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FIBEX-treated rice straw as a feed ingredient for lactating dairy cows
Animal Feed Science and Technology 103 (2003) 41–50
FIBEX-treated rice straw as a feed ingredient for lactating dairy cows夽 P.J. Weimer a,b,∗ , D.R. Mertens a , E. Ponnampalam c , B.F. Severin c , B.E. Dale d
d
a United States Department of Agriculture, Agricultural Research Service, US Dairy Forage Research Center, 1925 Linden Drive West, Madison, WI 53706, USA b Department of Bacteriology, University of Wisconsin, Madison, WI, USA c Michigan Biotechnology Institute, Lansing, MI 48909, USA Department of Chemical Engineering, Michigan State University, East Lansing, MI 48824, USA
Received 7 December 2001; received in revised form 12 August 2002; accepted 21 August 2002
Abstract Treatment of rice straw by the proprietary FIBEX process resulted in increased in vitro digestibility by ruminal microorganisms due to a reduced lag time, increased rate of digestion, increased extent of digestion, and possible removal of inhibitory agents present in untreated rice straw. To determine the value of treated rice straw as a feed ingredient for lactating dairy cows, production parameters and milk composition were determined in a feeding trial with thirteen primparous and six multiparous cows in a switchback design involving two diets and 21 days periods. One diet was a conventional dairy diet that contained alfalfa hay, corn grain, soybean meal (SBM) and several byproduct feeds. The other diet contained these same feed ingredients, but with levels of alfalfa hay, corn grain and SBM that were altered somewhat to provide energy, neutral detergent fiber (35.8%), acid detergent fiber (25.8%) and crude protein (18.0%) levels similar to the treated rice straw added at 7% of dry matter. The diet that contained treated rice straw supported higher neutral detergent fiber intake and milk yield. Milk produced from cows fed the two diets had similar levels of protein, urea nitrogen and lactose. Based on its increased in vitro fermentability at higher fiber content, FIBEX-treated rice straw may be useful as a feed ingredient for lactating dairy cows. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Digestion kinetics; Fiber; Milk; Milk composition; Rice straw
Abbreviations: ADF, acid detergent fiber; CP, crude protein; DMI, dry matter intake; MUN, milk urea nitrogen; NDF, neutral detergent fiber; OM, organic matter; SBM, soybean meal; TMR, total mixed ration 夽 Mention of specific products is for informational purposes only, and does not imply a warranty or endorsement by USDA over other products not mentioned. ∗ Corresponding author. Tel.: +1-608-264-5408; fax: +1-608-264-5147. E-mail address: [email protected] (P.J. Weimer). 0377-8401/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 8 4 0 1 ( 0 2 ) 0 0 2 8 2 - 1
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1. Introduction Rice straw is an agricultural residue that is a disposal problem for the rice industry in the state of California as well as other parts of the world. Approximately 1.5 × 109 kg of rice straw is produced annually in the state, and it has historically been disposed of by field incineration. Implementation of new California law has mandated annual reductions in incineration to improve local air quality and, since September 2001, incineration of rice straw has proceeded only on a “permit-to-burn” basis as required for rice disease control. It has been estimated that this means that approximately 80% of the rice straw will have to be disposed of by other means (Forrest et al., 1997). One possible use of rice straw is as a feed for ruminants, if it could provide sufficient energy in spite of its high fiber content. However, because of its high ash content (16–18% of dry matter (DM); Crocker et al., 1998) and the poor digestibility of its organic matter (OM), rice straw is considered to have a very low value as a ruminant feed ingredient under animal production conditions above maintenance (Forrest et al., 1997). Successful incorporation of rice straw into ruminant rations will require economical treatment that substantially increases its digestibility. While enhanced digestibility of rice straw has been reported with several treatments (Hart et al., 1975; Garrett et al., 1979; Han et al., 1989), none have been implemented commercially. The ammonia fiber explosion (AFEX) process of (Dale, 1986; Dale et al., 1996), and the more recent and improved FIBEX process (Dale and Weaver, 2000, 2001) offer several process advantages. These include increased reactivity of the treated straw and ease of recovery of the chemical treatment agents, and both make this treatment of rice straw more viable than traditional ammoniation treatments. The AFEX process is a batch process, while the FIBEX process is continuous. Preliminary experiments (data not shown) indicated that treatment of rice straw by the FIBEX process increased in vitro DM digestibility. The present study was undertaken to determine the kinetic profiles and to establish quantitatively the kinetic parameters for the fermentation of rice straw before and after its treatment by the FIBEX process under various regimes of moisture content, NH3 /substrate ratio, time, temperature and pressure; and to determine if the treated rice straw can be incorporated into dairy diets at a modest level (7% of DM) without decreasing ration palatability, milk yield or milk quality. 2. Materials and methods 2.1. Materials Rice straw was harvested in the Sacramento valley of California and then baled and stored indoors prior to use. The rice straw samples were either untreated, or treated under various combinations of conditions. Treatments were in a highly-modified 3.8 l Autoclave Engineers stainless steel pressure vessel (Snap-Tite, Erie, PA, USA) that contained 100 g of rice straw. The vessel was modified with appropriate pumps for addition of ammonia, stirring, remote controls and extra-large outlet vents to permit very rapid reductions in reactor pressure. Three treatment parameters were fixed: straw moisture content (18, 30, or 40%, w/v), NH3 : straw weight ratio (0.5, 0.75, or 1.0), and reaction time (i.e. the time at which the pressure
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was rapidly released; 5 or 10 min). Two treatment conditions, temperature and pressure, varied during the course of the reaction as the sealed vessel was heated. Temperature values reported are the mean of the temperature at the start of the reaction, and the temperature just prior to rapid release of pressure. Pressure values are reported as the mean of three values: the initial reactor pressure, the maximum pressure that was reached ∼3 min into the reaction, and the pressure just prior to its rapid release at the end of the incubation. A bulk sample of several tonnes of treated rice straw was prepared at the Tennessee Valley Authority biomass pilot plant facility in Muscle Shoals, AL, USA. Straw was chopped to a nominal 2.54 cm length, and hydrated to ∼50% DM by passage under water spray nozzles. Wet straw was fed continuously to a hydrolyzer unit (Sunds Defibrator Inc., Minneapolis, MN, USA) that contained a vertical impregnator screw which mixed the wet straw with ammonia, at 300 g/kg dry straw. Heat was applied via an external steam jacket, and the temperature (110–132 ◦ C) and pressure (12.9–15.0 atm) were maintained by opening and closing input and output valves of the hydrolyzer. Upon attaining the desired temperature and pressure, jacket steam flow was reduced, as energy of mixing and heat of dissolution of ammonia was sufficient to maintain temperature and pressure. Treated biomass exiting the hydrolyzer was passed through a continuous flow dryer to obtain a final product (designated TVA270) of ∼85% DM. 2.2. Fermentations Inoculum was prepared from ruminal contents of two fistulated Holstein cows fed a total mixed ration (TMR) that contained corn silage, corn grain, alfalfa hay, soybean meal (SBM), and supplemental vitamins and minerals. Ruminal fluid, 400 ml from each cow, was squeezed through four layers of cheesecloth and collected into a graduated cylinder purged with CO2 . The squeezed solids, 200 g from each cow, were blended under CO2 in a Waring Blender (15 s low speed, then 45 s high speed) containing 800 ml of buffer. The buffer (Goering and Van Soest, 1970) consisted of (per liter): 1.0 g NH4 HCO3 , 8.75 g NaHCO3 , 1.43 g Na2 HPO4 , 1.55 g KH2 PO4 , 0.15 g MgSO4 ·7H2 O, 2.5 g Trypticase, 0.125 ml resazurin (0.1%, w/v) and 0.125 ml micromineral solution (per liter: 132 g CaCl2 ·2H2 O, 100 g MnCl2 ·4H2 O, 10 g CoCl2 ·6H2 O; 80 g FeCl3 ·6H2 O). The ruminal fluid and blended solids were combined and filtered through four layers of cheesecloth into a CO2 purged graduated cylinder, and the filtrate was placed into a water-jacketed (39 ◦ C), CO2 purged stirring chamber for inoculation of fermentation vials. In vitro fermentations were conducted using a continuous on-line gas production system that permitted simultaneous measurement of headspace pressure in 40 experimental vials (Weimer et al., 2000). Samples (∼100 mg, dried OM basis, and weighed to the nearest 0.1 mg), contained in volume-calibrated (to 0.01 ml) 60 ml serum bottles, were suspended in 5.7 ml of buffer (Goering and Van Soest, 1970; see above) and 0.3 ml of reducing agent (6.5 mg each of cysteine and Na2 S·9H2 O per ml of 0.04 N NaOH), under a CO2 gas phase. Vials were prewarmed to 39 ◦ C and inoculated with 4.0 ml of diluted ruminal inoculm (as above). Blank vials contained buffer, reducing agent, and inoculum, but no exogenously added substrate. Details of the gas production measurement system and the time-staggered loading of samples into the instrument are described elsewhere (Mertens and Weimer, 1998). Incubations were conducted for 72 h, during which time approximately
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200 headspace pressure measurements were made for each sample. Net gas production after blank subtraction was fit to a dual-pool exponential model as described previously (Weimer et al., 2000), using the NONLIN program of the SAS statistical software package (SAS, 1985). The model included separate terms for the rapidly degraded (soluble) and slowly degraded (fiber) fractions of the substrate. 2.3. Analyses DM was determined gravimetrically after drying at 105 ◦ C for 18 h. Ash content of the dry residue was determined gravimetrically following incineration at 550 ◦ C for 4 h. N content was determined by combustion analysis (model FP2000 N analyzer, Leco Instruments, St. Joseph, MI, USA) on air-dried samples. Following fermentation, neutral detergent fiber (NDF) was determined by the method of Weimer et al. (1990), using sodium sulfite but not ␣-amylase. NDF is expressed on a non-ash-free basis. 2.4. Feeding trial The animal trial was conducted using a protocol approved by the University of Wisconsin Animal Care Committee. Fourteen multiparous and six primiparous Holstein cows were divided into two groups balanced for age, body weight (554 ± 63 kg), days in milk (71 ± 28 days), and milk production (43.0±5.0 kg per day). Groups were fed two diets in a switchback arrangement consisting of a 2 days adaptation period to the new diet (i.e. new and old diet in a ratio of 33:67 on day 1, 67:33 on day 2, and 100:0 on day 3), followed by 18 days of feeding the new diet. The control (C) diet and the diet (R) supplemented with treated rice straw (Table 1) were balanced for NDF, acid detergent fiber (ADF), crude protein (CP), Ca, Mg, and P. Diets were based on alfalfa hay and corn grain, supplemented with various byproduct feeds commonly used in northern California (Grasser et al., 1995). Rations were formulated as a TMR blended from alfalfa, whole cottonseed, and a milled mixture that contained all other feed ingredients (including the rice straw for diet R). Cows were fed once daily at about 13:30 h to approximately 10% orts, and orts were collected daily and weighed. During the last week of each period, orts were spread evenly through each feed bunk just prior to daily feeding, and a one-eighth subsample was collected for each cow for analysis. After their return to the laboratory, each orts sample was spread evenly and subsampled again, air dried, and ground through a Wiley mill having a 2 mm screen. The ground orts were analyzed (in quadruplicate) for DM, NDF, ADF, CP and ash. Milk was collected from twice daily milkings at 11:00 and 20:00 h. Milk samples from day 20 (PM milking) and day 21 (AM milking) of each period were collected for commercial analysis of fat, CP, and lactose (AgSource, Verona, WI). Milk urea nitrogen (MUN) was determined using a commercial urea N assay kit (Sigma, St. Louis, MO) following deproteinization of the sample with trichloroacetic acid. 2.5. Statistical analyses Main effects on milk production and milk composition variables were determined by ANOVA using the general linear model procedure of SAS (SAS Institute, 1985), with
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Table 1 Formulated composition of control diet and diet amended with FIBEX-treated rice straw Control
Rice straw
Ingredient composition (g/kg DM)a Alfalfa hay Corn grain, dry kernel Whole linted cottonseed Treated rice straw Beet pulp, pelleted Corn gluten feed, dehydrated Wheat middlings Soybean meal, 48% CP solvent Beet molasses, liquid Monosodium phosphate Magnesium oxide Salt and vitamin mixtureb
450 183 120 – 80 80 40 23.5 20 1.0 1.3 1.0
350 206 120 70 80 80 40 29.5 20 1.8 1.6 1.0
Chemical composition (g/kg DM) NDF ADF CP Ash Ca Mg P
358 258 180 70 8.4 3.5 4.1
357 258 180 70 7.1 3.5 4.1
a
Dry matter content was 89.7% for the control diet and 89.5% for rice straw diet. TM Vit Pak (Professional Products and Services, Prairie du Sac, WI, USA) contained per gram: 229 mg Ca, 56 mg Zn, 46 mg Mn, 22 mg Fe, 12 mg Cu, 0.4 mg Co, 0.9 mg I, 0.32 mg Se, 7084 IU Vitamin A, 2200 IU Vitamin D3, 17.6 IU Vitamin E. b
diet, cow and period as independent variables. A second analysis was performed with diet, period and cow maturity (primiparous versus multiparous) as independent variables. Comparisons among means were performed using a paired t-test at a probability level of 0.05.
3. Results 3.1. Characteristics of rice straw Untreated rice straw (74.4% NDF, 18.9% ash, and 3.8% CP) was light tan in color and odorless. Treated rice straws were darker in color and retained a sawdust or bagasse-like odor. All treated rice straws had slightly lower NDF and ash contents than untreated straw (Table 2). CP content was increased up to 350% by treatment. The highest CP levels were in the low moisture straw samples treated at high NH3 :straw ratios for longer times. The large stock of treated rice straw supplied for the production trial displayed similar characteristics to the small samples, except that the production trial scale material was darker in color and contained, as a small percent of the total, clumps of about 2 cm size material
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Table 2 Treatment conditions used and composition of resulting rice straw materials Rice straw samplea
Treatment conditions
Untreated 28 41 66 75 82 87 90 93 96 99 103
Composition after treatment
DM (%)
Ratiob
T (◦ C)c
P (atm)d
Time (min)
DM (%)
NDF (%DM)
Ash (%DM)
CP (%DM)
– 82 70 70 70 60 60 60 60 60 60 60
– 1.0 1.0 1.0 1.0 0.75 0.5 0.75 1.0 0.5 0.75 0.5
– 91 86 79 91 108 97 88 90 81 90 87
– 26.3 26.3 24.8 24.3 24.7 18.9 22.5 25.4 18.7 21.9 18.5
– 10 10 10 10 5 5 5 5 10 10 10
90.6 87.8 90.1 76.7 81.3 75.5 82.6 78.0 79.5 74.2 78.0 80.5
74.4 63.3 63.1 64.5 61.9 72.5 70.8 70.5 66.4 70.9 67.1 69.2
18.9 17.3 17.1 16.8 15.4 16.7 16.3 16.2 16.9 16.8 16.8 16.4
3.8 16.9 17.4 13.0 14.8 8.3 7.1 8.2 8.6 7.0 9.9 7.6
1.1
0.8
1.0
Pooled S.E.
0.42
a
Pretreated sample number, provided to facilitate comparison with Table 3. Weight ratio of NH3 to rice straw. c Temperature. d Pressure. b
that resisted breakup in the TMR wagon. Despite this, there was little visible sorting by the cows during feeding. 3.2. In vitro studies The first in vitro run compared a control sample of rice straw that had not been treated to the 11 samples treated at benchtop scale. The second run compared the untreated control sample with rice straw that had been treated at large scale to obtain material for the animal feeding study. Measurement of net gas production from the rice straws incubated with a mixed ruminal inoculum for selected periods of time during the digestion revealed that untreated rice straw depressed gas production slightly (by a maximum of 15 ml gas/g DM for ∼10 h relative to blank vials that contained the ruminal inoculum without added substrate; data not shown), suggesting that untreated rice straw may have contained a soluble inhibitor of ruminal fermentation. Gas production in almost all of the FIBEX-treated samples exceeded that of the untreated rice straw at all measured time points during fermentation. In run 1, untreated rice straw contained a very small rapidly fermented fraction, and its fiber fraction was fermented slowly (k2 = 0.0353 h−1 ) after a time lag of 10.4 h (Table 3). FIBEX treatment increased (P < 0.05) the rate of digestion (k2 ) of the fiber fraction by 41–69%, and reduced (P < 0.05) the lag time (L2 ) prior to digestion of this fraction by 26–38%. Within the range of treatment conditions tested, there was no differential effect (P > 0.05) of moisture content, ammonia/straw ratio, time, or temperature on the total amount, rate constant or time lag of gas production from the slowly digested fraction. This suggests that the FIBEX treatment process is effective over a wide range of process conditions.
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Table 3 Kinetic values for fermentation of untreated and FIBEX-treated rice straw, as determined from in vitro gas production measurements and application of a two-pool exponential model Run
Rice straw samplea
Kinetic values A (ml/g OM)b
B (ml/g OM)c
k1 (h−1 )d
k2 (h−1 )e 0.0353 d 0.0604 c,d 0.0593 c,d 0.0583 c 0.0564 c 0.0561 c 0.0541 c 0.0558 c 0.0499 c 0.0543 c 0.0561 c 0.0518 c
1
Untreated 28 41 66 75 82 87 90 93 96 99 103
1.6 d 29.3 c 27.8 c 23.8 c 25.0 c 17.1 c 16.8 c 7.8 c,d 10.2 c 13.9 c 14.3 c 23.0 c
127.7 101.6 99.2 152.0 116.2 174.6 161.6 155.1 155.5 158.4 150.6 142.6
<0.01 0.482 0.636 0.318 0.618 1.25 0.028 16.041 7.120 0.034 0.436 0.152
2
Untreated TVA270
<0.1 d 25.2 c
159.9 180.8
0.164 0.236
2.9
14.3
11.043
Pooled S.E.
0.0420 d 0.0795 c 0.0241
L1 (h)f
L2 (h)g
0.23 0.13 0.03 0.14 0.07 0.22 0.09 0 0.09 0.11 0.16 2.12
10.40 c 6.92 d 7.17 d 6.43 d 6.95 d 6.43 d 7.15 d 7.15 d 7.35 d 7.67 d 6.97 d 7.13 d
<0.01 0.06
9.79 d 5.53 c
0.75
0.83
Means (n = 3) in the same column within each run that have different letters (c, d) differ (P < 0.05). a Pretreated sample number, provided to facilitate comparison with Table 2. b A: ml gas produced from rapidly digested fraction/g OM. c B: ml gas produced from slowly digested fraction/g OM. d k : rate constant for rapidly digested fraction (h−1 ). 1 e k : rate constant for slowly digested fraction (h−1 ). 2 f L : lag time for rapidly digested fraction (h). 1 g L : lag time for slowly digested fraction (h). 2
All FIBEX treatments (Table 3) shifted up to 22% of the substrate from the slowly-digested pool into the rapidly digested pool, and this pool was digested at rates (k1 ) that usually fell in the range of 0.3–1.3 h−1 . Rates outside of these ranges were associated with problems with the model, yielding either a lag time of zero, or very small rapidly digested pools (A/(A + B) < 0.05). In particular, samples no. 28 and no. 41, which had a higher DM content at treatment displayed a greater shift of substrate to the rapidly digested fraction, but total gas production was not higher than that of untreated rice straw. Rice straw treated in the large scale equipment increased the rate of gas production from the slowly-digesting pool by 89%, and decreased lag time by 44% (Tables 3 and 4). 3.3. Production trial One of the R cows stopped eating a few days into the trial and so was removed. The other cows readily ate both rations, and there was no visible sorting. None of the cows displayed hyperexcitability, as has been reported for ruminants consuming 50% or more of a diet of rice straw treated with ammonia for greater than 3 h at greater than 70 ◦ C (Perdock and Leng, 1987).
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Table 4 Feed intake and production of cows fed diets with and without FIBEX-treated rice straw Control Intake (kg per day) DM OM NDF ADF CP Production (kg per d) Milk Fat Protein Lactose Energy (MJ per day)a Milk composition (%) Fat (%) Protein (%) Lactose (%) Urea N (mM) a
Rice
Pooled S.E.
P>F 0.151 0.199 <0.001 0.349 0.804
25.0 22.0 7.0 5.2 4.0
25.9 22.9 8.1 5.3 4.0
2.9 2.1 0.7 0.5 0.1
38.3 1.47 1.14 1.83 114.0
39.6 1.41 1.19 1.86 113.6
1.6 0.11 0.05 0.19 6.1
0.020 0.062 0.011 0.671 0.914
3.86 2.99 4.77 5.11
3.55 3.00 4.82 5.29
0.22 0.10 0.11 0.83
<0.001 0.664 0.197 0.626
Calculated using Equation I of Tyrrell and Reid (1965).
Feeding of ration R resulted in increases (P < 0.05) in both NDF intake and milk yield that averaged 1.1 and 1.3 kg per day, respectively. A decline (P < 0.05) in milk fat % of 0.3 occurred with ration R. Despite higher levels of inorganic N in the treated rice straw, levels of protein and MUN did not differ between the diets, and the protein contents of the milk were essentially identical. 4. Discussion Rice straw, while abundant worldwide, is one of the least desirable biomass resources as an animal feed due to its low digestibility and high ash content (Garrett et al., 1979). Utilization of rice straw generated in California will require its diversion into alternate uses such as building materials, composites, land application materials and feedstocks for chemicals produced by fermentation. Although few viable commercial applications of these alternate uses have emerged, all have been characterized as more promising than the use of untreated rice straw as a livestock feed (Forrest et al., 1997). Treatment of rice straw by the FIBEX process resulted in enhancement of in vitro digestibility, reduction in the lag time before the start of the fermentation, a shift of a portion of the rice straw from the slowly digested to the rapidly digested pool, and an increased rate of digestion of the slowly digested pool. Overall, these results extend previous in vitro studies, conducted at a few time points, which demonstrated the effectiveness of ammonia treatment under temperature or pressure in enhancing enzymatic (Dale and Moreira, 1982; Dale et al., 1996) or ruminal (Sirohi et al., 1988; Wanapat et al., 1990) digestibility of low quality agricultural residues.
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Based on previous studies of ammoniation of biomass (Weimer et al., 1986), it is likely that most of the N in the treated rice straw was in the form of unreacted NH3 , acetamide (formed by ammoniolysis of acetyl groups in hemicellulose) and hemicellulose amides (formed by ammoniolysis of ester linkages between lignin and hemicelluloses). Because the diets were formulated on a CP basis, the rice straw amended diet contained a larger fraction of its CP in NH3 , a form of N that can be utilized less efficiently by ruminal microbes for growth. Nevertheless, milk protein levels did not differ between the two diets, suggesting that diet CP intake was not limiting milk protein synthesis. The poor potential of rice straw as a livestock feed has been inferred from several studies, most of which were conducted in developing countries. In these studies, beef cattle, calves, heifers or sheep at low levels of production were fed untreated or treated rice straw as the primary, or sole, energy source in the diet (Han et al., 1989; Maeng and Chung, 1989; Yoon et al., 1983). Such studies have shown that treatments with ammonia or urea, typically under static conditions at ambient temperature and pressure, considerably enhance digestibility and weight gain relative to untreated rice straw. Few studies have examined treated rice straw under production conditions more typical of developed countries. In one California study, Garrett et al. (1979) investigated weight gain in slaughter cattle and lambs fed diets that contained untreated or treated (with ammonia or NaOH) rice straw at 36 or 72% of the diet (as fed basis), with the remainder of the diet containing alfalfa hay, barley grain, cottonseed meal and molasses. These workers found that treated straws resulted in substantial improvements in weight gain and digestibility in animals fed the rice straw at 72%, but not 36%, of the diet, when compared to diets containing similar levels of untreated rice straw. In contrast to the many studies of the effect of feeding treated rice straw on in vitro digestibility and ruminant weight gain, there have been to our knowledge no published studies on the incorporation of treated rice straw into dairy rations for cows at high levels of production. That NDF intake and milk yield can be sustained with inclusion of 7% of DM of FIBEX-treated rice straw suggests that the treated rice straw has a high energy value.
Acknowledgements We thank C.L. Odt and M. Becker for excellent technical assistance; M. Moore and W. Burleson for engineering assistance in treating the rice straw; L. Strozinski and the USDFRC barn crew for animal handling; R.P. Walgenbach for supplying hay for the cow trial; and M.S. Allen for stimulating discussions. This research was supported by Trust Fund Agreement 58-3655-0-407 between MBI International and the USDA-Agricultural Research Service. References Crocker, L.M., DePeters, E.J., Fadel, J.G., Essex, S.E., Perez-Monti, H., Taylor, S.J., 1998. Ash content of detergent fibers in feeds, digesta, and feces and its relevance in fiber digestibility calculations. J. Dairy Sci. 81, 1010–1014. Dale, B.E., 1986. Method for increasing the reactivity of cellulose. US patent 4,600,590. Dale, B.E., Moreira, M.J., 1982. A freeze-explosion technique for increasing cellulose hydrolysis. Biotechnol. Bioeng. Symp. Ser. 12, 31–43.
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Dale, B.E., Weaver, J.K., 2000. Process for treating cellulosic materials. US patent 6,106,888. Dale, B.E., Weaver, J.K., 2001. Apparatus for treating cellulosic materials. US patent 6,176,176. Dale, B.E., Leong, C.K., Pham, T.K., Esquivel, V.M., Rios, I., Latimer, V.M., 1996. Hydrolysis of lignocelluloses at low enzyme levels: application of the AFEX process. Biores. Technol. 56, 111–116. Forrest, L., Williams, J., Collin, I., Holtzer, R., Lindberg, D., Maben, L., Merz, J., Parsons, G., Waite, W., 1997. Report of the Advisory Committee on Alternatives to Rice Straw Burning. California Air Resources Board and California Department of Food and Agriculture, Sacramento, CA. Garrett, W.N., Walker, H.G., Kohler, G.O., Hart, M.R., 1979. Response of ruminants to diets containing sodium hydroxide or ammonia treated rice straw. J. Anim. Sci. 48, 92–103. Goering, H.K., Van Soest, P.J., 1970. Forage Fiber Analysis: Apparatus, Reagents, Procedures and Some Applications. Agriculture Handbook 379. US Department of Agriculture, Washington, DC. Grasser, L.A., Fadel, J.G., Garnett, I., DePeters, E.J., 1995. Quantity and economic importance of nine selected by-products used in California dairy rations. J. Dairy Sci. 78, 962–971. Han, I.K., Ha, J.K., Garrett, W.N., Hinman, N., 1989. The energy value of rice straw for ruminants as influenced by treatment with anhydrous ammonia or mixing with alfalfa. Asian–Aust. J. Anim. Sci. 2, 115–121. Hart, M.R., Graham, R.P., Hanni, P.J., Tockwell, W.C., Walker Jr., H.G., Kohler, G.O., Waiss Jr., A.C., Garrett, W.N., 1975. Processing methods to improve the feed value of rice straw. Feedstuffs 47 (39), 22. Maeng, W.J., Chung, T.Y., 1989. Nutritive value and growth response of cattle fed ammonia treated rice straw. Asian–Austr. J. Anim. Sci. 2, 1–6. Mertens, D.R., Weimer, P.J., 1998. Method for measuring gas production kinetics. In: Deaville, E.R., Owen, E., Adesogan, A.T., Rymer, C., Huntington, J.A., Lawrence, T.L.J. (Eds.), In Vitro Techniques for Measuring Nutrient Supply to Ruminants. British Society of Animal Science Occasional Publication 22, Edinburgh, UK, p. 209–211. Perdock, H.B., Leng, R.A., 1987. Hyperexcitability in cattle fed ammoniated roughages. Anim. Feed Sci. Technol. 17, 121–143. SAS Institute, SAS User’s Guide: Statistics, Version 5 Edition, SAS Inst. Inc., Cary, NC, 1985. Sirohi, U.S., Hong, B.J., Koegel, R.G., Broderick, G.A., Shinners, K.J., Straub, R.J., 1988. Mechanical and chemical treatments to modify the digestibility of alfalfa stems. Trans. Am. Soc. Agric. Eng. 31, 668–671. Tyrrell, H.F., Reid, J.T., 1965. Prediction of the energy value of cow’s milk. J. Dairy Sci. 48, 1215–1223. Wanapat, M., Varvikko, T., Vanhatalo, A., 1990. The influence of selected chemical treatments on the ruminal degradation and subsequent intestinal digestion of cereal straw. Asian–Austr. J. Anim. Sci. 3, 75–83. Weimer, P.J., Chou, Y.-C.T., Weston, W.M., Chase, D.B., 1986. Effect of supercritical ammonia on the physical and chemical structure of ground wood. Biotechnol. Bioeng. Symp. Ser. 17, 5–18. Weimer, P.J., Lopez-Guisa, J.M., French, A.D., 1990. Effect of cellulose fine structure on the kinetics of its digestion by mixed ruminal microorganisms in vitro. Appl. Environ. Microbiol. 56, 2421–2429. Weimer, P.J., Hackney, J.M., Jung, H.-J.G., Hatfield, R.D., 2000. Fermentation of a bacterial cellulose/xylan composite by mixed ruminal microflora: implications for the role of polysaccharide matrix interactions in plant cell wall biodegradability. J. Agric. Food Chem. 48, 1727–1733. Yoon, C.S., Choi, E.S., Oh, T.K., Lee, N.H., Kim, C.W., 1983. Effects of aqueous ammonia-treated rice straw on feed intake, nutritive value, and rumen characteristics (sheep). Kor. J. Anim. Sci. 25, 613–622.
FIBEX-treated rice straw as a feed ingredient for lactating dairy cows夽 P.J. Weimer a,b,∗ , D.R. Mertens a , E. Ponnampalam c , B.F. Severin c , B.E. Dale d
d
a United States Department of Agriculture, Agricultural Research Service, US Dairy Forage Research Center, 1925 Linden Drive West, Madison, WI 53706, USA b Department of Bacteriology, University of Wisconsin, Madison, WI, USA c Michigan Biotechnology Institute, Lansing, MI 48909, USA Department of Chemical Engineering, Michigan State University, East Lansing, MI 48824, USA
Received 7 December 2001; received in revised form 12 August 2002; accepted 21 August 2002
Abstract Treatment of rice straw by the proprietary FIBEX process resulted in increased in vitro digestibility by ruminal microorganisms due to a reduced lag time, increased rate of digestion, increased extent of digestion, and possible removal of inhibitory agents present in untreated rice straw. To determine the value of treated rice straw as a feed ingredient for lactating dairy cows, production parameters and milk composition were determined in a feeding trial with thirteen primparous and six multiparous cows in a switchback design involving two diets and 21 days periods. One diet was a conventional dairy diet that contained alfalfa hay, corn grain, soybean meal (SBM) and several byproduct feeds. The other diet contained these same feed ingredients, but with levels of alfalfa hay, corn grain and SBM that were altered somewhat to provide energy, neutral detergent fiber (35.8%), acid detergent fiber (25.8%) and crude protein (18.0%) levels similar to the treated rice straw added at 7% of dry matter. The diet that contained treated rice straw supported higher neutral detergent fiber intake and milk yield. Milk produced from cows fed the two diets had similar levels of protein, urea nitrogen and lactose. Based on its increased in vitro fermentability at higher fiber content, FIBEX-treated rice straw may be useful as a feed ingredient for lactating dairy cows. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Digestion kinetics; Fiber; Milk; Milk composition; Rice straw
Abbreviations: ADF, acid detergent fiber; CP, crude protein; DMI, dry matter intake; MUN, milk urea nitrogen; NDF, neutral detergent fiber; OM, organic matter; SBM, soybean meal; TMR, total mixed ration 夽 Mention of specific products is for informational purposes only, and does not imply a warranty or endorsement by USDA over other products not mentioned. ∗ Corresponding author. Tel.: +1-608-264-5408; fax: +1-608-264-5147. E-mail address: [email protected] (P.J. Weimer). 0377-8401/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 8 4 0 1 ( 0 2 ) 0 0 2 8 2 - 1
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1. Introduction Rice straw is an agricultural residue that is a disposal problem for the rice industry in the state of California as well as other parts of the world. Approximately 1.5 × 109 kg of rice straw is produced annually in the state, and it has historically been disposed of by field incineration. Implementation of new California law has mandated annual reductions in incineration to improve local air quality and, since September 2001, incineration of rice straw has proceeded only on a “permit-to-burn” basis as required for rice disease control. It has been estimated that this means that approximately 80% of the rice straw will have to be disposed of by other means (Forrest et al., 1997). One possible use of rice straw is as a feed for ruminants, if it could provide sufficient energy in spite of its high fiber content. However, because of its high ash content (16–18% of dry matter (DM); Crocker et al., 1998) and the poor digestibility of its organic matter (OM), rice straw is considered to have a very low value as a ruminant feed ingredient under animal production conditions above maintenance (Forrest et al., 1997). Successful incorporation of rice straw into ruminant rations will require economical treatment that substantially increases its digestibility. While enhanced digestibility of rice straw has been reported with several treatments (Hart et al., 1975; Garrett et al., 1979; Han et al., 1989), none have been implemented commercially. The ammonia fiber explosion (AFEX) process of (Dale, 1986; Dale et al., 1996), and the more recent and improved FIBEX process (Dale and Weaver, 2000, 2001) offer several process advantages. These include increased reactivity of the treated straw and ease of recovery of the chemical treatment agents, and both make this treatment of rice straw more viable than traditional ammoniation treatments. The AFEX process is a batch process, while the FIBEX process is continuous. Preliminary experiments (data not shown) indicated that treatment of rice straw by the FIBEX process increased in vitro DM digestibility. The present study was undertaken to determine the kinetic profiles and to establish quantitatively the kinetic parameters for the fermentation of rice straw before and after its treatment by the FIBEX process under various regimes of moisture content, NH3 /substrate ratio, time, temperature and pressure; and to determine if the treated rice straw can be incorporated into dairy diets at a modest level (7% of DM) without decreasing ration palatability, milk yield or milk quality. 2. Materials and methods 2.1. Materials Rice straw was harvested in the Sacramento valley of California and then baled and stored indoors prior to use. The rice straw samples were either untreated, or treated under various combinations of conditions. Treatments were in a highly-modified 3.8 l Autoclave Engineers stainless steel pressure vessel (Snap-Tite, Erie, PA, USA) that contained 100 g of rice straw. The vessel was modified with appropriate pumps for addition of ammonia, stirring, remote controls and extra-large outlet vents to permit very rapid reductions in reactor pressure. Three treatment parameters were fixed: straw moisture content (18, 30, or 40%, w/v), NH3 : straw weight ratio (0.5, 0.75, or 1.0), and reaction time (i.e. the time at which the pressure
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was rapidly released; 5 or 10 min). Two treatment conditions, temperature and pressure, varied during the course of the reaction as the sealed vessel was heated. Temperature values reported are the mean of the temperature at the start of the reaction, and the temperature just prior to rapid release of pressure. Pressure values are reported as the mean of three values: the initial reactor pressure, the maximum pressure that was reached ∼3 min into the reaction, and the pressure just prior to its rapid release at the end of the incubation. A bulk sample of several tonnes of treated rice straw was prepared at the Tennessee Valley Authority biomass pilot plant facility in Muscle Shoals, AL, USA. Straw was chopped to a nominal 2.54 cm length, and hydrated to ∼50% DM by passage under water spray nozzles. Wet straw was fed continuously to a hydrolyzer unit (Sunds Defibrator Inc., Minneapolis, MN, USA) that contained a vertical impregnator screw which mixed the wet straw with ammonia, at 300 g/kg dry straw. Heat was applied via an external steam jacket, and the temperature (110–132 ◦ C) and pressure (12.9–15.0 atm) were maintained by opening and closing input and output valves of the hydrolyzer. Upon attaining the desired temperature and pressure, jacket steam flow was reduced, as energy of mixing and heat of dissolution of ammonia was sufficient to maintain temperature and pressure. Treated biomass exiting the hydrolyzer was passed through a continuous flow dryer to obtain a final product (designated TVA270) of ∼85% DM. 2.2. Fermentations Inoculum was prepared from ruminal contents of two fistulated Holstein cows fed a total mixed ration (TMR) that contained corn silage, corn grain, alfalfa hay, soybean meal (SBM), and supplemental vitamins and minerals. Ruminal fluid, 400 ml from each cow, was squeezed through four layers of cheesecloth and collected into a graduated cylinder purged with CO2 . The squeezed solids, 200 g from each cow, were blended under CO2 in a Waring Blender (15 s low speed, then 45 s high speed) containing 800 ml of buffer. The buffer (Goering and Van Soest, 1970) consisted of (per liter): 1.0 g NH4 HCO3 , 8.75 g NaHCO3 , 1.43 g Na2 HPO4 , 1.55 g KH2 PO4 , 0.15 g MgSO4 ·7H2 O, 2.5 g Trypticase, 0.125 ml resazurin (0.1%, w/v) and 0.125 ml micromineral solution (per liter: 132 g CaCl2 ·2H2 O, 100 g MnCl2 ·4H2 O, 10 g CoCl2 ·6H2 O; 80 g FeCl3 ·6H2 O). The ruminal fluid and blended solids were combined and filtered through four layers of cheesecloth into a CO2 purged graduated cylinder, and the filtrate was placed into a water-jacketed (39 ◦ C), CO2 purged stirring chamber for inoculation of fermentation vials. In vitro fermentations were conducted using a continuous on-line gas production system that permitted simultaneous measurement of headspace pressure in 40 experimental vials (Weimer et al., 2000). Samples (∼100 mg, dried OM basis, and weighed to the nearest 0.1 mg), contained in volume-calibrated (to 0.01 ml) 60 ml serum bottles, were suspended in 5.7 ml of buffer (Goering and Van Soest, 1970; see above) and 0.3 ml of reducing agent (6.5 mg each of cysteine and Na2 S·9H2 O per ml of 0.04 N NaOH), under a CO2 gas phase. Vials were prewarmed to 39 ◦ C and inoculated with 4.0 ml of diluted ruminal inoculm (as above). Blank vials contained buffer, reducing agent, and inoculum, but no exogenously added substrate. Details of the gas production measurement system and the time-staggered loading of samples into the instrument are described elsewhere (Mertens and Weimer, 1998). Incubations were conducted for 72 h, during which time approximately
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200 headspace pressure measurements were made for each sample. Net gas production after blank subtraction was fit to a dual-pool exponential model as described previously (Weimer et al., 2000), using the NONLIN program of the SAS statistical software package (SAS, 1985). The model included separate terms for the rapidly degraded (soluble) and slowly degraded (fiber) fractions of the substrate. 2.3. Analyses DM was determined gravimetrically after drying at 105 ◦ C for 18 h. Ash content of the dry residue was determined gravimetrically following incineration at 550 ◦ C for 4 h. N content was determined by combustion analysis (model FP2000 N analyzer, Leco Instruments, St. Joseph, MI, USA) on air-dried samples. Following fermentation, neutral detergent fiber (NDF) was determined by the method of Weimer et al. (1990), using sodium sulfite but not ␣-amylase. NDF is expressed on a non-ash-free basis. 2.4. Feeding trial The animal trial was conducted using a protocol approved by the University of Wisconsin Animal Care Committee. Fourteen multiparous and six primiparous Holstein cows were divided into two groups balanced for age, body weight (554 ± 63 kg), days in milk (71 ± 28 days), and milk production (43.0±5.0 kg per day). Groups were fed two diets in a switchback arrangement consisting of a 2 days adaptation period to the new diet (i.e. new and old diet in a ratio of 33:67 on day 1, 67:33 on day 2, and 100:0 on day 3), followed by 18 days of feeding the new diet. The control (C) diet and the diet (R) supplemented with treated rice straw (Table 1) were balanced for NDF, acid detergent fiber (ADF), crude protein (CP), Ca, Mg, and P. Diets were based on alfalfa hay and corn grain, supplemented with various byproduct feeds commonly used in northern California (Grasser et al., 1995). Rations were formulated as a TMR blended from alfalfa, whole cottonseed, and a milled mixture that contained all other feed ingredients (including the rice straw for diet R). Cows were fed once daily at about 13:30 h to approximately 10% orts, and orts were collected daily and weighed. During the last week of each period, orts were spread evenly through each feed bunk just prior to daily feeding, and a one-eighth subsample was collected for each cow for analysis. After their return to the laboratory, each orts sample was spread evenly and subsampled again, air dried, and ground through a Wiley mill having a 2 mm screen. The ground orts were analyzed (in quadruplicate) for DM, NDF, ADF, CP and ash. Milk was collected from twice daily milkings at 11:00 and 20:00 h. Milk samples from day 20 (PM milking) and day 21 (AM milking) of each period were collected for commercial analysis of fat, CP, and lactose (AgSource, Verona, WI). Milk urea nitrogen (MUN) was determined using a commercial urea N assay kit (Sigma, St. Louis, MO) following deproteinization of the sample with trichloroacetic acid. 2.5. Statistical analyses Main effects on milk production and milk composition variables were determined by ANOVA using the general linear model procedure of SAS (SAS Institute, 1985), with
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Table 1 Formulated composition of control diet and diet amended with FIBEX-treated rice straw Control
Rice straw
Ingredient composition (g/kg DM)a Alfalfa hay Corn grain, dry kernel Whole linted cottonseed Treated rice straw Beet pulp, pelleted Corn gluten feed, dehydrated Wheat middlings Soybean meal, 48% CP solvent Beet molasses, liquid Monosodium phosphate Magnesium oxide Salt and vitamin mixtureb
450 183 120 – 80 80 40 23.5 20 1.0 1.3 1.0
350 206 120 70 80 80 40 29.5 20 1.8 1.6 1.0
Chemical composition (g/kg DM) NDF ADF CP Ash Ca Mg P
358 258 180 70 8.4 3.5 4.1
357 258 180 70 7.1 3.5 4.1
a
Dry matter content was 89.7% for the control diet and 89.5% for rice straw diet. TM Vit Pak (Professional Products and Services, Prairie du Sac, WI, USA) contained per gram: 229 mg Ca, 56 mg Zn, 46 mg Mn, 22 mg Fe, 12 mg Cu, 0.4 mg Co, 0.9 mg I, 0.32 mg Se, 7084 IU Vitamin A, 2200 IU Vitamin D3, 17.6 IU Vitamin E. b
diet, cow and period as independent variables. A second analysis was performed with diet, period and cow maturity (primiparous versus multiparous) as independent variables. Comparisons among means were performed using a paired t-test at a probability level of 0.05.
3. Results 3.1. Characteristics of rice straw Untreated rice straw (74.4% NDF, 18.9% ash, and 3.8% CP) was light tan in color and odorless. Treated rice straws were darker in color and retained a sawdust or bagasse-like odor. All treated rice straws had slightly lower NDF and ash contents than untreated straw (Table 2). CP content was increased up to 350% by treatment. The highest CP levels were in the low moisture straw samples treated at high NH3 :straw ratios for longer times. The large stock of treated rice straw supplied for the production trial displayed similar characteristics to the small samples, except that the production trial scale material was darker in color and contained, as a small percent of the total, clumps of about 2 cm size material
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Table 2 Treatment conditions used and composition of resulting rice straw materials Rice straw samplea
Treatment conditions
Untreated 28 41 66 75 82 87 90 93 96 99 103
Composition after treatment
DM (%)
Ratiob
T (◦ C)c
P (atm)d
Time (min)
DM (%)
NDF (%DM)
Ash (%DM)
CP (%DM)
– 82 70 70 70 60 60 60 60 60 60 60
– 1.0 1.0 1.0 1.0 0.75 0.5 0.75 1.0 0.5 0.75 0.5
– 91 86 79 91 108 97 88 90 81 90 87
– 26.3 26.3 24.8 24.3 24.7 18.9 22.5 25.4 18.7 21.9 18.5
– 10 10 10 10 5 5 5 5 10 10 10
90.6 87.8 90.1 76.7 81.3 75.5 82.6 78.0 79.5 74.2 78.0 80.5
74.4 63.3 63.1 64.5 61.9 72.5 70.8 70.5 66.4 70.9 67.1 69.2
18.9 17.3 17.1 16.8 15.4 16.7 16.3 16.2 16.9 16.8 16.8 16.4
3.8 16.9 17.4 13.0 14.8 8.3 7.1 8.2 8.6 7.0 9.9 7.6
1.1
0.8
1.0
Pooled S.E.
0.42
a
Pretreated sample number, provided to facilitate comparison with Table 3. Weight ratio of NH3 to rice straw. c Temperature. d Pressure. b
that resisted breakup in the TMR wagon. Despite this, there was little visible sorting by the cows during feeding. 3.2. In vitro studies The first in vitro run compared a control sample of rice straw that had not been treated to the 11 samples treated at benchtop scale. The second run compared the untreated control sample with rice straw that had been treated at large scale to obtain material for the animal feeding study. Measurement of net gas production from the rice straws incubated with a mixed ruminal inoculum for selected periods of time during the digestion revealed that untreated rice straw depressed gas production slightly (by a maximum of 15 ml gas/g DM for ∼10 h relative to blank vials that contained the ruminal inoculum without added substrate; data not shown), suggesting that untreated rice straw may have contained a soluble inhibitor of ruminal fermentation. Gas production in almost all of the FIBEX-treated samples exceeded that of the untreated rice straw at all measured time points during fermentation. In run 1, untreated rice straw contained a very small rapidly fermented fraction, and its fiber fraction was fermented slowly (k2 = 0.0353 h−1 ) after a time lag of 10.4 h (Table 3). FIBEX treatment increased (P < 0.05) the rate of digestion (k2 ) of the fiber fraction by 41–69%, and reduced (P < 0.05) the lag time (L2 ) prior to digestion of this fraction by 26–38%. Within the range of treatment conditions tested, there was no differential effect (P > 0.05) of moisture content, ammonia/straw ratio, time, or temperature on the total amount, rate constant or time lag of gas production from the slowly digested fraction. This suggests that the FIBEX treatment process is effective over a wide range of process conditions.
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Table 3 Kinetic values for fermentation of untreated and FIBEX-treated rice straw, as determined from in vitro gas production measurements and application of a two-pool exponential model Run
Rice straw samplea
Kinetic values A (ml/g OM)b
B (ml/g OM)c
k1 (h−1 )d
k2 (h−1 )e 0.0353 d 0.0604 c,d 0.0593 c,d 0.0583 c 0.0564 c 0.0561 c 0.0541 c 0.0558 c 0.0499 c 0.0543 c 0.0561 c 0.0518 c
1
Untreated 28 41 66 75 82 87 90 93 96 99 103
1.6 d 29.3 c 27.8 c 23.8 c 25.0 c 17.1 c 16.8 c 7.8 c,d 10.2 c 13.9 c 14.3 c 23.0 c
127.7 101.6 99.2 152.0 116.2 174.6 161.6 155.1 155.5 158.4 150.6 142.6
<0.01 0.482 0.636 0.318 0.618 1.25 0.028 16.041 7.120 0.034 0.436 0.152
2
Untreated TVA270
<0.1 d 25.2 c
159.9 180.8
0.164 0.236
2.9
14.3
11.043
Pooled S.E.
0.0420 d 0.0795 c 0.0241
L1 (h)f
L2 (h)g
0.23 0.13 0.03 0.14 0.07 0.22 0.09 0 0.09 0.11 0.16 2.12
10.40 c 6.92 d 7.17 d 6.43 d 6.95 d 6.43 d 7.15 d 7.15 d 7.35 d 7.67 d 6.97 d 7.13 d
<0.01 0.06
9.79 d 5.53 c
0.75
0.83
Means (n = 3) in the same column within each run that have different letters (c, d) differ (P < 0.05). a Pretreated sample number, provided to facilitate comparison with Table 2. b A: ml gas produced from rapidly digested fraction/g OM. c B: ml gas produced from slowly digested fraction/g OM. d k : rate constant for rapidly digested fraction (h−1 ). 1 e k : rate constant for slowly digested fraction (h−1 ). 2 f L : lag time for rapidly digested fraction (h). 1 g L : lag time for slowly digested fraction (h). 2
All FIBEX treatments (Table 3) shifted up to 22% of the substrate from the slowly-digested pool into the rapidly digested pool, and this pool was digested at rates (k1 ) that usually fell in the range of 0.3–1.3 h−1 . Rates outside of these ranges were associated with problems with the model, yielding either a lag time of zero, or very small rapidly digested pools (A/(A + B) < 0.05). In particular, samples no. 28 and no. 41, which had a higher DM content at treatment displayed a greater shift of substrate to the rapidly digested fraction, but total gas production was not higher than that of untreated rice straw. Rice straw treated in the large scale equipment increased the rate of gas production from the slowly-digesting pool by 89%, and decreased lag time by 44% (Tables 3 and 4). 3.3. Production trial One of the R cows stopped eating a few days into the trial and so was removed. The other cows readily ate both rations, and there was no visible sorting. None of the cows displayed hyperexcitability, as has been reported for ruminants consuming 50% or more of a diet of rice straw treated with ammonia for greater than 3 h at greater than 70 ◦ C (Perdock and Leng, 1987).
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Table 4 Feed intake and production of cows fed diets with and without FIBEX-treated rice straw Control Intake (kg per day) DM OM NDF ADF CP Production (kg per d) Milk Fat Protein Lactose Energy (MJ per day)a Milk composition (%) Fat (%) Protein (%) Lactose (%) Urea N (mM) a
Rice
Pooled S.E.
P>F 0.151 0.199 <0.001 0.349 0.804
25.0 22.0 7.0 5.2 4.0
25.9 22.9 8.1 5.3 4.0
2.9 2.1 0.7 0.5 0.1
38.3 1.47 1.14 1.83 114.0
39.6 1.41 1.19 1.86 113.6
1.6 0.11 0.05 0.19 6.1
0.020 0.062 0.011 0.671 0.914
3.86 2.99 4.77 5.11
3.55 3.00 4.82 5.29
0.22 0.10 0.11 0.83
<0.001 0.664 0.197 0.626
Calculated using Equation I of Tyrrell and Reid (1965).
Feeding of ration R resulted in increases (P < 0.05) in both NDF intake and milk yield that averaged 1.1 and 1.3 kg per day, respectively. A decline (P < 0.05) in milk fat % of 0.3 occurred with ration R. Despite higher levels of inorganic N in the treated rice straw, levels of protein and MUN did not differ between the diets, and the protein contents of the milk were essentially identical. 4. Discussion Rice straw, while abundant worldwide, is one of the least desirable biomass resources as an animal feed due to its low digestibility and high ash content (Garrett et al., 1979). Utilization of rice straw generated in California will require its diversion into alternate uses such as building materials, composites, land application materials and feedstocks for chemicals produced by fermentation. Although few viable commercial applications of these alternate uses have emerged, all have been characterized as more promising than the use of untreated rice straw as a livestock feed (Forrest et al., 1997). Treatment of rice straw by the FIBEX process resulted in enhancement of in vitro digestibility, reduction in the lag time before the start of the fermentation, a shift of a portion of the rice straw from the slowly digested to the rapidly digested pool, and an increased rate of digestion of the slowly digested pool. Overall, these results extend previous in vitro studies, conducted at a few time points, which demonstrated the effectiveness of ammonia treatment under temperature or pressure in enhancing enzymatic (Dale and Moreira, 1982; Dale et al., 1996) or ruminal (Sirohi et al., 1988; Wanapat et al., 1990) digestibility of low quality agricultural residues.
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Based on previous studies of ammoniation of biomass (Weimer et al., 1986), it is likely that most of the N in the treated rice straw was in the form of unreacted NH3 , acetamide (formed by ammoniolysis of acetyl groups in hemicellulose) and hemicellulose amides (formed by ammoniolysis of ester linkages between lignin and hemicelluloses). Because the diets were formulated on a CP basis, the rice straw amended diet contained a larger fraction of its CP in NH3 , a form of N that can be utilized less efficiently by ruminal microbes for growth. Nevertheless, milk protein levels did not differ between the two diets, suggesting that diet CP intake was not limiting milk protein synthesis. The poor potential of rice straw as a livestock feed has been inferred from several studies, most of which were conducted in developing countries. In these studies, beef cattle, calves, heifers or sheep at low levels of production were fed untreated or treated rice straw as the primary, or sole, energy source in the diet (Han et al., 1989; Maeng and Chung, 1989; Yoon et al., 1983). Such studies have shown that treatments with ammonia or urea, typically under static conditions at ambient temperature and pressure, considerably enhance digestibility and weight gain relative to untreated rice straw. Few studies have examined treated rice straw under production conditions more typical of developed countries. In one California study, Garrett et al. (1979) investigated weight gain in slaughter cattle and lambs fed diets that contained untreated or treated (with ammonia or NaOH) rice straw at 36 or 72% of the diet (as fed basis), with the remainder of the diet containing alfalfa hay, barley grain, cottonseed meal and molasses. These workers found that treated straws resulted in substantial improvements in weight gain and digestibility in animals fed the rice straw at 72%, but not 36%, of the diet, when compared to diets containing similar levels of untreated rice straw. In contrast to the many studies of the effect of feeding treated rice straw on in vitro digestibility and ruminant weight gain, there have been to our knowledge no published studies on the incorporation of treated rice straw into dairy rations for cows at high levels of production. That NDF intake and milk yield can be sustained with inclusion of 7% of DM of FIBEX-treated rice straw suggests that the treated rice straw has a high energy value.
Acknowledgements We thank C.L. Odt and M. Becker for excellent technical assistance; M. Moore and W. Burleson for engineering assistance in treating the rice straw; L. Strozinski and the USDFRC barn crew for animal handling; R.P. Walgenbach for supplying hay for the cow trial; and M.S. Allen for stimulating discussions. This research was supported by Trust Fund Agreement 58-3655-0-407 between MBI International and the USDA-Agricultural Research Service. References Crocker, L.M., DePeters, E.J., Fadel, J.G., Essex, S.E., Perez-Monti, H., Taylor, S.J., 1998. Ash content of detergent fibers in feeds, digesta, and feces and its relevance in fiber digestibility calculations. J. Dairy Sci. 81, 1010–1014. Dale, B.E., 1986. Method for increasing the reactivity of cellulose. US patent 4,600,590. Dale, B.E., Moreira, M.J., 1982. A freeze-explosion technique for increasing cellulose hydrolysis. Biotechnol. Bioeng. Symp. Ser. 12, 31–43.
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