An in-vitro method for prediction of the digestible crude protein content in pig feeds

An in-vitro method using commercially available enzymes for the prediction of the in-vivo digestible crude protein content was developed and tested on seven feedstuffs and 16 diets for pigs. Fat-extracted feed samples were consecutively incubated with pepsin at pH 1 and pancreatin at pH 6.8. From the nitrogen content of the feed sample and of the residue after incubation the in-vitro digestibility of the crude protein was calculated. Using the linear regression of in-vitro on in-vivo digestible crude protein of samples obtained in feeding trials, the in-vivo digestible crude protein content (DXP_p) in g kg^?1 dry matter could be predicted. For feedstuffs and diets the correlation was 0.99 and 0.95 and the residual standard deviation 17 and 6 g kg^?1 dry matter, respectively. In a similar procedure the nitrogen solubilised during incubation with enzymes was analysed. The regression value was similar to that of the original procedure. However, this procedure was abandoned because it was more laborious.     

Laboratory Assays and Near-Infrared Reflectance Spectroscopy for Estimates of Feeding Value of Corn Silage

Corn silages samples from the Virginia Tech Forage Testing Program were classified by color, presence or absence of mold, aroma, and fermentation type. In the sample of 142 corn silages, in vitro digestible organic matter averaged 59.8% (range 38.5 to 74.7%) and indicated a range of silage quality. Simple and multiple regression of in vitro digestible organic matter on chemical constituents were derived for the full data set and within fermentation groups. Acid detergent fiber and dry matter explained the largest portion of the variation of digestibility. Simple regression on the full data set had coefficients of determination of .352 and .208 with standard errors of prediction of 5.29 and 5.86 for acid detergent fiber and dry matter. Multiple regression analyses improved coefficient of determination and standard error slightly.Corn silage in vitro digestible organic matter was predicted by near infrared reflectance techniques. A calibration equation resulted in coefficient of determination of .88 and standard error 5.38. The calibration equation was tested for prediction of an additional 90 corn silages. Regression of digestibility predicted by near infrared reflectance resulted in coefficient of determination of .37 and standard error of 4.04. Prediction of corn silage digestibility by near infrared reflectance or laboratory methods was similar.     

Polyethylene glycol as an indigestible marker to estimate fecal output in dairy cows

The objective of this study was to evaluate the accuracy of fecal output measurements using polyethylene glycol (PEG) as an external marker determined by near-infrared reflectance spectroscopy. In addition, the accuracy of dry matter intake predictions based on fecal output and digestibility estimated using an internal marker [indigestible neutral detergent fiber (iNDF)] was assessed. The experiment was conducted using 6 lactating dairy cows fed 2 different diets. Polyethylene glycol was administered twice daily into the rumen and the diurnal pattern of fecal concentrations and recovery in feces were determined. To evaluate the effects of alternative marker administration and sampling schemes on fecal output estimates, the passage kinetics of PEG in the digestive tract of dairy cows was determined and used for simulation models. The results indicate that PEG was completely recovered in feces and, thus, fecal output was accurately estimated using PEG. Good agreement between measured and predicted dry matter intake (standard error of prediction = 0.86 kg/d, R² = 0.81) indicates good potential to determine feed intake using PEG in combination with iNDF. The precision of cow-specific digestibility estimates based on iNDF was unsatisfactory, but for a group of cows iNDF provided an accurate estimate of dry matter digestibility. The current study indicated that, to overcome inherent day-to-day variation in feed intake and fecal output, the minimum of 4 fecal spot samples should be collected over 4 d. Preferably, these samples should be distributed evenly over the 12-h marker administration interval to compensate for the circadian variation in fecal PEG concentrations.     

Utility of near-infrared reflectance spectroscopy to predict nutrient composition and in vitro digestibility of total mixed rations

Total mixed ration (TMR) samples (n = 110) were analyzed for dry matter (DM), crude protein (CP), soluble CP, neutral detergent fiber (NDF), NDF CP, starch, ash, fat, total ethanol-soluble carbohydrate, and nonfiber carbohydrate (NFC). Rapidly and slowly degraded and undegraded in situ CP fractions and in vitro DM, organic matter, and NDF digestibility were determined on each TMR. The TMR were scanned using near-infrared reflectance spectroscopy (NIRS); spectra were retained with NIRS calibration and cross-validation statistics were determined using partial least squares regression methods. The CP, NDF, starch, in vitro DM, and in vitro indigestible NDF contents of TMR were predicted by NIRS with good degrees (R² >0.85) of accuracy with proportionally low standard errors of prediction. Moderate utility of NIRS to predict the NFC (R² = 0.83) and fat content (R² = 0.81) of TMR was observed. Rapidly, slowly, and undegraded in situ CP fractions in TMR were not well predicted by NIRS. Similarly, soluble CP, NDF CP, total ethanol-soluble carbohydrate, and in vitro NDF digestibility (% of NDF) were not well predicted by NIRS. Ratios of nutrient range to reference laboratory method error were calculated and found to be positively related (R² = 0.84) to NIRS predictability of a given TMR nutrient, suggesting some laboratory procedures were not precise enough to yield suitable NIRS predictions. Data suggest that NIRS has utility to predict basic nutrients such as CP, NDF, starch, NFC, and fat in TMR. However, difficulty was observed using NIRS in predicting key biological nutrients in TMR such as in situ CP fractions and in vitro NDF digestibility. Difficulty of NIRS in predicting these nutrients is related to the level of reference method error in relationship to the range of nutrient values in TMR, but other sources of prediction error may exist.     

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     

Fecal starch as an indicator of total-tract starch digestibility by lactating dairy cows

To test whether total-tract starch digestibility by lactating dairy cattle could be predicted accurately from concentration of starch in fecal dry matter (FS), data from 8 digestibility trials, 30 diets, and 564 individual starch measurements were compiled from trials conducted at the University of Wisconsin-Madison. Total-tract starch digestibility by individual cows was determined from the concentrations of starch in total mixed rations and feces (rectal grab samples) and concentrations of several external or intrinsic feed markers. Fecal starch concentration was closely and linearly related to total-tract starch digestibility (R² = 0.94). Differences in fecal sampling time for FS, such as day within week or week, did not influence determination of FS concentration. In contrast, time of day when fecal samples were taken influenced FS concentration, but the differences were minimal (mean ± standard error of the mean = 0.4 ± 0.1). These data suggest that on-farm collection of feces from individual cows or pens of cows may be sampled only once per day. Fecal pH was not related to FS when FS was only 1 to 3%, indicating that fecal pH was not a good index of FS and not practical as a tool to assess total-tract starch digestibility for lactating dairy cows when fecal starch excretion is low. An equation was developed to predict FS using near-infrared reflectance spectroscopy of dried ground fecal samples; the equation had moderate to good accuracy (R² = 0.83–0.94) and a low standard error of prediction. Fecal starch concentration can be used to monitor total-tract starch digestibility.     

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.     

Effect of irradiation and other processing methods on in-vitro digestibility of rapeseed protein

Abstract. Effect of irradiation (1 kGy), autoclaving (121°C at 103.5 kPa for 5, 10, 15, 20, 25 and 30 min), dry heating (121°C for 5, 10, 15, 20, 25, 30 and 60 min), sprouting (36 h) and their combination on in-vitro digestibility of rapeseed protein was studied. Digestibility was significantly affected by processing methods (P < 0.05). Digestibility of untreated rapeseed protein was 85.7%. Irradiation alone and irradiation plus dry heating showed no effect on the digestibility, while irradiation plus autoclaving markedly improved (88.9%) the digestibility. The digestibility was influenced by the time of autoclaving and dry heating. Maximum value for in-vitro digestibility was recorded for 60 min of dry heating (91.8%). Sprouting of rapeseed exhibited a significant decrease (82.8%) in the digestibility.     

Application of Near Infrared Spectroscopy for Indirect Evaluation of “Monthong” Durian Maturity

Durian contains thick rind which restricts light penetration into the pulp region. Indirect prediction of pulp dry matter as a reference of maturity was investigated using spectral information from the rind and stem. Partial least squares regression was performed to model variation in the pulp dry matter using the rind and stem absorbance. The rind model showed better performance in predicting the dry matter content than the stem model. However, the accuracy was relatively poor (correlation coefficient of prediction, r_p = 0.76 and root mean square error of prediction, RMSEP = 1.82%) compared with that of the reference pulp model (r_p = 0.83 and RMSEP = 1.61%). The rind model was superior to the stem model in the classification of durian samples into immature, early-mature, and mature classes based on the number of days after anthesis and the dry matter content. Effective wavelengths were chosen from the regression coefficients of the corresponding models and used to create a simplified classification model. A combination of both rind and stem spectral data at selected wavelengths provided the highest accuracy of classification (94.4%).     

Effect of radiation and other processing methods on protein quality of sunflower meal

The effects of gamma irradiation from a ⁶⁰Co source (10 and 20 kGy), dry heating (121 °C for 10, 20 and 30 min), autoclaving (121 °C at 103.5 kPa for 10, 20 and 30 min) and their combination on chlorogenic acid, soluble protein, available lysine and in-vitro protein digestibility of sunflower meal were studied. The moisture content of the raw sample was 78 g kg⁻¹ as is and on a dry matter basis. The meal contained 26.7 g kg⁻¹ chlorogenic acid, 330 g kg⁻¹ crude protein, 78.5% soluble protein and 2.63 g 16 g N⁻¹ available lysine. Digestibility of raw meal was 81.5%. Chlorogenic acid, soluble protein and available lysine of raw meal decreased during dry heating, autoclaving and radiation processing. The digestibility was significantly affected by processing method (P < 0.05), as well as by the time of dry heating and autoclaving. The influence of combination methods revealed that irradiation alone had a little effect on chlorogenic acid and in-vitro protein digestibility. Autoclaving plus irradiation up to 20 kGy markedly improved the digestibility (90%). Therefore, the results suggested that the combination of autoclaving for 10 min plus irradiation up to 20 kGy has a beneficial effect on the protein quality of sunflower meal with little effect on its content of soluble protein, available lysine and markedly reduced chlorogenic acid by 87%, more than other processing methods. © 1999 Society of Chemical Industry     

Agriculture group symposium reclamation and restoration of soils

Most of the observed variation between n.i.r. spectra in any sample collection is due to particle size variation; in addition, absorbance readings are highly inter-correlated. Application of multiple linear regression techniques to such spectral data produces a multiplicity of solutions which vary in the wavelengths selected and in predictive accuracy. Evaluation of all or most of these calibrations requires a significant amount of time. In the present study, alternative data treatment methods are described which reduce the effect of particle size variations, select only those wavelengths which contain significant information, and overcome the problem of inter-correlation by means of principal component analysis. These methods were applied to the analysis of dried silage for crude protein (CP) and in vitro dry matter digestibility (IVDMD); accuracy of the novel data treatments (best standard error of prediction of CP and IVDMD equal to 0.63 and 2.7, respectively) was better than that generally achieved by more conventional statistical techniques.     

Effect of increasing the amount of hay fed on Holstein calf performance and digestibility from 2 to 4 months of age

A good transition from a mainly liquid diet to a solid diet of concentrates and forages is important considering the small size and development of the calf's rumen. However, the optimal amount of hay or other high-fiber ingredients in the diet of recently weaned calves is not well defined. The objective of this trial was to determine the effects of feeding 0, 5, or 10% chopped grass hay (6.5% crude protein, 64.6% neutral detergent fiber) with a textured, high-starch starter (20.5% crude protein, 38.4% starch, 14.1% neutral detergent fiber; protein pellet, whole corn, and oats) on performance and digestion in Holstein steer calves between 2 and 4 mo of age. Forty-eight calves (initial body weight = 90.7 ± 2.15 kg) were housed in group pens (4 per pen) and fed diets and water for ad libitum intake. Feed offered and refused was measured daily. Calf body weight, hip width, and body condition score (1–5 scale) were measured initially and at 28 and 56 d. Fecal samples were collected from the pen floor with care not to sample bedding material and composited by pen during d 5–9, 26–30, and 47–51 to estimate apparent total-tract digestibility using acid-insoluble ash. Data were analyzed as a completely randomized design with repeated measures and pen as the experimental unit. As grass hay increased, dry matter intake (kg/d) decreased linearly but tended to change quadratically. Dry matter intake as a % of body weight changed quadratically with increasing hay, increasing from 0 to 5%, and decreasing from 5 to 10% hay. Average daily gain (1.15, 1.12, and 0.95 kg/d), feed efficiency (0.336, 0.319, and 0.309 kg of average daily gain/kg of dry matter intake), and hip width change (4.6, 4.7, and 4.1) decreased linearly with 0, 5, and 10% hay, respectively. Overall estimates of dry matter, organic matter, neutral detergent fiber, acid detergent fiber, and crude protein digestibility changed quadratically with hay, increasing from 0 to 5%, and decreasing from 5 to 10% hay, whereas digestibility of starch, sugar, and fat decreased linearly with increasing hay. Digestibility of dry matter, organic matter, neutral detergent fiber, and acid detergent fiber increased from 2 to 3 mo of age, and decreased from 3 to 4 mo of age. Digestibility of starch decreased linearly and digestibility of fat and crude protein increased linearly with age. Digestive capacity did not appear mature by 4 mo of age. Feeding 5% chopped hay supported optimal digestion and growth in calves 2 to 4 mo of age, which agrees with previously published research.     

The influence of dietary fibre sources on growth,feed efficiency and digestibilities of dry matter and protein in rats

Hulls from Tower canola (TCH), Regent canola (RCH) and soya beans (SBH) were included at 10 or 20% in soya bean meal based diets for rats, to compare the effects of these fibre sources on growth, feed consumption, feed efficiency and dry matter and protein digestibilities. A soya bean meal based control diet and another diet containing a purified fibre source (Alphafloc) at a 10% level, were included for a further comparison. Each of the diets was fed to six rats in a 4-week feeding trial. The diets gave similar weight gain, feed consumption and feed efficiency values. The control diet had the highest mean coefficient of dry matter digestibility (80.8%) and the 20% SBH and Alphafloc diets had the lowest (72.4 and 72.2%). The canola hull and 10% SBH and Alphafloc diets had intermediate values (73.2–75.0%). There was a highly significant negative correlation between the dietary fibre content and the dry matter digestibility of the diets. The control and Alphafloc diets showed the highest and similar apparent (81.4 and 79.9%) and true (86.8 and 85.3%) digestibility values for dietary protein. The 20% canola and soya bean hull diets showed the lowest apparent (71.4–73.7%) and true (76.9–79.4%) digestibility coefficients. The 10% canola and soya bean hull diets had intermediate apparent and true protein digestibility values (73.2-75.3 and 78.4–80.6%, respectively). The chemical analysis of the fibre sources showed that Alphafloc had the highest cellulose content (88%) and the lowest lignin content (0.6%), while canola hulls had the lowest cellulose content (25.4–28.4%) and the highest lignin content (26.6–28.9%). Soya bean hulls had intermediate cellulose (50%) and low lignin (1.3%) contents. The results suggest that cellulose did not have a detrimental effect on the dietary protein digestibility but lignin and/or some other undetermined factors in the hulls had an adverse effect on protein digestibility.     

A meta-analysis on the effect of dietary application of exogenous fibrolytic enzymes on the performance of dairy cows

The aim of this study was to use meta-analytical methods to estimate effects of adding exogenous fibrolytic enzymes (EFE) to dairy cow diets on their performance and to determine which factors affect the response. Fifteen studies with 17 experiments and 36 observations met the study selection criteria for inclusion in the meta-analysis. The effects were compared by using random-effect models to examine the raw mean difference (RMD) and standardized mean difference between EFE and control treatments after both were weighted with the inverse of the study variances. Heterogeneity sources evaluated by meta-regression included experimental duration, EFE type and application rate, form (liquid or solid), and method (application to the forage, concentrate, or total mixed ration). Only the cellulase-xylanase (C-X) enzymes had a substantial number of observations (n = 13 studies). Application of EFE, overall, did not affect dry matter intake, feed efficiency but tended to increase total-tract dry matter digestibility and neutral detergent fiber digestibility (NDFD) by relatively small amounts (1.36 and 2.30%, respectively, or <0.31 standard deviation units). Application of EFE increased yields of milk (0.83 kg/d), 3.5% fat-corrected milk (0.55 kg/d), milk protein (0.03 kg/d), and milk lactose (0.05 kg/d) by moderate to small amounts (<0.30 standard deviation units). Low heterogeneity (I?² statistic <25%) was present for yields and concentrations of milk fat and protein and lactose yield. Moderate heterogeneity (I?² = 25 to 50%) was detected for dry matter intake, milk yield, 3.5% fat-corrected milk, and feed efficiency (kg of milk/kg of dry matter intake), whereas high heterogeneity (I?² > 50%) was detected for total-tract dry matter digestibility and NDFD. Milk production responses were higher for the C-X enzymes (RMD = 1.04 kg/d; 95% confidence interval: 0.33 to 1.74), but were still only moderate, about 0.35 standardized mean difference. A 24% numerical increase in the RMD resulting from examining only C-X enzymes instead of all enzymes (RMD = 1.04 vs. 0.83 kg/d) suggests that had more studies met the inclusion criteria, the C-X enzymes would have statistically increased the milk response relative to that for all enzymes. Increasing the EFE application rate had no effect on performance measures. Application of EFE to the total mixed ration improved only milk protein concentration, and application to the forage or concentrate had no effect. Applying EFE tended to increase dry matter digestibility and NDFD and increased milk yield by relatively small amounts, reflecting the variable response among EFE types.     

Chemometric Formulas Based on Physical Properties of Single-cooked Milled Rice Grains for Determination of Amylose and Protein Contents

ABSTRACT: Chemometric formulas for predicting amylose content (AC) and protein content (PC) were developed based on the surface and overall physical properties of single-cooked milled rice grains as predictive variables. The formula with 8 predictors for AC determination exhibited the highest accuracy (coefficient of determination: R²= 0.952, standard error of calibration: SEC = 1.77) for calibration and the lowest standard error of prediction (SEP = 2.07) for unknown samples (AC: 0 to 30%). The formula with 7 predictors was effective in enhancing the prediction accuracy (SEP = 1.32) among non-waxy samples in a narrow range of AC (15 to 20%). The formula with 8 predictors for PC determination showed a higher accuracy (R²= 0.449 and 0.470) for both calibration and prediction than that of a conventional 3-grain method (R²= 0.168 and 0.124). It was possible to accurately determine AC using physical measurement of single grains instead of chemical analysis.     

Determination of Forage Quality by near Infrared Reflectance Spectroscopy: Efficacy of Broad-Based Calibration Equations, , ,

Two experiments were conducted to determine 1) if statistical clustering of near infrared spectra would aid in selection of samples to establish calibration equations, and 2) if broad-based calibration equations were capable of accurately determining forage quality. In Experiment 1, clustering of spectra did not have any advantage over random selection as a means to select samples. In Experiment 2, 990 hay samples representing a large diversity of species, maturity, cutting, and chemical composition, were collected from 31 states. Approximately 50% of the samples were used in this study. Samples were separated into calibration and validation sets, either on a random basis or by subset of samples from individual states into validation sets. Based on randomly selected samples, the standard error of validation and bias were dry matter (.47, −.05%); CP (.84, .06% dry matter); ADF (2.24, .18% dry matter); NDF (2.16, 17% dry matter); in vitro dry matter digestibility (30.3, −.40%). There was a trend toward increased bias for ADF, NDF, and in vitro dry matter digestibility when samples from particular states, rather than randomly selected samples, were used as validation sets.     

Effect of gamma irradiation parameters on the in-vitro digestibility of β-lactoglobulin

Radiation level and protein conformation during irradiation may modify a protein's response to ionising energy and change its nutritional value. Effects of gamma irradiation on protein in-vitro digestibility and amino acid release were investigated using β-lactoglobulin as a model protein. Irradiation with ⁶⁰Co was performed at a range of 1–50 kGy on liquid or frozen samples atA_w 0.93, with pH adjusted to 5.2 or 7.0, and on dry samples atA_w 0.13. Amino acid composition, in-vitro protein digestibility and amino acid release were not impaired by irradiation at the highest dose of 50 kGy. Thus the nutritional quality of β-lactoglobulin was not affected by irradiation in a dose range likely to be used in food processing.     

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 manure volatile solid output of lactating dairy cows

Organic matter (OM) in livestock manure consisting of biodegradable and nonbiodegradable fractions is known as volatile solids (VS). According to the Intergovernmental Panel on Climate Change (IPCC) Tier 2 guidelines, methane produced by stored manure is determined based on VS. However, only biodegradable OM generates methane production. Therefore, estimates of biodegradable VS (dVS; dVS = VS ? lignin) would yield better estimates of methane emissions from manure. The objective of the study was to develop mathematical models for estimating VS and dVS outputs of lactating dairy cows. Dry matter intake, dietary nutrient contents, milk yield and composition, body weight, and days in milk were used as potential predictor variables. Multicollinearity, model simplicity, and random study effects were taken into account during model development that used 857 VS and dVS measurements made on individual cows (kg/cow per day) from 43 metabolic trials conducted at the USDA Energy and Metabolism laboratory in Beltsville, Maryland. The new models and the IPCC Tier 2 model were evaluated with an independent data set including 209 VS and dVS measurements (kg/cow per day) from 2 metabolic trials conducted at the University of California, Davis. Organic matter intake (kg/d) and dietary crude protein and neutral detergent fiber contents (% of dry matter) were significantly associated with VS. A new model including these variables fitted best to data. When evaluated with independent data, the new model had a root mean squared prediction error as a percentage of average observed value (RMSPE) of 12.5%. Mean and slope biases were negligible at <1% of total prediction bias. When energy digestibility of the diet was assumed to be 67%, the IPCC Tier 2 model had a RMSPE of 13.7% and a notable mean bias for VS to be overpredicted by 0.4 kg/cow per day. A separate model including OM intake as well as dietary crude protein and neutral detergent fiber contents as predictor variables fitted best to dVS data and performed well on independent data (RMSPE = 12.7%). The Cornell Net Carbohydrate and Protein System model relying on fat-corrected milk yield and body weight more successfully predicted dry matter intake (DMI; RMSPE = 14.1%) than the simplified (RMSPE = 16.9%) and comprehensive (RMSPE = 23.4%) models to predict DMI in IPCC Tier 2 methodology. New models and the IPCC Tier 2 model using DMI from the Cornell Net Carbohydrate and Protein System model predicted VS (RMSPE = 17.7–19.4%) and dVS (RMSPE = 20%) well with small systematic bias (<10% of total bias). The present study offers empirical models that can accurately predict VS and dVS of dairy cows using routinely available data in dairy farms and thereby assist in efficiently determining methane emissions from stored manure.     

A cellulase digestion technique for predicting the dry matter digestibility of grasses

A digestion technique using a commercially-available crude cellulase preparation from Trichoderma viride is described. The enzyme showed cellulase, hemicellulase and proteolytic activity when tested on herbage or herbage polysaccharides. A high correlation (r = 0.92, P < 0.001, residual standard deviation 2.5) was found between a simple one stage enzyme digestion and in vivo dry matter digestibility for a range of grass species and varieties. In vitro dry matter digestibility and detergent fibre were also determined on the same samples and the results correlated with in vivo dry matter digestibility. The cellulase method is rapid and reproducible and particularly well suited for the evaluation of plant material in breeding programmes.