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Effect of Method of Application of a Fibrolytic Enzyme Product on Digestive Processes and Milk Production in Holstein-Friesian Cows

J. D. Sutton^*, R. H. Phipps^*, D. E. Beever^*, D. J. Humphries^*, G. F. Hartnell, J. L. Vicini and D. L. Hard^,1

^* Centre for Dairy Research, Department of Agriculture, University of Reading, Reading RG6 6AR, UK
Animal Agriculture Business, Monsanto Co., St Louis, MO 63198

Corresponding Author:
J. D. Sutton; email: j.d.sutton{at}reading.ac.uk.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Four multiparous cows with cannulas in the rumen and proximal duodenum were used in early lactation in a 4 x 4 Latin square experiment to investigate the effect of method of application of a fibrolytic enzyme product on digestive processes and milk production. The cows were given ad libitum a total mixed ration (TMR) composed of 57% (dry matter basis) forage (3:1 corn silage:grass silage) and 43% concentrates. The TMR contained (g/kg dry matter): 274 neutral detergent fiber, 295 starch, 180 crude protein. Treatments were TMR alone or TMR with the enzyme product added (2 kg/1000 kg TMR dry matter) either sprayed on the TMR 1 h before the morning feed (TMR-E), sprayed only on the concentrate the day before feeding (Concs-E), or infused into the rumen for 14 h/d (Rumen-E). There was no significant effect on either feed intake or milk yield but both were highest on TMR-E. Rumen digestibility of dry matter, organic matter, and starch was unaffected by the enzyme. Digestibility of NDF was lowest on TMR-E in the rumen but highest postruminally. Total tract digestibility was highest on TMR-E for dry matter, organic matter, and starch but treatment differences were nonsignificant for neutral detergent fiber. Corn silage stover retention time in the rumen was reduced by all enzyme treatments but postruminal transit time was increased so the decline in total tract retention time with enzymes was not significant. It is suggested that the tendency for enzymes to reduce particle retention time in the rumen may, by reducing the time available for fibrolysis to occur, at least partly explain the variability in the reported responses to enzyme treatment.

Key Words: dairy cow • fibrolytic enzymes • digestion processes • milk production

Abbreviation key: Concs-E = enzyme product sprayed on concentrate only, Control = TMR fed with no added enzyme, Rumen-E = enzyme product infused into the rumen, TMR-E = TMR diet plus enzyme product

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Attempts to improve feed efficiency in dairy cows by the use of direct-fed fibrolytic enzymes applied to the feed at or only hours before feeding have yielded variable production responses. Feed intake responses have generally been small and inconsistent (Yang et al., 1999; Rode et al., 1999; Kung et al., 1999; Schingoethe et al., 1999; Phipps et al., 2000; Vicini et al., 2003) with only occasional significant increases (Lewis et al., 1999). Milk yield responses have generally been positive but often not significantly so while changes in milk fat and protein have been both positive and negative but also generally nonsignificant (Beauchemin et al., 1999; Lewis et al., 1999; Schingoethe et al., 1999; Yang et al., 1999; 2000; Kung et al., 2000; Phipps et al., 2000; Rode et al., 1999; Vicini et al., 2003).

Enzymes have been applied to different portions of the diets including the forage component, the concentrate component, or the complete TMR but there have been few direct comparisons of these different methods. Beauchemin et al. (1999) suggested that the effects of enzymes might be greater when applied to dry feeds. Yang et al. (2000) compared treating either the TMR or the concentrate only. They concluded that improvements in digestibility of DM, OM, and CP, but not NDF, tended to be greater when the concentrate was treated than when the TMR was treated and only concentrate treatment increased milk yield. In a similar comparison Phipps et al. (2000) found no significant differences between the two methods of applying a fibrolytic enzyme although a numerical increase in milk yield of 1.5 kg/d over the control diet was recorded for the cows receiving the enzyme-treated TMR compared with 0.3 kg/d for cows receiving the enzyme-treated concentrate.

Measurements of total tract digestibility in dairy cows have generally shown positive responses to fibrolytic enzymes with variable but often significant increases in the digestion of DM, OM, NDF, ADF, and N (Yang et al., 1999; 2000; Rode et al., 1999, Beauchemin et al., 1999; 2000). Beauchemin et al. (1999), using cows with rumen and duodenal cannulas, noted that while an enzyme product applied to a TMR had little effect on ruminal fiber digestion, total tract digestibility was increased suggesting that at least part of the mechanism of action of the enzymes was associated with postruminal digestion. In contrast, in a similar study using the same enzyme product but applying it to the hay or to both the hay and concentrates, Yang et al. (1999) also reported increases in total tract fiber digestibility but in this experiment the effect was within the rumen. In both these experiments the enzymes tended to increase particle outflow rate from the rumen associated with a reduction in rumen liquid viscosity. Changes in VFA proportions have generally been very small.

This variability in responses to the application of fibrolytic enzymes is disappointing and suggests that a more basic understanding of their mode of action would contribute to an explanation. This was approached in the present experiment by imposing three different methods of applying a fibrolytic enzyme to the feed of lactating dairy cows in order to try to identify its site of action on the feed and by making measurements of the digestive processes accompanying these treatments. Effects on milk yield and composition were also studied.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Cows and Management
Four multiparous Holstein-Friesian cows, previously fitted with a simple T-shaped flexible cannula in the duodenum about 5 cm beyond the pylorus and a rumen cannula (10 cm diameter), were used in a 4 x 4 Latin square experiment with 5-wk periods. They started on experiment 3 to 8 wk after calving at BW ranging from 558 to 688 (mean 630) kg. From calving until the experiment began, the cows were adapted to the Control diet containing no added enzymes. They were retained in individual concrete tie-stalls with rubber mats and wood shavings as bedding. Exercise was confined to movement to and from weigh-scales at the end of each period of the experiment. The daily rations, in the form of a TMR, were given in two equal feeds at 0900 and 1600 h; orts were removed and weighed daily at 0800 h. The cows had free access to drinking water at all times and were milked in their tie-stalls at 0600 and 1530 h.

Feeds and Diets
The diets and feeds were identical to those used in the accompanying feeding trial (Trial 2 of Vicini et al., 2003). The corn silage was ensiled without additives. The grass silage was prepared from the first-cut of a perennial ryegrass sward cut and ensiled with AddSafe (ammonium tetraformate; Verdugt b.v., Tiel, The Netherlands) at 3 L/1000 kg DM. The concentrate was prepared as a loose mix at the farm feed mill. The TMR was offered ad libitum. It was prepared daily and had the following ingredient composition (kg/t (DM basis)): grass silage 142.5; corn silage 427.5; concentrate 390.0; Regumaize 44 (Intermol, Avonmouth, UK) 4.0. Regumaize 44 is a molasses/urea supplement containing 93.5 g urea/kg fresh weight. The concentrate consisted of (kg/t (DM basis)): milled wheat, 515; rapeseed meal, 259; soybean meal, 151; fish meal, 36; Megalac (Volac Ltd, Royston, UK), 15; minerals, 23.

Treatments
Treatments were based on a comparison of three different methods of adding a fibrolytic enzyme product to the diet, all provided at the same daily inclusion rate. The rate was 82% of that used in Trial 2 of Vicini et al. (2003). The enzyme product used (Biovance Technologies, Inc., Omaha, NE) was extracted from Trichoderma longibrachiatum and contained xylanase and endoglucanase activities of 26,483 and 2645 mol.min^-1g^-1, respectively. The methods of measurement, and full details of all enzyme activities are described by Vicini et al. (2003). The daily amounts of enzyme product were measured by weight. Treatments were:

1. TMR fed ad libitum with no added enzyme (Control).
   
2. Control TMR diet plus enzyme product (TMR-E) added at 2 kg/1000 kg DM (equivalent to 1.64 L/1000 kg DM). The enzyme product was diluted with water such that 10 kg of the diluted enzyme solution was added per 1000 kg TMR fresh weight. Diluted enzyme solution was sprayed on to the TMR and mixed once daily within 1 h of morning feeding. This treatment matched the feeding trial technique (Vicini et al., 2003) and was equivalent to an intake of 0.38 L solution/d at a daily TMR DMI of 20 kg/d.
   
3. Same total inclusion rate of enzyme product per kg diet DM as in TMR-E but the enzyme solution was sprayed on to the concentrate only (Concs-E). The enzyme product was diluted in water such that the diluted solution was added to the concentrate mix at 20 kg/1000 kg fresh weight. The solution was mixed with concentrate daily on the day before it was fed. The intake of enzyme solution was 0.18 L/d at a TMR DMI of 20 kg/d.
   
4. The enzyme product was infused into the rumen (Rumen-E), using a peristaltic pump, at the same daily rate as in TMR-E starting 1 h before the morning feed and ending at 2200 h to match the main period of feed intake. The daily dose of enzyme product was diluted in 0.56 L water to allow an infusion rate of 40 ml/h over 14 h.
   

Measurements
Five-week periods were used with changeover and adaptation in wk 1 to 3, rumen and duodenal sampling for 3 d in wk 4 and total feces collection for digestibility and rate of passage measurements for 6 d during wk 5. Two separate weeks were used for these measurements to reduce the stress on the cows, particularly that caused by the frequent sampling of feces during the early stages of the rate of passage measurements. Diets were offered ad libitum during the first 18 d of each period but for the remaining 17 d the amount offered to each cow was restricted to the average amount it consumed during d 13 to 18 to reduce orts and day-to-day fluctuations in intake during the measurements periods.

Duodenal digesta flow was measured by the Faichney dual-marker method (Faichney, 1975) as described previously (Abdalla et al., 1999). Co-EDTA and Yb acetate were infused into the rumen as duodenal digesta flow markers. Three duodenal samples (approximately 800 ml each) were taken at 6-h intervals on each of the 3 sampling d. Sampling started at 0630 h on d 1 and 2 h later on each successive day to cover the period from 0630 h to 2230 h. The nine duodenal samples were bulked into a single sample and processed as described previously (Abdalla et al., 1999).

Rumen samples were taken at the same time as the duodenal samples. The pH was measured immediately. One sub-sample was acidified with concentrated sulfuric acid (36N) and stored at -20°C for subsequent analysis for ammonia. The other sub-sample was also stored at -20°C; daily bulks were subsequently prepared from these sub-samples for analysis for VFA.

Milk yield was measured daily, and milk samples were taken for analysis at both milkings on 4 successive d in wk 4 and for 6 successive d in wk 5.

Total digestibility and rate of passage were measured simultaneously. Methods of feces and urine collection, sampling, and processing for analysis were described by Sutton et al. (1997; 1998). Rate of passage was measured using Cr-mordanted corn silage stover that was included with the morning feed on d 1 of the fecal sampling period. Corn silage was dried at 60°C for 48 h, and the stover was separated from the grain and any large pieces of stalk by "winnowing" using a domestic fan. The methods of mordanting were based on the techniques of Uden et al. (1980). Starting 7 h after the dose was administered, all voided feces were collected for periods that increased from between 3.5 and 5 h for the first 39 h after dosing to 12 h after 65 h. The mean collection times for each period were: 9, 13, 18, 23, 26.5, 30, 34, 37.5, 42, 47, 51, 55, 59, 67, 79, 91, 103, 115, 127, and 139 h. after dosing. The feces in each collection period were mixed thoroughly, and a subsample was dried at 100°C for 48 h before analysis for total Cr by atomic absorption spectrosopy (Gasa et al., 1991). An aliquot was also retained and added to a frozen 6-d bulk for subsequent analysis for digestibility measurements.

Viscosity of rumen and duodenal digesta fluid were measured using a technique similar to that described by Yang et al. (1999) but making the measurements with a rotating viscometer. Samples were taken 1 h prefeeding and 3 and 7 h after the morning feed on 1 d during wk 5. They were stored frozen until the end of the experiment. They were then thawed and warmed to 39°C. Larger particles were removed by passing the digesta through a 105 micron mesh sieve. The viscosity of the strained fluid was then measured.

Analyses
All analyses were conducted out using standard chemical methods as described previously (Sutton et al., 1997; 1998; Abdalla et al., 1999). All DM values for the silages are reported on a volatile-corrected basis. The NDF and ADF were analyzed using the Ankom Fiber Analyzer (Ankom Technology Corp., Fairport, NY).

Calculations
Flow of nutrients at the duodenum was determined from mathematical calculation of true digesta flow (Faichney, 1975) based on the measured concentrations of Yb and Co in whole digesta as collected and in a low-solids digesta fraction obtained by centrifuging whole digesta at 3500 x g for 20 min. Apparent digestibility anterior to the duodenum was calculated as the difference between nutrient intake and calculated nutrient flow at the duodenum and is reported as rumen digestibility.

Apparent digestibility of the same diets in the total tract was measured in the same cows in the following week.

There were small differences in DMI between the duodenal and fecal measurement periods ranging between 0.28 and 0.74 kg DM/d for the four treatments. To reconcile the results from the two periods, all calculations were related to the mean intake of each nutrient measured during both the duodenal and fecal collections. It was assumed that the efficiency of digestion (digestibility coefficient) was unaffected by these minor adjustments. The amounts of nutrients digested postruminally were calculated by difference between adjusted flow at the duodenum and the adjusted fecal output, and this was then related to the duodenal flow to give postruminal digestibility which is therefore a measure of the digestibility of a nutrient entering the duodenum from the abomasum, not of a nutrient ingested in the feed.

Parameters to describe rate of passage were calculated according to Dhanoa et al. (1985). The model describes passage in terms of a series of rate constants and a time delay. Data were resolved into a slow rate constant (k₁) and a fast rate constant (k₂) representing passage through two major pools within the digestive tract, and a time delay representing flow through a tube and also through minor pools. Interpretation of these parameters is subject to much debate. Based on the conclusions of Gasa et al. (1991), it was assumed for the purposes of this paper that both rate constants reflect activities in the rumen with k₂ representing rates of breakdown of large particles to small particles and k₁ the rate of passage of the small particles out of the rumen while transit time is considered to describe the passage of particles through other, smaller pools plus passage through the intestines. The reciprocal of the rate constants gives the mean retention time of a particle in its pool.

Statistical Analyses
The statistical significance of treatment effects was determined by analysis of variance with effects for cows, periods and diets (Lawes Agricultural Trust, 1990). Differences between individual treatment means at P < 0.05 were determined using Duncan’s Multiple Range Test.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Composition of the Feeds
The silages were of good quality (Table 1). The corn silage was mature (360 g DM/kg) with a high starch content.

View larger version (16K): [in this window] [in a new window]   Figure 1. Rumen ammonia concentrations from 0630 h to 2230 h for cows fed Control (), TMR-E (), Concs-E () or Rumen-E (•). Feeding times are shown ().

View larger version (12K): [in this window] [in a new window]   Figure 2. Rumen pH from 0630 h to 2230 h for cows fed Control (), TMR-E (), Concs-E () or Rumen-E (•). Feeding times are shown ().

The molar proportion of acetic acid was numerically lower, and the molar proportions of propionic and n-valeric acids were numerically higher with all enzyme treatments than with Control, though not all the differences reached significance. The ratio of acetic plus n-butyric acids to propionic acid was numerically lower with all treatments than with Control, significantly so (P < 0.05) with Concs-E and Rumen-E.

Digesta Viscosity
Rumen fluid viscosity tended to be lower on enzyme treatments than Control but the only significant difference was for TMR-E 1 h prefeeding (Table 10). There was no consistent pattern for duodenal fluid though, in contrast to the results for rumen fluid, values tended to be higher on enzyme treatments than Control 1 h prefeeding.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Production Responses
Treatment TMR-E corresponded to treatment Enzyme B in the early lactation feeding trial (Trial 2) of Vicini et al. (2003) and treatment T2 in the mid-lactation feeding trial of Phipps et al. (2000). Production responses to the inclusion of the enzyme in the TMR were similar in all three experiments with nonsignificant increases in milk yield (1.5, 0.9, and 0.8 kg/d, respectively) and only minor changes in feed intake (0.4, -0.2 and 0.4 kg/d, respectively). However the significant increase in milk protein yield observed in the present trial was not found in either feeding trial and must be viewed with some caution. The tendency for milk fat content to be lower on all enzyme treatments than on Control in the present experiment was in agreement with the results of the accompanying feeding trial (Trial 2, Vicini et al., 2003) but milk fat responses reported elsewhere have not shown a consistent pattern (Yang et al., 19992000; Lewis et al., 1999; Schingoethe et al., 1999; Beauchemin et al., 1999; Rode et al., 1999, Kung et al., 2000; Vicini et al., 2003).

The nonsignificant increases in OM intake and digestibility on TMR-E in the present trial resulted in a nonsignificant increase in digestible OM intake of 0.55 kg/d or 3.9%. This increase in digestible OM intake is equivalent to approximately 9.5 MJ metabolizable energy (ME) (at 17.5 MJ ME/kg digestible OM) and, though small, is theoretically sufficient to support the production of the observed extra 1.5 kg milk (at approximately 5 MJ ME/kg milk).

It was hoped that comparison of the responses to the three methods of applying the enzyme would help to define its mode of action. There were no significant differences in feed intake or milk yield among the three enzyme treatments. Milk protein concentration was highest on Concs-E while milk protein yield was higher on both TMR-E and Concs-E than on Control with Rumen-E intermediate. In the associated feeding trial (Phipps et al., 2000), method of enzyme application also had no significant effects on feed intake or milk yield or composition. These results conflict with the conclusion of Beauchemin et al. (1999), from results of several studies, that fibrolytic enzymes are most effective when added to the dry components of the feed as this allows greater opportunities for the enzyme to adhere to the feed and so enhance digestion. This conclusion was lent some support by results of a subsequent experiment in which there was a significantly higher milk volume when the concentrate was treated rather than the TMR, though fat-corrected milk yield did not increase (Yang et al., 2000).

Rumen Digestive Processes
There were no significant differences among the three methods of enzyme addition in digestibility of DM or OM in the rumen. Rumen digestibility of NDF was significantly higher with Rumen-E than TMR-E but total tract digestibility of NDF was unaffected by the treatments. It follows, therefore, that postruminal digestibility was enhanced on TMR-E and was significantly higher than on Rumen-E. This trend for a shift in the site of NDF digestion to the postruminal tract on TMR-E is in agreement with results reported by Beauchemin et al. (1999), also involving enzyme treatment of a TMR. These workers argued that this effect reflected the rapid separation of the enzyme from the TMR in the rumen, and its passage to the intestines where it remained active. If that were the mode of action in the present experiment, one would expect to see the same trend with Rumen-E where the enzyme was infused directly into the rumen fluid yet the opposite was observed with enhanced rumen fiber digestion. There appears to be no single unifying explanation for these various observations.

The extent of rumen digestion is the resultant of the conflicting effects of digestive capacity and retention time. Assuming that both k₁ and k₂ describe particle movements within the rumen (Gasa et al., 1991), all three methods of enzyme addition in the present experiment resulted in a reduced rate of breakdown of large particles to small particles (k₂) but enhanced rate of small particle passage out of the rumen (k₁). On this interpretation, it was calculated that mean particle retention time in the rumen was reduced by between 7.1 and 10.4 h by the enzyme treatments, though this effect, while substantial, was not significant. This tendency for a reduction in retention time was associated with a rather more variable reduction in rumen fluid viscosity, particularly in the prefeeding sample, which may have contributed to the increased rate of passage. Tendencies for increased rate of particle passage out of the rumen and reduced rumen fluid viscosity with enzyme-treated feeds have also been reported by Beauchemin et al. (1999) and Yang et al. (1999). It was argued by Beauchemin et al. (1999) that the enhanced rumen particle outflow rate was an explanation for the trends for a shift in the site of fiber digestion from the rumen to the hind-gut in the presence of enzymes, but this fails to explain why similar effects on rate of passage were seen with all three methods of enzyme addition in the present experiment yet rumen NDF digestion was enhanced on Rumen-E and depressed on TMR-E. It seems reasonable to suggest that the tendency for enzymes to reduce particle retention time in the rumen may, by reducing the time available for fibrolysis to occur, at least partly explain the variability in the reported responses to enzyme treatment.

The absence of any response in DMI to the increased rate of particle passage from the rumen with added enzymes suggests that, in this experiment, feed intake was controlled by factors other than rumen fill.

The changes in rumen VFA proportions in response to enzyme addition in the present experiment were relatively small in agreement with other reports (Kung et al., 1999; Yang et al., 1999; Beauchemin et al., 1999; Beauchemin et al., 2000), indicating that fibrolytic enzymes have only small and inconsistent effects on rumen fermentation products. The changes in the present experiment, though small, did result in a significant reduction in the ratio of acetic plus butyric acids to propionic acid which, on the basis of regressions calculated for cows given diets of hay and concentrates (Sutton et al., 1988), would have been sufficient on average to account for the small reduction in milk fat content on all enzyme treatments.

Of more potential significance in the context of the effects of enzymes on fiber digestion in the rumen was the low rumen pH in the present experiment. At values substantially below 6.0 for most of the day it seems highly likely that fiber digestion in the rumen would have been adversely affected. On the other hand, the fibrolytic activity of this enzyme has been shown to be pH-sensitive in laboratory studies (Vicini et al., 2003) with maximum activity at pH values between 4.0 and 6.0 and a sharp decline at higher pH values. It could thus be argued that the low rumen pH values in the present experiment might have enhanced the fibrolytic activity of the enzyme compared with diets producing more usual rumen pH values in the range 5.8 to 6.5, yet the observed responses in NDF and ADF digestion in the rumen were very variable.

Total Tract Digestibility
The effects of the enzymes on total tract digestibility in the present experiment were small. OM digestibility was slightly but significantly higher on TMR-E than Concs-E but no differences in NDF, ADF or total N digestibility were established while the significant differences in starch digestibility were too small to be of any practical consequence. In a series of digestibility measurements with lactating cows by the Lethbridge group, both OM and NDF digestibility have generally been enhanced by the enzymes whether they were added to the TMR or the concentrates (Beauchemin et al., 1999; Yang et al., 1999; Rode at al., 1999; Yang et al., 2000) though with some evidence that this may be reversed at high levels of inclusion (Beauchemin et al., 2000). The reasons for the difference in responses are unclear but do not appear to relate to the use of different enzyme sources.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Within the present experiment the most favorable production responses were obtained when the enzyme product was applied to the TMR, and there was evidence, though nonsignificant, that milk production was highest on this treatment, possibly because digestible OM intake was increased on this treatment. However it is difficult to explain why, when all three methods of enzyme addition had similar effects on rumen fermentation and digesta kinetics, only TMR-E had a significant effect on rumen NDF digestion and why, in particular, this was negative. Taking results from elsewhere into account, there is strong evidence that fibrolytic enzymes do enhance particle outflow rate from the rumen and, in some instances, tend to shift fiber digestion from the rumen to the postruminal tract. The reasons for this are also unclear and are difficult to relate to the hypothesis that it reflects the passage of the fibrolytic enzymes to the intestines in the liquid digesta since direct infusion of the enzymes into the rumen in the present experiment failed to have any significant effect on fiber digestion compared with Control and resulted in higher rumen digestion and lower postruminal digestion than enzyme treatment of the TMR. The conflict between reduced rumen retention time and enhanced fibrolytic activity appears to offer one possible explanation for the variable responses reported in the literature.

The experiment has provided clear evidence that fibrolytic enzymes added to the diet or infused directly into the rumen are capable of manipulating the processes of rumen digestion in lactating dairy cows. However further studies of the mode of action of such enzymes will be necessary if consistent, and positive responses are to be achieved.

	ACKNOWLEDGEMENTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
This project was funded by Monsanto Company. Statistical analyses were conducted by Mrs. R. J. Elliott, digesta kinetics were calculated by Mr. J. Gallagher of the Applied Statistics Department of the University of Reading and chemical analyses were carried out by Dr. I. Mueller-Harvey and colleagues in the Analytical Laboratory of the Faculty of Agriculture and Food of the University of Reading.

	FOOTNOTES

 
¹ Current address, Renessen LLC, Bannockburn, IL 60015.

Received for publication June 11, 2002. Accepted for publication August 20, 2002.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 


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