J. Anim Sci. 2008. 86:3497-3503. doi:10.2527/jas.2008-0885
© 2008 American Society of Animal Science
OPEN ACCESS ARTICLE
Manipulation of rumen ecology by dietary lemongrass (Cymbopogon citratus Stapf.) powder supplementation1
M. Wanapat*,2,
A. Cherdthong*,
P. Pakdee* and
S. Wanapat
* Tropical Feed Resources Research and Development Center (TROFREC), Faculty of Agriculture, Khon Kaen University, Khon Kaen, 40002, Thailand; and
Department of Plant Science and Natural Resources, Faculty of Agriculture, Khon Kaen University, Khon Kaen, 40002, Thailand
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Abstract
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This experiment was conducted to investigate the effect of lemongrass [Cymbopogon citratus (DC.) Stapf.] powder (LGP) on rumen ecology, rumen microorganisms, and digestibility of nutrients. Four ruminally fistulated crossbred (Brahman native) beef cattle were randomly assigned according to a 4 x 4 Latin square design. The dietary treatments were LGP supplementation at 0, 100, 200, and 300 g/d with urea-treated rice straw (5%) fed to allow ad libitum intake. Digestibilities of DM, ether extract, and NDF were significantly different among treatments and were greatest at 100 g/d of supplementation. However, digestibility of CP was decreased with LGP supplementation (P < 0.05), whereas ruminal NH3-N and plasma urea N were decreased with incremental additions of LGP (P < 0.05). Ruminal VFA concentrations were similar among supplementation concentrations (P > 0.05). Total viable bacteria, amylolytic bacteria, and cellulolytic bacteria were significantly different among treatments and were greatest at 100 g/d of supplementation (4.7 x 109, 1.7 x 107, and 2.0 x 109 cfu/mL, respectively). Protozoal populations were significantly decreased by LGP supplementation. In addition, efficiency of rumen microbial N synthesis based on OM truly digested in the rumen was enriched by LGP supplementation, especially at 100 g/d (34.2 g of N/kg of OM truly digested in the rumen). Based on this study, it could be concluded that supplementation of LGP at 100 g/d improved digestibilities of nutrients, rumen microbial population, and microbial protein synthesis efficiency, thus improving rumen ecology in beef cattle.
Key Words: lemongrass powder • manipulation • microbial protein synthesis • rumen ecology • rumen fermentation • supplementation
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INTRODUCTION
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In the last few years, there has been an increasing interest in exploiting natural products as feed additives to solve problems in animal nutrition and livestock production (Wallace et al., 2002
). Herbs have been evaluated for their ability to alter ruminal fermentation and improve nutrient utilization in ruminants (Wang et al., 2000; Greathead, 2003). In addition, supplementation of herbs to ruminants could possibly decrease stress to the animals (Hosoda et al., 2006). When dried herbs were fed to lactating cows, the characteristic smell of cow milk was suppressed due to the transmission of components peculiar to such herbs into the milk of cows (Ando et al., 2001).
Lemongrass [Cymbopogon citratus (DC.) Stapf.] is one herb of interest, and it is widely used in tropical countries, especially in Southeast Asia in human foods. Citral is a key component of the essential oils extracted from lemongrass that is necessary for vitamin A synthesis. More recently, essential oils have attracted attention for their potential as alternatives to feed antibiotics and growth promoters in livestock (Wallace, 2004). Essential oils from a variety of sources have been shown to alter growth and metabolism of several types of bacteria, including rumen bacteria. However, many of the investigations conducted to date on essential oils have been laboratory-based (i.e., in vitro incubations) and of a short-term nature (McIntosh et al., 2003; Newbold et al., 2004; Castillejos et al., 2005; Benchaar et al., 2007). Effects of lemongrass on antibacterial (Valero and Salmeroìn, 2003), antioxidant (Cheel et al., 2005), antinociceptive (Viana et al., 2000), and antihyper-NH3-producing ruminal bacterial (McIntosh et al., 2003) activities have been studied. In addition, Hosoda et al. (2006) investigated the effects of the supplementation in the diet of Holstein steers with 3 herbs, especially lemongrass leaf, on blood metabolites and rumen fermentation, but the effects on rumen microbes have not yet been clearly investigated. The objective of this experiment was to study effects of dried lemongrass [C. citratus (DC.) Stapf.] powder (LGP) supplementation on rumen ecology, rumen microorganisms, microbial protein synthesis, and digestibility of nutrients in beef cattle.
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MATERIALS AND METHODS
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All procedures involving animals were approved by the Ethical Principles for the Use of Animals for Scientific Purposes of the National Research Council of Thailand.
Animals, Treatments, and Experimental Design
Four ruminally fistulated crossbred (Brahman x native) beef cattle steers with initial BW of 200 ± 50 kg were randomly assigned according to a 4 x 4 Latin square design to investigate the effect of LGP with urea-treated rice straw (UTS; 5% urea, after method of Wanapat, 1999) as a roughage source on rumen ecology, rumen microorganisms, microbial protein synthesis, and digestibility of nutrients. The dietary treatments were as follows: supplementation with LGP at 0, 100, 200, and 300 g/d. Concentrates containing 13% CP and 75% TDN were offered at 0.5% of BW/d, and UTS was provided for ad libitum intake. The LGP was prepared from whole fresh lemongrass (C. citratus (DC.) Stapf.; 10 to 12 mo], chopped and dried at 60°C for 2 d, ground to pass a 1-mm screen using a Cyclotech Mill (Tecator, Höganäs, Sweden), and then mixed in concentrate. All animals were kept in individual pens, and water was available for ad libitum consumption. The experiment was conducted for 4 periods, and each period lasted 21 d. During the first 14 d, all animals were fed respective diets for ad libitum intake, whereas during the last 7 d, the animals were moved to metabolism crates for total collection during which time they were restricted to 90% of the previous voluntary feed intake of straw and supplemented with concentrate at 0.5% of BW daily to ensure total feed intake. Chemical composition of concentrate, LGP, and UTS are shown in Table 1.
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Table 1. Ingredients and chemical compositions of concentrate, urea-treated rice straw (UTS), and lemongrass powder (LGP)
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Data Collection and Sampling Procedures
Feeds were sampled and fecal samples were collected from the total collection of each individual steer on each treatment during the last 7 d of each period at morning and afternoon feeding. Composited samples were dried at 60°C, ground (1-mm screen using Cyclotech Mill, Tecator), and then analyzed for DM, ether extract, ash, CP content (AOAC, 1985), and NDF and ADF (Goering and Van Soest, 1970). At the end of each period, rumen fluid and jugular blood samples were collected at 0, 2, 4, and 6 h after feeding. At the time of sampling, 10 mL of blood was drawn into each of the tubes. Each tube contained 12 mg of EDTA. Approximately 200 mL of rumen fluid was taken at each time from the middle part of the rumen using a 60-mL hand syringe. Temperature and pH of rumen fluid were measured using a portable pH and temperature meter (Hanna Instruments HI 8424 microcomputer, Singapore). Rumen fluid samples were then filtered through 4 layers of cheesecloth. Samples were divided into 3 portions; 1 portion was used for NH3-N analysis with 5 mL of 1 M H2SO4 added to 50 mL of rumen fluid. The mixture was centrifuged at 16,000 x g for 15 min, and the supernatant was stored at –20°C before NH3-N analysis using the micro-Kjeldahl methods (AOAC, 1985) and VFA analysis using HPLC (Samuel et al., 1997). A second portion was fixed with 10% formalin solution in sterilized 0.9% saline solution. The total direct count of bacteria, protozoa, and fungal zoospores were made by the methods of Galyean (1989) based on the use of a hemocytometer (Boeco, Hamburg, Germany). Another portion was cultured for groups of bacteria using a roll-tube technique (Hungate, 1969) for identifying bacteria groups (cellulolytic, proteolytic, amylolytic, and total viable count bacteria).
A blood sample (about 10 mL) was collected from a jugular vein (at the same time as rumen fluid sampling) into tubes containing 12 mg of EDTA, and plasma was separated by centrifugation at 500 x g for 10 min and stored at –20°C until analysis of plasma urea N according to the method of Crocker (1967). Urine samples were analyzed for total N (IAEA, 1997), and allantoin in urine was determined by HPLC as described by Chen and Gomes (1995). The amount of microbial purines absorbed was calculated from purine derivative excretion based on the relationship derived by Chen and Gomes (1995).
Statistical Analysis
Statistical analyses were performed using the GLM procedure (SAS Inst. Inc., Cary, NC). Data were analyzed using the model Yijk = µ + Mi + Aj + Pk + 
ijk, where Yijk = observation from animal j, receiving diet i, in period k; µ = the overall of mean; Mi = the mean effect of LGP concentration (i = 1, 2, 3, 4); Aj = the effect of animal (j = 1, 2, 3, 4); Pk = the effect of period (k = 1, 2, 3, 4); and ijk = the residual error. Treatment means were statistically compared by the new multiple range test of Duncan (Steel and Torrie, 1980).
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RESULTS AND DISCUSSION
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Chemical Composition of Feeds
The chemical compositions of concentrate, roughage, and LGP are presented in Table 1
. Concentrate diets contained 13.1% CP and 75% TDN on a DM basis. The concentrate contained 70% cassava chip and, therefore, low NDF. The UTS contained 58.4% DM and 8.4% CP on a DM basis and was similar to that reported by Wanapat (2000). Furthermore, ether extract content of LGP was 1.57% on a DM basis.
Effect on Feed Intake and Digestibility
The effects of LGP concentration on feed intake of beef cattle are presented in Table 2. Total DMI was not significantly affected (P < 0.05) by LGP supplementation concentration. These results were similar to previous work by Hosoda et al. (2006), which supplemented lemongrass leaf to dairy steers. Similarly, Benchaar et al. (2007) observed no change in DMI when dairy cows were fed a mixture of essential oil compounds at 750 mg/d. The CP digestibility was significantly different (P < 0.05) and was greatest in control group (77.9%). Apparent digestibilities of DM, ether extract, and NDF were significantly different (P < 0.05) among treatments with the greatest values for beef cattle fed LGP at 100 g/d (Table 2). Ando et al. (2003) reported that supplementation of essential oil (peppermint source) could increase nutrient digestibilities significantly. However, in our study, slightly less nutrient digestibilities were found when increasing concentration of LGP. This result showed that supplementation of LGP at 100 g/d was most suitable.
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Table 2. Feed intakes and apparent digestibility of beef cattle fed different concentrations of lemongrass powder (LGP)
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Characteristics of Ruminal Fermentation and Blood Metabolites in Cattle
Measured rumen variables included temperature, pH, NH3-N, and VFA. Plasma urea N was also determined to investigate the relationship with rumen NH3-N and protein utilization. The pattern of ruminal fermentation and overall means are presented in Table 3. Rumen fluid pH and temperature were not altered among treatments, and the values were stable at pH 6.4 to 6.5 and temperature of 38.7 to 39.6°C, and the pH was within the range considered optimal for microbial digestion of fiber and protein [6.0 to 7.0; Hoover (1986)]. Supplementation with LGP decreased (P < 0.05) ruminal NH3-N and plasma urea N. Similarly, supplementation of essential oil from peppermint herb or high essential oil at 3,000 mg/L significantly decreased NH3-N concentration (Ando et al., 2003; Busquet et al., 2006). Ruminal NH3-N is a major source of N for microbial protein synthesis (Bryant, 1974; Erdman et al., 1986). Ruminal NH3-N concentrations were 15.7 to 19.1 mg/dL and were close to those previously reported by Church and Santos (1981) and Wanapat and Pimpa (1999).
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Table 3. Rumen temperature, NH3-N, plasma urea N, and VFA concentration as affected by feeding different concentrations of lemongrass powder (LGP) in beef cattle
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Decreasing rumen NH3-N concentrations also resulted in decreasing concentrations of plasma urea N. Concentrations of plasma urea N are highly correlated to the concentration of NH3 production in the rumen (Preston et al., 1965; Lewis, 1975). There is considerable evidence that essential oils may affect rumen microbial fermentation (McIntosh et al., 2000; McEwan et al., 2002). Wallace et al. (2002) suggested that the main mechanism of action of essential oils was the inhibition of bacterial attachment to feed particles, and subsequently, NH3 production (deamination) from AA was decreased. This effect was mediated by the effects of essential oils particularly on hyper-NH3-producing bacteria. McEwan et al. (2002) reported that addition of essential oils resulted in a reduction in the number and diversity of hyper-NH3-producing bacteria, resulting in decreased rate of NH3 production from AA. Reduction in protein degradation suggests that at least part of the effects of essential oils can be attributed to decreased proteolysis (Molero et al., 2004). In contrast, Hosoda et al. (2006) reported that urea N concentrations were increased significantly (5.0 to 5.4 mg/dL) by lemongrass leaf supplementation.
The production of total VFA, acetate acid, propionic acid, and butyric acid proportions, acetic:propionic ratio, and acetic plus butyric:propionic ratio are shown in Table 3. There were no significant differences (P > 0.05) in VFA concentrations. Total VFA concentrations in all treatments ranged from 105.6 to 114.1 mM and were similar to those reported by France and Siddons (1993). Moreover, LGP supplementation had no effects on other VFA variables. These results were in agreement with Hosoda et al. (2006), who reported that supplementation of lemongrass leaf at 5% of the diet did not alter VFA concentration in the rumen in dairy steers.
Rumen Microorganism Population
Table 4 presents the rumen microorganism population data. Ruminal microbial counts and variable bacteria were significantly different (P < 0.01) among treatments; bacteria, zoospores, total variable bacteria, amylolytic bacteria, and cellulolytic bacteria were greatest when LGP was supplemented at 100 g/d and decreased when supplemented at 200 and 300 g/d, which correlates with the greatest DM and NDF digestibility when LGP was supplemented at 100 g/d. These results showed effects of essential oil from LGP, which changed diversity of rumen microorganism. Many essential oils have dose-dependent effects on bacteria, protozoa, and fungi (Greathead, 2003). In general, gram-positive bacteria appeared to be more susceptible to inhibition by plant essential oil compounds than did gram-negative bacteria (Davidson and Naidu, 2000). This effect has been related to the presence of an outer membrane on gram-negative organisms, which endows them with a hydrophilic surface that acts as a strong impermeability barrier (Nikaido, 1994). The activity of LGP affects electron transport, ion gradients, protein translocation, phosphorylation steps, and other enzyme-dependent reactions, causing the affected bacteria to lose chemiosmotic control (Ultee et al., 1999). In our study, supplementation of LGP at 200 and 300 g/d decreased bacterial populations relative to 100 g/d of LGP, possibly due to decreases of gram-positive bacteria. Moreover, proteolytic bacterial populations were decreased with increasing concentration of LGP (1.4 to 0.7 x 108 cfu/mL). Similarly, Wallace et al. (2002) reported that hyper-NH3-producing bacteria as proteolytic bacteria group were the most sensitive of rumen bacteria to essential oil in pure culture. Ruminobacter amylophilus and Prevotella spp. as hyper-NH3-producing bacteria have a great capability to generate NH3 from AA (Russell et al., 1991) and may be key organisms in mediating these effects. In addition, R. amylophilus was inhibited by essential oil concentrations of at least 200 mg/L (McIntosh et al., 2003). Protozoal populations tended to be decreased with increasing concentration of LGP in the diets. In agreement with these observations, Ando et al. (2003) reported that supplementation of essential oil from peppermint decreased protozoal populations significantly (P < 0.05).
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Table 4. Effect of concentration of lemongrass powder (LGP) supplementation in concentrate on ruminal microbes and viable bacteria in beef cattle
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N Balance and Efficiency of Microbial Protein Synthesis
As shown in Table 5, N intake, excretion of N, and N absorption were not affected by treatments. Nitrogen retention was not affected by 100 g/d of LGP but was decreased when 200 or 300 g/d was supplemented. With regards to N utilization, Owens and Zinn (1988) stated that N excretion and N retention should reflect differences in N metabolism, because N retention was the most important index of the protein nutrition status of ruminants.
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Table 5. Effect of concentration of lemongrass powder (LGP) supplementation in concentrate on N balance, excretion of urinary purine derivatives (PD), and microbial N supply in cattle
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Supplementation at 100 g/d of LGP resulted in the greatest allantoin absorption. However, efficiency of microbial N synthesis was not affected by 100 g/d of LGP, suggesting that any increase in microbial N synthesis was related to increases in diet digestion. Microbial N supplies from the rumen are summarized in Table 5. The microbial N supply as calculated from purine derivative excretion using the equation of Chen and Gomes (1995) ranged from 43.1 to 57.5 g of N/d. The efficiency of rumen microbial protein synthesis was decreased as concentration of LGP supplementation increased above 100 g/d. Based on the results of this experiment, supplementation of LGP at 100 g/d resulted in improved DM digestibility, rumen microbial population, and microbial protein supply.
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Footnotes
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1 We express our sincere thanks to the Tropical Feed Resources Research and Development Center (TROFREC), Khon Kaen University, Thailand Research Fund (TRF) through the Royal Golden Jubilee PhD Program for providing financial support for the research and use of the research facilities. 
2 Corresponding author: metha{at}kku.ac.th
Received for publication January 19, 2008.
Accepted for publication August 8, 2008.
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LITERATURE CITED
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|---|
Ando, S., T. Nishida, M. Ishida, K. Hosoda, and E. Bayaru. 2003. Effect of peppermint feeding on the digestibility, ruminal fermentation and protozoa. Livest. Prod. Sci. 82:245–248.
Ando, S., T. Nishida, M. Ishida, Y. Kochi, K. Kami, and S. Se. 2001. Transmission of herb essential oil to milk and change of milk flavor by feeding dried herbs to lactating cows. Nippon Shokuhin Kagaku Kogaku Kaishi 48:142–145.
AOAC. 1985. Official Methods of Analysis. Assoc. Offic. Anal. Chem., Washington, DC.
ARC. 1990. The Nutrient Requirements of Ruminant Livestock. Suppl. 1. Commonwealth Agricultural Bureaux, Slough, Farnham Royal, UK.
Benchaar, C., H. V. Petit, R. Berthiaume, D. R. Ouellet, J. Chiquette, and P. Y. Chouinard. 2007. Effects of essential oils on digestion, ruminal fermentation, rumen microbial populations, milk production, and milk composition in dairy cows fed alfalfa silage or corn silage. J. Dairy Sci. 90:886–897.[Abstract/Free Full Text]
Bryant, M. P. 1974. Nutritional features and ecology of predominant anaerobic bacteria of the intestinal tract. Am. J. Clin. Nutr. 27:1313–1319.[Medline]
Busquet, M., S. Calsamiglia, A. Ferret, and C. Kamel. 2006. Plant extracts affect in vitro rumen microbial fermentation. J. Dairy Sci. 89:761–771.[Abstract/Free Full Text]
Castillejos, L., S. Calsamiglia, A. Ferret, and R. Losa. 2005. Effects of a specific blend of essential oil compounds and the type of diet on rumen microbial fermentation and nutrient flow from a continuous culture system. Anim. Feed Sci. Technol. 119:29–41.[CrossRef]
Cheel, J., C. Theoduloz, J. Rodriìguez, and G. Schmeda-Hirschmann. 2005. Free radical scavengers and antioxidants from lemongrass (Cymbopogon citratus (DC.) Stapf.). J. Agric. Food Chem. 53:2511–2517.[CrossRef][Medline]
Chen, X. B., and M. J. Gomes. 1995. Estimation of microbial protein supply to sheep and cattle based on urinary excretion of purine derivative—An overview of the technique details. Occasional publication 1992. International Feed Resources Unit, Rowett Research Institute, Aberdeen, UK.
Chen, X. B., D. J. Kyle, and E. R. Ørskov. 1993. Measurement of allantoin in urine and plasma by high-performance liquid chromatography with precolumn derivatization. J. Chromatogr. 617:241–247.[Medline]
Church, D. C., and A. Santos. 1981. Effect of graded levels of soybean meal and of a nonprotein nitrogen-molasses supplement on consumption and digestibility of wheat straw. J. Anim. Sci. 53:1609–1615.[Abstract/Free Full Text]
Crocker, C. L. 1967. Rapid determination of urea nitrogen in serum or plasma without deproteinization. Am. J. Med. Technol. 33:361–365.[Medline]
Davidson, P. M., and A. S. Naidu. 2000. Phyto-phenols. Pages 265–293 in Natural Food Antimicrobial Systems. A. S. Naidu, ed. CRC Press, Boca Raton, FL.
Erdman, R. A., G. H. Proctor, and J. H. Vandersall. 1986. Effect of rumen ammonia concentration on in situ rate and extent of digestion of feedstuffs. J. Dairy Sci. 69:2312–2320.[Abstract/Free Full Text]
France, J., and R. C. Siddons. 1993. Volatile fatty acid production. Pages 107–122 in Quantitative Aspects of Ruminant Digestion and Metabolism. J. M. Forbes and J. France, ed. CAB International, Willingford, UK.
Galyean, M. 1989. Pages 107–122 in Laboratory Procedure in Animal Nutrition Research. Department of Animal and Life Science, New Mexico State University, Las Cruces.
Goering, H. K., and P. J. Van Soest. 1970. Forage Fiber Analyses (Apparatus, Reagents, Procedures, and Some Applications). Agriculture Handbook No. 379. ARS-USDA, Washington, DC.
Greathead, H. 2003. Plant and plant extracts for improving animal productivity. Proc. Nutr. Soc. 62:279–290.[CrossRef][Medline]
Hoover, W. H. 1986. Chemical factors involved in ruminal fiber digestion. J. Dairy Sci. 69:2755–2766.[Abstract/Free Full Text]
Hosoda, K., K. Kuramoto, B. Eruden, T. Nishida, and S. Shioya. 2006. The effects of three herbs as feed supplements on blood metabolites, hormones, antioxidant activity, IgG concentration, and ruminal fermentation in Holstein steers. Asian-australas. J. Anim. Sci. 19:35–41.
Hungate, R. E. 1969. A roll tube method for cultivation of strict anaerobes. Page 117–131 in Methods in Microbiology. J. R. Norris and D. W. Ribbons, ed. Academic Press, New York, NY.
IAEA. 1997. Determination of purine derivative in urine. Page 31–37 in Estimation of the Rumen Microbial Protein Production from Purine Derivatives in Rumen. Animal Production and Health Section, Vienna, Austria.
Lewis, D. 1975. Blood urea concentration in relation to protein utilization in the ruminant. J. Agric. Sci. (Camb.) 48:438–446.
McEwan, N. R., R. C. Graham, R. J. Wallace, R. Losa, P. Williams, and C. J. Newbold. 2002. Effect of essential oils on ammonia production by rumen microbes. Reprod. Nutr. Dev. 42(Suppl. 1):S65. (Abstr.)
McIntosh, F. M., C. J. Newbold, R. Losa, P. Williams, and R. J. Wallace. 2000. Effects of essential oils on rumen fermentation. Reprod. Nutr. Dev. 40:221–222. (Abstr.)
McIntosh, F. M., P. Williams, R. Losa, R. J. Wallace, D. A. Beever, and C. J. Newbold. 2003. Effect of essential oil on ruminal metabolism and their protein metabolism. Appl. Environ. Microbiol. 69:5011–5014.[Abstract/Free Full Text]
Molero, R., M. Ibars, S. Calsamiglia, A. Ferret, and R. Losa. 2004. Effects of a specific blend of essential oil compounds on dry matter and crude protein degradability in heifers fed diets with different forage to concentrate ratios. Anim. Feed Sci. Technol. 114:91–104.[CrossRef]
Newbold, C. J., F. M. McIntosh, P. Williams, R. Losa, and R. J. Wallace. 2004. Effects of a specific blend of essential oil compounds on rumen fermentation. Anim. Feed Sci. Technol. 114:105–112.[CrossRef]
Nikaido, H. 1994. Prevention of drug access to bacterial targets: Permeability barriers and active efflux. Science 264:382–388.[Abstract/Free Full Text]
Owens, F. N., and R. Zinn. 1988. Protein metabolism of ruminant animals. Pages 227–249 in The Ruminant Animal Digestive Physiology and Nutrition. D. C. Church, ed. Waveland Press Inc., Prospect Heights, IL.
Preston, R. L., D. D. Schnakanberg, and W. H. Pfander. 1965. Protein utilization in ruminants. I. Blood urea nitrogen as affected by protein intake. J. Nutr. 86:281–287.[Abstract/Free Full Text]
Russell, J. B., R. Onodera, and T. Hino. 1991. Ruminal protein fermentation: New perspectives on previous contradictions. Pages 681–697 in Physiological Aspects of Digestion and Metabolism in Ruminants: Proceedings of the Seventh International Symposium on Ruminant Physiology. T. Tsuda, Y. Sasaki, and R. Kawashima, ed. Academic Press, London, UK.
Samuel, M., S. Sagathewan, J. Thomas, and G. Mathen. 1997. An HPLC method for estimation of volatile fatty acids of ruminal fluid. Indian J. Anim. Sci. 69:805–807.
Steel, R. G. D., and J. H. Torrie. 1980. Principles and Procedures of Statistics. McGraw Hill Book Co., New York, NY.
Ultee, A., E. P. W. Kets, and E. J. Smid. 1999. Mechanism of action of carvacrol on the food-borne pathogen Bacillus cereus. Appl. Environ. Microbiol. 65:4606–4610.[Abstract/Free Full Text]
Valero, M., and M. C. Salmeroìn. 2003. Antibacterial activity of 11 essential oils against Bacillus cereus in tyndallized carrot broth. Int. J. Food Microbiol. 85:73–81.[CrossRef][Medline]
Viana, G. S. B., T. G. Vale, R. S. N. Pinho, and F. J. A. Matos. 2000. Antinociceptive effect of the essential oil from Cymbopogon citratus in mice. J. Ethnopharmacol. 70:323–327.[Medline]
Wallace, R. J. 2004. Antimicrobial properties of plant secondary metabolites. Proc. Nutr. Soc. 63:621–629.[CrossRef][Medline]
Wallace, R. J., N. R. McEwan, F. M. McIntosh, B. Teferedegne, and C. J. Newbold. 2002. Natural products as manipulators of rumen fermentation. Asian-australas. J. Anim. Sci. 15:10–21.
Wanapat, M. 1999. The use of local feed resources for livestock production in Thailand. Pages 59–72 in Feeding of Ruminant in Tropical Based on Local Feed Resources. M. Wanapat, ed. Khon Kaen Publishing Co. Ltd., Khon Kaen, Thailand.
Wanapat, M. 2000. Rumen manipulation to increase the efficient use of local feed resources and productivity of ruminants in the tropics. Asian-australas. J. Anim. Sci. 13(Suppl.):59–67.
Wanapat, M., and O. Pimpa. 1999. Effect of ruminal NH3-N levels on ruminal fermentation, purine derivatives, digestibility and rice straw intake in swamp buffaloes. Asian-australas. J. Anim. Sci. 12:904–907.
Wang, Y., T. A. McAllister, L. J. Yanke, and P. R. Cheeke. 2000. Effect of steroidal saponin from Yucca schidigera extract on ruminal microbes. J. Appl. Microbiol. 88:887–896.[CrossRef][Medline]
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Abstract
INTRODUCTION
