versão On-line ISSN 1870-0462
Trop. subtrop. agroecosyt vol.14 no.3 Mérida Set./Dez. 2011
Effects of exogenous enzymes on nutrients digestibility and growth performance in sheep and goats
Efecto de las enzimas exógenas sobre la digestibilidad de nutrientes y el comportamiento productivo en ovinos y caprinos
A. Z. M. Salema,b*, M. El-Adawyb, H. Gadoc, L.M. Camachod, M. González-Ronquilloa, H. Alsersyb, B. Borhamib
ª Departamento de Nutrición Animal, Facultad de Medicina Veterinaria y Zootecnia,Universidad Autónoma del Estado de México, México
b Department of Animal Production, Faculty of Agriculture (El-Shatby), Alexandria University, Alexandria, Egypt
c Department of Animal Productions, Faculty of Agriculture, Ain Shams University, Cairo, Egypt
d Facultad de Medicina Veterinaria y Zootecnia, Universidad Autónoma de Guerrero, E-mail address: firstname.lastname@example.org
* Corresponding author
Submitted February 02, 2011
Accepted June 06, 2011
Revised received June 07, 2011
Six crossbred sheep (32.00±0.603 kg body weight (BW)) and 6 Baladi goats (18.00±0.703 kg BW) were used in 2 x 2 factorial design to evaluate the effect of exogenous enzymes of ZADO® (i.e., ENZ) and on nutrients digestibility and growth performance. Animals were fed on wheat straw ad libitum and restricted amount of commercial concentrate with (+ENZ) or without (-ENZ) 10 g/animal/day of ZADO® to cover 120% of their maintenance requirements. Nutrients digestibilities were increased (P<0.01) in +ENZ groups and it was better in goats than sheep. Goats had the lowest total dry matter intake (DMI) that associated with an increased in digestibility and average daily gain (ADG) more than sheep. Feed efficiency, metabolizable protein intake and net energy for growth occurred sheep and goats diets of +ENZ and the highest (P<0.01) values were observed in goats received +ENZ diet. These results suggested a good performance of goats than sheep received ENZ under the critical conditions of shortage feedstuffs in Egypt.
Key words: enzymes; sheep; goats; digestibility; average daily gain.
Seis corderos encastados (32±0.603 kg de peso vivo (PV)) y 6 cabras Baladi (18±0.703 kg de PV) fueron usados en un experimento factorial 2x2 para evaluar el efecto de las enzimas exógenas de ZADO® (ENZ), sobre la digestibilidad de nutrientes y el comportamiento productivo. Los animales se alimentaron con paja de trigo ad libitum y cantidades restringidas de un concentrado comercial con (+ENZ) y sin (-ENZ) 10 g/animal/día de ZADO® para cubrir el 120% de las necesidades de mantenimiento. La digestibilidad de los nutrientes se incrementó (P<0.01) en los grupos de +ENZ y la respuesta fue mejor en las cabras que en los borregos. Las cabras presentaron el más bajo consumo de materia seca (CMS) que estuvo asociado con un incremento en la digestibilidad y en la ganancia diaria de peso (GDP), comparadas con los borregos. La eficiencia alimenticia, el consumo de proteína metabolizable y de energía neta para el crecimiento, presentaron los valores más altos (P<0.01) en las cabras recibiendo las dietas de +ENZ. Estos resultados sugieren un buen comportamiento de las cabras recibiendo enzimas (+ENZ) comparadas con los borregos, bajo las condiciones críticas por los cortos periodos de disponibilidad de alimento en Egipto.
Palabras clave: Enzimas; borregos; cabras; digestibilidad; ganancia diaria de peso.
Twenty-two million tons of plant by-products or crop residues are produced annually in Egypt (United States Department of Agriculture, 2002). These by-products are generate plentiful, inexpensive and available year round, but are not efficiently utilized. Indeed more than eight million tons, which could potentially be used as animal feed, is wasted or burnt. Some of these residues, especially wheat and rice straws, are used as fuels, or as bulky residues on walkways. Use of these by-products in animal feeds could decrease the pollution of atmosphere. Only about four million tons of cereal straws, mainly wheat straw, are available at present as feeds for livestock (Hathout, 1984). These lignocellulotic by-products are widely spread. Such residues usually contain high amounts of fibrous and low protein content. They are characterized by a poor nutritive value that affects negatively the feed intake and digestibility. Offering the crop residues in large amount may allow animals, particularly sheep and goats.
It is well established that the nutritive value could be improved substantially by different methods of chemical, physical and for microbiological treatments. Microbial treatment probably conducted by administration of microbial cells, microbial extracts or microbial enzymes such as cellulases. However, microbial treatments improve the nutritive value of these lignocellulosic by -products, as well as palatability, feed intake, and animal performance (Colombatto et al, 2007; Di Francia et al, 2007; Gado et al, 2009 and 2011). A wide range of fibrolytic enzymes are currently commercially available for this purpose to be used with ruminants (Beauchemin et al, 2000; Colombatto et al, 2007; Gado et al, 2009 and 2011). Furthermore, exogenous enzymes work in synergy with rumen microbial enzymes, which increases their hydrolytic potential within the rumen (Eun et al, 2007; Gado et al, 2009 and 2011). To date, it has not been possible to predict the potential of exogenous feed enzymes to increase cell wall degradation in the rumen based on their biochemical characterization alone (Colombatto et al., 2003). Nsereko et al. (2000) reported that enzyme products containing xylanases and esterases had stimulatory effects on fiber degradation of alfalfa hay in vitro, whereas Colombatto et al. (2003) indicated that some xylanases and proteases improved in vitro degradation of alfalfa hay.
The objective of the current study was to evaluate the effect of exogenous enzymes of a commercial product of enzymes on growth performance and digestibility in sheep and goats fed on wheat straw ad libitum as well as a restricted amount of commercial concentrate to cover 120% of their maintenance requirements.
MATERIALS AND METHODS
Treatment of what straw with ZADO®
Two hundred grams of chopped what straw (1-3 cm) were treated with ZADO® enzymes (i.e., ENZ) with the proportion of one liters of ENZ per ton) in a plastic bag (60 x 60 cm) according to the procedures of Gado (1997). ZADO® is a patented product manufactured by the Academy of Scientific Research and Technology, Egypt, and contains a mix of anaerobic bacteria and their enzymes of cellulases (7.1 unit/g), xylanases (2.3 unit/g), alpha amylase (61.5 unit/g), protease (29.2 unit/g) in a powder form obtained through an anaerobic fermentation process (Gado, 1997). Enzymes solution was mixed with water at the rate of 2:1 of the amount of what straw, 4% w/w molasses, 3% urea, 0.3% w/w formic acid and 0.3% w/w acetic acid, before applied on the straw. The bag was sealed and kept under the room temperature for 30 days before used in the in vitro study.
The two stage technique of Tilley and Terry (1963) was used to study the effect of the biological treatment of the tested roughages on in vitro dry matter digestibility. Rumen liquor was obtained from two fistulated crossbred rams kept on high quality hay. The fluid was strained through four layers of cheese cloth. The McDougal buffer was prepared, then it was added mixed with rumen liquor at the ratio of (2 buffer: 1 rumen liquor).This mixture was saturated with CO2 and warmed at 39°C in a water bath. A volume of 250 ml of the mixture was added to each polyethylene tube containing 0.5g air dried sample (in triplicate), then saturated with CO2 and tightly closed with rubber stopper fitted with outlet valve and incubated at 39°C in a water bath for 48 hours. Tubes were well shaken twice daily during incubation period. At the end of the incubation period, 6 ml of HC1 (20%) was added gradually to each tube followed by 2 ml of 5% pepsin. Tubes were closed and incubated in the water bath at 39°C for another 24 hours. Samples were filtered using a dry weighed Whatman filter paper (No. 54) and the residue was washed with boiled water; the filter paper and residue was dried at 100°C overnight and weighed after cooling in desiccators.
Animals, management and growth performance trial
Six crossbred sheep (32.00±0.603 kg body weight (BW)) and 6 Baladi goats (18.00±0.703 kg BW) were used to evaluate effects of ENZ on feed intake, apparent digestibility and animal performance. The growth study was lasted for 65 days followed by one week for a digestibility trail. Sheep and goats were randomly divided into two groups of three to create two experimental groups per each species. Animals were fed on wheat straw ad libitum and restricted amount of commercial concentrate (Table 1) were offered with or without 10 g/animal/day of ENZ to cover 120% of their maintenance requirements. Animals were individually fed and had free access to fresh water. Changes in body weight were recorded each 15 days during the experimental period. Wheat straw offered and orts were measured daily during the experimental periods.
At the end of the growth trial of the 65 day experiment, all lambs of each treatment were used in a digestibility trial. Feed offer and feed refusals and total feces output were daily recorded for one week to determine the effect of ENZ and animal species on the apparent digestibility. Representative samples of straw, concentrate, refusals and faeces were collected daily and dried at 55°C to determine daily intake of DM for each animal. Other sub-samples of each material were bulked, mixed, and ground through a lmm sieve for further laboratory analysis.
Ground samples of feeds, refusals and feces were analyzed for dry matter (DM) by drying samples at 105°C for 24 h in a forced air oven. Ash was determined after igniting samples in a muffle furnace at 550°C for 4 h. Crude protein (CP) was determined by a Kjeldahl method (AOAC, 1990; ID 954.01). Ether extract (EE) was determined by Soxhlet method (AOAC, 1990; ID 920.39). Neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin were determined. NDF was assayed without the use of an alpha amylase but with use of sodium sulfite. Both NDF and ADF are expressed without residual ash.
Metabolizable energy intake (kJ/kg BW0.75) was estimated according to Luo et al. (2004) as:
Metabolizable energy intake = 533 + (43.2 x ADG (g/kgBW0.75))
where: ADG is the average daily gain (g/kg BW0.75) of sheep and goats during the 65 days of the growth performance experiment.
Net energy required for growth (Mcal/kg BW0.75/d) was estimated according to NRC, (1985) as:
Net energy required for growth = 644 - 2.61 x MBW
where: MBW is the metabolic body weight (MBW = kg BW0.75)
A 2 x 2 factorial experimental design (2 animal species (sheep and goats) x2 treatments (with or without ENZ)) were used to analyze the data of body weight changes, feed intake, feed efficiency, Metabolizable energy intake, and net energy required for gain during the growth trial. Also the nutrient components of total feed intake, straw consumption and digestibility during the digestibility trial. The 'PROC GLM' of SAS (1999), with methods of Steel and Tome (1980), was used to determine differences due to animal species and ENZ. In the case of significant interactions (i.e., P<0.05), Duncan's multiple-range test (Duncan, 1955) was used to separate means within animal species.
Addition of enzymes (i.e., ENZ) improved (P<0.05) in vitro dry matter digestibility during the first 4 h and from 24 to 48 h after incubations, while decried at 6h (Table 2).
Total dry matter intake (i.e., DMI) was increased from 76 to 84 g/kg BW0.75 in goats, but it was not affected in sheep. Digestibility of DM was increased (P<0.01) by 5 and 11%, in sheep and goats respectively by addition of ENZ, while NDF digestibility was increased (P<0.01) by 7 and 9%, respectively. OM and CP digestibility were increased (P<0.01) also in both animal species with ENZ diets. However, the nutritive value was improved in both species and it appears to be higher (P<0.05) in goats than in sheep (Table 3).
In the growth performance trial, DMI was increased (P<0.05) by addition the daily addition of ENZ to sheep and goats diets during the 65 days of the experimental. Total DMI was increased (P<0.01) in sheep than goats, while average daily gain (ADG) was increased (P<0.01) goats than sheep with the addition of ENZ (2.2 and 6.3 g/kg BW0.75, respectively). Feed efficiency was increased in goats than sheep with ENZ addition. An increased (P<0.01) in metabolizable protein intake and net energy for growth occurred by ENZ addition sheep and goats diets and the highest (P<0.01) values were observed in goats received ENZ diet (Table 4).
It was speculated that the addition of ZADO® (i.e., ENZ) increased (P<0.05) total feed intake in sheep and goats (Tables 3 and 4). Some results reported an effect of providing exogenous fibrolytic enzymes on feed intake of dairy cows or beef steers (Schingoethe et al, 1999; Gado et al, 2009). DM digestibility was improved by addition of ENZ by 4 and 11%, in sheep and goats, respectively. Improvement of nutrient digestibility by addition of ENZ probably due to the beneficial effects of ENZ on fiber hydrolysis and rumen fermentation activity (Gado et al, 2006, 2009 and 2011) and this results were confirmed in vitro (Table 2). Beauchemin et al. (2003) reported that supplementing the diet with E. faecium increased (P<0.05) the proportion of propionate and, consequently, decreased (PO.10) the proportion of butyrate in ruminal fluid compared with the control regarding to its roles in stimulating the presence of lactic acid-utilizing bacteria, which produce propionate. Similarly, Kim et al. (2000) reported increased propionate concentrations in steers fed L. plantarum, another lactic acid-producing bacterium. NDF digestibility was increased (PO.01) in sheep and goats treated groups by about 7 and 9%, respectively (Table 2). This effect may be due to the ability of ENZ to lose lignocellulotic bonds in fiber (Bassuny et al, 2003).
Improve the NDF digestibility by addition of ENZ may be also due to increase their degradability in the rumen which could reduce the physical fill in the rumen over time thereby allowing higher voluntary feed intake (Dado and Allen, 1995). Improved the nutrient digestibility in animals could be also refer to the improvement in ruminal fermentation activities, by addition of ENZ to diet (Gado et al, 2006, 2009 and 2011). ENZ may improve the stimulation of ruminal microorganism's activity by reducing the NH3-N concentration in the rumen liquor throughout incorporation of NH3-N into microbial protein (Gado et al, 2006). This effect attributed to an increase in microbial colonization of feed particles and speculated that exogenous enzymes may act similarly to primary bacterial colonization Yang et al. (1999), and increase the dietary energy utilization and rumen fermentation. Colombatto et al. (2007) reported an improvement in vitro ruminal fermentation activity and cell wall digestibility of alfalfa stems by addition of exogenous fibrolytic enzyme in cow. Zadrazil (1977) reported an increase of 12 % in the in vitro digestibility of wheat straw incubated with Pleurotus florida, and Ibrahim and Pearce (1980) observed an increase in digestibility of barley straw by 10 units, with Peniophora gigantea.
Improvement of the average daily gain (i.e., ADG, Table 4) by addition of ENZ probably due to the improvement in nutrient digestibility of diets (Table 3) which reflect on improving the feed efficiency (Table 4). Supplementing diets with enzymes has been shown to improve feed efficiency and daily gain of feedlot cattle (Swinney-Floyd et al, 1999; Galyean et al, 2000). Ware et al. (1988) Improving the nutrient digestibility and animal's performance may be due to the positive effect of ENZ on ruminal fermentation activity. Gado et al. (2006) reported an improvement in ruminal fermentation activity by treating of rice straw with ENZ.
Improved ADG in sheep and goats could be also explained by an increase in the available nutrients to animals for deposition and growth (Lewis et al, 1999). ENZ addition increased the ADG by 51 and 69% in sheep and goats, respectively. These results are in agreement with Beauchemin et al. (1995) who reported significant improved growth and body weight gain by adding an enzyme product containing xylanase and cellulase activities to alfalfa hay of growing beef cattle by up to 30% or high concentrate ration (Beauchemin et al, 1999). Meanwhile, McAllister et al. (1999) observed that average daily gain was related to the enzyme concentration. Dong et al. (1995) reported that direct fed cellulases had the ability to improve the growth of Holstein calves when administrated orally. However, improving the growth performance of sheep and goats with addition of ENZ suggested to have a marked effect on increasing the total microbial population in the rumen (Yang et al, 1999), and increased microbial protein synthesis (Gado et al, 2009). Yang et al. (1999) and Beauchemin et al. (2000) reported that the increase in nutrient digestibility (Table 3) is due to the increase or stimulation in the total microbial population. However, Beauchemin et al. (1995) and Lewis et al. (1999) indicated that the improved performance might be due to increased digestibility which yields more energy and/or nutrient availability to rumen microbes because of enzyme feeding. Beauchemin et al. (1997) and Yang et al. (1999) concluded that fibrolytic enzymes can be used to improve the digestibility of treated diets and provide more nutrients for production. Fibrolytic enzymes contain a wide variety of polysaccharidase enzymes that solubilize fiber and provide some essential nutrients or growth factors to rumen microorganisms. Di Francia et al. (2007) who observed an improvement in average daily gain and digestive efficiency of fibre with supplementation of A. oryzae fermentation extract and S. cerevisiae culture on the calf starter.
Feeding efficiency expressed as kg feed/kg body weight was significantly improved (P<0.05) for ENZ addition groups compared to control (Table 4). However, this response was mainly due to the effect of cellulase feeding on feed intake and digestibility. However, feed efficiency (P<0.05) was improved by 35% with addition of ENZ, and this was associated with increased of 60% in ADG. Beauchemin et al. (2000) reported an 11% improvement in feed conversion ratio resulting from a 5% decrease in feed intake from enzyme treated ration associated with a 6% increase in body weight gain. En earlier study of the same author of Beauchemin et al. (1995) reported a 10% improvement in the feed conversion ratio of steers fed dry forages resulting from improved digestibility of enzyme-supplemented ration.
Effect of animal species
Sheep and goats increased the amount of straw intake when the amount offered was increased to allow animals to refuse more than the rate of 10 to 20% of amount offered, normally adopted in ad libitum feeding trials. Our research has aimed to define how much straw needs to be consumed in goats and sheep, to enable them to select the more nutritious components of straw, after eating the restricted amount of concentrate in absence of presence of ENZ. Differences in gut morphology, rumen size, and physiology, such as rumen motility (Tisserand et al, 1991), offer an explanation as to differences between the two species. Attempts have been made to explain the observed differences in diet selection, on grounds of nutrient requirements and physiology, which postulate that goats differ from sheep in energy, nitrogen, dietary fibre requirements, digestive capacity and the rate of passage of undigested residues (Brown and Johnson, 1985; Lu, 1988).
Sheep and goats in our study were fed less than 60% of their DM required for the growth (NRC, 1985) to give the animal chance to increase the amount ingested from the wheat straw. Goats had the lowest (P<0.05) total DM intake (Table 4) and associated with an improvement in nutrient digestibility and ADG more than sheep (625 and 743g/animal/d, for goats and sheep, respectively). Both goats and sheep increased their total intake with increasing amounts of straw offered, under addition of ENZ in concentrate, and this was reflected in increasing rates of live- weight gain. Growth rates of goats were higher than for sheep; although intakes were higher in sheep than goats. The species differences were probably also a reflection due to the higher mature weight of the sheep genotype used than goats, and may be reflect also the higher efficiency of goats than sheep in feed utilization.
Addition of enzymes of ZADO® enzymes improved nutrients digestibility in sheep and goats. The improvement was better in goats than in sheep. Goats had the lowest total dry matter intake that associated with an improvement in nutrient digestibility and average daily gain more than sheep. These results suggested a good performance of goats than sheep under the critical conditions of shortage feedstuffs during the dry season in Egypt.
AOAC. 1990. Association of Official Analytical Chemists International, Official methods of analysis (15th Ed.). Arlingtion, V.A. [ Links ]
Beauchemin, K.A., Jones, S.D., Rode, L.M., Sewalt, V.J. 1997. Effects of fibrolytic enzymes in corn or barley diets on performance and carcass characteristics of feed lot cattle. Canadian Journal of Animal Science. 77: 645-653. [ Links ]
Beauchemin, K.A., Rode, L.M., Karren, D. 1999. Use of feed enzymes in feedlot finishing diets. Canadian Journal of Animal Science. 79: 243-246. [ Links ]
Beauchemin, K.A., Rode, L.M., Maekawa, M., Morgavi, D.P., Kampen, R. 2000. Evaluation of a non starch polysaccharidase feed enzyme in dairy cow diets. Journal of Dairy Science. 83: 543-553. [ Links ]
Beauchemin, K.A., Rode, L.M., Sewalt, V.J. 1995. Fibrolytic enzymes increase fiber digestibility and growth rate of steers fed dry forages. Canadian Journal of Animal Science. 75: 641-644. [ Links ]
Beauchemin, K.A., Yang, W.Z., Morgavi, D.P., Ghorbani, G.R., Kautz, W., Leedle, J.A.Z. 2003. Effects of bacterial direct-fed microbials and yeast on site and extent of digestion, blood chemistry, and subclinical ruminal acidosis in feedlot cattle. Journal of Animal Science. 81: 1628-1640. [ Links ]
Brown, L.E., Johnson, W.L. 1985. Intake and digestibility of wheat straw diets by goats and sheep. Journal of Animal Science. 60: 1318-1323. [ Links ]
Bassuny, S.M., Abdel-Aziz, A.A., El-Sayis, M.F., Abdulla, M.A. 2003. Fibrous crop byproducts as feed. 2- Effect of chemical and biological treatments on feed intake, nutritive values and some ruminal and blood constituents. Egyptian Journal of Nutrition and Feeds. 6: 901-912. [ Links ]
Colombatto, D., Morgavi, D.P., Fuñado, A.F., Beauchemin, K.A. 2003. Screening of exogenous enzymes for ruminant diets: Relationship between biochemical characteristics and in vitro ruminal degradation. Journal of Animal Science. 81: 2628-2638. [ Links ]
Colombatto, D., Moulda, F.L., Bhat, M.K., Owena, E. 2007. Influence of exogenous fibrolytic enzyme level and incubation pH on the in vitro ruminal fermentation of alfalfa stems. Animal Feed Science Technology. 137: 150-162. [ Links ]
Dado, R.G., Allen, M.S. 1995. Intake limitations, feeding behavior, and rumen function of cows challenged with rumen fill from dietary fiber or inert bulk. Journal of Dairy Science. 78: 118-133. [ Links ]
Di Francia, A., Masucci, F., De Rosa, G., Varricchio, M.L., Proto, V. 2007. Effects of Aspergillus oryzae extract and a Saccharomyces cerevisiae fermentation product on intake, body weight gain and digestibility in buffalo calves. Animal Feed Science Technology. 140: 67-77. [ Links ]
Dong, Y., Bae, H.D., McAllister, T.A., Mathison, G.W., Cheng, K.J. 1995. The effect of supplementary fibrolytic enzymes, bromoethelenesulfunate and monensin on digestibility of grass hay and methane production. Proceedings, vol. 46. Western Section, American Society of Animal Science, USA, p. 434. [ Links ]
Duncan, D.B. 1955. Multiple ranges and multiple F-test. Biometrics. 11: 42. [ Links ]
Eun, J.-S., Beauchemin, K.A., Schulze, H. 2007. Use of an in vitro fermentation bioassay to evaluate improvements in degradation of alfalfa hay due to exogenous feed enzymes. Animal Feed Science Technology. 135: 315-328. [ Links ]
Gado, H. 1997. Effect of enzymatic treatments for poor quality roughages on fiber digestibility and nitrogen metabolism in Baladi goats. Egyptian Journal of Nutrition and Feeds. 50-56. (Special issue) [ Links ]
Gado, H., Nasr, S.A., Mohamed, B.K., Mahrous, A.A. 2006. Effect of biological treatments on the nutritive value of rice straw. Egyptian Journal of Nutrition and Feeds. 9 (2): 207-219. [ Links ]
Gado, H.M., Salem, A.Z.M., Odongo, N.E., Borhami, B.E. 2011. Effect of exogenous enzymes ensiled with orange pulp on digestion, blood metabolites and growth performance in lambs. Animal Feed Science Technology. 165: 131-136. [ Links ]
Gado, H.M., Salem, A.Z.M., Robinson, P.H., Hassan, M. 2009. Influence of exogenous enzymes on nutrient digestibility, extent of ruminal fermentation as well as milk production and composition in dairy cows. Animal Feed Science Technology. 154, 36-46. [ Links ]
Galyean, M.L., Nunnery, G.A., Defoor, P.J., Salyer, G.B., Parsons, C.H. 2000. Effects of live cultures of Lactobacillus acidophilus (Strains 45 and 51) and Propionibacterium freudenreichii PF-24 on performance and carcass characteristics of finishing beef steers. African Journal of Agricultural Research. 4: 548-552. [ Links ]
Hathout, M.K. 1984. Use of liquid supplements, molasses blocks and anhydrous ammonia to improve the feeding quality of agricultural by products. UNDP/FAO beef industry development and related ruminant production system project. 21 pp. [ Links ]
Ibrahim, M.N.M., Pearce, G.R. 1980. Effects of white rot-fungi on the composition and In vitro digestibility of crop by production. Agricultural Wastes. 2:199-205. [ Links ]
Kim, S.W., Standford, D.G., Roman-Rosario, H., Yokoyama, M.T., Rust, S.R. 2000. Potential use of Propionibacterium acidipropionici, strain DH42, as a direct-fed microbial for cattle. Journal of Animal Science. 78:1225 (Abstr. [ Links ]).
Lewis, G.E., Sanchez, W.K., Hunt, C.W., Guy, M.A., Pritchard, G.T., Swanson, B.I., Trearcher, R.J. 1999. Effect of direct fed fibrolytic enzymes on the lactational performance of dairy cows. Journal of Dairy Science. 82: 611-617. [ Links ]
Lu, CD. 1988. Grazing behavior and diet selection of goats. Small Ruminant Research. 1: 205-216. [ Links ]
Luo, J., Goetsch, A.L., Nsahlai, I.V., Sahlu, T., Ferrell, C.L., Owens, F.N., Galyean, M.L., Moore, J.E., Johnson, Z.B. 2004. Metabolizable protein requirements for maintenance and gain of growing goats. Small Ruminant Research. 53: 309-326. [ Links ]
Nsereko, V.L., Morgavi, D.P., Rode, L.M., Beauchemin, K.A., McAllister TA. 2000. Effects of fungal enzyme preparations on hydrolysis and subsequent degradation of alfalfa hay fiber by mixed rumen microorganisms in vitro. Animal Feed Science Technology. 88: 153-170. [ Links ]
NRC. 1985. Nutrient Requirements of Domestic animals. National Research council, Washington, DC, USA. [ Links ]
SAS. 1999. SAS/STAT User's Guide, Version 6, 4th ed. SAS Institute, Cary, NC, USA. [ Links ]
Schingoethe, D.J., Stegman, G.A., Treacher, R.J. 1999. Response of lactating dairy cows to a cellulase and xylanase enzyme mixture applied to forages at the time of feeding. Journal of Dairy Science. 82: 996-1003. [ Links ]
Steel, R.G.D., Torrie, J.H. 1980. Principles and Procedures of Statistics, 2nd ed. McGraw-Hill International, New York, NY, USA. [ Links ]
Swinney-Floyd, D., Gardner, B.A., Owens, F.N., Rehberger, T., Parrott, T. 1999. Effect of inoculation with either strain P-63 alone or in combination with Lactobacillus acidophilus LA53545 on performance of feedlot cattle. Journal of Animal Science. 77:77. [ Links ]
Tilley, J.A., Terry, R.A. 1963. A two stage technique for the digestion of forage crops. Journal of the British Grassland Society. 18: 104-111. [ Links ]
Tisserand, J.L., Hadjipanayiotou, M., Gihad, E.A. 1991. Digestion in goats. In: Morand-Fehr, P. (Ed.), Goat Nutrition. Pudoc, Wageningen, the Netherlands, pp. 46-60. [ Links ]
United States Department of Agriculture 2002. Agricultural Statistics 2002. National Agricultural Statistics Service. United States Government Printing Office, Washington, DC. [ Links ]
Ware, D.R., Read, P.L., Manfredi, E.T. 1988. Pooled summary of eight feedlot trials evaluating performance and carcass characteristics of steers fed Lactobacillus acidophilus strain BT138. Journal of Animal Science. 66: 436. [ Links ]
Yang, W.Z., Beauchemin, K.A., Rode, L.M. 1999. Effects of an enzyme feed additive on extent of digestion and milk production of lactating dairy cows. Journal of Dairy Science. 82: 391-403. [ Links ]
Zadrazil, F. 1977. The conversation of straw into feed by Basidiomycetes. European Journal of Applied Microbiology. 4: 273-281. [ Links ]