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The influence of stage of lactation and corresponding diets on rates of protein degradation (kd) is largely unstudied. Study objectives were to measure and compare in situ ruminal kd of crude protein (CP) and estimate rumen CP escape (rumen-undegradable protein; RUP) of selected feeds by cows at 3 stages of lactation fed corresponding diets, and to determine the incubation times needed in an enzymatic in vitro procedure, using 0.2 units of Streptomyces griseus protease per percent of true CP, that predicted in situ RUP. Residue CP was measured after in situ fermentation for 4, 8, 12, 24, 36, 48, and 72 h of 5 protein sources and 3 total mixed rations, which were fed to the in situ cows. Two nonlactating (dry) cows and 2 cows each at 190 (mid) and 90 (peak) days of lactation were used. Each pair of cows was offered free-choice diets that differed in composition to meet their corresponding nutrient requirements. Diets had decreasing proportions of forages and contained (dry matter basis) 11.9, 15.1 and 16.4% CP and 54.3, 40.3 and 35.3% neutral detergent fiber, for dry, mid, and peak TMR (TMR1, TMR2, and TMR3), respectively. Intakes were 10.3, 21.4, and 23.8kg of dry matter/d, respectively. Kinetic CP fractions (extractable, potentially degradable, undegradable, or slowly degradable) were unaffected by treatment. Lag time and kd varied among feeds. The kd was faster for all feeds (0.136/h) when incubated in dry-TMR1 cows compared with mid-TMR2 (0.097/h) or peak-TMR3 (0.098/h) cows, and no differences in lag time were detected. Calculated RUP, using estimated passage rates for each cow based on intake, differed between dry-TMR1 (0.382) and mid-TMR2 (0.559) or peak-TMR3 (0.626) cows, with a tendency for mid-TMR2 to be different from peak-TMR3. Using the average kd and lag time obtained from dry-TMR1 to calculate RUP for mid-TMR2 and peak-TMR3 cows using their passage rates reduced RUP values by 6.3 and 9.5 percentage units, respectively. Except for that of herring meal, in vitro residue CP at 6, 12, and 48h of enzymatic hydrolysis was correlated (r=0.90) with in situ RUP of peak-TMR3, mid-TMR2, and dry-TMR1, respectively. Although confounded within treatments, stage of lactation, diet, and intake appeared to affect CP degradation parameters and RUP. Using kd from nonlactating cows, or the RUP calculated from them, may bias diet evaluation or ration formulation for lactating cows. In addition, enzymatic in vitro predictions of RUP should be measured using incubation times that are appropriate for lactating cows.

Rice straw is unique relative to other cereal straws in being low in lignin and high in silica. Unlike other cereal straws taller varieties of rice straws tend to be leafy while the leaves are less digested than stems. This may contribute to higher straw value with rice yield. There is genetic variation in straw quality but has not been exploited and tends to be smaller than environmental variation. Effort in plant breeding has been to develop short varieties with higher grain yield. This development has reduced straw quantity but not nutritive value. The relationship between plant genetics and silica metabolism is virtually uninvestigated, although reviews from plant physiology indicate it is a major factor. Silica and lignin in that order are the primary limiting factors in rice straw quality. Silicon is a nutrient element which has been overlooked largely because of its assumed inertness, but also because of its geochemical abundance that so greatly exceeds its metabolic use by plants and animals. Silicon is involved in several major roles in rice: carbohydrate synthesis, grain yield, phenolic synthesis and plant cell wall protection. These vectors interact with each other to eliminate statistical association of silica and lignin with straw digestibility when varieties are compared. Yield of grain is highly related to silica content of straw, which reflects soil availability. There are no detailed studies on rice straw lignin. Most papers reporting lignin contents in rice straw have used acid-detergent lignin by either the sulfuric acid or permanganate versions. There are undoubtedly soluble phenolics in rice straw that need investigation. The effects of ammonia and urea on silica is to crack the silicified cuticular layer. Silica is not dissolved by these reagents in contrast to the action of sodium hydroxide. Treatments on rice straw follow those applied to other lignified materials. In order of frequency of reports, urea followed by ammonia with comparatively fewer papers on sodium hydroxide, steam and pressure treatments or exploded by pressure release, and only one or two papers on acid treatments and white rot fungi. There are reports on animal supplementation and a few growth studies with young animals. Field surveys in India and the southeast Asian countries only report the use of urea, although it appears less efficient than ammonia. Farmer acceptance is related to their perceptions on costs, labor, equipment, health, safety, i.e. the exposure to ammonia vapor, economic and other social factors. The various papers reporting treatments have used animal digestion trials; a variety of in sacco , in vitro digestions with rumen organisms or cellulase, some in combination with pepsin digestion or neutral-detergent extraction. Gas production from in vitro rumen fermentation has also been used. Results are expressed mainly on dry matter basis and fewer reports on organic matter. Results are difficult to compare and standardization of procedures is badly needed. However, most treatments with ammonia and urea show some increase in digestibility and intake where measured in in vivo trials. In vitro and in sacco evaluations tend to overestimate improvement in digestibility.

The Hyblean pastures are characterized by a great variety of native forages, and offering opportunity for selective feeding by animals. Over 100 plant species belonging to over 25 families occur, although not all of these may occur in single pasture.1 The occurrence of pasture species and the selective forage behaviour of dairy cattle in very complex pastures was part of a larger study on the influence of diet upon cheese flavour. The plant diversity may contribute to cheese flavour.2 The animals were individually followed on the pasture and the kind of species and plant parts selected were recorded.3 The volatile constituents of the above-ground (aerial) parts of the most commonly occurring and selected plant species in the Hyblean pasture were extracted by steam distillation and analysed by GC–olfactometry (GC–O) and GC–MS. The number of odour-active compounds identified in the plants ranged from 12 in Sinapis to 26 in Erodium. Copyright © 2004 John Wiley & Sons, Ltd.

The Cornell Net Carbohydrate and Protein System (CNCPS), a mechanistic model that predicts nutrient requirements and biological values of feeds for cattle, was modified for use with sheep. Published equations were added for predicting the energy and protein requirements of sheep, with a special emphasis on dairy sheep, whose specific needs are not considered by most sheep-feeding systems. The CNCPS for cattle equations that are used to predict the supply of nutrients from each feed were modified to include new solid and liquid ruminal passage rates for sheep, and revised equations were inserted to predict metabolic fecal N. Equations were added to predict fluxes in body energy and protein reserves from BW and condition score. When evaluated with data from seven published studies (19 treatments), for which the CNCPS for sheep predicted positive ruminal N balance, the CNCPS for sheep predicted OM digestibility, which is used to predict feed ME values, with no mean bias (1.1 g/100 g of OM; P > 0.10) and a low root mean squared prediction error (RMSPE; 3.6 g/100 g of OM). Crude protein digestibility, which is used to predict N excretion, was evaluated with eight published studies (23 treatments). The model predicted CP digestibility with no mean bias (-1.9 g/100 g of CP; P > 0.10) but with a large RMSPE (7.2 g/100 g of CP). Evaluation with a data set of published studies in which the CNCPS for sheep predicted negative ruminal N balance indicated that the model tended to underpredict OM digestibility (mean bias of -3.3 g/100 g of OM, P > 0.10; RMSPE = 6.5 g/100 g of OM; n = 12) and to overpredict CP digestibility (mean bias of 2.7 g/100 g of CP, P > 0.10; RMSPE = 12.8 g/100 g of CP; n = 7). The ability of the CNCPS for sheep to predict gains and losses in shrunk BW was evaluated using data from six studies with adult sheep (13 treatments with lactating ewes and 16 with dry ewes). It accurately predicted variations in shrunk BW when diets had positive N balance (mean bias of 5.8 g/d; P > 0.10; RMSPE of 30.0 g/d; n = 15), whereas it markedly overpredicted the variations in shrunk BW when ruminal balance was negative (mean bias of 53.4 g/d, P < 0.05; RMSPE = 84.1 g/d; n = 14). These evaluations indicated that the Cornell Net Carbohydrate and Protein System for Sheep can be used to predict energy and protein requirements, feed biological values, and BW gains and losses in adult sheep.

A database was developed from 16 scientific publications to explore mechanisms controlling rumen turnover. The database included 70 treatment means (43 cattle and 27 sheep) from experiments in which rumen contents were measured by complete manual evacuation or by slaughter. Rumen turnover was estimated as the ratio between rumen contents (kg of DM) and feed intake (kg of DM/h). Predictors were intake, body weight (BW), metabolic BW (BW0.75), and the dietary components crude protein (CP), neutral detergent fiber (NDF), neutral detergent solubles (NDS), acid detergent lignin and ash. The best linear models obtained to predict rumen turnover (T) for NDF, NDS, dry matter (DM) and acid detergent lignin (LIGN), respectively, were: T NDF = 23.84 - 10.26 ln(D-NDFI); r 2 : 0.28, P T NDS = 17.08 - 13.39 ln(D-NDSI); r 2 : 0.76, P T DM = 20.16 - 10.14 ln(D-NDSI); r 2 : 0.65, P T LIGN = 37.69 - 30.77 ln(D-NDFI); r 2 : 0.70, P These curvilinear relationships were likely due, at least for NDF and lignin, to the increase in rumen NDF content (% of BW) that occurred when intake of dietary, or forage, NDF (% of BW) increased. In the database, turnover of NDF and NDS showed additive behavior. No differences were found between cattle and sheep in rumen NDF, NDS and DM turnovers. When fed at the same level of intake of forage NDF (% of BW), sheep had significantly lower rumen NDF contents (% of BW) than cattle. The rumen evacuation technique is a valuable tool to explore interspecies relationships. The use of this large dataset derived from the scientific literature improved the understanding of the relationships existing among feed intake, body size and the components of rumen turnover, and allowed their quantification.

This study examined the selective foraging behaviour of dairy cattle on very complex pastures as a part of a larger study on the influence of diet upon cheese flavour [Selective grazing on Sicilian pasture by cattle and effects on Ragusano cheese, Ph.D. dissertation, Cornell University, Ithaca, NY, 2003]. Sicilian pastures can contain over 100 plant species belonging to over 25 families, although not all of these species may occur in a single pasture. A grazing study was conducted on a farm with a group of 13 lactating Friesian cows. Milk was used to make cheeses that were evaluated in a separate study. Pasture composition and selection of plant species by cows were studied in the years 1999 and 2000. Qualities of mixed selected forage were uniformly very high and did not vary greatly over season and years. While pasture composition varied between years, animal selection was highly correlated with species incidence ( r =0.83). Animal choices tend to follow occurrence. A few species remained uneaten including Carduus (thistle) and Biscutella . The dominant species consumed belonged to the plant families Asteraceae (Compositae), Cruciferae , Malvaceae and Fabaceae . This information was used in a larger study to relate pasture species to flavour of cheese.

Two experiments were conducted to evaluate use of chromium mordanted neutral detergent residue (Cr-NDr) and cobalt EDTA (Co-EDTA) as predictors of dry matter intake (DMI) in high producing grazing dairy cows. The first experiment was conducted with 10 lactating Holstein cows individually fed a total mixed ration (TMR) in confinement, and dosed with Cr-NDr and Co-EDTA twice daily at milking times for 12-days to validate the markers used for the second experiment. The Cr-NDr accounted for 96% of the variation ( r 2 ) in DMI, while Co-EDTA underpredicted DMI by 43% ( r 2 =0.65). The second experiment was conducted on a pasture-based dairy farm, to evaluate the use of Cr-NDr to predict DMI of grazing dairy cows. 15 and 14 high producing dairy cows in trial 1 and 2, respectively, were dosed twice a day at milking times with Cr-NDr for 12-days. Mean total DMI estimated from marker recoveries were unrealistically high (5.95 and 5.52% of body weight for trials 1 and 2, respectively). It was concluded that either diurnal variation in fecal excretion of the marker or a failure in the technique of collecting pasture samples that reflected the cows’ true grazing selection in order to determine pasture composition occurred.

The effects of enzyme concentration and time of incubation upon protein degradation were examined using protease from Streptomyces griseus . In the first experiment six samples of feeds were used to determine saturation kinetics and extent of protein degradation. Saturation occurred only at very high and impractical concentrations (>33 U/ml) that caused excessive degradation. The concentration that came closest to expected in vivo degradation based on (literature values) was about 3.3 U/ml. In the second experiment 14 feeds with known in situ degradation values obtained from other laboratories were degraded using enzyme concentrations of 0.33, 1.0, 2.4, 3.3 and 6.6 U/ml and for 0, 4, 8, 12, 18, 24, 36 and 48 h. Most of the enzyme–time combinations gave high correlations with the in situ values. However, high concentrations and longer times tended to overdigest and low concentrations and shorter times to underdigest. Deviations from unity provided a measure of the over- or underdigestion. Enzyme concentrations were estimated for zero deviation at the respected times of incubation. These values are inversely proportional to the time of incubation and provide a continuous function between time and concentrations. Any time–concentration combination can be chosen for valid laboratory measurement using a batch incubation. Analysis of the regression of enzyme concentration upon the reciprocal of time indicated a lag time for the in vitro relative to the in situ, which was about 1.9 h. The in vitro extents of digestion were calculated using a rate of digestion derived from the time sequence digestion data, and this value integrated with a 6% rate of passage (same as that used in the calculation of the in situ data). When deviations from unity were regressed upon logarithm of enzyme concentration, a single value for optimal enzyme concentration of 1.5 U/ml was obtained, which is less than the 3.3 value observed with the literature values. A procedure is offered by which in vivo and in situ values could be calibrated for enzymatic activity.

A study was conducted to investigate chewing activity in domestic donkeys eating long-stem, high-fiber forage. Five donkeys (body weight 198±15 kg) were fed 2 types of forage containing equal amounts of fiber (65% neutral detergent fiber: NDF) at two levels of crude protein (CP). Forage consumed was either a mixed legume/orchard grass hay (CP 13.7%) or a grass hay (CP 6.5%). Chewing rate (chews/min) and rate of feed consumption (min/kg of dry matter (DM) or of NDF) were determined by direct observation. The study was designed as a two-period cross-over design with 3 sets of observations per animal per diet. There was no significant effect of protein level or forage type on average chewing rate (53±2 chews/min), time to consume 1 kg of DM (120±12 min) or 1 kg of NDF (184±18 min). Chewing rate was no different at the start vs. end of a 1-h meal for animals eating mixed legume/grass hay, but was significantly (P

1. Sugary fruits dominate the annual diet of Cedar Waxwings (Bombycilla cedrorum), whereas lipid-rich foods dominate the diets of frugivorous thrushes. Nutrient utilization and preferences of Cedar Waxwings and thrushes fed sugary and lipid-rich natural fruits were assessed to ascertain the potential for nutrient-based specializations that could explain diet selection in nature. 2. Compared allometrically, Cedar Waxwings showed higher rates of sugar assimilation from sugary fruits than did thrushes, by virtue of higher intake rates, and achieved the highest energy assimilation rates when eating a sugary fruit. A trade-off to this digestive strategy appears to be less efficient utilization of lipids when eating exclusively lipid-rich fruits. 3. Thrushes digested lipids more efficiently than Cedar Waxwings as a function of intake rate or estimated retention time, and thrushes achieved the highest energy assimilation rates when eating a lipid-rich fruit. Specialization to a diet rich in lipids appears to limit the rate at which sugary fruits can be processed. 4. Within each bird species, sugar digestive efficiencies were high and were not reduced at higher intake rates. Lipids were consumed at lower rates than sugars, and lipid digestive efficiencies declined with increasing intake rates. Frugivorous birds modulated digestive processing of fruits according to the time needed for efficient digestion and/or absorption of sugars and lipids, respectively. 5. Rate of nitrogen intake, not sugar assimilation, positively influenced body mass changes of birds. Sugary fruits appear nutritionally rich in energy, but limited in protein for avian frugivores. Relatively high intake rates and low protein requirements of Cedar Waxwings suggest that specialization to sugary, low-protein diets involves traits that facilitate acquisition and conservation of protein/amino acids. 6. Cedar Waxwings and thrushes show digestive specialization to the utilization of sugars and lipids, respectively, as dominant dietary nutrients. These traits explain patterns of food selection by these birds in the laboratory and in nature. Variation in the value of particular fruit nutrients to different birds renders the dietary descriptor of ‘frugivore’ ambiguous in a nutritional context.

This study was undertaken to investigate research and outreach priorities for Progetto Ibleo (Project Ibleo), a center created in 1990 with tripartite government funding to serve dairy producers in the Hyblean region of Sicily. Data comprised values for production and composition of milk from 1984 to 1989 from 35 herds of Modicana cows on a system based on pasture and that from 69 input-intensive herds of Holstein cows, associated lactation and reproduction measures, and yield and composition of forages from 4 of these farms in 1988. Season had a large effect on the neutral detergent fiber and crude protein composition of forages, production and composition of milk, and predicted yield of fresh Ragusano cheese manufactured from the milk of these cows. The poorest forage quality and the poorest cow performance were observed in summer and fall months (May to October). Lactation curves that were flat, without a discernible peak, or convex were observed for both systems, especially for cows calving in spring and in the dry summer seasons (March to July). These abnormalities, signifying substantial sacrifices in production potential, probably had a complex etiology that stemmed from low nutrient intake and high neutral detergent fiber and low crude protein composition of the grazed and preserved forages. Research and outreach priorities to support the Hyblean dairy industry should include chemical evaluation of forages and other feedstuffs, low moisture ensiling of high quality winter forages, better formulation of diets that are dense with nutrients, and the shifting of calving patterns to better exploit high quality winter forages.

The methods of Krishnamoorthy et al. [Krishnamoorthy, U., Sniffen, C.J., Stern, M.D., Van Soest, P.J., 1983. Evaluation of a mathematical model of rumen digestion and an in vitro simulation of rumen proteolysis to estimate the rumen undegraded nitrogen content of feedstuffs. Br. J. Nutr. 50, 555–568] and Roe et al. [Roe, M.B., Sniffen, C.J., Chase, L.E., 1990. Proc. Cornell Nutrition Conference, Dept. of Animal Science, Cornell University, Ithaca, NY, pp. 81–88], and a new one presented in this paper have been compared, and a revised procedure is proposed using a fixed ratio of enzyme to true protein (TP) determined by tungstic acid precipitation. A comparison of the three methods shows that they are statistically different. The ratio of enzyme has also significant effect ( p >0.01) on the estimate of degradable nitrogen when compared to the fixed concentration of enzyme in the original method. The effect of buffer pH (6.7 vs. 8) on degradation of protein sources was also statistically significant ( p >0.05) with somewhat higher degradation at pH 8.

The precipitation of protein by condensed and hydrolysable tannins was evaluated with the radial diffusion method of Hagerman (1987) using bovine serum albumin (BSA) and isolated leaf protein from fresh alfalfa (Medicago sativa). Alfalfa leaf protein (AALP) was included at two concentrations, 25 and 156 mg N litre-1, at pH 6·8 and 39°C to simulate rumen conditions. The condensed tannins were purified from lyophilised samples of Arachis pintoi, Desmodium ovalifolium, Gliricidia sepium, Manihot esculenta and quebracho (Schinopsis balansae). Hydrolysable tannins from tannic acid (TA) were used as well. There was a significant interaction (P

The acetate complex of praseodymium chelated to EDTA (Pr-EDTA) was evaluated as a marker of the liquid phase turnover in the rumen. Five rumen fistulated Holstein Friesian cows in week 9 of lactation were fed four times a day a total mixed ration at two levels of intake: high (100% of voluntary intake) and low (80% of voluntary intake). Ruminal turnover time was estimated by a continuous dose of Pr-EDTA during 3 consecutive days followed by total rumen emptying, and calculated as the ratio of net rumen contents to intake in a 24 h period. A pulse dose of cobalt chelated to EDTA (Co-EDTA) was used to estimate liquid rumen turnover time calculated from the slope of its excretion curve, and was considered the control. Praseodymium turnover time was not affected by level of intake (P > 0.05). Compared with Co-EDTA, turnover time values were different (10.8 h vs. 14.7 h, respectively; P

The Cornell Net Carbohydrate Protein Model (Chalupa et al., 1991; Sniffen et al., 1992) has developed the need for uniform procedures to partition feed nitrogen into A, B, and C fractions (Pichard and Van Soest, 1977). While carbohydrate fractions are relatively standardized (based on NDF, ADF with corrections for ash, protein, and lignin), the fractionation of plant nitrogen has been open to considerable variation in procedures. This has led to non-uniformity among reported values for nitrogen fractions. This paper recommends reliable procedures for nonprotein nitrogen (NPN) and buffer-soluble protein. These procedures have been examined for reproducibility and relevance to biological expectations. Procedures for acid-detergent insoluble nitrogen (ADIN), and neutral-detergent insoluble nitrogen (NDIN) are also included as they are required for the model. Some alternatives in certain procedures are offered.

Oxygen consumption (VO2) and concentration of venous blood metabolites were measured in donkeys trained to run and to pull loads on a treadmill. VO2 in two donkeys running at maximal speed on a 9.8% slope was 110 +/- 2 ml.min-1.kg-1, approximately 22 times preexercise VO2. Average heart rate at maximal VO2 (VO2max) was 223 +/- 2 beats/min, five times the preexercise heart rate. Blood lactate increased 14-fold, and blood glucose did not change (P > 0.05). Animals running up a 4% incline and incremental draft loading of five donkeys walking on the level were also studied. The total energy cost of walking unloaded was 2.86 +/- 0.06 J.m-1.kg live wt-1. During low- to medium-intensity draft work for 25 min, glucose fell below preexercise values (P < 0.05), whereas plasma hematocrit and cortisol increased (P < 0.05). Blood lactate remained unchanged up to approximately 40% VO2 max but increased 170% at approximately 60% VO2max. The responses in donkeys are similar to those of exercising horses except for the rapid decline in blood glucose observed during low-intensity exercise and the lower lactate levels at both the high-intensity exercise and the apparent anaerobic threshold.

Objectives of this study were to compare three nutritional management strategies for dual-purpose herds in Venezuela in 1987 using a deterministic, multiperiod linear programming model of a representative farm. The model maximized discounted net margin (total revenues minus variable costs) from the herd for a 3-yr cow replacement cycle partitioned into six periods. The periods accounted for seasonal variation in forage availability and quality, and the model provided information about optimal animal inventories, animal sales, land in forage, and feed supplements. We compared current nutritional management practices and alternatives allowing optimal supplementation with commercial concentrate, molasses, cassava root, and urea. Iteration between the programming model and results from the Cornell Net Carbohydrate and Protein System assured technical coefficients consistent with predicted animal performance. Compared with management practices relying on commercial concentrate, optimal use of molasses and urea permitted increases in the stocking rate. Productivity and profit were restricted primarily by energy intake, which was constrained by intakes of NDF and DM. Alternative management strategies changed the relative importance of nutrient requirements and feed intake constraints. Thus, optimal interventions to alleviate nutritional constraints will vary with current management. Mobilizing adipose and protein tissues during lactation was optimal for most strategies. Supplementing with molasses and urea instead of commercial concentrate was the most profitable strategy, increasing herd net margin by 16% compared to the predominant feeding strategy in the late 1980s.

Not only feed but also respective bolus particle size could alter diet efficiency and cow performance. The objective of this project was to characterize particle size of selected feeds and respective swallowed boli. Feed samples included 6 different particle length rye grass hay samples, 1 grass silage, 1 corn silage, and 1 total mixed ration (TMR). Rye grass hay samples consisted of long hay and chopped hay particles retained on the 19- (19_PSPS hay), 8- (8_PSPS hay), and 1.18-mm (1.18_PSPS hay) Penn State Particle Separator (PSPS) screens and those collected on the pan (PSPS_pan hay). A sixth hay treatment was rye grass forage cut at 50-mm lengths and dried to hay (50-mm hay). Treatments were offered to 4 nonlactating and 4 lactating cows following rumen evacuation. Swallowed boli were collected and the number of chews per gram of ingested feed dry matter was determined. Feed and bolus particles of lengths ≥5mm were collected on a 1.6-mm screen using a horizontal wet sieving technique. This cut point was chosen, as the literature suggests that most fecal particles are shorter than 5mm. Dry matter proportions on this screen (PROP_1.6) were determined and particle lengths of retained particles were measured by image analysis. Mean particle lengths (ML) were calculated considering particles ≥5mm in length. Boli of long hay, of 19_PSPS hay, of 8_PSPS hay, and of 50-mm hay had similar ML of 10 to 11mm. Bolus PROP_1.6 were also similar between these treatments, ranging from 0.54 to 0.69. Bolus particle lengths and distributions of these treatments were not related to respective hay particles. Bolus of 1.18_PSPS hay had PROP_1.6 of 0.51 and a smaller ML of 8mm. The PSPS_pan hay had PROP_1.6 of only 0.33, but was still chewed intensely. Apparently, little particle size reduction occurred when cows ate the TMR or the silages. Feed and respective bolus PROP_1.6 were as follows: 0.66 and 0.59 in grass silage, 0.52 and 0.55 in corn silage, and 0.44 and 0.38 in the TMR. Feed and respective bolus ML were as follows: 13.8 and 11.6mm in grass silage, 12.0 and 11.2mm in corn silage, and 13.1 and 12.5mm in the TMR. Rye grass hay particles retained on PSPS screens ≥8mm, with ML of at least 25mm were longer compared with TMR particles, but respective bolus particles were shorter. Bolus particle size is not associated with the size of large feed particles chewed to a constant size that is appropriate for deglutition. This size may be related to feed chemical composition.

The objective of this work was to study the effects of both Klason lignin (KL) and acid detergent lignin (ADL) on in vitro neutral detergent fibre (NDF) digestion (IVNDFd) i n an effort to assess if acid labile phenolic compounds affect the rate of degradation ( k d). Eighty five forages (lucerne, maize silages and grasses) were analyzed for NDF, ADL, KL and IVNDFd (6, 12, 24, 30, 36, 48, and 96 h fermentations were used for k d estimations). Correlations were estimated among li gnin types (KL vs . ADL), lignin and extent of IVNDFd, and lignin type and NDF kd and tested for significance. Within and among all forage types, the correlation between ADL and KL was in general positive when on NDF basis and high and positive when on DM basis (0.77 to 0.90). Within and among all forages, only ADL was consistently negatively correlated with IVNDFd at all time points (-0.54 to -0.94). Co rrelations among forages for NDF kd and lignin type were not consistent. Among all forages, KL was negativel y correlated with IVNDFd and NDF kd. The correlation between IVNDFd and ADL increased as fermentation length increased among all forages. However, the correlation of KL and IVNDFd was greatest up to 48 h of fermentation suggesting that the soluble pheno lics affected both the rate and extent of IVNDFd. Unlike ADL, KL disappeared during IVNDFd, and in most forages there was a high negative correlation assoc iated with the difference between KL and ADL ( �L) and IVNDFd, except for brown midrib hybrids maize and early cut grasses that had a different behaviour. Am ong

The Cornell Net Carbohydrate and Protein System (CNCPS) has a kinetic submodel that predicts ruminal fermentation. The ruminal microbial population is divided into bacteria that ferment structural carbohydrate (SC) and those that ferment nonstructural carbohydrate (NSC). Protozoa are accommodated by a decrease in the theoretical maximum growth yield (.50 vs .40 g of cells per gram of carbohydrate fermented), and the yields are adjusted for maintenance requirements (.05 vs .150 g of cell dry weight per gram of carbohydrate fermented per hour for SC and NSC bacteria, respectively). Bacterial yield is decreased when forage NDF is < 20% (2.5% for every 1% decrease in NDF). The SC bacteria utilize only ammonia as a N source, but the NSC bacteria can utilize either ammonia or peptides. The yield of NSC bacteria is enhanced by as much as 18.7% when proteins or peptides are available. The NSC bacteria produce less ammonia when the carbohydrate fermentation (growth) rate is rapid, but 34% of the ammonia production is insensitive to the rate of carbohydrate fermentation. Ammonia production rates are moderated by the rate of peptide and amino acid uptake (.07 g of peptide per gram of cells per hour), and peptides and amino acids can pass out of the rumen if the rate of proteolysis is faster than the rate of peptide utilization. The protein-sparing effect of ionophores is accommodated by decreasing the rate of peptide uptake by 34%. Validation with published data of microbial flow from the rumen gave a regression with a slope of .94 and an r2 of .88.

An analysis of the turnover in steady state of compartment in the digestive tract of the ruminant is presented, with reference to the rumen compartment. Equations are derived governing concentration of a component in the feed to that within and passing out of the rumen. Also, relationships between dietary components having different ruminal turnover times from one another and from total rumen contents are developed, and the metabolic component accounted for. A method of calculating microbial outflow and efficiency based on rumen emptying is proposed, as are graphical procedures for assessing the behaviour of dietary and metabolic components within the rumen.

There is a need to standardize the NDF procedure. Procedures have varied because of the use of different amylases in attempts to remove starch interference. The original Bacillus subtilis enzyme Type IIIA (XIA) no longer is available and has been replaced by a less effective enzyme. For fiber work, a new enzyme 1 1The heat stable amylase, formerly Number 5426, has been changed by Sigma as of July 1991. The original procedure required .2 ml of this enzyme. The replacement. Number A3306, is four times stronger, and 50 μl are used per sample. has received AOAC approval and is rapidly displacing other amylases in analytical work. This enzyme is available from Sigma (Number A3306; Sigma Chemical Co., St. Louis, MO). The original publications for NDF and ADF (43, 53) and the Agricultural Handbook 379 (14) are obsolete and of historical interest only. Up to date procedures should be followed. Triethylene glycol has replaced 2-ethoxyethanol because of reported toxicity. Considerable development in regard to fiber methods has occurred over the past 5 yr because of a redefinition of dietary fiber for man and monogastric animals that includes lignin and all polysaccharides resistant to mammalian digestive enzymes. In addition to NDF, new improved methods for total dietary fiber and nonstarch polysaccharides including pectin and β-glucans now are available. The latter are also of interest in rumen fermentation. Unlike starch, their fermentations are like that of cellulose but faster and yield no lactic acid. Physical and biological properties of carbohydrate fractions are more important than their intrinsic composition.

Heating forages and feeds will generate Maillard products of low digestibility which are signalled by a rise in the nitrogen (N) content of acid-detergent fibre (ADIN). Two sets of data from digestion trials with sheep were mathematically examined by the methods of Lucas. The first set, taken from studies of distillers grains, exhibited some digestibility of ADIN, but showed a high positive correlation between fecal N and ADIN and a negative one with nitrogen digestibility and ADIN. Earlier conclusions as to the ineffectiveness of ADIN as a method of evaluation are refuted. The second set of data referred to ammoniated forages with their untreated controls. The treated forages are shown to contain soluble indigestible organic matter and nitrogen in the ratio of 8.83:1 ± 0.11, agreeing with the expected composition of Maillard polymers. With these forages the fecal N loss considerably exceeds the ADIN estimate, in contrast to the distillers grains. The excess is due in part to the presence of indigestible soluble non-ammonia nitrogen (SNAN) that is associated with a soluble indigestible organic fraction. The existence of indigestible soluble N and organic matter constitutes the basis for severe criticism of gravimetric laboratory procedures, including nylon bags, used in evaluating treated forages and feeds, as these procedures will fail to recover the soluble indigestible components and thus over-value treated forages. The use of ADIN as a marker for heat damage and the Maillard reaction is validated, but in treated forages an additional examination for absorbances at 280 and 320 nm, and SNAN is recommended.

This simulation study was to evaluate low cost feeding strategies in response to higher cost of commercial concentrates to maintain current milk sales from dual purpose cattle herds in the humid lowlands of western Venezuela. Data were from farm surveys in 1987 and 1988. Baseline net margins from milk and beef per cow per year were $132 and $99 for two farm cases with average daily milk of 10 and 7kg/cow and grazing mature forage supplemented with commercial concentrate. Alternative diets were 1) improving forage quality by more intensive grazing; 2) replacing commercial concentrate with a mixture of cassava tuber ( Manihol esculenta ), urea, and molasses: and 3) supplementing grazing with a mixture of molasses and urea. Alternatively priced feeding strategies were compared by partial budgeting. Using less mature forage was always more profitable than mature grass. Feeding molasses and urea with mature forage increased profits at least $64/cow on the high milk yield farm and $44/cow on the low milk yield farm compared with feeding commercial concentrate. The most costly cassava mixture with mature forage increased annual profit over the baseline diet at least $11/ cow on the high milk yield farm and by $22/cow on the low yield farm. Efficient use of existing feed resources may enhance economical livestock production in the humid lowlands of Venezuela.

Red kidney beans were stored for eight months under three storage conditions: 1) 0°C; 2) 30°C - 80070 RH; 3) 40°C - 80070 RH. Hardness of cooked whole beans from treatments 2 and 3 increased during storage. Application of the detergent system for analysis of cell wall components to whole ground cotyledons showed significant increases in cell wall content, cell wall nitrogen and hemicellulose for cotyledons of treatment 3. These increases were highly correlated with hardness of cooked beans. Acid detergent residue, lignin and cellulose contents of cotyledons did not change in any of the treatments. The synthesis of nitrogen containing compounds in cell walls during adverse storage may be a contributing factor in the development of hardness by hindering dissolution of the middle lamella during cooking.

Raw milk from 13 cows fed TMR supplemented with native pasture and from 13 cows fed only TMR on one farm was collected separately 4 times with an interval of 15 d between collections. Two blocks (14 kg each) of cheese were made from each milk. The objective was to determine the influence of consumption of native plants in Sicilian pastures on the aroma compounds present in Ragusano cheese. Milk from cows that consumed native pasture plants produced cheeses with more odor-active compounds. In 4-mo-old cheese made from milk of pasture-fed cows, 27 odor-active compounds were identified, whereas only 13 were detected in cheese made from milk of total mixed ration-fed cows. The pasture cheeses were much more rich in odor-active aldehyde, ester, and terpenoid compounds than cheeses from cows fed only total mixed ration. A total of 8 unique aroma-active compounds (i.e., not reported in other cheeses evaluated by gas chromatography olfactory) were detected in Ragusano cheese made from milk from cows consuming native Sicilian pasture plants. These compounds were 2 aldehydes ([E,E]-2,4-octadienal and dodecanal), 2 esters (geranyl acetate and [E]-methyl jasmonate), 1 sulfur compound (methionol), and 3 terpenoid compounds (1-carvone, L(-) carvone, and citronellol). Geranyl acetate and (E)-methyl jasmonate were particularly interesting because these compounds are released from fresh plants as they are being damaged and are part of a possible plant defense mechanism against damage from insects. Most of the odor-active compounds that were unique in Ragusano cheese from pasture-fed cows appeared to be compounds created by oxidation processes in the plants that may have occurred during foraging and ingestion by the cow. Some odor-active compounds were consistently present in pasture cheeses that were not detected in the total mixed ration cheeses or in the 14 species of pasture plants analyzed. Either these compounds were present in other plants not analyzed, created in the rumen or in cheese after the pasture-plant material had been consumed, or the compounds were lost in the method of sample extraction used for the plant analysis (i.e., steam distillation) versus the solid-phase microextraction method used for the cheeses. This research has demonstrated clearly that some unique odor-active compounds found in pasture plants can be transferred to the cheese.

A steady-state model of the production, absorption, passage, and concentration of ruminal VFA and pH is developed from published literature data and is structured to use the feed descriptions and inputs from the net carbohydrate and protein system. Included are the effects of pH on growth rate and yield of structural and non-structural carbohydrate-fermenting bacteria; production of acetate, propionate, butyrate, lactate, and methane; conversion of lactate to VFA; ruminal absorption of acids; and prediction of ruminal pH from dietary measures and from ruminal buffering and acidity. The root mean square error of predicted total VFA concentration was 12 mM. Individual VFA fractions were inadequately predicted. In a review of literature data, effective NDF (eNDF) provided a better correlation with ruminal pH than forage or NDF. Digestion rate of NDF remained at normal levels above pH 6.2, which corresponds to a minimum eNDF of 20% of dietary DM. Further research is needed to determine the individual VFA produced from carbohydrate fractions at various pH, the appropriateness of partitioning the starch and pectin carbohydrate pool into slowly and rapidly degraded fractions, and the effect on microbial yield, total tract digestibility, and predicted energy values of feeds.

The growth performance of Landim and Africander breeds was compared using data collected from 1968 to 1981 at the Chobela Research Station in Mozambique. Animals from both breeds were managed together in groups by age and sex, except when separated for breeding. Growth traits were body weights at birth, weaning at 7 mo, 18 mo, and first calving, and pre- and postweaning daily growth rates. These traits were analyzed using a mixed-effects least squares model containing breed, year-season of birth, sex, the nested effect of parity within breed, a linear regression on dam's age, and the random effect of sire within breed. Africander calves were 16, 9, and 7% heavier ( P < .01) than Landim calves at birth, weaning, and 18 mo (18 ± 6 kg heavier than the 237-kg Landim average). However, there was no detectable difference for age-adjusted weight at first calving and postweaning daily growth rate. Diminishing weight and growth differences with advancing age may indicate adaptation by the Landim to the prevailing environmental limitations in southern Mozambique, especially through younger ages at puberty and at first calving.

The Cornell Net Carbohydrate and Protein System (CNCPS) has a submodel that predicts rates of feedstuff degradation in the rumen, the passage of undegraded feed to the lower gut, and the amount of ME and protein that is available to the animal. In the CNCPS, structural carbohydrate (SC) and nonstructural carbohydrate (NSC) are estimated from sequential NDF analyses of the feed. Data from the literature are used to predict fractional rates of SC and NSC degradation. Crude protein is partitioned into five fractions. Fraction A is NPN, which is trichloroacetic (TCA) acid-soluble N. Unavailable or protein bound to cell wall (Fraction C) is derived from acid detergent insoluble nitrogen (ADIP), and slowly degraded true protein (Fraction B3) is neutral detergent insoluble nitrogen (NDIP) minus Fraction C. Rapidly degraded true protein (Fraction B1) is TCA-precipitable protein from the buffer-soluble protein minus NPN. True protein with an intermediate degradation rate (Fraction B2) is the remaining N. Protein degradation rates are estimated by an in vitro procedure that uses Streptomyces griseus protease, and a curve-peeling technique is used to identify rates for each fraction. The amount of carbohydrate or N that is digested in the rumen is determined by the relative rates of degradation and passage. Ruminal passage rates are a function of DMI, particle size, bulk density, and the type of feed that is consumed (e.g., forage vs cereal grain).

The Cornell Net Carbohydrate and Protein System (CNCPS) has equations for predicting nutrient requirements, feed intake, and feed utilization over wide variations in cattle (frame size, body condition, and stage of growth), feed carbohydrate and protein fractions and their digestion and passage rates, and environmental conditions. Independent data were used to validate the ability of the CNCPS to predict responses compared to National Research Council (NRC) systems. With DMI in steers, the CNCPS had a 12% lower standard error of the Y estimate (Sy.x) and three percentage units less bias than the NRC system. For DMI in heifers, both systems had a similar Sy.x but the NRC had four percentage units less bias. With lactating dairy cows' DMI, the CNCPS had a 12% lower Sy.x. Observed NEm requirement averaged 5% under NRC and 6% under CNCPS predicted values at temperatures above 9 degrees C but were 18% over NRC and 9% under CNCPS at temperatures under 9 degrees C. Energy retained was predicted with an R2 of .80 and .95 and a bias of 8 and 4% for the NRC and CNCPS, respectively. Protein retained was predicted with an R2 of .75 and .85 with a bias of 0 and -1% for NRC and CNCPS, respectively. Biases due to frame size, implant, or NEg were small. Body condition scores predicted body fat percentage in dairy cows with an R2 of .93 and a Sy.x of 2.35% body fat. The CNCPS predicted metabolizable protein allowable ADG with a bias of 1.6% with a Sy.x of .07 kg compared to values of -30% and .10 kg, respectively for the NRC system.

An analysis of the compartmental scheme used to determine the rate and extent of ruminal degradation of feeds is presented. Attention is given to the kinetic representation of the degradation of the potentially degradable fraction. Changing the kinetic order of the rate, and introducing indigestible substrate inhibition and microbial activity into its representation, are investigated. This leads to response functions such as the Gompertz and logistic for describing the cumulative disappearance of potentially degradable substrate during in-sacco and in-vitro incubation.

Dietary fibers are not uniform, chemically or in their nutritive and biological properties, the only common ground being their resistance to mammalian digestive enzymes. The AOAC method for total fiber is subject to inferences from ash, protein, tannins and resistant starches. These interferences can be reduced by urea enzymatic dialysis. The measurement of soluble and insoluble fiber is nutritionally relevant, since physical properties greatly modify dietary effects of fiber. Insoluble fiber is conveniently measured as neutral-detergent fiber. This procedure has been improved by reducing the starch interference and the time of analysis. Physical and biological properties of dietary fiber can be measured by using relevant procedures for hydration capacity, metal ion exchange capacity and rate of fermentation. The lignin and tannin content modify the characteristics of dietary fiber.

We used chemical composition and in vitro digestibility data from temperate and tropical forages to develop relationships between indices of lignification and forage indigestible NDF. Neutral detergent fiber indigestibility increased nonlinearly as the lignin concentration of the NDF increased. Differences in estimated indigestible NDF using equations developed for a specific forage class (C3 and C4 grasses and legumes) were small and are probably not biologically significant when compared to those estimated from a common equation. Selected equations were compared with the Cornell Net Carbohydrate and Protein System (CNCPS) for the prediction of ADG. The linear equation (2.4 times NDF lignin content) used by the CNCPS and the Beef NRC had some of the largest errors due to mean bias. A log-log model [4.37 x (lignin/NDF)(.84)] provided the best combination of low total prediction error, low mean bias, and minimal error due to regression bias when permanganate lignin was used. A similar equation based on sulfuric acid lignin [6.17 x (lignin/NDF)(.77)] also met the above criteria. These equations then were evaluated with the CNCPS model against animal growth data from diets ranging in forage quality. Regardless of the equation used for predicting unavailable fiber, the CNCPS underpredicted daily gain, with mean biases ranging from -.10 to -.22 kg/d. Regression bias ranged from .13 to .14 kg/d and the coefficients differed from unity (P = .0001). The new equations gave numerically lower energy allowable ADG by steers compared to the linear equation currently used by the CNCPS model. The estimates were lower due to a higher predicted indigestible NDF, which resulted in a lower estimated forage energy value.

Fertility and reproductive performance of Landim and Africander females were compared using data collected from 1968 to 1981 at the Chobela Research Station in Mozambique. Breeds were managed together and grouped by age and sex, except when separated for breeding. Traits were relative fertility (probability of fertile females calving from the first breeding season), age at first calving, first calving interval, and subsequent calving intervals. calving rates were tested by x2 procedures with equal expected frequencies in each subclass. The statistical model included breed, the random effect of sire within breed, year-season of birth or calving, and calving group within breed. Landim survivors were more fertile (P < .05) than the Africander ones throughout their recorded lifetimes. Landim females were 1.32 +/- .21 mo (or 3%) younger at first calving and had a 48 +/- 12 d (or 11%) shorter interval between first and second calving than the Africander average of 473 d. When reproductive and growth information were combined to compute an annual index of beef offtake expressed as 18-mo calf yield per unit of dam's weight at first calving, Landim cows annually yielded 30% more calf weight (P < .001) than Africander cows per kilogram of their own body maintenance despite lighter body weights at 18 mo. Superior fertility of Landim females led to greater beef offtake from higher calving rates. Greater fertility and relatively less feed to maintain the reproducing herd are probable mechanisms for a population to adapt to nutrient-limiting environments such as the one in southern Mozambique.

Total and phosphate buffer insoluble amino acids were determined for corn grain and silage, dried brewer's grain, timothy hay, and soybean meal. In addition, amino acid compositions of the acid detergent residue and neutral detergent residue were determined, and soluble amino acids were estimated for each feedstuff. Variation of amino acid concentrations among protein fractions as percent of total amino acid was measured in the buffer insoluble, soluble, neutral detergent fiber, and acid detergent fiber fractions within a feed as well as among feedstuffs. Insoluble noncell-wall, neutral detergent, and acid detergent amino acids as a percentage of total individual amino acid (neutral detergent fiber or acid detergent fiber amino acid/total individual amino acid × 100) for soybean meal, brewer's grain, corn grain, timothy, and corn silage were 73.2, 8.5, 5.6; 31.2, 54.5, 16.3; 72.1, 16.2, 4.6; 18.0, 55.6, 8.2; 14.6, 20.8, and 4.8. Recovery of amino acid nitrogen as percent of total Kjeldahl nitrogen varied among and within fractions studied.

Nitrogen in selected feedstuffs was fractionated based on solubility in mineral solvents and detergent solutions. Six solvents with either a continuous mixing procedure at constant temperature or an intermittent mixing procedure at room temperature were compared for nitrogen solubility. Nitrogen solubility varied with type of solvent. Borate-phosphate buffer was more stable than other solvents. Borate-phosphate buffer had a correlation coefficient of .92 with insoluble nitrogen obtained with autoclaved rumen fluid. Insoluble nitrogens obtained by continuous or intermittent mixing techniques were not significantly different. The latter procedure is simple and avoids the need for special extraction equipment for estimation of nitrogen solubility. In most feedstuffs, a large fraction of soluble nitrogen was in the form of nonprotein nitrogen. Oats and peanut meal contained a significant amount of soluble true protein (43.3 and 24.3% of total nitrogen). Neutral detergent insoluble nitrogen and acid detergent insoluble nitrogen content of feed samples varied among feedstuffs and were not a constant proportion of neutral detergent or acid detergent fiber.

Depressions in digestibility of both diet and feed fractions were measured in two diets fed at two intakes to dairy cattle. A low forage diet of 32% forage and 68% concentrate (dry matter) and a high forage diet of 83% forage and 17% concentrate were fed to dry cows at maintenance and lactating cows at ad libitum intake. Lactating cows consumed 42.1 and 32.2 g dry matter/kg body weight on the low forage and high forage diets whereas dry cows consumed 12.0 and 13.0. Energy digestibilities were 67.5 and 64.0% for lactating cows on the low forage and high forage diets and 73.7 and 67.6% for dry cows. Depressions in digestibility for dry matter, neutral detergent fiber, hemicellulose, cellulose, energy, and cell solubles per unit of intake were greater on the low forage diet. Retention time of concentrate increased by .44 units for each unit increase in retention time of forage. Retention times in the total tract for forage and concentrates were 62 and 73% less at low intake on the low forage diet. Similar results for the high forage diet were 80 and 81%. Retention times of concentrate and forage were correlated with digestibility of gross energy.

1. The water-holding capacities (WHC) of four sources of fibre were measured using dialysis membranes and osmotic-suction pressures of 45, 89 and 178 mosmol/l (1, 2 and 4 atm). At all pressures, pectin had the highest WHC, followed by cabbage (Brussicu oleruceu) and lucerne (Medicago sativu) and then cellulose. A suction pressure of 89 mosmol/l (2 atm) was used in the subsequent fermentation study since it had the lowest standard error of the mean and most closely approximated physiological conditions.2. The four fibres were anaerobically fermented in vitro with human faecal inoculum for 24 h. The WHC of the fermentation residues were measured. The potential water-holding capacity (PWHC), a function of the extent of fermentability and the WHC of the fermentation residues, was highest for lucerne, followed by cellulose, then cabbage and, finally, pectin. Only the PWHC values ranked the four fibres in the same order as in vivo values.3. It was concluded that the ethanol-insoluble residues containing unfermented fibre organic matter and microbial organic matter, both of which hold water, should be used to calculate PWHC and to predict the effect of fibre on rate of passage and faecal mass in humans.

An enzymatic procedure using Trichoderma viride carbohydrases, a fungal hemicellulase, and pepsin was developed to provide a laboratory method for predicting forage digestibility. The amount of forage dry matter solubilized by enzymes and incubation buffer was less than that in vivo or by in vitro fermentation by rumen microorganisms. Total forage dry matter solubilized by the enzymatic procedure was correlated (.92) with in vitro digestibility. Simple correlation coefficients between in vivo true digestibility of 18 forages and total dry matter solubilized by enzymes and buffer was .87; that soluble in the buffer only, .65; and that solubilized by the enzymes, .82. Correlation coefficients with in vivo true digestible amount of cell-wall and protein were greater when the forage species were considered separately than when pooled together. With this restriction, the enzymatic procedure can be a useful method for predicting forage digestibility. Fermentations with rumen inoculum however, provided more accurate predictions of in vivo digestibility in a variety of forage species.

The effect on true dry matter digestibility of Philippine feedstuffs was studied with different sources of rumen fluid inocula and varying fermentation time in an in vitro sysytem. In one experiment differences in true dry matter digestion in vitro were nil among three sources of rumen fluid inocula (buffalo, cattle-Philippines, cattle-Cornell University).For commonly fed tropical feedstuffs in the other experiment rumen fluid from the cattle at Cornell gave lower digestibilities. True dry matter digestibility in vitro increased for each 24 h increase in fermentation periods of 48, 72, and 96 h. Differences in digestibility between cattle and buffalo in metabolism studies (in vivo) cannot be explained by differences in rumen fluid.

1. Digesta passage and retention were measured in heifers, sheep, goats, equines and rabbits of varying body-weights when given timothy (Phleum pratense) hay.2. Two passage markers were compared, cobalt (III) ethylene diamine tetraacetate (CoEDTA) and chromiummordanted timothy fibre for liquid and solid phase respectively. Both markers were injected into the rumen of the ruminants and into the caecum of the equines andrabbits.3. In ruminants, two different sets of rate constants (k1 and k2) were derived from a two-pool model for marker passage, using a graphical approach and a computer-based non-linear least-squares curve-fitting technique.4. Retention times, due to unidirectional flow through the gastrointestinal tract (transit time) and due to pool effects (mean retention time, MRT), were calculated.5. Curve fitting was only successful for the excretion of liquids in ruminants. The two-pool model was not applicable to the passage of solids.6. Apparent retention of liquid was always shorter than for solids in all species, except in rabbits. However absorption of CoEDTA was too large in the rabbits to determine liquid retention accurately. Times for first appearance of the two markers were similar within animal groups.7. MRT values were lowest in the rabbit, intermediate in equines and high in the ruminants. The MRT values (h) of solids and liquid respectively were: large heifers 65, 18; small heifers 48, 20; goats 41, 28: sheep 57, 26: equines 23, 18; rabbits 5·3, not determined.8. Liquid retention seemed to decrease somewhat with increasing body-weight in the ruminants. Solids retention decreased with decreasing body-weight in the ruminants, but sheep had longer retention times than goats of similar size. Equines exhibited large individual variation in retention of the liquid or solid markers, seemingly unrelated to size. Noeffect of size was seen in the retention of solids in the rabbits.

When mixed ruminal bacteria were incubated in an artificial medium with isolated plant cell walls, cell wall digestion and ammonia utilization were increased by low concentrations ( M ) of carbon-4 and carbon-5vol.tile fatty acids (isobutyric, isovaleric, valeric, and 2-methylbutyric). Carbon-4 and carbon-5 acid supplementation also increased cell wall digestion of intact forages. No pattern was observed between protein content of the feed and response to carbon-4 and carbon-5vol.tile fatty acids. Only the branch-chain acids (isovaleric, isobutyric, and 2-methylbutyric) stimulated bacterial growth and plant cell wall digestion. No synergisms were observed among the branched-chain acids, and they could replace each other. Valeric acid, a straight chain compound, was without effect, and phenylpropionic and phenylacetic acids likewise did not improve digestibility. The peptide source, Trypticase, enhanced cell wall digestion more than carbon-4 and carbon-5vol.tile fatty acids alone, and this observation suggested that fiber digesting bacteria may be stimulated directly by amino acids or peptides.