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Efficacy of exogenous cellulase on digestibility in lambs and growth of dairy calves
Livestock Production Science 87 (2004) 207 – 214 www.elsevier.com/locate/livprodsci
Efficacy of exogenous cellulase on digestibility in lambs and growth of dairy calves H.H. Titi *, M.J. Tabbaa Department of Animal Production, Faculty of Agriculture, University of Jordan, Amman 11942, Jordan Received 9 January 2003; received in revised form 16 July 2003; accepted 29 July 2003
Abstract Two experiments were carried out to investigate the efficacy of direct feeding a fibrolytic enzyme on lamb digestibility and on the performance of growing milk-type calves. In the first experiment, 10 lambs were divided into two groups, cellulase treated and a control, and placed in metabolic crates for two periods of 12 days each in a switchover design. For the feeding trial, 16 male and 15 female Friesian calves were utilized in a repeated measure complete randomized design. Each of the two sexes was allocated into one of two groups and fed the same ration, either treated or not with exogenous cellulase. All animals were treated individually. A total mixed ration was offered ad libitum to males and in a restricted feeding regime to females. The digestibility study showed that treated lambs had higher ( P < 0.05) digestibilities for dry matter, organic matter, crude fiber, neutral and acid detergent fiber. Also, they retained more ( P < 0.05) nitrogen in their bodies than the control lambs. Treated males had higher ( P < 0.05) gain than control ones. No differences were reported between female groups. No differences were observed in feed intake, average feed intake and daily feed intake in both sexes. Enzyme-treated males showed improved ( P < 0.05) feeding efficiency compared to no cellulases while no differences were obtained with females. Financial analysis showed no differences in feed or total costs while gross and total income were higher for treated animals than untreated ones. These results demonstrated the benefits of using fibrolytic enzyme additives to improve total tract digestibility and enhance growth performance of milk calves and replacement heifers. D 2003 Elsevier B.V. All rights reserved. Keywords: Calves; Digestibility; Growth performance; Financial analysis; Cellulases
1. Introduction Fiber digestion in the rumen is a limiting factor in ruminant production systems and, thus, many researches have been devoted to maximizing production through manipulation of rumen activities. A wide range * Corresponding author. Tel.: +962-6-535-5511; fax: +962-6530-0077. E-mail address: [email protected] (H.H. Titi). 0301-6226/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.livprodsci.2003.07.012
of fibrolytic enzymes are currently commercially available for this purpose to be used with ruminants (Beauchemin et al., 2000; Yang et al., 2000). Such enzymes are effective means of improving nutrient utilization of forages and yielding more metabolizable energy for ruminants (Dong et al., 1995; Lewis et al., 1996). The precise mode of action of the exogenous enzyme mixtures in ruminant diets has not been demonstrated. However, addition of fibrolytic enzymes had a marked effect on increasing the total
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microbial population in the rumen (Feng et al., 1996; Yang et al., 1999), and increased microbial protein synthesis (Rode et al., 1999). Yang et al. (1999) and Beauchemin et al. (2000) reported that the increase in digestibility is due to the increase or stimulation in the total microbial population. These conclusions were based on the hypothesis that increasing fiber digestibility would enhance rumen microbial protein synthesis (Hristov et al., 1998). Total tract and ruminal digestibilities were improved due to feeding exogenous fibrolytic enzymes for ruminant animals (Lewis et al., 1995; Rode et al., 1999; Yang et al., 1999). However, Beauchemin et al. (1999b) reported minimal effects on ruminal digestion but increased total tract nutrients digestibility. Hristov et al. (1998) revealed that addition of a fibrolytic enzyme resulted in increased concentration of soluble reducing sugars and decreased NDF content. Enzyme treatment increased in vitro dry matter and organic matter digestibility (Dong et al., 1995; Feng et al., 1996). Furthermore, some studies proposed that feed enzymes might help to overcome or minimize the depression in fiber digestion that occurs at lower ruminal pH due to feeding high concentrate diets (Lewis et al., 1996; Beauchemin et al., 1999a). Recent studies stated that feeding exogenous fibrolytic enzymes had positive effects on lactating dairy cows and growing cattle. Fibrolytic enzymes supplemented to steers or growing heifers fed dry forages or high concentrate diets increased body weight gain with minor effects on feed intake or feed conversion ratio (Beauchemin et al., 1995, 1999a). However, the same enzyme mixture resulted in 11% improvement in feed conversion of feedlot cattle fed grain-based diets (Beauchemin et al., 1997). Meanwhile, McAllister et al. (1999) obtained improved average daily gain, feed intake, and feed conversion ratio of feedlot cattle fed enzyme-treated silage. The effect of fibrolytic enzymes on livestock performance has to be evaluated more thoroughly. At the same time we are not aware of any study in which the effect of exogenous enzymes on dairy calves performance has been examined. Therefore, the purpose of this study was twofold: to evaluate the effect of feeding fibrolytic enzymes on the performance of fattened milk-type calves and to evaluate the effect of such cellulases on the performance of replacement heifers.
2. Materials and method This study was carried out in the Jordan University Agricultural Research Station located in the central valley of Jordan. A preliminary digestibility study was conducted to determine the affectivity of the cellulase enzyme utilized in this study. Ten Awassi lambs were randomly divided into two treatments. Body weight was considered in the randomization. Average live weight of lambs in both groups ranged between 34.8 and 35.2 kg. Lambs were housed in individual metabolic crates for the whole experimental period. The same ration was fed both groups; however, the enzyme was added only to the treated group. Table 1 shows the proximate composition and chemical compositions of used ration. Animals were utilized for two study periods in a switchover design. The adaptation periods lasted for 7 days, and the collection periods lasted for another 5 days. Lambs were fed at their ad libitum level during the adaptation period and at 90% of voluntary intake during the collection period. Daily feed and the ort were collected and weighted. Fresh water was available for each lamb all the time. Before starting the experiment, lambs were vaccinated and treated against internal and external parasites. Table 1 Ingredient composition and proximate analysis of rations fed to Friesian calves and Awassi lambs % in ration Ingredients Barley SBM Chopped wheat straw Wheat bran Lime stone DCP Salt Vitamins and minerals Total Proximate analysis Dry matter (DM) Crude protein (CP) Crude fiber (CF) NDF ADF Ash ME (MJ/kg DM)a a
Calculated based on NRC (1989).
60 10 15 10 2 1.4 1.5 0.1 100
90.4 14.8 10.5 48.5 13.2 4.4 9.3
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Feces and urine were collected and measured daily for each lamb during the collection periods. At the end of each collection period, fecal samples were composited for each lamb and a 10% subsample of the composite was taken for analysis. Collected feces were dried and stored for later analysis. The urine was collected in plastic jars containing 300 ml of 3 N H2SO4 solution and then a 10% blend of the diluted urine was taken daily and stored in a refrigerator for later analysis. Urine was composited for each lamb alone and only one sample of each lamb was taken for analysis. Feces were analyzed for proximate and Van Soest analysis, while urine was analyzed for nitrogen (Georing and Van Soest, 1970; AOAC, 1990). Digestibility coefficients of dry matter (DM), crude protein (CP), crude fiber (CF), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined. Nitrogen balance was calculated to determine the proportion of the feed protein utilized by the lamb for synthesizing body tissues and compounds. Analysis of variance was performed on the data. Treatment means were compared using the least significant differences (LSD) test (Steel and Torrie, 1986). 2.1. Feeding trial A total of 31 weaned dairy-type calves, 16 males and 15 females, were randomly selected to be utilized in this study. Initial ages ranged between 9 and 11 months and weighed between 155 and 231 kg for males and 167 and 231 kg for females. Animals were housed individually for a fattening period of 196 days. All calves were fasted overnight and weighed at the beginning of the experiment and then every 28 days to the end of the study. Calves were allocated randomly into one of two treatments. Sex was considered in randomization among treatment groups. Treatments included males supplemented with fibrolytic enzyme, males without enzyme, females supplemented with and females without enzyme. The same ration was fed to all animals in the experiment; however, feeding regime differs between males and females. Total mixed ration was offered as ad libitum for males and according to the NRC (1989) recommendations for females that were raised for replacement. Percent composition and proximate analysis of the fed ration are presented in Table 1. Enzyme utilized was fungal cellulase derived from Trichoderma spp. supple-
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mented at a rate of 150 g/ton of forage consumed (Maxicel 200R, George A. Jeffreys, Salem, VA, USA). Enzyme characterization showed that it contains 200 unit/mg cellulase activity at pH 7.0 with at least 80% activity between pH 5.5 and 7.5 and 35 and 65 jC. Requirements for 1 ton of the ration were diluted in 500 g of ground corn, mixed with the micronutrient part of the ration and added to the concentrate part at mixing. Ration was mixed daily or every other day before feeding. Animals were vaccinated for enterotoxaemia and treated against internal parasites before starting the experiment. Ration was introduced gradually to animals for a period of 7 days followed by another 7 days for adaptation. Feed was offered once daily in early morning and refusals were removed and recorded daily before feeding. Fresh clean water and mineral blocks were available for the whole experimental period. Samples for analysis were collected at mixing time and sent directly for analysis. Analysis was carried out according to the standard procedures of the AOAC (1990). The Kjeldahl method for N analysis was used for protein content determination utilizing a 1031 Kjaltec analyzer unit and multiplying the result with 6.25. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined according to Georing and Van Soest (1970). Overall daily feed intake, total gain, gain, average daily gain and feed conversion ratio were calculated. Data for initial cost, feed cost, total cost, gross income, net income and ratio (net income/total cost) were calculated and used for financial analysis of utilizing fibrolytic enzymes in calves fattening. Initial cost was calculated from values of buying calves at the beginning of the experiment while feed cost was obtained by multiplying dry matter consumed per animal with its cost. Total costs were the values of feed cost, labor costs and enzyme costs for the treated groups. Gross income represents the values of selling calves at their final weights by the end of the experiment. Meanwhile, net income values are the values of the gross income after subtracting total cost values. All values were processed on per head basis according to the local prices used in the markets with the national currency (Jordanian dinar, JD). One US dollar is equal to JD0.71. Statistical analysis of data was performed utilizing the general linear model (GLM) of SAS (1998). The
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model was designed to determine the effect of treatment and sex on parameters measured throughout the experiment. Initial weights were used as a covariate for statistical analysis. Least square means for all variables in the study were calculated and the protected LSD test was used to determine significant differences. Furthermore, week effect was introduced in the model in a repeated measure design to study growth behavior throughout the experiment (Steel and Torrie, 1986).
3. Results and discussion The effect of enzyme treatment on digestibility coefficients and N-balance are presented in Table 2. Fibrolytic enzymes increased ( P < 0.05) dry matter and organic matter digestibilities of treated lambs compared to those of control. Most of the published literature reported increased total tract digestibilities of dry matter, organic matter or both, following treatment with a fibrolytic enzyme mixture (Dong et al., 1995; Feng et al., 1996; Lewis et al., 1996; Beauchemin et al., 1999b, 2000; Rode et al., 1999; Yang et al., 1999). Meanwhile, some other studies observed no effect of treatment with an exogenous fibrolytic enzyme on dry matter or organic digestibilities (McAllister et al., 1999, 2000; Lewis et al., 1999; Yang et al., 2000). However, present results are opposite to that obtained by Yang et al. (2000) who reported that enzymatic treatment was most efficacious in improving digestibility of high forage diets fed to sheep. A similar trend was observed for the crude fiber, NDF and ADF digestibility coefficients. Treated Table 2 Digestibility coefficients of Awassi lambs fed diets supplemented with a cellulase enzyme Digestibility (%)
Treated
Untreated
SE
P
Dry matter Organic matter Crude fiber Crude protein NDF ADF N-retained (g/head/day)
66.3a 78.3a 47.3a 73.5 42.5a 44.5a 10.3a
63.6b 74.8b 44.8b 72.1 40.0b 41.2b 8.8b
0.7 0.7 0.6 0.8 0.7 0.7 1.3
0.03 0.03 0.02 0.06 0.04 0.03 0.03
ab Means with different letters in the same line within the same forage type are significantly different ( P < 0.05).
lambs had higher ( P < 0.05) digestibilities than untreated ones. However, no differences were observed in crude protein digestibility between treated and control lambs. Dong et al. (1995) reported that enzyme treatment resulted in improved crude fiber digestion. Similar results for NDF and ADF were obtained by others who reported improved digestibilities following treatment with fibrolytic enzyme mixtures (Feng et al., 1996; Lewis et al., 1996, 1999; Beauchemin et al., 1999b; Yang et al., 1999; McAllister et al., 2000). The reason for no differences in crude protein digestibility could most probably be due to the fact that the ration used was a concentrate one that is easily digestible. Yang et al. (2000) concluded that exogenous fibrolytic enzymes seemed to improve digestion only when digestion is incomplete, but no effects occur when digestion is high and that enzyme products were most efficacious for high forage diets to sheep. However, Beauchemin et al. (1999b) observed that exogenous enzyme supplementation tended to increase total tract crude protein digestibility by about 4%. Enzyme-treated lambs retained more ( P < 0.05) nitrogen (g/head/day) in their bodies than those fed the control diet. These findings are in agreement with those obtained by McAllister et al. (1999, 2000) who reported a significant increase in N-retained, enzymetreated diets. Although not measured in this experiment, increased N retention would suggest increased microbial protein synthesis. Increased ruminal microbial protein synthesis following addition of fibrolytic enzymes was indicated in several studies (Hristov et al., 1998; Beauchemin et al., 1999b; Rode et al., 1999). However, Beauchemin et al. (1999b, 2000) reported that increased availability of fermentable carbohydrates after enzyme feeding would likely result in considerably reduced ruminal ammonia-N and stimulate microbial growth. The substantial improvement in digestibility observed in the present study was mostly a result of enzyme addition. Beauchemin et al. (1999b) concluded that the effects of exogenous enzyme supplementation were related to digestibility, mainly because of enhanced ruminal digestion. It was speculated that improved digestibility caused by enzyme treatment of feed was related to improved microbial colonization (Yang et al., 1999). However, Beauchemin et al.
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values than untreated ones. Obtained results were expected and were mainly due to the feeding strategy followed since females were raised as a replacement group and fed according to the NRC guidelines. The restricted feeding prevented them from showing high growth rates or reporting any differences in gain, thus leading to no differences between the two females groups. Figs. 1 and 2 show the growth pattern for both males and females, respectively, when data were analyzed utilizing the repeated measure design. The data present the average gain during two consecutive weighing periods. Males had similar growth pattern during the whole experimental period (Fig. 1). However, except for the 28- and 140-day periods, differences in gain were significant ( P < 0.05), favoring the cellulase-treated group. The average gain for the female groups was variable. The enzyme-fed group gained more ( P < 0.05) at 28, 84 and 196 days of experiment, while no differences ( P> 0.05) in gain were observed at 56 or 112 days. Control females gained higher ( P < 0.05) body weight during the second half of the experiment except for the final results. The reason for this fluctuation in gain is not clear, but it could be a result of the feeding program. However, such data emphasize the effect of direct feeding of fungal cellulase to growing calves raised for meat or as replacement heifers. Intake of treated groups was not different from untreated ones for both sexes. Males were fed ad libitum while females were fed according to the NRC (1989) guidelines. However, treated animals of both sexes consumed more feed than controls. It seemed that feeding cellulase enzyme had led to more efficient
(2000) speculated that improved digestibility was due to improved colonization and by stimulating the endogenous enzyme activity within the rumen. Average initial weights were similar for treated and untreated groups in both sexes. Final weights were higher ( P < 0.05) for treated males than control ones, while no differences were observed between treated and untreated female calves. Males fed cellulase had higher ( P < 0.05) growth performance than unfed males (Table 3). Total gain, average gain (gain between two consecutive weights) and average daily gain were higher ( P < 0.05) for the treated males than those for untreated ones. It appeared that fibrolytic enzymes could improve growth performance of dairy male calves under fattening conditions. Dong et al. (1995) reported that direct fed cellulases had the ability to improve the growth of Holstein calves when administrated orally. Improved growth in males could be explained by an increase in the available nutrients to calves for deposition and growth (Lewis et al., 1995, 1999). These results are in agreement with others who reported significant improved growth and body weight gain that ranged between 9% and 30% of steers fed dry forages (Beauchemin et al., 1995) or high concentrate ration (Beauchemin et al., 1999a). Meanwhile, McAllister et al. (1999) observed that average daily gain was quadratically related to the enzyme concentration. Growth performance of the female group, studied with the same measures as males, did not show any differences compared to untreated females not fed cellulases in their ration. Variations in results obtained were narrow, which was reflected in lack of significance. Yet, treated females had numerically higher
Table 3 Means for performance and growth characters of Friesian calves supplemented with cellulase enzyme
No. Initial weight (kg) Final weight (kg) Total gain (kg) Average gain (kg) Average daily gain (kg/head/day) Average feed intake (kg) Total feed intake (kg) Daily feed intake (kg) Feed conversion ratio ab
Male +
Male
4 189.2 461.2a 271.9a 38.4a 1.39a 300.4 2103.0 10.7 7.7a
4 188.0 414.0b 226.0b 32.3b 1.15b 266.9 1868.2 9.5 8.5b
SE
5.4 3.3 1.0 0.03 9.7 7.8 0.3 0.3
P
Female +
Female
SE
P
0.03 0.01 0.03 0.02 0.07 0.08 0.11 0.04
4 221.5 389.2 167.1 23.9 0.9 186.3 1275.9 6.7 8.2
3 184.7 339.8 154.0 22.0 0.8 174.3 1217.5 6.22 8.91
5.0 1.2 0.9 0.03 4.6 8.5 0.2 0.5
0.08 0.15 0.16 0.13 0.18 0.20 0.21 0.32
Means with different letters within the same species are significantly different ( P < 0.05).
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Fig. 1. Growth pattern of Friesian calves treated with cellulase enzyme.
utilization of the feed utilized and, thus, more growth. Improved digestibility of feed due to enzyme supplementation might result in satisfying requirements and thus resulting in similar feed intake. Some results reported no effect of providing exogenous fibrolytic enzymes on feed intake of dairy cows or beef steers (Schingoethe et al., 1999; Rode et al., 1999). However, Beauchemin et al. (2000) reported an 11% improvement in feed conversion ratio resulting from a 5% decrease in feed intake from enzymetreated ration associated with a 6% increase in body weight gain. Some studies indicated that the improved performance of fibrolytic-enzyme-fed animals was mainly
attributed to increased feed intake (Yang et al., 1999; Beauchemin et al., 2000). However, Beauchemin et al. (1995) and Lewis et al. (1995, 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. This would most probably increase microbial growth
Fig. 2. Growth pattern of Friesian heifers treated with cellulase enzyme.
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and rumen population which, in turn, would increase microbial protein synthesis (Hristov et al., 1998; Beauchemin et al., 1999b, 2000; Yang et al., 1999). Feeding efficiency or feed conversion ratio expressed as kg feed/kg body weight was significantly improved ( P < 0.05) for treated male group compared to control males. However, no differences were observed between treated and untreated females. A good explanation of this could be due to the feeding strategy that caused treated males to gain weight more than females. However, this response was mainly due to the effect of cellulase feeding on feed intake since treated females showed no significant ( P>0.05) differences in growth performance compared to control untreated females. Meanwhile, treated males showed significant differences ( P < 0.05) in both growth parameters and feed intake, which was reflected on improved FCR. 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. Likewise, Beauchemin et al. (1997) reported an 11% improvement in the feed conversion ratio of feedlot finishing cattle fed high concentrate diets. However, the data of the present study are also in agreement with previous results that concluded that the feed conversion ratio or feeding efficiency of dairy cattle improved significantly (Lewis et al., 1999; McAllister et al., 1999; Rode et al., 1999) or numerically (Beauchemin et al., 1999a,b) as a result of direct feeding of different exogenous cellulases. Meanwhile, Yang et al. (2000) concluded no effect of adding exogenous fibrolytic enzymes on the efficiency of feed utilization of lactating dairy cows. Financial analysis data showed no differences in feed cost between treatments for both sexes. However, treatment groups were numerically higher. This increase was mainly attributed to increased feed intake obtained when utilizing enzymes. Likewise, no differences were observed in total cost between treated and untreated groups of both sexes. Gross income and net income (gross income total costs) were higher ( P < 0.05) for groups fed enzyme-treated diets compared to those of control ones. Values for gross income depend mainly on the final weights, which were higher for treated calves than those for controls. Ratio of net income to total costs was higher ( P < 0.05) in treated groups than in control groups for both sexes. Income was mainly a
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function of selling calves after fattening. Treatment with fibrolytic enzymes resulted in higher ( P < 0.05) final weights, which resulted in higher gross income from treated groups compared to untreated groups. Meanwhile, no differences were observed in total costs between treated and untreated groups. Improved net income and ratio were a function of improved gain and final weights in treated groups as a result of adding enzyme. We are not aware of any published data concerning the financial analysis of using exogenous fibrolytic enzymes in livestock production. However, McAllister et al. (2000) reported that enzymatic treatment of lambs fed either a concentrate diet or a forage diet had no effect on the rail grade prices of carcass cuts for both diets. Although the number of animals used in this study is not large enough, one can conclude that feeding fibrolytic enzymes to dairy calves can modify their growth rate and has a positive effect on their performance. Such results are desirable in new farming systems.
References Association of Official Analytical Chemists, 1990. Official Methods of Analysis, 15th ed. AOAC, Arlington, VA. Beauchemin, K.A., Rode, L.M., Sewalt, V.J., 1995. Fibrolytic enzymes increase fiber digestibility and growth rate of steers fed dry forages. Can. J. Anim. Sci. 75, 641. 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 feedlot cattle. Can. J. Anim. Sci. 77, 645. Beauchemin, K.A., Rode, L.M., Karren, D., 1999a. Use of feed enzymes in feedlot finishing diets. Can. J. Anim. Sci. 79, 243. Beauchemin, K.A., Yang, W.Z., Rode, L.M., 1999b. Effects of grain source and enzyme additive on site and extent of nutrient digestion in dairy cows. J. Dairy Sci. 82, 378. 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. J. Dairy. Sci. 83, 543. 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. Feng, P., Hunt, C.W., Pritchard, G.T., Julien, W.E., 1996. Effect of enzyme preparations and in vitro degradation and in vitro digestive characteristics of mature cool-season grass forage in beef steers. J. Anim. Sci. 74, 1349.
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Georing, H.K., Van Soest, P.J., 1970. Forage fiber analysis. Agriculture Handbook, vol. 379. Agr. Res. Serv., USDA, Washington, DC. Hristov, A.N., McAllister, T.A., Cheng, K., 1998. Effect of dietary or abomasal supplementation of exogenous polysaccharide-degrading enzymes on rumen fermentation and nutrient digestibility. J. Anim. Sci. 76, 3146. Lewis, G.E., Sanchez, W.K., Treacher, R., Hunt, C.W., Prithcard, G.T., 1995. Effect of direct-fed fibrolytic enzymes on lactational performance of midlactation Holstein cows. Proceedings, vol. 46. Western Section, American Society of Animal Science, USA, p. 310. Lewis, G.E., Hunt, C.W., Sanchez, W.K., Treacher, R., Pritchard, G.T., Feng, P., 1996. Effect of direct fed fibrolytic enzymes on digestive characteristics of a forage based diet fed to beef steers. J. Anim. Sci. 74, 3020 – 3028. 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. J. Dairy Sci. 82, 611. McAllister, T.A., Oosting, S.J., Popp, J.D., Mir, Z., Yanke, L.J., Hristov, A.N., Treacher, R.J., Cheng, K.J., 1999. Effect of exogenous enzyme on digestibility of barley silage and growth performance of feedlot cattle. Can. J. Anim. Sci. 79, 353.
McAllister, T.A., Stanford, K., Bae, H.D., Treacher, R.J., Hristove, A.N., Baah, J., Shelford, J.A., Cheng, K.J., 2000. Effect of a surfactant and exogenous enzymes on digestibility of feed and on growth performance and carcass traits of lambs. Can. J. Anim. Sci. 80, 35. National Research Council, 1989. Nutrient Requirements of Dairy Cattle, 6th rev. ed. Natl. Acad. Sci., Washington, DC. Rode, L.M., Yang, M.Z., Beauchmen, K.A., 1999. Fibrolytic enzyme supplements for dairy cows in early lactation. J. Dairy Sci. 82, 2121. SAS, 1998. SAS/STAT User’s Guide, Release 7.0 ed. SAS Institute, Cary, NC. 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. J. Dairy Sci. 82, 996. Steel, G.D.R., Torrie, H.J., 1986. Principles and Procedures of Statistics, 2nd ed. McGraw-Hill, Singapore. Yang, W.Z., Beauchemin, K.A., Rode, L.M., 1999. Effect of an enzyme feed additive on extent of digestion and milk production of lactating dairy cows. J. Dairy Sci. 82, 391. Yang, W.Z., Beauchemin, K.A., Rode, L.M., 2000. A comparison of methods of adding fibrolytic enzymes to lactating cow diets. J. Dairy Sci. 83, 2512.
Efficacy of exogenous cellulase on digestibility in lambs and growth of dairy calves H.H. Titi *, M.J. Tabbaa Department of Animal Production, Faculty of Agriculture, University of Jordan, Amman 11942, Jordan Received 9 January 2003; received in revised form 16 July 2003; accepted 29 July 2003
Abstract Two experiments were carried out to investigate the efficacy of direct feeding a fibrolytic enzyme on lamb digestibility and on the performance of growing milk-type calves. In the first experiment, 10 lambs were divided into two groups, cellulase treated and a control, and placed in metabolic crates for two periods of 12 days each in a switchover design. For the feeding trial, 16 male and 15 female Friesian calves were utilized in a repeated measure complete randomized design. Each of the two sexes was allocated into one of two groups and fed the same ration, either treated or not with exogenous cellulase. All animals were treated individually. A total mixed ration was offered ad libitum to males and in a restricted feeding regime to females. The digestibility study showed that treated lambs had higher ( P < 0.05) digestibilities for dry matter, organic matter, crude fiber, neutral and acid detergent fiber. Also, they retained more ( P < 0.05) nitrogen in their bodies than the control lambs. Treated males had higher ( P < 0.05) gain than control ones. No differences were reported between female groups. No differences were observed in feed intake, average feed intake and daily feed intake in both sexes. Enzyme-treated males showed improved ( P < 0.05) feeding efficiency compared to no cellulases while no differences were obtained with females. Financial analysis showed no differences in feed or total costs while gross and total income were higher for treated animals than untreated ones. These results demonstrated the benefits of using fibrolytic enzyme additives to improve total tract digestibility and enhance growth performance of milk calves and replacement heifers. D 2003 Elsevier B.V. All rights reserved. Keywords: Calves; Digestibility; Growth performance; Financial analysis; Cellulases
1. Introduction Fiber digestion in the rumen is a limiting factor in ruminant production systems and, thus, many researches have been devoted to maximizing production through manipulation of rumen activities. A wide range * Corresponding author. Tel.: +962-6-535-5511; fax: +962-6530-0077. E-mail address: [email protected] (H.H. Titi). 0301-6226/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.livprodsci.2003.07.012
of fibrolytic enzymes are currently commercially available for this purpose to be used with ruminants (Beauchemin et al., 2000; Yang et al., 2000). Such enzymes are effective means of improving nutrient utilization of forages and yielding more metabolizable energy for ruminants (Dong et al., 1995; Lewis et al., 1996). The precise mode of action of the exogenous enzyme mixtures in ruminant diets has not been demonstrated. However, addition of fibrolytic enzymes had a marked effect on increasing the total
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microbial population in the rumen (Feng et al., 1996; Yang et al., 1999), and increased microbial protein synthesis (Rode et al., 1999). Yang et al. (1999) and Beauchemin et al. (2000) reported that the increase in digestibility is due to the increase or stimulation in the total microbial population. These conclusions were based on the hypothesis that increasing fiber digestibility would enhance rumen microbial protein synthesis (Hristov et al., 1998). Total tract and ruminal digestibilities were improved due to feeding exogenous fibrolytic enzymes for ruminant animals (Lewis et al., 1995; Rode et al., 1999; Yang et al., 1999). However, Beauchemin et al. (1999b) reported minimal effects on ruminal digestion but increased total tract nutrients digestibility. Hristov et al. (1998) revealed that addition of a fibrolytic enzyme resulted in increased concentration of soluble reducing sugars and decreased NDF content. Enzyme treatment increased in vitro dry matter and organic matter digestibility (Dong et al., 1995; Feng et al., 1996). Furthermore, some studies proposed that feed enzymes might help to overcome or minimize the depression in fiber digestion that occurs at lower ruminal pH due to feeding high concentrate diets (Lewis et al., 1996; Beauchemin et al., 1999a). Recent studies stated that feeding exogenous fibrolytic enzymes had positive effects on lactating dairy cows and growing cattle. Fibrolytic enzymes supplemented to steers or growing heifers fed dry forages or high concentrate diets increased body weight gain with minor effects on feed intake or feed conversion ratio (Beauchemin et al., 1995, 1999a). However, the same enzyme mixture resulted in 11% improvement in feed conversion of feedlot cattle fed grain-based diets (Beauchemin et al., 1997). Meanwhile, McAllister et al. (1999) obtained improved average daily gain, feed intake, and feed conversion ratio of feedlot cattle fed enzyme-treated silage. The effect of fibrolytic enzymes on livestock performance has to be evaluated more thoroughly. At the same time we are not aware of any study in which the effect of exogenous enzymes on dairy calves performance has been examined. Therefore, the purpose of this study was twofold: to evaluate the effect of feeding fibrolytic enzymes on the performance of fattened milk-type calves and to evaluate the effect of such cellulases on the performance of replacement heifers.
2. Materials and method This study was carried out in the Jordan University Agricultural Research Station located in the central valley of Jordan. A preliminary digestibility study was conducted to determine the affectivity of the cellulase enzyme utilized in this study. Ten Awassi lambs were randomly divided into two treatments. Body weight was considered in the randomization. Average live weight of lambs in both groups ranged between 34.8 and 35.2 kg. Lambs were housed in individual metabolic crates for the whole experimental period. The same ration was fed both groups; however, the enzyme was added only to the treated group. Table 1 shows the proximate composition and chemical compositions of used ration. Animals were utilized for two study periods in a switchover design. The adaptation periods lasted for 7 days, and the collection periods lasted for another 5 days. Lambs were fed at their ad libitum level during the adaptation period and at 90% of voluntary intake during the collection period. Daily feed and the ort were collected and weighted. Fresh water was available for each lamb all the time. Before starting the experiment, lambs were vaccinated and treated against internal and external parasites. Table 1 Ingredient composition and proximate analysis of rations fed to Friesian calves and Awassi lambs % in ration Ingredients Barley SBM Chopped wheat straw Wheat bran Lime stone DCP Salt Vitamins and minerals Total Proximate analysis Dry matter (DM) Crude protein (CP) Crude fiber (CF) NDF ADF Ash ME (MJ/kg DM)a a
Calculated based on NRC (1989).
60 10 15 10 2 1.4 1.5 0.1 100
90.4 14.8 10.5 48.5 13.2 4.4 9.3
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Feces and urine were collected and measured daily for each lamb during the collection periods. At the end of each collection period, fecal samples were composited for each lamb and a 10% subsample of the composite was taken for analysis. Collected feces were dried and stored for later analysis. The urine was collected in plastic jars containing 300 ml of 3 N H2SO4 solution and then a 10% blend of the diluted urine was taken daily and stored in a refrigerator for later analysis. Urine was composited for each lamb alone and only one sample of each lamb was taken for analysis. Feces were analyzed for proximate and Van Soest analysis, while urine was analyzed for nitrogen (Georing and Van Soest, 1970; AOAC, 1990). Digestibility coefficients of dry matter (DM), crude protein (CP), crude fiber (CF), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined. Nitrogen balance was calculated to determine the proportion of the feed protein utilized by the lamb for synthesizing body tissues and compounds. Analysis of variance was performed on the data. Treatment means were compared using the least significant differences (LSD) test (Steel and Torrie, 1986). 2.1. Feeding trial A total of 31 weaned dairy-type calves, 16 males and 15 females, were randomly selected to be utilized in this study. Initial ages ranged between 9 and 11 months and weighed between 155 and 231 kg for males and 167 and 231 kg for females. Animals were housed individually for a fattening period of 196 days. All calves were fasted overnight and weighed at the beginning of the experiment and then every 28 days to the end of the study. Calves were allocated randomly into one of two treatments. Sex was considered in randomization among treatment groups. Treatments included males supplemented with fibrolytic enzyme, males without enzyme, females supplemented with and females without enzyme. The same ration was fed to all animals in the experiment; however, feeding regime differs between males and females. Total mixed ration was offered as ad libitum for males and according to the NRC (1989) recommendations for females that were raised for replacement. Percent composition and proximate analysis of the fed ration are presented in Table 1. Enzyme utilized was fungal cellulase derived from Trichoderma spp. supple-
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mented at a rate of 150 g/ton of forage consumed (Maxicel 200R, George A. Jeffreys, Salem, VA, USA). Enzyme characterization showed that it contains 200 unit/mg cellulase activity at pH 7.0 with at least 80% activity between pH 5.5 and 7.5 and 35 and 65 jC. Requirements for 1 ton of the ration were diluted in 500 g of ground corn, mixed with the micronutrient part of the ration and added to the concentrate part at mixing. Ration was mixed daily or every other day before feeding. Animals were vaccinated for enterotoxaemia and treated against internal parasites before starting the experiment. Ration was introduced gradually to animals for a period of 7 days followed by another 7 days for adaptation. Feed was offered once daily in early morning and refusals were removed and recorded daily before feeding. Fresh clean water and mineral blocks were available for the whole experimental period. Samples for analysis were collected at mixing time and sent directly for analysis. Analysis was carried out according to the standard procedures of the AOAC (1990). The Kjeldahl method for N analysis was used for protein content determination utilizing a 1031 Kjaltec analyzer unit and multiplying the result with 6.25. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined according to Georing and Van Soest (1970). Overall daily feed intake, total gain, gain, average daily gain and feed conversion ratio were calculated. Data for initial cost, feed cost, total cost, gross income, net income and ratio (net income/total cost) were calculated and used for financial analysis of utilizing fibrolytic enzymes in calves fattening. Initial cost was calculated from values of buying calves at the beginning of the experiment while feed cost was obtained by multiplying dry matter consumed per animal with its cost. Total costs were the values of feed cost, labor costs and enzyme costs for the treated groups. Gross income represents the values of selling calves at their final weights by the end of the experiment. Meanwhile, net income values are the values of the gross income after subtracting total cost values. All values were processed on per head basis according to the local prices used in the markets with the national currency (Jordanian dinar, JD). One US dollar is equal to JD0.71. Statistical analysis of data was performed utilizing the general linear model (GLM) of SAS (1998). The
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model was designed to determine the effect of treatment and sex on parameters measured throughout the experiment. Initial weights were used as a covariate for statistical analysis. Least square means for all variables in the study were calculated and the protected LSD test was used to determine significant differences. Furthermore, week effect was introduced in the model in a repeated measure design to study growth behavior throughout the experiment (Steel and Torrie, 1986).
3. Results and discussion The effect of enzyme treatment on digestibility coefficients and N-balance are presented in Table 2. Fibrolytic enzymes increased ( P < 0.05) dry matter and organic matter digestibilities of treated lambs compared to those of control. Most of the published literature reported increased total tract digestibilities of dry matter, organic matter or both, following treatment with a fibrolytic enzyme mixture (Dong et al., 1995; Feng et al., 1996; Lewis et al., 1996; Beauchemin et al., 1999b, 2000; Rode et al., 1999; Yang et al., 1999). Meanwhile, some other studies observed no effect of treatment with an exogenous fibrolytic enzyme on dry matter or organic digestibilities (McAllister et al., 1999, 2000; Lewis et al., 1999; Yang et al., 2000). However, present results are opposite to that obtained by Yang et al. (2000) who reported that enzymatic treatment was most efficacious in improving digestibility of high forage diets fed to sheep. A similar trend was observed for the crude fiber, NDF and ADF digestibility coefficients. Treated Table 2 Digestibility coefficients of Awassi lambs fed diets supplemented with a cellulase enzyme Digestibility (%)
Treated
Untreated
SE
P
Dry matter Organic matter Crude fiber Crude protein NDF ADF N-retained (g/head/day)
66.3a 78.3a 47.3a 73.5 42.5a 44.5a 10.3a
63.6b 74.8b 44.8b 72.1 40.0b 41.2b 8.8b
0.7 0.7 0.6 0.8 0.7 0.7 1.3
0.03 0.03 0.02 0.06 0.04 0.03 0.03
ab Means with different letters in the same line within the same forage type are significantly different ( P < 0.05).
lambs had higher ( P < 0.05) digestibilities than untreated ones. However, no differences were observed in crude protein digestibility between treated and control lambs. Dong et al. (1995) reported that enzyme treatment resulted in improved crude fiber digestion. Similar results for NDF and ADF were obtained by others who reported improved digestibilities following treatment with fibrolytic enzyme mixtures (Feng et al., 1996; Lewis et al., 1996, 1999; Beauchemin et al., 1999b; Yang et al., 1999; McAllister et al., 2000). The reason for no differences in crude protein digestibility could most probably be due to the fact that the ration used was a concentrate one that is easily digestible. Yang et al. (2000) concluded that exogenous fibrolytic enzymes seemed to improve digestion only when digestion is incomplete, but no effects occur when digestion is high and that enzyme products were most efficacious for high forage diets to sheep. However, Beauchemin et al. (1999b) observed that exogenous enzyme supplementation tended to increase total tract crude protein digestibility by about 4%. Enzyme-treated lambs retained more ( P < 0.05) nitrogen (g/head/day) in their bodies than those fed the control diet. These findings are in agreement with those obtained by McAllister et al. (1999, 2000) who reported a significant increase in N-retained, enzymetreated diets. Although not measured in this experiment, increased N retention would suggest increased microbial protein synthesis. Increased ruminal microbial protein synthesis following addition of fibrolytic enzymes was indicated in several studies (Hristov et al., 1998; Beauchemin et al., 1999b; Rode et al., 1999). However, Beauchemin et al. (1999b, 2000) reported that increased availability of fermentable carbohydrates after enzyme feeding would likely result in considerably reduced ruminal ammonia-N and stimulate microbial growth. The substantial improvement in digestibility observed in the present study was mostly a result of enzyme addition. Beauchemin et al. (1999b) concluded that the effects of exogenous enzyme supplementation were related to digestibility, mainly because of enhanced ruminal digestion. It was speculated that improved digestibility caused by enzyme treatment of feed was related to improved microbial colonization (Yang et al., 1999). However, Beauchemin et al.
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values than untreated ones. Obtained results were expected and were mainly due to the feeding strategy followed since females were raised as a replacement group and fed according to the NRC guidelines. The restricted feeding prevented them from showing high growth rates or reporting any differences in gain, thus leading to no differences between the two females groups. Figs. 1 and 2 show the growth pattern for both males and females, respectively, when data were analyzed utilizing the repeated measure design. The data present the average gain during two consecutive weighing periods. Males had similar growth pattern during the whole experimental period (Fig. 1). However, except for the 28- and 140-day periods, differences in gain were significant ( P < 0.05), favoring the cellulase-treated group. The average gain for the female groups was variable. The enzyme-fed group gained more ( P < 0.05) at 28, 84 and 196 days of experiment, while no differences ( P> 0.05) in gain were observed at 56 or 112 days. Control females gained higher ( P < 0.05) body weight during the second half of the experiment except for the final results. The reason for this fluctuation in gain is not clear, but it could be a result of the feeding program. However, such data emphasize the effect of direct feeding of fungal cellulase to growing calves raised for meat or as replacement heifers. Intake of treated groups was not different from untreated ones for both sexes. Males were fed ad libitum while females were fed according to the NRC (1989) guidelines. However, treated animals of both sexes consumed more feed than controls. It seemed that feeding cellulase enzyme had led to more efficient
(2000) speculated that improved digestibility was due to improved colonization and by stimulating the endogenous enzyme activity within the rumen. Average initial weights were similar for treated and untreated groups in both sexes. Final weights were higher ( P < 0.05) for treated males than control ones, while no differences were observed between treated and untreated female calves. Males fed cellulase had higher ( P < 0.05) growth performance than unfed males (Table 3). Total gain, average gain (gain between two consecutive weights) and average daily gain were higher ( P < 0.05) for the treated males than those for untreated ones. It appeared that fibrolytic enzymes could improve growth performance of dairy male calves under fattening conditions. Dong et al. (1995) reported that direct fed cellulases had the ability to improve the growth of Holstein calves when administrated orally. Improved growth in males could be explained by an increase in the available nutrients to calves for deposition and growth (Lewis et al., 1995, 1999). These results are in agreement with others who reported significant improved growth and body weight gain that ranged between 9% and 30% of steers fed dry forages (Beauchemin et al., 1995) or high concentrate ration (Beauchemin et al., 1999a). Meanwhile, McAllister et al. (1999) observed that average daily gain was quadratically related to the enzyme concentration. Growth performance of the female group, studied with the same measures as males, did not show any differences compared to untreated females not fed cellulases in their ration. Variations in results obtained were narrow, which was reflected in lack of significance. Yet, treated females had numerically higher
Table 3 Means for performance and growth characters of Friesian calves supplemented with cellulase enzyme
No. Initial weight (kg) Final weight (kg) Total gain (kg) Average gain (kg) Average daily gain (kg/head/day) Average feed intake (kg) Total feed intake (kg) Daily feed intake (kg) Feed conversion ratio ab
Male +
Male
4 189.2 461.2a 271.9a 38.4a 1.39a 300.4 2103.0 10.7 7.7a
4 188.0 414.0b 226.0b 32.3b 1.15b 266.9 1868.2 9.5 8.5b
SE
5.4 3.3 1.0 0.03 9.7 7.8 0.3 0.3
P
Female +
Female
SE
P
0.03 0.01 0.03 0.02 0.07 0.08 0.11 0.04
4 221.5 389.2 167.1 23.9 0.9 186.3 1275.9 6.7 8.2
3 184.7 339.8 154.0 22.0 0.8 174.3 1217.5 6.22 8.91
5.0 1.2 0.9 0.03 4.6 8.5 0.2 0.5
0.08 0.15 0.16 0.13 0.18 0.20 0.21 0.32
Means with different letters within the same species are significantly different ( P < 0.05).
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Fig. 1. Growth pattern of Friesian calves treated with cellulase enzyme.
utilization of the feed utilized and, thus, more growth. Improved digestibility of feed due to enzyme supplementation might result in satisfying requirements and thus resulting in similar feed intake. Some results reported no effect of providing exogenous fibrolytic enzymes on feed intake of dairy cows or beef steers (Schingoethe et al., 1999; Rode et al., 1999). However, Beauchemin et al. (2000) reported an 11% improvement in feed conversion ratio resulting from a 5% decrease in feed intake from enzymetreated ration associated with a 6% increase in body weight gain. Some studies indicated that the improved performance of fibrolytic-enzyme-fed animals was mainly
attributed to increased feed intake (Yang et al., 1999; Beauchemin et al., 2000). However, Beauchemin et al. (1995) and Lewis et al. (1995, 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. This would most probably increase microbial growth
Fig. 2. Growth pattern of Friesian heifers treated with cellulase enzyme.
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and rumen population which, in turn, would increase microbial protein synthesis (Hristov et al., 1998; Beauchemin et al., 1999b, 2000; Yang et al., 1999). Feeding efficiency or feed conversion ratio expressed as kg feed/kg body weight was significantly improved ( P < 0.05) for treated male group compared to control males. However, no differences were observed between treated and untreated females. A good explanation of this could be due to the feeding strategy that caused treated males to gain weight more than females. However, this response was mainly due to the effect of cellulase feeding on feed intake since treated females showed no significant ( P>0.05) differences in growth performance compared to control untreated females. Meanwhile, treated males showed significant differences ( P < 0.05) in both growth parameters and feed intake, which was reflected on improved FCR. 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. Likewise, Beauchemin et al. (1997) reported an 11% improvement in the feed conversion ratio of feedlot finishing cattle fed high concentrate diets. However, the data of the present study are also in agreement with previous results that concluded that the feed conversion ratio or feeding efficiency of dairy cattle improved significantly (Lewis et al., 1999; McAllister et al., 1999; Rode et al., 1999) or numerically (Beauchemin et al., 1999a,b) as a result of direct feeding of different exogenous cellulases. Meanwhile, Yang et al. (2000) concluded no effect of adding exogenous fibrolytic enzymes on the efficiency of feed utilization of lactating dairy cows. Financial analysis data showed no differences in feed cost between treatments for both sexes. However, treatment groups were numerically higher. This increase was mainly attributed to increased feed intake obtained when utilizing enzymes. Likewise, no differences were observed in total cost between treated and untreated groups of both sexes. Gross income and net income (gross income total costs) were higher ( P < 0.05) for groups fed enzyme-treated diets compared to those of control ones. Values for gross income depend mainly on the final weights, which were higher for treated calves than those for controls. Ratio of net income to total costs was higher ( P < 0.05) in treated groups than in control groups for both sexes. Income was mainly a
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function of selling calves after fattening. Treatment with fibrolytic enzymes resulted in higher ( P < 0.05) final weights, which resulted in higher gross income from treated groups compared to untreated groups. Meanwhile, no differences were observed in total costs between treated and untreated groups. Improved net income and ratio were a function of improved gain and final weights in treated groups as a result of adding enzyme. We are not aware of any published data concerning the financial analysis of using exogenous fibrolytic enzymes in livestock production. However, McAllister et al. (2000) reported that enzymatic treatment of lambs fed either a concentrate diet or a forage diet had no effect on the rail grade prices of carcass cuts for both diets. Although the number of animals used in this study is not large enough, one can conclude that feeding fibrolytic enzymes to dairy calves can modify their growth rate and has a positive effect on their performance. Such results are desirable in new farming systems.
References Association of Official Analytical Chemists, 1990. Official Methods of Analysis, 15th ed. AOAC, Arlington, VA. Beauchemin, K.A., Rode, L.M., Sewalt, V.J., 1995. Fibrolytic enzymes increase fiber digestibility and growth rate of steers fed dry forages. Can. J. Anim. Sci. 75, 641. 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 feedlot cattle. Can. J. Anim. Sci. 77, 645. Beauchemin, K.A., Rode, L.M., Karren, D., 1999a. Use of feed enzymes in feedlot finishing diets. Can. J. Anim. Sci. 79, 243. Beauchemin, K.A., Yang, W.Z., Rode, L.M., 1999b. Effects of grain source and enzyme additive on site and extent of nutrient digestion in dairy cows. J. Dairy Sci. 82, 378. 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. J. Dairy. Sci. 83, 543. 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. Feng, P., Hunt, C.W., Pritchard, G.T., Julien, W.E., 1996. Effect of enzyme preparations and in vitro degradation and in vitro digestive characteristics of mature cool-season grass forage in beef steers. J. Anim. Sci. 74, 1349.
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Georing, H.K., Van Soest, P.J., 1970. Forage fiber analysis. Agriculture Handbook, vol. 379. Agr. Res. Serv., USDA, Washington, DC. Hristov, A.N., McAllister, T.A., Cheng, K., 1998. Effect of dietary or abomasal supplementation of exogenous polysaccharide-degrading enzymes on rumen fermentation and nutrient digestibility. J. Anim. Sci. 76, 3146. Lewis, G.E., Sanchez, W.K., Treacher, R., Hunt, C.W., Prithcard, G.T., 1995. Effect of direct-fed fibrolytic enzymes on lactational performance of midlactation Holstein cows. Proceedings, vol. 46. Western Section, American Society of Animal Science, USA, p. 310. Lewis, G.E., Hunt, C.W., Sanchez, W.K., Treacher, R., Pritchard, G.T., Feng, P., 1996. Effect of direct fed fibrolytic enzymes on digestive characteristics of a forage based diet fed to beef steers. J. Anim. Sci. 74, 3020 – 3028. 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. J. Dairy Sci. 82, 611. McAllister, T.A., Oosting, S.J., Popp, J.D., Mir, Z., Yanke, L.J., Hristov, A.N., Treacher, R.J., Cheng, K.J., 1999. Effect of exogenous enzyme on digestibility of barley silage and growth performance of feedlot cattle. Can. J. Anim. Sci. 79, 353.
McAllister, T.A., Stanford, K., Bae, H.D., Treacher, R.J., Hristove, A.N., Baah, J., Shelford, J.A., Cheng, K.J., 2000. Effect of a surfactant and exogenous enzymes on digestibility of feed and on growth performance and carcass traits of lambs. Can. J. Anim. Sci. 80, 35. National Research Council, 1989. Nutrient Requirements of Dairy Cattle, 6th rev. ed. Natl. Acad. Sci., Washington, DC. Rode, L.M., Yang, M.Z., Beauchmen, K.A., 1999. Fibrolytic enzyme supplements for dairy cows in early lactation. J. Dairy Sci. 82, 2121. SAS, 1998. SAS/STAT User’s Guide, Release 7.0 ed. SAS Institute, Cary, NC. 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. J. Dairy Sci. 82, 996. Steel, G.D.R., Torrie, H.J., 1986. Principles and Procedures of Statistics, 2nd ed. McGraw-Hill, Singapore. Yang, W.Z., Beauchemin, K.A., Rode, L.M., 1999. Effect of an enzyme feed additive on extent of digestion and milk production of lactating dairy cows. J. Dairy Sci. 82, 391. Yang, W.Z., Beauchemin, K.A., Rode, L.M., 2000. A comparison of methods of adding fibrolytic enzymes to lactating cow diets. J. Dairy Sci. 83, 2512.