A NOTE ON THE SUITABILITY OF THE IN VITRO DIGESTIBILITY TECHNIQUE FOR VERY SMALL PLANT SAMPLES

The two-stage in vitro digestibility technique was scaled down to use 0.1 g samples. The accuracy of predicting in vivo DM digestibility by the use of micro-samples was studied, using 35 samples of four grass species of known in vivo digestibility. When the sample size was reduced from the normal 0.5 g to 0.1 g, the residual standard deviation of the regression relating in vitro to in vivo DM digestibility was increased from ±2.5 to ±3.4 digestibility units. Grinding the samples more finely than through a 1.0 mm screen did not improve the accuracy of predicting in vivo digestibility. It was concluded that the in vitro method may be used with micro-samples where necessary, but with less accuracy than the macro-technique. For maximum accuracy, the use of standards of known in vivo digestibility is necessary.     

Prediction of legume silage digestibility from various laboratory methods

The potential of different laboratory methods to predict legume silage organic matter digestibility (OMD) in vivo was evaluated by using data from thirty‐three pure legume silages in seven experiments. The samples were analysed for crude protein concentration, cell wall composition, in vitro digestibility by the methods of Tilley and Terry [Journal of the British Grassland Society, 18 (1963) , 104–111; OMD_T&T], pepsin‐cellulase solubility (OMS) and gas production (OMD_GAS), and for indigestible neutral‐detergent fibre concentration in situ (INDF). The relationships between the results obtained by the laboratory methods and in vivo OMD, all expressed as ratios, were studied using linear univariate regression models with experiment as a random variable (mixed model). Legume silage digestibility could be estimated with acceptable accuracy by different in vitro methods, but not from the chemical composition of the samples. The highest accuracy in OMD prediction was found with OMS (RMSE 0·0113; R² = 0·965) followed by OMD_GAS (RMSE 0·0149; R² = 0·944), OMD_{T& T} (RMSE 0·0149; R² = 0·940) and INDF (RMSE 0·0168; R² = 0·925). The relationships between the in vitro methods and in vivo digestibility are not universal, and should be determined separately for each laboratory and type of forage. Part of the error in OMD prediction can be attributed to errors in in vivo OMD determination.     

Comparison of two in vitro procedures using rumen liquor-pepsin or pepsin-cellulase for prediction of forage digestibility

Seventy-three samples of grass and legume herbage of known in vivo digestibility were used to compare an in vitro procedure comprising incubation with pepsin followed by cellulase (Jones and Hayward, 1975) with the Tilley and Terry (1963) procedure using rumen liquor followed by pepsin. The results obtained using the pepsin-cellulase method proved to be highly repeatable. On the basis of the residual standard deviation of the regression of in vivo dry matter digestibility (DMD) on dry matter digested in vitro (g/100 g DM), the pepsin-cellulase method was shown to be only slightly less accurate than the rumen liquor-pepsin method for combinations of both primary growth and regrowth of grasses (r.s.d. ±1.80 and ±1.46 respectively). However, the pepsin-cellulase method was noticeably less accurate than the rumen liquor-pepsin method when used on legume herbages (r.s.d. ±3.17 and ±1.91) or on grass and legume herbages combined (r.s.d. ±3.80 and ±1.60). For the rumen liquor-pepsin method one regression equation predicting DMD having the form, Y= 1.02 X? 0.41, was permissible. For the pepsin-cellulase method separate regression equations were necessary for grasses (species and growth stages combined) having the form, Y = 0.56 X+ 34.7, and for each legume species. It was concluded that the pepsin cellulase method was of value for grass samples, and, within species, for legumes because of its accuracy and precision and its speed and convenience relative to the rumen liquor-pepsin procedure; however, for legume species combined, and presumably for grass-legume mixtures, it was not sufficiently accurate.     

THE EFFECT OF METHOD OF DETERMINATION OF ACID-DETERGENT FIBRE ON ITS RELATIONSHIP WITH THE DIGESTIBILITY OF GRASSES

The acid-detergent fibre (ADF) contents of 50 grass samples of known in vivo and in vitro digestibility were determined by hydrolysing with acid for 1, 2, 3,4, 5, and 6 h. The 50 samples used consisted of 6 Lolium perenne, 9 Cenchrus ciliaris, 15 Chloris gayana, 10 Digitaria spp., and 10 Setaria spp. Regression and residual standard deviations (RSD) were calculated for each hydrolysis time for each grass and for all 50 samples. Increasing the hydrolysis time decreased the RSD for Lolium perenne and Setaria, had no effect on Chloris gayana and Digitaria and increased the RSD for Cenchrus ciliaris regressions. For regressions based on all 50 samples die RSD varied between ±4.8 and 5.0 digestibility units with only minor differences between hydrolysis times. Correcting the ADF for contaminating ash generally increased the RSD. Changing the acid strength from the 10 N recommended by van Soest (8) did not lead to any major improvement in the RSD for regressions based on Cenchrus ciliaris, but with Setaria the RSD was reduced from ±2.8 to 1.7 digestibility units when 2N acid was used and hydrolysis was extended to 2 h. It was concluded that unless the optimum conditions for determining ADF for each grass are known then the in vitro technique provides digestibility estimates with a lower error.     

EFFECT OF SOME GREEN-CROP-DRYING PROCESSES ON THE DIGESTIBILITY AND VOLUNTARY INTAKE OF HERBAGE BY SHEEP

The effect of artificial drying under commercial conditions on the digestibility and voluntary intake of herbage by sheep was studied, using either van den Broek (900°C inlet temperature) or Swiss Combi (1100°C inlet temperature) triple-pass drum-type driers. Organic-matter digestibility of chopped dried herbage was 8·3, 5·8 and 5·3% lower than that of fresh herbage in Experiments 1, 2 and 3, respectively. Packaging chopped dried grass into ‘cobs’ caused a further reduction in OM digestibility of up to 2·8%. Pre-milling plus packaging (i.e. ‘pelleting’) depressed OM digesti bility of chopped dried grass by 5 to 6 percentage units. Digestibility of dried grass in its various physical forms was further reduced when offered ad lib.; the greatest fall (9·4%) occurred with pellets and the smallest fall (0·8?1·3%) with loose chopped material; cobs were intermediate at 4·3?7·0%.     

Effect of structure of a tropical pasture on ingestive behaviour, digestibility of diet and daily intake by grazing cattle

The effect of the structure of a tropical pasture, based on Dichanthium spp., on the ingestive behaviour, in vivo digestibility of the diet and herbage intake by eight Creole tethered heifers was studied. Two levels of nitrogen fertilizer (0 and 50 kg ha^?1) were applied to plots after each grazing cycle and there were 28 d between each of the three grazing cycles. Four heifers grazed individual subplots daily on each plot for 14 d in each of the successive grazing cycles. Simultaneous measurements of bite depth, bite mass, biting rate, short‐term intake rate and daily grazing time were made in two 4‐d periods at the end of each 14‐d period. The in vivo organic matter digestibility (OMD) and daily herbage organic matter intake (OMI, expressed on a kg LW^0·75 basis) were also measured at the same times. Relationships among pasture characteristics and ingestive behaviour were similar to those reported in other short‐term studies: pasture height was highly correlated with bite depth, bite mass and biting rate (r = 0·91, r =0·79 and r = ?0·68, respectively, P < 0·001). Pasture variables had lower correlations with grazing time and short‐term intake rate than with bite depth, bite mass and biting rate. Pasture structure was more highly correlated with OMD than OMI: leaf mass and length and also the extended tiller length were highly correlated with OMD (r = 0·77, r = 0·76 and r = 0·72, respectively, P < 0·001) whereas the crude protein concentration of the herbage was correlated with OMI and digestible OMI (r = 0·50 and r = 0·69, respectively, P < 0·001). Ingestive behaviour variables, as well as OMD, were correlated more with pasture characteristics than was OMI.     

Effect of stage of maturity and chop length on the chemical composition and utilization of formic acid-treated ryegrass and formic acid silage by sheep

Two areas of an early-heading perennial ryegrass cv. Cropper were harvested by either a precision-chop or a flail harvester at around 50% ear emergence (15 May 1978) and 14d later (29 May). Formic acid (85%) was applied at the rate of 2·2 litres t^-1. Mature crossbred wethers were used in a 2 × 2 factorial design to determine the effect of stage of maturity and method of harvesting (chop length) on the in vivo digestibilities of formic acid-treated grass in experiment 1 and formic acid silage in experiment 2. Apparent digestibility coefficients were determined at a fixed level of feeding for both grass and silage and at ad libitum access to feed for silage only. There were no significant differences in the concentrations of crude protein (CP), ether extract (EE), acid-detergent fibre (ADF) or acid-detergent lignin (ADL) in grass or silages of differing chop lengths but the later cut forages had significantly higher ADF and ADL concentrations and lower CP concentrations than the early-cut forages. The ADF and ADL concentrations were also higher in the silages than in the corresponding grasses. In general, the fermentation characteristics of precision-chopped silage were better than for the corresponding flail-cut silage but date of harvest was a more important determinant of quality and the late, flail-cut silage had the highest butyrate and ammonia N concentrations and the highest pH (411) of any treatment. There was a significantly higher intake of precision-chopped as compared with flail-cut silage with both the early-and the late-cut silage but there were no significant differences attributable to stage of maturity (i.e. date of harvest) or significant interaction between chop length and maturity. The slightly increased intake of early harvested, precision-chopped silage as compared with late precision-chopped silage was not significant. Dry matter digestibility (DMD) of the grass decreased at a rate of 0004 units d^-1 post 50% ear emergence. The results of experiment 2 indicated a decrease of 0·207 units d^-1 in silage fed at a similar level. The late-cut silage (DMD 0·292, mean of both harvesting treatments) thus had a significantly lower digestibility than the corresponding grass (mean DMD 0·247). Chop length had a variable influence on the DMD of both grass and silage fed at a fixed level but treatment differences were non-significant. However, a trend towards higher digestibility of flail-cut as compared with precision-chopped silage was apparent and this became statistically significant when the animals were allowed ad libitum access to feed. This may be a response to the generally lower intake of flail-cut silage.     

THE ERROR IN PREDICTING PASTURE DRY–MATTER DIGESTIBILITY FROM FOUR DIFFERENT METHODS OF ANALYSIS FOR LIGNIN

The lignin content of 50 samples of five grasses of known in vivo digestibility were determined by the methods of Armitage, van Soest and two modifications of the van Soest technique. The error in predicting DM digestibility varied from ±3.1 for tbe Armitage metbod to ±5.0 for the van Soest method. This error compares nnfavourably witb ±2.1 previonsly obtained on tbe same samples with the in vitro technique of Tilley and Terry.     

Effect of rotary-drum-drier exit temperature and length of pre-drying storage time on digestibility of dried grass cobs

The effect of exit temperature of a rotary-drum-drier and of the length of pre-drying storage time on chemical composition and digestibility of dried grass cobs was investigated in two experiments. Increasing exit temperature from 77 to 166°C reduced WSC, NFE and available lysine content and increased CF content of dried grass. In vitro and in vivo DM digestibility was reduced by 16.4 and 24.5 percentage units respectively. Increasing length of pre-drying storage time also reduced WSC and available lysine content and reduced in vitro and in vivo DM digestibility by 2.4 and 5.1 percentage units respectively. The greatest reduction in in vivo digestibility in both experiments occurred in the CP fraction.     

A comparison of methods of predicting the in vivo digestibility of heather by sheep

Methods of predicting the in vivo dry matter digestibility (DMD) of heather were examined in studies on ten samples of heather which had been fed to sheep in standard digestibility trials. DMD was predicted with similar accuracy from estimates of in vitro dry matter digestibility (in vitro DMD) and from the concentration of cell-wall constituents. In vitro DMD was found to be between 10 and 18 percentage units lower than DMD. Freeze drying the samples was the only modification to the technique which both increased in vitro DMD and the accuracy of the prediction of DMD. Other modifications attempted were the use of different liquor sources, changes in first-stage incubation time and dilution rate, and nitrogen supplementation of the inocula. The concentration of nitrogen or undigested dietary nitrogen in the faeces could not be used to predict the digestibility of heather with precision. It was concluded that the DMD of a heather diet could be satisfactorily predicted from the in vitro DMD of samples collected from sheep fistulated at the oesophagus.     

Production, survival and nutritive value of the perennial legumes Dorycnium hirsutum and D. rectum subjected to different cutting heights

Dorycnium hirsutum and D. rectum are perennial legumes which may have potential for use as pastures for the control of groundwater recharge in southern Australia. Little is known about the quality of the forage of Dorycnium species for grazing livestock or how these species respond to cutting. The effect of cutting height on plant survival, production of dry matter (DM), the proportion of leaf, edible stem (approximately <5 mm diameter) and woody stem in the DM and the nutritive value of the edible components was investigated. Biomass above five cutting‐height treatments (uncut, ground level, 5–8 cm, 10–15 cm and 15–30 cm above ground level) was removed at 8‐week intervals from plots of D. hirsutum and D. rectum from September 2002 to July 2003. In both species, plants subjected to lower cutting height treatments produced less DM above the height of the cut than those cut at higher heights. DM production declined over time in all treatments. Plants cut to ground level failed to regrow after the second harvest in D. hirsutum and the fourth harvest in D. rectum. Thus, these Dorycnium species were susceptible to high severity defoliations at 8‐week intervals. Negligible inedible woody stem was present in regrowth of both species after 8 weeks but D. hirsutum regrowth had a higher proportion of leaf (0·72) than D. rectum (0·56). Plants left uncut accumulated a large proportion of inedible woody stem in the DM (0·69 in both species) by July 2003, particularly at the base of the plant. Edible DM from regrowth of D. hirsutum and D. rectum had crude protein (CP) concentrations of 120 and 150 g kg^?1 DM; dry matter digestibility (DMD) values of 0·45 and 0·58; organic matter digestibility (OMD) values of 0·50 and 0·64; neutral‐detergent fibre (NDF) concentrations of 370 and 290 g kg^?1 DM; and acid‐detergent fibre (ADF) concentrations of 260 and 210 g kg^?1 DM, respectively. Medicago sativa, grown under similar conditions, had higher digestibility values (0·63 DMD and 0·66 OMD) and similar CP concentrations to D. rectum (140 g kg^?1 DM), but higher concentrations of NDF and ADF (410 and 290 g kg^?1 DM). Leaf material from both Dorycnium species had a higher nutritive value than edible stems, with DMD and OMD values of leaf of D. rectum being 0·68 and 0·74 respectively. Uncut plants had a much lower nutritive value of edible DM than the regrowth from cut treatments; older material was also of a lower nutritive value. The relatively low nutritive value of even the young regrowth of Dorycnium species suggests that forage quality is a major limitation to its use. Forage of Dorycnium species could be used during periods when other sources of forage are in short supply but infrequent grazing it is likely to produce forage of a low nutritive value.     

The effect of feeding animals ad libitum vs. at maintenance level on the in vivo digestibility of mown herbage from two permanent grasslands of different botanical composition

The aim of this experiment was to study the effect of feeding level (FL) on the digestibility of unconserved forage obtained from two permanent grasslands cut at three different dates during the first cycle of growth. Forage was offered to Texel sheep (wethers), at maintenance level and at ad libitum level. Differences in voluntary intake (VI) between grasslands were also tested. Organic matter digestibility (OMD) measured at ad libitum level and at VI was 13% higher on harvested forage from grassland rich in forbs (GRF) than grassland rich in grasses (GRG) at early herbage growth stages, but these differences were no longer found at later maturity stages. In GRF, there were no differences for OMD, at either FL at the young growth stages, but at the end of the cycle the OMD obtained at ad libitum level (0·56) was higher than that at maintenance level (0·50). However, in GRG, at an early stage of forage maturity, OMD at ad libitum level (0·67) was lower than that at maintenance level (0·70), but this difference was no longer found at the end of the growth cycle. In conclusion, the effect of FL on the digestibility of unconserved forage from permanent grasslands depends on the type of grassland. These differences are mainly explained by the different botanical composition of the grassland types.     

The validity of in vitro techniques using rumen fluid or cellulase for predicting changes in the dry matter digestibility of grasses caused by fertilizer calcium, sulphur, phosphorus and nitrogen

Sixty-four samples were used to measure the accuracy of in vitro techniques using rumen fluid-pepsin or pepsin-cellulase for predicting digestibility of grasses grown with different levels of fertilizer calcium(Ca), sulphur(S), phosphorus (P) and nitrogen (N). In each case, fertilizers changed in vivo dry matter digestibility (DMD) and the in vitro techniques accurately predicted the changes in in vivo DMD caused by fertilizer Ca, P and N. The in vitro techniques gave biased estimates of in vivo DMD in studies with fertilizer S. This bias was caused by a decrease in the digestive efficiency of the sheep when fed the unfertilized feed. It was concluded that biased estimates of DMD may be associated with low fertilizer levels and these cannot be eliminated by improving the in vitro techniques and would also apply to estimates of DMD based on chemical analysis of the feed.     

In vitro total and methane gas production as influenced by rate of nitrogen application, season of harvest and perennial ryegrass cultivar

The effects of rate of inorganic nitrogen (N) fertilization (0, 80 or 160 kg N ha^?1 per regrowth), season of harvest (regrowths 1, 2 and 3) and perennial ryegrass (Lolium perenne L.) cultivar [classified as having either a normal or elevated water soluble carbohydrate (WSC) concentration genotype] on in vitro gas production and digestibility were assessed. Increased N fertilizer application significantly decreased total gas production (TGP), methane (CH₄) production and organic matter digestibility (OMD). The results suggest that the decreases in TGP and CH₄ production were associated with a restriction in organic matter (OM) fermentation and an altered crude protein (CP) to structural carbohydrate ratio rather than a modification in the stoichiometry of fermentation. Season of harvest only significantly (P < 0·05) altered in vitro OMD and CH₄ production at 8 h, despite altering the chemical composition of the herbage. Cultivar effects on all measured in vitro parameters were not significant presumably because the elevated WSC concentration trait was not expressed strongly in the study.     

Determination of nutritive value of forages in south Texas using an in vitro gas production technique

The objectives of this study were to use the in vitro gas production (IVGP) technique to evaluate the pattern and parameters of anaerobic fermentation of forages from south Texas pastures throughout the year to (i) obtain empirical relationships between the IVGP technique fermentation parameters and chemical composition of the forages and (ii) develop equations to compute total digestible nutrients (TDN). During four consecutive years (2006–2009), forage samples were collected monthly (n = 39) at the King Ranch, TX, and chemical analyses and IVGP were obtained. For 2006, 2007, 2008 and 2009, the average lag times, h, were 6·47 ± 0·54, 7·75 ± 0·65, 7·49 ± 2·01 and 5·44 ± 1·46, and the average ratio of millilitre of gas per milligram of dry matter was 0·41 ± 0·11, 0·34 ± 0·09, 0·34 ± 0·07 and 0·26 ± 0·10 respectively. There was a moderate negative correlation (r = ?0·53) between lignin and neutral detergent fibre (NDF) and a moderate positive correlation (r = 0·58) between crude protein and NDF digestibility. The predicted fractional passage rate (kp) by the large ruminant nutrition system model using the level 2 solution was on average 0·0366 h^?1. The average computed TDN assuming a kp of 0·04 h^?1 was 55·9%. We concluded the IVGP technique may be used to predict TDN values of warm‐season forages.     

THE VOLUNTARY INTAKE AND DIGESTIBILITY BY SHEEP OE LEAF AND STEM FRACTIONS OF LOLIUM PERENNE

The leaves of tropical grasses are eaten in larger quantities than stems of similar DM digestibility. To determine whether the same fact applied to a temperate grass, studies were made with leaf and stem fractions of Lolium perenne. The leaves of L. perenne had a 20% higher voluntary intake than the stems, white the DM digestibilities were only slightly higher (67·3%ν. 64·8%). The leaves also had a larger surface area/g, a higher initial (12 h) fermentation rate in vitro, larger content of pepsin-soluble DM, and a smaller energy require ment to grind I g DM in a laboratory mill compared with the stems. The difference in voluntary intake between the leaves and stems of L. perenne was smaller than that for a number of tropical grasses.     

The effects of defoliating grass in winter or spring on herbage yields and ensilage characteristics

Under Irish conditions, the digestibility in May of grass managed for silage production is sometimes lower than expected. In each of two successive years, replicate field plots were established to examine the effects of three defoliation heights (uncut or cut to a stubble height of 10 or 5 cm) applied in winter and/or spring on herbage yields harvested in May and again in July, and on chemical composition and conservation characteristics associated with first‐cut silage. Swards that were not defoliated in December or March had a dry‐matter (DM) yield and in vitro DM digestibility (DMD) in mid‐May of 6597 kg ha^?1 and 736 g kg^?1, respectively, in Year 1, and corresponding values of 7338 kg ha^?1 and 771 g kg^?1 in Year 2. Defoliating swards to 5 cm in December reduced (P < 0·001) May DM yields compared to swards that were not defoliated in both December and March, while herbage DMD in May increased (P < 0·001) when defoliated in December or March. There were no clear effects of defoliation height or its timing on herbage ensilability or resultant conservation efficiency characteristics. The effects of defoliation on July yield were the reverse of those observed for May, while the total yield of the December and March defoliations plus the two silage harvests increased as defoliation height was lowered in Year 2 only. It is concluded that defoliation in winter and/or spring can increase herbage digestibility but will likely reduce DM yields in May.     

Effects of the proportions of high or medium digestibility grass silage and concentrates in the diet of beef cattle on liveweight gain, carcass composition and fatty acid composition of muscle

Abstract An experiment was carried out over 2 years to evaluate the effects of increasing the proportion of cereal‐based concentrates in diets containing high‐digestibility and conventional medium‐digestibility grass silages on the dry‐matter (DM) intake, liveweight gain and carcass composition of beef cattle, and to examine the effects of grazed grass and the ratio of grass silage:concentrates in the diet on the fatty acid composition of selected muscle tissues. Late‐maturing steers (n = 231) were offered diets based on high‐digestibility (HD) (0·743 digestible organic matter (DOM) in DM) or medium‐digestibility (MD) (0·643 DOM in DM) grass silages supplemented with barley/soyabean meal‐based concentrates. The concentrates constituted 0·20, 0·40, 0·60 and 0·80 of total DM of the diets, which were offered ad libitum (AL). The two diets, which contained 0·80 concentrates, were also offered at 0·80 of AL intake. A further group of fourteen animals were given the medium‐digestibility silage only for 5 months and then grazed perennial ryegrass pastures for a further 5 months (silage/pasture treatment). For the diets containing HD silage and 0·20, 0·40, 0·60 and 0·80 concentrate, and 0·80 concentrate at 0·8 of AL intake, the DM intakes were 9·4, 10·2, 10·4, 10·2 and 8·1 (s.e. 0·16) kg d^?1, respectively, and daily carcass gains were 0·67, 0·78, 0·77, 0·79 and 0·62 (s.e. 0·029) kg d^?1, respectively; for those containing MD silage and 0·20, 0·40, 0·60 and 0·80 concentrate, and 0·80 concentrate at 0·8 of AL, the DM intakes were 8·2, 9·3, 10·1, 10·1 and 8·0 (s.e. 0·16) kg d^?1, respectively, and daily carcass gains were 0·38, 0·48, 0·64, 0·77 and 0·56 (s.e. 0·029) kg d^?1 respectively. Increasing the proportion of concentrates in silage‐based diets decreased the concentration of omega‐3 (ω‐3) polyunsaturated fatty acids (PUFA) (P < 0·001) and increased the concentration of ω‐6 PUFA (P < 0·001) in muscle. Cattle on the silage/pasture treatment had the highest concentration of ω‐3 PUFA in muscle (51 g kg^?1 lipid), this value being over three times that for animals given diets containing MD silage and 0·80 concentrate in the diet. These results demonstrate the potential of HD silage made from perennial ryegrass relative to high concentrate diets. The consumption of pasture‐finished beef could make a significant contribution towards increasing the intake of ω‐3 PUFA in the human diet.     

Estimation of nitrogen concentration and in vitro dry matter digestibility of herbage of warm-season grass pastures from canopy hyperspectral reflectance measurements

Remote sensing of nitrogen (N) concentration and in vitro dry matter digestibility (IVDMD) in herbage can help livestock managers make timely decisions for adjusting stocking rate and managing pastures during the grazing season. Traditional laboratory analyses of N and IVDMD are time-consuming and costly. Non-destructive measurements of canopy hyperspectral reflectance of pasture may provide a rapid and inexpensive means of estimating these measures of nutritive value. Using a portable spectroradiometer, canopy reflectance was measured in eight warm-season grass pastures in the USA in June and July in 2002 and 2003 to develop and validate algorithms for estimating N concentration and IVDMD of herbage. Nitrogen concentration of herbage was linearly correlated (r = 0·82; P < 0·001) with a ratio of reflectance in the 705- and 1685-nm wavebands (R₇₀₅/R₁₆₈₅) and IVDMD was correlated with R₇₀₅/R₅₃₅ (r = 0·74; P < 0·001). Compared with simple linear regressions of N concentration and IVDMD in herbage with two-waveband reflectance ratios, multiple regression, using maximum r² improvement, band-depth analysis with step-wise regression, and partial least-squares regression enhanced the correlation between N concentration and IVDMD of herbage and canopy reflectance values (0·81 ≤ |r| ≤ 0·90; P < 0·001). Validation of the prediction equations indicated that multiple regression only slightly improved accuracy of a model for predicting N concentration and IVDMD of herbage compared with simple linear regression of reflectance ratios. Results suggest that the N concentration and IVDMD of herbage of warm-season grass pastures can be rapidly and non-destructively estimated during the grazing season using canopy reflectance in a few narrow wavebands.