J. Anim Sci. 2007. 85:2575-2581. doi:10.2527/jas.2006-490
© 2007 American Society of Animal Science
Influence of surfactant supplementation and maceration on the feeding value of rice straw in growing-finishing diets for Holstein steers1
A. Plascencia*,
M. A. Lopez-Soto*,
M. F. Montaño*,
J. G. Serrano*,
R. A. Ware
and
R. A. Zinn,2
* Universidad Autónoma de Baja California, México; and
Department of Animal Science, University of California, Davis 95616
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Abstract
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Two trials were conducted to evaluate the interaction of the maceration process and surfactant (Tween 80) supplementation on feeding value of rice straw. Treatments were steam-flaked, corn-based diets containing 14% forage (DM basis), which was 1) Sudangrass hay; 2) ground rice straw; 3) ground rice straw plus 0.22% Tween 80; 4) macerated rice straw; and 5) macerated rice straw plus 0.22% Tween 80. In the maceration process, rice straw was passed through 2 sequentially placed pairs of corrugated rolls set at zero tolerance under a ram pressure of 62,050 millibars, similar to a conventional grain roller mill, except that the opposing rolls operated at different speeds (12 and 14 rpm, respectively). Sudangrass hay and rice straw (native and macerated) were ground through a 2.6-cm screen before incorporation into complete mixed diets. In trial 1, 125 Holstein steers (292 ± 1.7 kg of BW) were used in a 188-d evaluation of the treatment effects on growth performance and carcass characteristics. In trial 2, 5 Holstein steers (224 ± 3.5 kg of BW) with cannulas in the rumen and proximal duodenum were used in a 5 x 5 Latin square design to evaluate the treatment effects on digestion. There were no interactions between maceration and surfactant on growth or carcass characteristics. Tween 80 did not influence the feeding value of rice straw. Compared with grinding alone, maceration of rice straw increased the carcass-adjusted ADG (6%, P < 0.10), G:F (6%, P < 0.05), and dietary NE (5%, P < 0.05); DMI was similar across treatments. Assuming NEm and NEg of Sudangrass hay are 1.18 and 0.62 Mcal/kg, the NEm and NEg were 0.61 and 0.13 Mcal/kg for ground rice straw and 1.21 and 0.65 Mcal/kg for macerated rice straw. There were no treatment interactions on characteristics of digestion. Tween 80 did not influence ruminal or total tract digestion of OM, starch, NDF, or N. Compared with grinding alone, maceration of rice straw increased ruminal digestion of OM (7.7%, P < 0.10) and NDF (30.8%, P < 0.05), and total tract digestion of OM (2.3%, P < 0.10), NDF (21.1%, P < 0.01), and N (3.7%, P < 0.05). Total tract digestion of OM, NDF, starch, and N for the Sudangrass diet corresponded closely with that of the macerated rice straw diets. Maceration increases the feeding value of rice straw to a level similar to that of good-quality (flag stage of maturity) Sudangrass hay, which is attributable to increased OM and NDF digestion. Effects of surfactant supplementation on growth performance and digestion are not appreciable.
Key Words: cattle • digestion • maceration • performance • rice straw • surfactant
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INTRODUCTION
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Torrentera et al. (2000)
and Ware et al. (2005) describe a process called maceration, whereby the digestibility and the NE value of forages may be enhanced. Maceration is a process designed to simulate chewing, or mastication. It consists of opposing corrugated rolls maintained within set tolerances of each other using hydraulic pressure. Opposing rolls, turning at differential speeds, crush and stretch the fiber, but the forage remains otherwise intact. The effects of indentation during maceration is intended to alter the structural integrity and density of the fiber, promoting microbial attachment and digestion (Hong et al., 1988a; Hintz et al., 1999) and enhancing the action of exogenous fibrolytic enzymes (Lopez-Soto et al., 2000; Ware et al., 2005). Tween 80 (IFN 8-08-031; a nonionic surfactant registered for use in the pharmaceutical and food industries) application increased in vitro cellulose degradation of barley straw (Kamande et al., 2000). Researchers postulated that Tween 80 increased detachment of fiber-digesting bacteria from insoluble substrates in the rumen fluid.
The objective of this study was to evaluate the influence of maceration and surfactant supplementation on the feeding value of rice straw in growing-finishing diets for feedlot cattle.
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MATERIALS AND METHODS
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Animal care, handling techniques, and surgical procedures were approved by the University of California Animal Care and Use Committee before initiation of these experiments.
Trial 1
One hundred twenty-five Holstein steers (292 ± 1.7 kg of BW) were used in a 188-d growth performance trial to evaluate the interaction of maceration process and surfactant (Tween 80) supplementation on growth performance and carcass characteristics. Upon arrival, steers were vaccinated for bovine rhinotracheitis-parainfluenza3 (TSV-2, SmithKline Beecham, West Chester, PA), clostridials (Fortress 8, SmithKline Beecham), and Mannheimia haemolytica (One Shot, SmithKline Beecham) and treated for parasites (Spotton, Miles, Shawnee Mission, KS). Steers were injected with 500,000 IU of vitamin A (Vita-jec A&D 500, RXV Products, Porterville, CA) on arrival and again on d 168. Cattle were blocked by BW and randomly assigned within BW groups to 25 pens (5 steers per pen). Pens were 43 m2, with 22 m2 of overhead shade, automatic waterers, and each feed bunk was 2.4 m long.
Composition of the experimental diets is shown in Table 1. Treatments consisted of steam-flaked, corn-based diets containing 14% forage (DM basis), which was 1) Sudangrass hay; 2) ground rice straw; 3) ground rice straw plus 0.22% of Tween 80 (a polyethylene sorbitol ester; Sigma Chemical, St. Louis, MO); 4) macerated rice straw; and 5) macerated rice straw plus 0.22% of Tween 80. Surfactant was incorporated as a component of the complete mixed diet at the time of batch mixing. All forages (Sudangrass hay and rice straw, native and macerated) were ground in a hammer mill (Bear Cat #1A-S, Westerns Land and Roller Co., Hastings, NE) with a 2.6-cm screen before incorporation into the complete mixed diets. Rice straw was macerated through 2 sequentially placed pairs of corrugated rolls (23.5 x 46 cm). Roll pairs were set at zero tolerance under a ram pressure of 62,050 millibars, in a manner similar to that of a conventional grain roller mill, except that the opposing rolls operated at different speeds (12 and 14 rpm, respectively). Thus, as the straw passed through the rolls under pressure the corrugations on the rolls produced bite marks in the straw that were augmented by the stretching effect of the differential speed of the opposing rolls. Maceration effects on a rice straw stem are depicted in Figure 1.
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Figure 1. Depiction of the maceration effect on rice straw stem. Maceration flattened the stem, placing incremental stress marks.
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Steam-flaked corn was prepared as follows: a chest (46 x 61 cm, corrugated) situated directly above the rollers was filled to capacity (440 kg) with corn and brought to a constant temperature (102°C) at atmospheric pressure using steam (boiler pressure 60 psi). Corn was steamed for 25 min before starting the rollers. Approximately 440 kg of the initial steam-processed grain that exited the rolls during the warm-up was not fed to the steers on this study. The tension of the rolls was adjusted to provide a flake density of 0.31 kg/L. The retention time of the grain in the steam chamber was set at approximately 25 min. The steam-flaked grain was allowed to air-dry before incorporation into the diet. Steers were allowed ad libitum access to feed and water throughout the experiment. Fresh feed was added twice daily.
Steers were implanted with Revalor-S (Intervet Inc., Millsboro, DE) on d 1 and 112 of the trial. Hot carcass weights were obtained from all steers at the time of slaughter. After the carcasses were chilled for 48 h, the following measurements were obtained: 1) LM area, taken by direct grid reading of the muscle at the 12th rib; 2) subcutaneous fat over the LM at the 12th rib taken at a location three-quarters of the length laterally from the backbone end; 3) KPH as a percentage of HCW; and 4) marbling score (USDA, 1997). Energy gain (EG, Mcal/d) was calculated by the equation EG = ADG1.097 x 0.0557 x BW0.75 (NRC, 1984). Maintenance energy (EM) was calculated by the equation EM = 0.084 x BW0.75 (Garrett, 1971). From the derived estimates of energy required for maintenance and gain, the NEm and NEg values of the diet were obtained using a quadratic formula 
, where a = –0.41 x EM, b = (0.877 x EM) + (0.41 x DMI) + EG, and c = –0.877 x DMI, and NEg = (0.877 x NEm) – 0.41 (Zinn and Shen, 1998).
For calculating steer performance, initial and final BW were reduced by 4% to account for digestive tract fill. Carcass-adjusted final BW was calculated by dividing individual HCW by the average dressing percent for all steers. Pens were used as experimental units. The trial was analyzed as a randomized complete block design. Forage treatment effects were separated by means of the following orthogonal polynomials: Sudangrass vs. rice straw, ground vs. macerated rice straw, no surfactant vs. surfactant, and the straw processing x surfactant interaction (Hicks, 1973).
Trial 2
Five ruminally and duodenally cannulated Holstein steers (224 ± 3.5 kg of initial BW) were used in a 5 x 5 Latin square design to evaluate treatment effects on characteristics of ruminal and total tract digestion. Composition of the experimental diets is shown in Table 1
, except for the inclusion of 0.40% chromic oxide, which was added as a digesta marker. Steers were maintained in individual pens with access to water at all times. Diets were fed at 0800 and 2000 daily. Dry matter intake was restricted to 2.1% of BW daily (4.76 kg/d). Experimental periods were 2 wk, with 10 d for diet adjustment and 4 d for the collection period. During collection, duodenal and fecal samples were collected twice daily as follows: d 1, 0750 and 1350; d 2, 0900 and 1500; d 3, 1050 and 1650; and d 4, 1200 and 1800. Individual samples consisted of approximately 750 mL of duodenal chyme and 200 g (wet basis) of fecal material. Samples from each steer and within each collection period were composited for analysis.
Upon completion of the trial, feed, duodenal and fecal samples were prepared for analysis by oven-drying at 70°C and grinding in a laboratory mill (MicroMill, Bel-Arts Products, Pequannock, NJ). Samples were oven-dried at 105°C until no further weight was lost and stored in tightly sealed glass jars. Samples were subjected to all or part of the following analyses: ash, Kjeldahl N, ammonia N (AOAC, 1984), ash-corrected NDF (adapted from Goering and Van Soest, 1970), starch (Zinn, 1990), chromic oxide (Hill and Anderson, 1958), and purines (Zinn and Owens, 1986). Microbial OM and N leaving the abomasum were calculated using purines as a microbial marker (Zinn and Owens, 1986). Organic matter fermented in the rumen was considered equal to OM intake minus the difference between the amount of total OM reaching the duodenum and microbial OM reaching the duodenum. Feed N escape to the small intestine was considered equal to total N leaving the abomasum minus ammonia N and microbial N and, thus, includes any endogenous contributions. This trial was analyzed as a 5 x 5 Latin square according to the following statistical model: Yijk = µ+ Ai + Pj + Tk + Eijk, where Ai is steer, Pj is period, Tk is treatment, and Eijk is residual error. For- age treatment effects were separated according to a 2 x 2 +1 factorial arrangement, as described for trial 1.
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RESULTS AND DISCUSSION
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Treatment effects on growth performance and carcass characteristics (trial 1) are shown in Tables 2 and 3. There were no interactions (P > 0.20) between maceration and surfactant on growth performance or carcass characteristics. Supplementation with 0.22% Tween 80 surfactant did not influence (P > 0.20) growth performance or carcass characteristics. In contrast, McAllister et al. (2003) observed a 7% increase in ADG when feedlot cattle were fed with a barley-based finishing diet contained 6.5% of barley silage as forage source supplemented with 0.20% Tween 80.
Compared with grinding alone, maceration of rice straw increased carcass-adjusted final BW (17.9 kg, P < 0.05), and ADG (6.1%, P = 0.07), but did not affect (P = 0.70) DMI. The similarity in DMI (averaging 8.0 kg/d) indicates that DMI was limited by something other than cattle’s genetic potential for growth. Based on NRC (1996), DMI is expected to be limited by dietary energy density when the NEm is less than 1.6 Mcal/kg. However, all diets contained greater than 2.1 Mcal/kg of NEm (Table 1). Mertens and Ely (1979) observed that dietary energy density limits energy intake only to the extent that it is associated with indigestible fiber intake. Defoor et al. (2002) observed that with steam-flaked corn-based finishing diets, increasing forage NDF (dietary NDF contributed by the forage components of the diet) from 5.0 to 8.5% of dietary DM decreased energy intake in finishing heifers. Based on a 7-trial summary, Galyean and Defoor (2003) proposed that growing-finishing diets containing greater than 10% forage NDF are likely to depress energy intake. Likewise, in a summary of 9 trials evaluating the relationship between growth performance and forage level in diets for feedlot cattle, Alvarez et al. (2004) observed that relative ADG was maximal within the interval of 4 to 8% forage NDF. When dietary forage NDF exceeded 8%, ruminal bulk fill limited energy intake. Accordingly, in the current study, wherein dietary forage NDF for all treatments was 
9.2%, it was expected that ruminal fill would limit DMI.
Observed dietary NE agreed closely (99 to 101%) with expected dietary NE (based on tabular values for individual dietary ingredients; NRC, 1984) for Sudangrass hay and ground rice straw supplemented diets. Consistent with previous studies (Charmley et al., 1999; Torrentera et al., 2000; Ware et al., 2005), gain efficiency, and dietary NE were greater (5.7 and 4.2%, respectively; P < 0.05) for macerated than for ground rice straw supplemented diets. Indeed, the NE values for the macerated rice straw supplemented diets were at least equivalent to that of Sudangrass hay supplemented diets. Given that the NEm and NEg values of Sudangrass hay were 1.18 and 0.62 Mcal/kg, respectively (NRC, 1996), the NEm and NEg values of ground rice straw were 0.61 and 0.13 Mcal/kg, respectively, whereas the corresponding values for macerated rice straw were 1.21 and 0.65 Mcal/kg. The NEm value for ground rice straw corresponds to a TDN value of 39% (TDN = 19.65 + 31.18 NEm, derived from NRC, 1996), in good agreement with White et al. (1974) and Willis et al. (1980) who observed TDN values for rice straw ranging from 38 to 44%. The low energy value of rice straw is attributed to its comparatively low soluble carbohydrate and protein content and to its distribution of highly lignified sclerenchymatous layer and tissues of the vascular bundles, making it resistant to penetration by digestive enzymes. Consequently, even finely grinding (1- vs. 4-cm screen) has had very little benefit for enhancing its value (White et al., 1971) and may even reduce digestibility to the extent that it decreases ruminal retention time (Coombe et al., 1979).
Compared with grinding alone, maceration of rice straw increased (P < 0.05) HCW (3.2%), dressing percent (1.7%), and quality grade (4.29 vs. 4.01). Carcass characteristics of steers fed Sudangrass supplemented diets were not different (P > 0.20) from those fed rice straw supplemented diets.
Treatment effects on characteristics of digestion (trial 2) are shown in Table 4. There were no treatment interactions (P > 0.20). Consistent with the trial 1, Tween 80 supplementation did not influence (P > 0.20) ruminal or total tract digestion of OM, starch, NDF, or N. Compared with grinding alone, maceration of rice straw increased of ruminal digestion of OM (7.7%, P < 0.10) and NDF (30.8%, P < 0.05). There were no treatment effects on ruminal microbial efficiency (g of microbial N/kg of OM fermented) or ruminal N efficiency (nonammonia N flow to duodenum as percentage of N intake), averaging 22.7 and 0.86, respectively. In contrast with previous studies (Moore et al., 1990; Lopez-Soto et al., 2000), ruminal NDF digestion was lower (21%, P < 0.05) for Sudangrass hay than for rice straw supplemented diets.
As with previous studies (Lopez-Soto et al., 2000; Torrentera et al., 2000), maceration of rice straw increased total tract digestion of OM (2.3%, P < 0.10), NDF (21.1%, P < 0.01), and N (3.7%, P < 0.05) compared with grinding alone. Total tract digestion of OM was greater (P < 0.05) for Sudangrass vs. rice straw-supplemented diets, due largely to the lower total tract digestion of the ground rice straw-supplemented diets. In good agreement with the growth performance study (trial 1; Table 2), total tract digestion of OM, NDF, starch, and N for the Sudangrass-supplemented diets corresponded closely with that of the macerated rice straw supplemented diets, averaging 101.5, 94.7, 100.3, and 102.9%, respectively.
In summary, maceration increases the feeding value of rice straw to a level similar to that of good-quality (harvested at the flag stage of maturity) Sudangrass hay. This enhancement is attributable to increased OM and NDF digestion. The effects of surfactant supplementation on growth performance and digestion are not appreciable.
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Footnotes
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1 Partially supported by the California Rice Research Board, and Fundación Produce de B.C., México. 
2 Corresponding author: razinn{at}ucdavis.edu
Received for publication July 21, 2006.
Accepted for publication April 30, 2007.
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LITERATURE CITED
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Abstract
INTRODUCTION
