oxide during this period.
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Table 2. Effect of applying ammonia (NH3) or a fibrolytic enzyme at cutting (Ec), baling (Eb), or feeding (Ef) to Bermudagrass hay on the voluntary intake of steers
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Figure 1. Effect of applying ammonia (NH3) or a fibrolytic enzyme at cutting (Ec), baling (Eb), or feeding (Ef) to Bermudagrass hay on DMI of growing steers (treatment x week interaction, P < 0.001). The control differed (P < 0.05) from NH3 at wk 2, 7, 9, 10, 11, and 12; from Ec at wk 5, 6, 8, 10, 11, and 12; from Eb at wk 4, 5, 6, and 9; and from Ef at wk 10.
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All treatments increased (P 0.01) the DM digestibility (DMD) of the hays (Table 3). Digestibilities of NDF and CP were increased (P < 0.001) by the NH3, Ec, and Eb treatments, whereas NDF digestibility tended to be increased (P = 0.09) by the Ef treatment. Steers had similar BW throughout the trial (Figure 2; P > 0.10). The initial and final BW, ADG, G:F, BCS, and hip height of the steers were not affected by treatment (P > 0.05; Table 4). Dietary treatments did not affect (P > 0.10) plasma glucose concentration (83.6 ± 6.4 mg/dL), plasma urea-N concentration (12.1 ± 3.0 mg/dL), rib eye area (d 6 = 37.7 ± 5.1 cm2, d 84 = 50.4 ± 5.8 cm2), or back (d 6 = 0.48 ± 0.1 cm, d 84 = 0.55 ± 0.1 cm), rump (d 6 = 0.35 ± 0.1 cm, d 84 = 0.37 ± 0.1 cm), or intramuscular fat percentage (d 6 = 3.80 ± 1.3, d 84 = 3.86 ± 1.2).
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Table 3. Effect of applying ammonia (NH3) or a fibrolytic enzyme at cutting (Ec), baling (Eb), or feeding (Ef) to Bermudagrass hay on the in vivo apparent digestibility of steer diets
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Figure 2. Effect of applying ammonia (NH3) or a fibrolytic enzyme at cutting (Ec), baling (Eb), or feeding (Ef) to Bermudagrass hay on weekly full BW (treatment x week interaction, P = 0.91). No treatment differed (P > 0.1) from the control.
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Table 4. Effect of applying ammonia (NH3) or a fibrolytic enzyme at cutting (Ec), baling (Eb), or feeding (Ef) to Bermudagrass hay on the growth performance of steers
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In Situ Rumen Degradability
The wash loss of the hays was decreased (P < 0.05) by treatment with Ec and Eb, and Ef treatment gave the same tendency (P = 0.07; Table 5). Ammonia treatment increased (P = 0.001) the potentially degradable fraction, the total degradable fraction, and the effective degradability of the hays, but enzyme treatment had no effect on these measures. The fractional degradation rate and lag phase were not affected (P > 0.10) by treatment.
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Table 5. Effect of applying ammonia (NH3) or a fibrolytic enzyme at cutting (Ec), baling (Eb), or feeding (Ef) to Bermudagrass hay on in situ degradation kinetics
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DISCUSSION
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The forage used in this study was similar in maturity and composition (Table 1
) to the untreated Bermudagrass forage used by Galloway et al. (1993) and Mandebvu et al. (1999). Ammonia treatment increased the CP concentration of the forage and reduced NDF, hemi-cellulose, and lignin concentrations as reported in other studies (Kunkle et al., 1983; Brown, 1988; Brown and Kunkle, 1992; Brown and Pate, 1997). In general, enzyme treatment had no similar effects on the chemical composition of the hays.
Ammonia and Ec treatment increased the DMI of the hays, partly because these treatments increased digestion of DM and NDF. Feng et al. (1996) reported that enzyme treatment increased the DMI and DMD of smooth bromegrass (Bromus inermis) by beef steers. In this study, Ec treatment, like ammoniation, improved the intake and digestibility of Bermudagrass. Enzyme treatment provides a safer, practical hay treatment for producers compared with ammoniation, because enzymes are benign and they do not present the handling and delivery challenges of ammoniation.
When the enzyme used in this study was applied at feeding to guineagrass (Panicum maximum Jacq.) hay in sheep diets, it increased both DMI and DMD (Tous et al., 2006), but effects of enzyme application at cutting or baling were not examined. The superior effect of the Ec treatment vs. the Eb and Ef treatments on DMI potentially resulted from greater moisture availability for enzyme dispersal and activity in the Ec treatment. The longer enzyme-substrate interaction time for Ec may also explain why it was more effective at increasing DMI than Ef. The Eb and Ef treatments did not affect DMI, ADG, or G:F but had beneficial effects on digestion of DM and NDF. Therefore, although the Ec treatment was more effective and is the recommended method of applying the enzyme, the Eb and Ef treatments can also be used to increase the digestibility of warm-season grass hays. In addition to improving the quality of the hay, enzyme treatment may have also enhanced digestion of the concentrate, particularly because it contained 77% soybean hulls on a DM basis. Yang et al. (2000) reported that fibrolytic enzyme addition to concentrates 1 mo before feeding increased diet digestion and milk production by dairy cows.
Ammoniation and Ec treatments increased the CP intake and CP digestibility of the hay, suggesting an increase in the provision of available N from these treatments. Both treatments also increased DMI and DMD, indicating that they increased energy supply. The reason these treatments did not increase ADG is not clear.
Like ammoniation (Brown and Kunkle, 1992), enzyme treatment may be used to improve the quality of warm-season grass hay fed to herd bulls, to cull cows held over the winter to improve their value, or to replacement heifers to allow earlier breeding. Ammoniated hay is not recommended for lactating cows because toxic imidazole compounds that can be produced during ammoniation can be transferred in the milk to calves (Brown and Kunkle, 1992). Enzyme-treated hay poses no toxicity risk; therefore, enzyme treatment is an effective method of improving the quality of warm-season grass hays fed to lactating cows.
Enzymes typically increase only the rate, not the extent, of forage and feed degradation (Feng et al., 1996). However, in this study neither the rate nor extent of degradation of the hay was increased by enzyme treatment for unknown reasons. In contrast, ammoniation increased the potentially degradable and total degradable fractions as well as the effective degradability of the forage, yet it did not improve the performance of the steers. Others have noted that the ADG response to ammoniation of medium-quality forages such as that used in this study is marginal because ammoniation is more effective on poor-quality forages (Brown and Kunkle, 1992). This explanation does not apply to this study because ammoniation increased DMI, DMD, and in situ degradability.
This study showed that applying Biocellulase A20 enzyme immediately after harvesting is as effective as ammoniation at increasing DMI and DMD of diets based on 5-wk regrowth Bermudagrass in beef steers. However, these improvements in intake and digestion did not affect animal performance. The enzyme was most effective at improving digestion and intake when applied at cutting, although it also increased digestion when applied at feeding or baling. Compared with ammoniation, application of this enzyme is a safer method of improving the quality of warm-season grass hays for cattle.
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Footnotes
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1 This work was supported by funds from South-East Milk Inc. Dairy Check-Off, and USDA Cooperative State Research, Education, and Extension Service Tropical Subtropical Agriculture Research Caribbean Basin Administrative Group. 
2 Corresponding author: adesogan{at}animal.ufl.edu
Received for publication November 1, 2006.
Accepted for publication December 17, 2007.
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Abstract
INTRODUCTION
