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Fibrolytic enzyme supplementation, a tool for enhancing energy intake in growing-finishing feedlot cattle |
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Author: R.A. ZINN and R.A. WARE - University of California (Courtesy of Alltech Inc.)
Digestion is a metabolic process that occurs largely through the catabolic action of enzymes. Limitations on rate of digestion are a function of (1) enzyme reactivity or velocity (enzyme:substrate affinity); (2) enzyme concentration; and (3) exposure rate of substrate to the enzymatic process. In all, it should be clear that there are many ways to promote enzymatic activity and hence, the digestive processes of cattle.
Factors affecting fiber digestion
Ruminants do not produce fibrolytic enzymes themselves, but depend entirely on a symbiotic relationship with microorganisms for the digestion of plant cell walls. Plant cell walls are comprised of a complex array of carbohydrate fractions including hemicellulose, cellulose and lignin that impart rigidity and structural stability needed for growth. These fractions are collectively termed neutral detergent fiber (NDF). Although cellulose is the predominant component of plant fiber, it is important to recognize that the cellulose microfibrils are tightly bound by covalent bonding in a matrix of other fiber components, particularly hemicelluloses and lignin. Analogous to reinforced concrete, digestion of cellulose is limited by this hemicellulose-lignin encasement.
Hemicellulose is composed of dense pentose polymers known as xylans. Fibrolytic bacteria hydrolyze these complex bundles of cellulose and xylans via extensive coordination or synergy between cellulase and xylanase enzymes that are held in close association as part of a marvelous fibrolytic complex (Tomme et al., 1995). During the course of digestion, hemicellulose and cellulose Fibrolytic enzyme supplementation, a tool for enhancing energy intake in growing-finishing feedlot cattle fractions are broken down into simpler sugars; lignin is indigestible.
Depending on hydration, cellulose crystallization and degree of cross linking, the digestion rates of plant fiber are quite variable. In stark contrast with starch digestion, ruminal digestion of pure cellulose, even under optimal conditions, is relatively slow, ranging between 3 to 12%/hr (Mertens, 1992). Fibrolytic enzymes are constitutive enzyme complexes, directly associated with the microorganisms that produce them. Hence, ruminal factors that influence the growth and dispersion of ruminal fibrolytic organisms will also directly affect fiber digestion. Critical factors that are known to suppress growth of fibrolytic microorganisms include supplemental fat, ionophores, antibiotics, and low ruminal pH.
SUPPLEMENTAL FAT
The negative associative effects of supplemental fat on ruminal fiber digestion are well documented (Brethour et al., 1957; Davison and Woods, 1960; Devendra and Lewis, 1974; Boggs et al., 1987; Zinn, 1988; 1989; 1994; Zinn and Plascencia, 1993; 1996). Depression of ruminal fibrolytic capacity with fat supplementation typically ranges between 15 and 40%. The basis for the depression is not due to physical coating of feed particles (Zinn and Plascencia, 1996), but rather to the toxic effects of supplemental fat on ruminal fibrolytic organisms, particularly protozoa. In vitro studies (Henderson, 1973; Maczulak et al., 1981) demonstrate that the unsaturated fatty acids, particularly C18:1, play the more active role in inhibiting ruminal cellulolytic microbes.
SUPPLEMENTAL IONOPHORES
One of the more consistent effects of ionophore supplementation on digestive function has been a reduction in ruminal fiber digestion (Simpson et al., 1976; Poos et al., 1979; Zinn, 1987; Zinn and Borquez, 1993).
ANTIBIOTICS
Tetracycline antibiotics have been found to be strong inhibitors of cellulose digestion both in vitro (Simpson et al., 1976; Baldwin et al., 1982) and in vivo (Tillman and McVicar, 1956; Evans et al., 1957; Zinn, 1992). As little as 22 mg of chlortetracycline/ kg of diet has decreased total tract fiber digestion in cattle by as much as 5 to 15%. Zinn (1992) observed that supplementing a 29% forage receiving diet with 130 mg/kg tetracycline reduced ruminal fiber digestion in Holstein steers by 30%.
RUMINAL PH
Ruminal pH affects fiber digestion through its influence on the specific growth rates of cellulolytic bacteria. Growth of cellulolytic bacteria is optimal at ruminal pH above 6.5. Between pH values of 6.5 to 6.0, the specific growth rate decreases 14%/ hr for every 0.1 unit decrease in ruminal pH.
Cellulolytic bacteria do not grow at ruminal pH below 6.0. This toxicity is due apparently to the inability of cellulolytic bacteria to regulate intracellular anion concentrations at lower ruminal pH (Russell and Wilson, 1996). Increasing the level of nonstructural carbohydrates (grain, molasses, bakery waste, etc.) in the diet, increasing level of feed intake, and(or) increasing the extent of grain processing are likely to depress ruminal pH.
Fiber ‘digestion’ versus ‘digestibility’
The term ‘digestibility’ is qualitative, referring to susceptibility to degradation. In contrast, the term ‘digestion’ refers to the extent of degradation. The extent of ruminal fiber digestion is a function of rate of digestion (Kd) and rate of passage (Kp) [digestion = Kd/(Kd + Kp]. A primary factor that influences rate of ruminal fiber digestion is the accessibility of substrate to the fibrolytic process, in particular, the physical chemical interactions of cellulose, hemicellulose and lignin. This is a unique characteristic of individual forages or fiber sources, and is influenced by stage of maturity, storage time post-harvesting, method of preservation and processing.
Aside from the unique physical-chemical aspects of the fiber sources, rate of ruminal fiber degradation will be influence by the ruminal fibrolytic capacity. This capacity is a function of ruminal microbial distribution and adaptation. As stated previously, this capacity will be greatly influenced by ruminal environmental factors, including pH and presence of toxins or inhibitors.
The retention time of fiber in the rumen, or the length of time that fiber is exposed to the fibrolytic process, is influenced by initial fiber particle size, rate of particle size reduction (chewing, rumination), particle density and rate of digestion. The basis for particle retention is not altogether certain. Larger particles may become trapped in or on the floating ruminal mat, thus restricting access to the reticuloomasal orifice. Larger particles may also be screened by omasal lamina and returned to the rumen, increasing retention time of larger particles.
Although particles of 5 cm may pass through the reticulo-omasal orifice (Welch, 1986), most particles leaving the rumen are smaller than 1 mm. Welch (1986) noted that more than half (55.2%) of the ruminal DM passed through a 0.8-mm sieve. While mastication during feed ingestion and rumen fermentation play key roles in the diminution of particulate matter, rumination is the most important activity in reducing the particle size of undigested coarse material. Selected stems from several different species and maturities of hay (2 cm in size) showed no change in physical form when incubated in ruminal fluid of fistulated steers in nylon bags for 10 days (Welch, 1982). Lengths of plastic ribbon 7- cm long with a 0.90 specific gravity required extensive rumination (particle size reduction) before they could pass from the rumen (Welch, 1982).
It is tempting to attribute size selection to the reticulo-omasal orifice. McBride et al., cited by Welch (1986), photographed the orifice using fiber optics and found that in feeder cattle the maximum opening was more than 4 mm, and more than 2 cm in cows (Welch, 1982); making it difficult to explain the separation solely on the basis of orifice action.
Since more than 50% of ruminal DM will pass a 600 μm sieve, other mechanisms, including particle density and integrity of the ruminal mat are also likely to play important roles. Whatever the mechanism, it is clear that feed particles must be reduced to a size of less than 1 mm before they are likely to pass on to the lower digestive tract. The relationship between initial particle size of fiber (before being eaten) and ruminal retention time is given by: Kp = 3.21 - .016eNDF, where eNDF refers to the initial particle size of forage (before ingestion).
A role for enzyme supplementation
It has been clearly demonstrated that deficiencies in fibrolytic capacity can be partially overcome by enzyme supplementation. Combinations of cellulase and xylanase enzymes have enhanced both in vitro (Feng et al., 1996; Howes et al., 1998), and in vivo (Ambrosia et al., 2001; Beauchemin et al., 1995, 1999; Lewis et al., 1996; Lopez-Soto et al., 2000; Murillo et al., 2000; Ware and Zinn, 2001; Ware et al., 2002; Zinn and Salinas, 1999) NDF digestion. Nevertheless, growing-finishing diets for feedlot cattle are characteristically low in forage. Will modest increases in fiber digestion enhance feedlot cattle growth performance when dietary NDF concentrations are low?
Of primary concern with respect to fiber digestion is its relationship with energy intake and hence animal performance. The rumen has an upper limit on its physical capacity. As the rate of ruminal fiber digestion decreases, the amount of slowly digestible OM remaining in the rumen increases. Zinn and Salinas (1999) observed that maximal dry matter (DM) intake in cattle is a predictable function of initial shrunk weight (IW, kg) of cattle when placed in the feedlot, current weight or average weight during interval of interest (W, kg), dietary NDF (%), forage eNDF (expressed as a percentage of forage NDF), and ruminal NDF digestion (PRDNDF, %): DMImax = (((.098 * IW) + 26.24) * (W.75)) / ((.01 * NDF * (1 - (.01 * PRDNDF))) / ((.77 - (.00386 * ENDF)) * (-.037 + (.042 * NDF) - (.00031 * (NDF2))))).
The influences of changes in ruminal NDF digestion on maximum DM intake and daily gain using the above model are shown Figure 1. In this example, we are simulating feedlot performance of a steer calf weighing 350 kg. The calf weighed 200 kg upon arrival into the feedlot, and is being fed a steamflaked corn-based finishing diet (NEm = 2.20 Mcal/ kg) containing 12% forage (ground sudangrass hay, 95% eNDF) and 14% NDF (DM basis).
Notwithstanding the very high energy density of the diet, the model predicts that when ruminal NDF digestion is less than 30%, DM intake will be less than optimal for achieving the steer’s genetic potential for growth. A 20% reduction in ruminal NDF digestion (from 30 to 24%) is expected to depress DM intake by 8% and daily gain by 12%.
We have completed three trials evaluating the influence of fibrolytic enzyme supplementation on feedlot cattle growth performance. Our first trial (Zinn and Salinas, 1999) involved 96 crossbred steer calves in a 64-day growing trial. Calves were blocked by weight and assigned within weight groupings to 16 pens (6 steers/pen). Treatments consisted of a steam-flaked corn-based growing diet containing 22% forage (sudangrass hay) top-dressed with 0 or 15 g/hd/d of FibrozymeTM (an enzyme blend having both xylanase and cellulase activity; Alltech Inc., Nicholasville, KY). Calves were allowed ad libitum access to experimental diets.
Fresh feed was provided twice daily (roughly 0700 and 1500 hrs). Fibrolytic enzyme supplementation increased final weight (3%, P<0.10), average daily gain (6%, P = 0.13), and DM intake (4.5%, P<0.05). Enzyme supplementation did not influence the net energy (NE) value of the diet.
In our second feedlot trial (Pereira and Zinn, 2001), 72 yearling crossbred steers were used in a 121-day growing-finishing trial to compare the effects of 0 vs 15 g/hg/d of FibrozymeTM on growth performance. During the first 84 days (growing phase), the basal diet contained 22% forage and 65% steam-flaked sorghum. From day 85 to 121 (finishing phase), the basal diet contained 12% forage and 75% steam-flaked sorghum. Enzyme supplementation increased average daily gain (ADG) by 6% (P<0.10) during the growing phase, and by 20% (P<0.05) during the finishing phase. Overall, enzyme supplementation increased carcass weight (2.7%, P<0.05) and ADG (10%, P<0.01).
In contrast with our first trial, enzyme supplementation did not influence (P>0.10) DM intake, but increased (P<0.10) dietary NE by 5.1% and gain efficiency by 6.3%. Increased ADG without concurrent increases in DM intake with enzyme supplementation was not expected, particularly during the late finishing phase when dietary fiber levels were low. Results of this trial suggest that enzyme supplementation may also enhance cattle performance in a manner independent of its effects on fiber digestion.
Figure 1. Influence of ruminal fiber digestion on DMI and ADG. Simulation based on Zinn and Salinas (1999) for 350 kg steer consuming a steam-flaked corn-based finishing diet (2.20 Mcal/kg NEm) containing 12% forage.
In our third feedlot trial (Ware et al., 2002), we examined the influence of level of enzyme supplementation (0, 5, 10, and 15 g/hd/d of FibrozymeTM on cattle performance. Ninety-six crossbred steer calves (184 kg) were used in 261- day randomized complete block experiment. Steers were blocked by weight and assigned to 16 pens (6 steers/pen). During the first 70 days (growing phase), the basal diet contained 22% forage (10% alfalfa hay, 12% sudangrass hay) and 64% steamflaked corn. From day 71 to 261 (finishing phase), the basal diet contained 12% forage (4% alfalfa hay, 8% sudangrass hay) and 76% steam-flaked corn. As with our first trial, enzyme supplementation increased DM intake and ADG during both the growing and finishing phases. Overall, enzyme supplementation increased ADG by 9% (linear component, P<0.05), and gain efficiency by 3% (linear component, P<0.10). Improvements in ADG were due to treatment effects on feed intake. The effect of enzyme supplementation on dietary NE was small (1%; cubic component, P = 0.13).
Optimum growth performance responses were obtained with 10 g/d enzyme supplementation.
Implications
Notwithstanding the high energy density and comparatively low NDF content of growingfinishing diets, fibrolytic enzyme supplementation can enhance growth performance of feedlot cattle.
This effect is due primarily to increased energy intake mediated by enhance ruminal fibrolytic capacity. However, enzyme supplementation may also enhance growth performance independently of its effects on fiber digestion, possibly in relation to increased ruminal turnover, and(or) alterations in end products of fermentation. Optimum growth performance in feedlot cattle may be obtained with as little as 10 g enzyme/hd/d.
References
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Zinn. R.A. and J. Salinas. 1999. Influence of Fibrozyme on digestive function and growth performance of feedlot steers fed a 78 % concentrate growing diet. In: Biotechnology in the Feed Industry, Proceedings of the 15th Annual Symposium (T.P. Lyons and K.A. Jacques, eds). Nottingham University Press. UK. Zinn, R.A. 1994. Detrimental effects of excessive dietary fat on feedlot growth performance and digestive function. Prof. Anim. Sci. 10:66-72.
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Authors: R.A. ZINN and R.A. WARE
Department of Animal Science, University of California, Davis, CA, USA
Author: R.A. ZINN and R.A. WARE - University of California (Courtesy of Alltech Inc.)
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 DISCUSSIONS ON THIS ISSUE.
 
| 02/13/2007 |
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aliyu lawal aliyu
Farmer/aliyu Farms
Kaduna - Nigeria |
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This is very interesting. I can use this supplement in my cattle fattening farm. Pls how can I get this supplement, I need it. THANKS A LOT.
Aliyu | Answer Checked by Engormix.com  |
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