The effect of pepsin pretreatment of herbage on the prediction of dry matter digestibility from solubility in fungal cellulase solutions

Cellulase preparations from different fungi differed markedly in their ability to solubilise herbage and cellulose; T. viride cellulase was the most active, solubilising 70% of cellulose paper in 24 h. The correlation of cellulase solubility with the in vivo and in vitro dry matter digestibility of grasses, and with the in vitro digestibility of legumes was markedly improved by pretreatment of the herbage with acid pepsin. Using the two stage technique, closely similar regression lines were obtained for predicting the in vitro digestibility of both grasses and legumes. Use of the pepsin treatment also enabled a less active Basidiomycete cellulase to be used with results very similar to those obtained with the T. viride enzyme. The technique is proposed as a more rapid, convenient and precise method of predicting digestibility than the usual in vitro procedure.     

Prediction of the digestibility of the dry matter of tropical forages from their solubility in fungal cellulase solutions.

Correlations between in vitro dry matter (DM) digestibility and amount of DM dissolved in acid pepsin and cellulase enzymes for 24 tropical forage samples gave a value of 0.91 but a high sample standard deviation of 6.50 and a coefficient of variation of 25 %. This suggests that the cellulase technique requires further study if it were to be used as a predictor of rumen liquor in vitro digestibility values for tropical grasses and legumes. An improved correlation of r = 0.98 with sample standard deviation of 2.29 was obtained when percent DM dissolved in acid-pepsin and cellulase enzymes was compared with the in vivo dry matter digestibility values of 11 tropical forage grasses and legumes. This result suggests that the pepsin-cellulase technique may be used to predict in vivo DM digestibility values in tropical grasses and legumes.     

The relationship between the in vivo digestibility of hay and its solubility in pepsin–hydrochloric acid and fungal cellulase solutions

The determination of the solubility of the organic matter (OM) of hay in pepsin-hydrochloric acid and fungal cellulase solution according to the method of Jones and Hayward¹ gave reproducible results when applied to four hays with solubilities of 51.5, 49.1, 63.5 and 40.2%. In addition the correlation of the soluble OM determined by the cellulase solubility technique and in vivo digestibility studies for 34 hays produced highly significant correlations for the digestibility of the OM in the dry matter (DM) (r=0.91, RSD ± 2.180) and the OM digestibility (r=0.91, RSD ± 2.362). These data indicate that the determination of the solubility of OM in fungal enzyme solution is an acceptable method for the prediction of in vivo digestibility of the OM in the DM of hays.     

Organic matter digestibility of poplar (Populus) and willow (Salix) forage trees and its in vitro prediction

Cuttings from poplar (Populus) and willow (Salix) trees are used increasingly as supplementary feed for livestock in summer‐dry and drought‐prone regions of New Zealand. The present experiment aimed to measure in vivo organic matter digestibility and digestibility of organic matter in the dry matter in tree fodder and investigated whether the in vitro system of Roughan and Holland can be used to predict in vivo organic matter digestibility and digestibility of organic matter in the dry matter in poplar and willow tree fodder, which contains high concentrations of secondary compounds, including condensed tannin. In vivo work showed that the digestibility of tree fodder declined from late spring to autumn (p < 0.05) and that this decline was much smaller than the decline in digestibility of grass‐based pastures in New Zealand over the same time period. Mean metabolizable energy concentrations and digestibilities were generally higher for willow than for poplar. The in vitro enzymatic system of Roughan and Holland can be used to predict in vivo digestibility of tree fodder. A standard curve using in vivo values determined with animals fed tree fodder would be preferable, owing to the very different chemical compositions of pasture and tree fodder, particularly the greater concentration of secondary compounds in willow and poplar. However, the accuracy and the range of prediction need to be improved. Willow and poplar had similar ME concentrations to high‐quality lucerne hay; willow cuttings also had similar ME and CT concentration to vegetative Lotus corniculatus, a high‐quality forage legume. Copyright © 2005 Society of Chemical Industry     

Predicting in-vivo digestibilities of herbages by exhaustive enzymic hydrolysis of cell walls

A potent cellulase solution was prepared from culture filtrates of an artificially-produced mutant of Trichoderma species. The filtrates were diluted to provide a standardised, simulated rumen liquor which was then used to study the correlation between cellulase digestibility and in-vivo digestibility of a range of plant materials. Cell walls of whole, dried plant material were either not attacked by the cellulase or were attacked only very slowly, but cell walls isolated by neutral-detergent extraction were readily hydrolysed. Cellulase digestibility, defined as the percentage of whole, dry plant material solubilised by neutral-detergent extraction followed by exhaustive hydrolysis with standardised cellulase, was highly correlated with in-vivo dry matter digestibility (DMD) (r=0.98) and predicted that parameter with reasonable accuracy (r.s.d., residual standard deviation = 2.83). The form of the regression equation was in-vivo DMD = 0.98 × cellulase solubility - 10.12, suggesting that the same factors limited cellulase and in-vivo digestibility. The method was simple and reliable and results were known within 48 h.     

Nutritive evaluation of herbage from permanent meadows by near‐infrared reflectance spectroscopy: 1. Prediction of chemical composition and in vitro digestibility

This study was implemented to evaluate the potential of near‐infrared reflectance spectroscopy (NIRS) technology to estimate the chemical composition and in vitro digestibility of botanically complex herbage mixtures characterised, moreover, by a noteworthy variation among samples in the maturity of the forage plants. A total of 107 herbage samples harvested from permanent meadows located in the uplands of León (northwestern Spain) were analysed to determine their chemical composition. In addition, the in vitro digestibility of each herbage sample was measured by two different in vitro procedures using buffered rumen fluid. A Bran + Luebbe InfraAlyzer 500 spectrophotometer was used to obtain the near‐infrared spectra corresponding to each herbage sample. Prediction equations developed for the estimation of the chemical components showed that NIRS technology could predict these parameters accurately, especially the crude protein and neutral detergent fibre contents ( in both cases). In vitro digestibility parameters could also be predicted with an acceptable degree of accuracy using NIRS technology, particularly the in vitro Tilley and Terry organic matter digestibility ( , standard error of prediction (SEP) = 2.165% organic matter) and the in vitro dry matter true digestibility measured according to the Goering and Van Soest procedure ( , SEP = 2.208% dry matter). Copyright © 2005 Society of Chemical Industry     

Ruminal degradation of tannin‐treated legume meals

The inefficiency of protein utilisation by ruminants fed protein concentrates (based on legume meals) causes serious economic loss and environmental damage owing to their rapid hydrolysis and deamination in the rumen. Thus efforts aimed at slowing the ruminal fermentation of such feeds are needed, and recent studies have observed potentially positive effects of tannins on ruminant nutrition under certain circumstances. Tannins are a complex group of naturally occurring plant polyphenols characterised by their ability to bind with proteins. This property of tannins is considered responsible for the decreased ruminal digestibility of forages both in vivo and in vitro. Under that perspective, commercial tannic acid was added at three proportions (10, 25 and 50 g kg^?1 on a dry matter basis) to four different legume meals (horse bean, kidney bean, soybean and pea), and the effect on in situ dry matter and crude protein ruminal disappearance was assessed. The results confirmed the dose‐dependent (although not persistent after 48 h) slowing of in situ digestibility, this effect being significant at the highest tannin treatment when compared with untreated samples. Scanning electron microscopy revealed that soybean seed endosperm cell walls were protected from digestion by the ruminal microbiota, while the digestion of starch granules was relatively unaffected by tannic acid. Electrophoresis of the protein fractions confirmed the lower digestibility of tannin‐treated seeds as well as the relative lack of alteration of the electrophoretic profile of individual proteins. Implications for the digestion of concentrates in ruminants are discussed. Copyright © 2004 Society of Chemical Industry     

In vitro digestibility of processed and fermented soya bean,cowpea and maize

Tropical legumes, ie soya bean and cowpea, were pre‐treated and subsequently fermented using pure cultures of Rhizopus spp. Impact of soaking, cooking and fermentation of the legumes on their digestibility was determined using an in vitro digestion method. Processing of white maize included, amongst others, natural lactic acid fermentation, cooking and saccharification using barley malt. An in vitro method was standardised to carry out comparative determinations of the dry matter digestibility of cereal and legume food samples as a function of processing conditions, without attempting to exactly mimic gastrointestinal digestion. Using this method based on upper digestive tract digestion, it was observed that digestibility of the legumes increased during cooking and fermentation. Cooking improved the total digestibility of both soya bean and cowpea from 36.5 to 44.8% and from 15.4 to 40.9% respectively. Subsequent fungal fermentation increased total digestibility only by about 3% for both soya bean and cowpea. Digestibility was also influenced by fungal strain and fermentation time. Cooking and subsequent saccharification using malt almost tripled total digestibility of white maize from 25.5 to 63.6%, whereas lactic fermentation of maize had no effect on in vitro dry matter digestibility. Although total digestibility of cooked legumes was only slightly improved by mould fermentation (3% for both soya bean and cowpea), the level of water‐soluble dry matter of food samples increased during fermentation with Rhizopus oryzae from 7.0 up to 27.3% for soya bean and from 4.3 up to 24.1% for cowpea. These fermented products could therefore play a role as sources of easily available nutrients for individuals suffering from digestive disorders. © 2000 Society of Chemical Industry     

The prediction of the digestibility of silages using cellulase

The use of the Jones and Hayward¹ two stage digestion technique for evaluating the digestibility of dried ground grass silages with digestible organic matter in the dry matter (in-vivo DOMD%) values ranging from 54 to 72 was investigated. By grinding the samples through a 0.75 mm screen and increasing the concentration of cellulase the digestion time could be reduced from 48 h (Jones and Hayward¹) to 24 h whilst maintaining a high degree of correlation with DOMD% (in-vivo). A number of silages were analysed by this modified technique and by the Tilley and Terry² (in-vitro) technique. Comparing the DOMD% values from both determinations with the DOMD% (in-vivo) values the correlation coefficient (r) in each case was 0.85 (with an r.s.d. of 2.3). The modified Jones and Hayward¹ technique is then as good a predictor of DOMD% as the Tilley and Terry² technique. The length of time and cost needed to predict DOMD% of silages has been reduced which is a distinct advantage when determinations are carried out on a routine basis for advisory purposes.     

Effects of an enzyme feed additive on extent of digestion and milk production of lactating dairy cows

A study was conducted using lactating Holstein cows with ruminal and duodenal cannulas in a 4 x 4 Latin square design to investigate fibrolytic enzyme supplementation on site and extent of nutrient digestion. The four diets consisted of 45% concentrate, 10% barley silage, and 45% cubed alfalfa hay (dry matter basis) and differed in enzyme supplementation: 1) control cubes, 2) cubes treated with 1 g of enzyme mixture/kg of cubes, 3) cubes treated with 2 g of enzyme mixture/kg of cubes, and 4) both concentrate and cubes treated with 1 g of enzyme mixture/kg of dry matter. The enzyme supplement contained primarily cellulase and xylanase activities. Digestion of organic matter and neutral detergent fiber in the total tract was higher for cows fed the high dosage of enzyme than for cows fed the control cubes. Ruminal digestibility of crude protein was higher, but that of organic matter and neutral detergent fiber was only numerically higher, for cows fed the high dosage of enzyme compared with that of cows fed the control cubes. Higher ruminal digestibility associated with the high dosage of enzyme resulted in more microbial protein synthesis. Milk production increased for cows fed the high dosage of enzyme compared with cows fed the control cubes and effects of the addition of enzyme on milk composition were minimal. The results demonstrated the benefits of using a fibrolytic enzyme additive to enhance feed digestion and milk production by dairy cows. The response to enzyme supplementation was affected more by amount of enzyme than by whether the enzyme was added to forage or concentrate.     

Comparison of in vitro techniques for predicting digestibility of mixed cereal straw and citrus by‐product diets in goats

Prediction of in vivo digestibility of different fibrous feedstuffs using five in vitro techniques (rumen fluid–pepsin, pepsin–cellulase, NDF–cellulase, amylase–NDF–cellulase and rumen fluid–NDF) was assessed using 13 different diets. Samples were grouped into four batches: (1) barley straw; (2) barley straw supplemented with urea; (3) barley straw treated with urea; and (4) barley straw treated with urea+NaOH. Batches 2, 3 and 4 were also supplemented with citrus by‐product at four different levels. The predictive power of the in vitro techniques was assessed using a simple linear regression analysis (Y=a+bX) between the coefficients of in vivo digestibility (Y) and the different in vitro methods (X). Rumen inoculum was significantly associated with in vivo organic matter digestibility (OMD) (r=0.778, P<0.01 and r=0.901, P<0.001 for rumen fluid–acid pepsin and rumen fluid–NDF, respectively). Pepsin–cellulase, NDF–cellulase and amylase–NDF–cellulase were also related with in vivo OMD (r=0.969, P<0.001; r =0.917, P<0.001 and r=0.920, P <0.001, respectively). These results suggest that using pepsin–cellulase provides the better predictive value (RSD 1.2). Bifactorial analysis demonstrated that all techniques were suitable for predicting the effect of the level of supplementation (P<0.001) and straw type (P <0.001) on in vivo OMD. © 1999 Society of Chemical Industry     

A comparison of methods of adding fibrolytic enzymes to lactating cow diets

Holstein cows (n = 43) in early lactation were used to investigate effects of method of adding fibrolytic enzymes to diets on feed intake, milk production, and digestibility. Cows were blocked according to parity and calving date and randomly assigned to three treatments: control, enzymes applied to the total mixed ration (E-TMR), or enzymes added to the barley-based concentrate (E-Conc). The enzyme product used was a proprietary blend that contained relatively high xylanase and low cellulase activities (Biovance Technol. Inc., Omaha, NE). An enzyme solution (50 mg of enzyme powder dissolved into 20 ml of water) was sprayed onto each kilogram of total mixed ration (dry matter basis) before feeding. Alternatively, 73 g of enzyme powder, dissolved in 20 L of water, was added per ton of concentrate (50 mg of enzyme/kg of diet dry matter). The total mixed rations contained 24% corn silage, 14% alfalfa hay, and 62% concentrate (dry matter basis) and were offered ad libitum. In vitro gas production assays and two experiments using sheep were conducted to measure the effects of enzyme treatment on digestibility. Dry matter intake (mean: 19.8 kg/d) was not affected by enzyme supplementation. Milk yield (kg/d) was higher for cows fed E-Conc (37.4) than for cows fed control (35.3) or E-TMR (35.2) with no effects on milk composition. Total tract digestibility (%) of dry matter was higher for E-Conc (66.6%) than for the control diet (63.9%) and intermediate for E-TMR (65.7%) when measured in dairy cows. However, the digestibility of the diets was substantially higher when measured in sheep than in dairy cows, with no effects of enzyme supplementation. The results indicate that fibrolytic enzymes have the potential to increase digestibility and milk production in dairy cows because digestion is low relative to potential digestibility. When digestion is higher, as was observed in lambs or in vitro, no improvement in digestibility occurs. Method of enzyme delivery must also be considered to maximize the benefits of using fibrolytic enzymes in dairy cow diets.     

Digestibility of silages in relation to their hydroxycinnamic acid content and lignin composition

BACKGROUND: The effectiveness of the analysis of cell wall‐bound hydroxycinnamic acids and the composition of lignin to evaluate the in vivo digestibility of a silage collection with unknown botanical composition was evaluated. RESULTS: Syringyl units content and total etherified phenols showed the highest correlation coefficients with in vivo dry matter digestibility (IVDMD) (r = ? 0.792 and r = ? 0.703, respectively), while guaiacyl units and total phenols showed the highest correlation coefficients with in vivo organic matter digestibility (IVOMD) (r = ? 0.871 and r = ? 0.817, respectively). Using the above‐mentioned chemical parameters, 10 equations were also developed to predict in vivo digestibility. The prediction of IVDMD produced a high adjusted R² value (0.710) using syringyl, total lignin, etherified total phenols, esterified ferulic acid and total phenol content as predictors. The prediction of IVOMD produced a higher adjusted R² value (0.821) using guaiacyl, total phenols, total ferulic acid and etherified p‐coumaric acid content as predictors. CONCLUSION: Cell wall digestibility depends on a multiplicity of factors and it is not possible to attribute a causal effect on in vivo digestibility to any single factor. However, syringyl and guaiacyl content and etherified phenols emerge as good predictors of digestibility. Copyright © 2010 Society of Chemical Industry     

Digestibility in vitro of dry mashed potato products

The in vitro digestibilities of potato granules and flakes were compared. The digestibility of flakes was superior to that of granules. By drum-drying mashed potatoes, as is customary in the manufacture of flakes, the digestibility was improved, whereas by repeatedly drying and wetting mashed potatoes, as in the manufacture of potato granules, digestibility was diminished. The dry matter content of mashed potatoes obtained by rehydrating potato granules was higher than that of rehydrated flakes. The influence of digestibility and dry matter content of rehydrated potato granules and flakes on digestion in humans is discussed.     

In-vitro digestibility of kale (Brassica oleracea) secondary xylem and parenchyma cell walls and their polysaccharide components

The cell walls of forage kale (Brassica oleracea L cvs Maris Kestrel, Vulcan and Thousandhead) stems were separated into parenchyma and secondary xylem fractions of high and low digestibility respectively. Previous work had shown that the lignified secondary xylem cell walls were the main components of the plant indigestible to ruminants. The cell walls were subjected to in-vitro digestion with fungal ‘cellulose’ and with rumen liquor. These two methods gave well correlated results except when secondary xylem cell walls were first delignified with chlorite, when their mean digestible organic matter in the dry matter (DOMD) was 41·9% with cellulase but 64·6% with rumen liquor. Chemical fractionation of the cellulase-digested residues showed that all fractions of the parenchyma cell walls, except the hemicelluloses from cv Thousandhead, were of high digestibility. In the secondary xylem cell walls the α-cellulose fraction had DOMD about 50%, the pectic fraction being more digestible and the hemicelluloses less digestible: but no one polysaccharide fraction in these cell walls was completely digested or untouched by digestion.     

Predicting dry matter digestibility from acid detergent fibre levels in grasses as affected by a pretreatment with neutral detergent

Acid detergent fibre was determined on 50 grass samples of known in vivo dry matter digestibility with and without a preliminary extraction with neutral detergent. Pretreatment with neutral detergent reduced the mean yield of acid detergent fibre from 41.5 to 36.8%. This decrease in acid detergent fibre was mainly due to a reduction in the level of ash which accounted for 57% of the difference in fibre level. The error in predicting dry matter digestibility of all feeds from acid detergent fibre was ±3.5 digestibility units and was increased to ±3.8 units following neutral detergent pretreatment. When acid detergent fibre was expressed on an ash-free basis the corresponding residual standard deviations were ±4.4 and ±4.5 units, respectively. It was concluded that a pretreatment with neutral detergent or expressing results on an ash-free basis did not improve the accuracy in predicting dry matter digestibility from acid detergent fibre.     

An In Vitro Digestibility Assay for Prediction of the Metabolizable Energy of Low-Calorie Dextrose Polymeric Bulking Agents

A method was developed to predict in vivo digestibility and metabolizable energy of dextrose polymers from in vitro enzyme digestibility measurements. A high correlation (r = 0.98) was established between in vivo true digestibility (TD) and in vitro percent dextrose yield (DY) for polymeric compounds representing a wide range of in vivo digestibility (22–96%). The linear regression equation describing this relationship was TD (%) = 1.11 DY + 10.68. The in vivo nitrogen-corrected true metabolizable energy (TMEn) of four test compounds was predicted from in vivo digestibility data with good accuracy using the linear regression equation TMEn (kcal/g) = 0.038 DY + 0.637 (r = 0.97). The in vitro method is most useful for predicting in vivo digestibility and metabolizable energy of dextrose polymers with in vitro dextrose yields less than 80% and in vivo metabolizable energy values less than 3.6 kcal/gram.     

Structural breakdown of starch-based foods during gastric digestion and its link to glycemic response: In vivo and in vitro considerations

The digestion of starch-based foods in the small intestine as well as factors affecting their digestibility have been previously investigated and reviewed in detail. Starch digestibility has been studied both in vivo and in vitro, with increasing interest in the use of in vitro models. Although previous in vivo studies have indicated the effect of mastication and gastric digestion on the digestibility of solid starch-based foods, the physical breakdown of starch-based foods prior to small intestinal digestion is often less considered. Moreover, gastric digestion has received little attention in the attempt to understand the digestion of solid starch-based foods in the digestive tract. In this review, the physical breakdown of starch-based foods in the mouth and stomach, the quantification of these breakdown processes, and their links to physiological outcomes, such as gastric emptying and glycemic response, are discussed. In addition, the physical breakdown aspects related to gastric digestion that need to be considered when developing in vitro–in vivo correlation in starch digestion studies are discussed. The discussion demonstrates that physical breakdown prior to small intestinal digestion, especially during gastric digestion, should not be neglected in understanding the digestion of solid starch-based foods.     

The effect of feeding a dry enzyme mixture with fibrolytic activity on the performance of lactating cows and digestibility of a diet for sheep

A dry enzyme mixture was added to the diets of lactating cows and growing lambs to evaluate its ability to improve milk production and nutrient digestibility, respectively. The enzyme mixture contained xylanase and cellulase activity over a broad range of pH (tested from 4 to 7). Twenty-four lactating cows between 50 and 150 d in milk and averaging about 40 kg of milk/ d were fed a total mixed ration (TMR) consisting of 26% [dry matter (DM) basis] corn silage, 17% alfalfa silage, 7% chopped alfalfa hay, and 50% concentrate. One-half of the cows were fed the TMR without supplementation and the remaining half of the cows were fed the same TMR supplemented with 10 g of the enzyme mixture/ cow per day. After 21 d, the treatments were crossed over for a second 21-d period. The dry enzyme mixture had no effect on DM intake, milk production, or milk composition. Addition of various concentrations of the enzyme mixture did not improve the in vitro digestion of neutral detergent fiber from the TMR. In a digestion trial, lambs were fed a commercial diet supplemented with 4 g of the enzyme mixture/lamb per day, and total feces and urine were collected. Although the ratio of enzyme to feed was much higher than it was in the experiment with lactating cows, addition of the enzyme mixture had no effect on the apparent digestion of DM, acid detergent fiber, neutral detergent fiber, or N in the diet.     

Prediction of the digestibility of forages by treatment of their cell walls with cellulolytic enzymes

A method is described for the prediction of the in vivo digestibility (d.m.d.) and in vivo cell wall digestibility of grasses: it involves incubating grass cell walls with a commercial cellulase for 16 h and measuring the optical density of the filtrate at 324 nm (O.D.). The prediction equation is based on a highly significant correlation (r = 0.978) between O.D. and d.m.d. using a total of 27 samples of three species of grass with d.m.d. between 60 and 83. The method could not be used for the prediction of d.m.d. of red clover and sainfoin due to their filtrates having low O.D. values. A second method for the prediction of d.m.d. of grasses is also described and is based on a highly significant correlation between d.m.d. and the percentage of cell walls digested by cellulase (r = 0.962): similar comparisons for the legumes gave lower correlation coefficients. Using either the O.D. or gravimetric method, inclusion of cell wall content in the regression equations reduced the S.D. of d.m.d. predictions.