Ruman degradation is crucial in the supply of dietary nutrients to meet the nutrient demands of the anaerobic microbes and body tissues of ruminant animals. Therefore, it is essential to study the dynamics of rumen degradation of various feeds before their potential use to formulate nutritious diets for ruminant animals. Amongst many methods that have been used in the past, the in sacco method has been the most effective method to study rumen degradation. However, this method is undesirable due to its implications for animal welfare and costs. While many in vitro methods have been tested as possible alternatives to the in sacco method to study rumen degradation of feeds, they were unable to remove the need to use fistulated animals to obtain rumen fluid. Although solubility, enzyme- and faeces-based in vitro methods do not require rumen fluid, they still need data from either the in sacco method or the rumen fluid-based in vitro methods for comparison and validation. Therefore, there is a need to develop in vitro methods that do not require the need to surgically modify ruminants to obtain rumen fluid to study rumen degradation. We review the potentials and problems associated with the existing methods to study rumen degradation and their implications for the animal industry in different situations.

Oxalic acid is found in high concentrations in some plants consumed by ruminants and may cause renal toxicity. To determine whether exposure to oxalic acid affects the capacity of the rumen of sheep and goats to degrade the compound, 20 animals (10 sheep and 10 goats) were dosed with free oxalic acid by gelatin capsule twice daily for 3 weeks at one of five levels (0·0, 0·3, 0·6, 0·9 and 1·2 mmol/kg live weight (M) per day). Rumen samples were collected by stomach tube in the week prior to the start of dosing and in each week of the 3-week experiment. Oxalic acid degradation capacity was measured by adding uC-labelled oxalic acid to rumen fluid in vitro and capturing evolved 14CO2. Rates of degradation increased with increasing level of administration (2·30, 4·71, 6·74, 9·83 and 13·90 mmol of oxalic acid degraded per I rumen fluid per day for doses 0·0, 0·3, 0·6, 0·9 and 1·2 mmol/kg M per day, respectively; P < 0·001). Rates of degradation increased during the dosing period (P < 0·001) with the largest increases occurring in the 1st week of dosing. Goats showed a greater response than sheep, with a higher mean oxalic acid degradation capacity (9·04 v. 5·95 mmol of oxalic acid degraded per I rumen fluid, P < 0·05). Oxalic acid administration did not influence plasma calcium concentration or cause renal function impairment as measured by plasma creatinine concentrations. The experiment demonstrated adaptation in the rumen to potential toxins in the host diet and suggests that the rumen micro-organisms of goats may have been more adapted to degrading oxalic acid than sheep.

Six cereal straws and two traditional hays were used to study the relationship between voluntary dry matter (DM) intake and chemical composition and ruminal degradation characteristics. The voluntary DM intake was measured during 60 days using Barbarin adult ewes given food individually in four groups of six animals. The forages were offered to the ewes twice daily and were supplemented with 10 g DM of soya-bean meal per kg M0·75 per day and 30 g per ewe per day of a commercial mixture of minerals and vitamins. The chemical composition and the leaf/stem (L/S) ratio of the forages were determined. Their ruminal degradation characteristics were measured by using the nylon bag technique according to the exponential model Dg = a + b (1 – e−ct). Crude protein contents of straws ranged from 22 to 35 g/kg DM and that of hays from 35 to 57 g/kg DM. The corresponding values of L/S ratio varied from 0·68 to 0·88. The voluntary DM intake was highly variable and the hays were ingested at greater amounts than the straws, although their degradable (b) and their rate of digestion (c) were not significantly different (P > 0·05).

Significant relationships were established between voluntary DM intake and the neutral-detergent fibre (R2 = −0·72; P < 0·001), acid-detergent fibre (R2 = −0·75; P < 0·001) and a values (R2 = 0·83; P < 0·001). The precision of the prediction was significantly improved using ruminal degradation characteristics (Syx = 4·42) compared with the chemical composition (Syx = 5·60).

A study urns conducted to determine the best method of preparation of silage and freshly cut forage samples for the estimation of rumen degradability by the nylon bag technique. Three types of forage were evaluated: a grass silage, a fresh grass (ryegrass) and a fresh legume (white clover). For each forage, six preparation methods were compared: chopping fresh (FRS); chopping and macerating fresh (FMC); chopping, freezing, thawing and macerating (FRZ); freeze-drying (FD); low-temperature oven-drying (45°C, 72 h) (OVD); high-temperature oven-drying (160°C, 90 min) (DHD). Dried samples were hammer-milled (2·5-mm screen). Chemical composition and rumen degradability were affected by the method of preparation. Protein fractions were sensitive to drying method, and oven-drying reduced nitrogen (N) solubility and degradability as the severity of the heating was increased. OVD and DHD gave lower estimates of N and dry matter (DM) solubility and degradability than FD. The effect of drying method on DM degradability was to reduce solubility and effective degradability, calculated for an outflow rate of 0·033 per h, but not potential degradability.

Silage DM degradability was less affected than that of fresh forages. Freshly prepared samples (FRS, FMC, FRZ) gave lower estimates of N and DM solubility and degradability than FD, the differences being least with silage and FRZ, which was the most effective at rupturing plant structures of the FRS, FMC and FRZ methods. Of the six preparation methods, freeze-drying was the most effective preparation method. FRZ and OVD were less effective, but similar to each other. The small particles (calculated) produced by grinding dried samples may result in an overestimation of zero time losses and hence the degradability of the sample. These undesirable effects might be minimized by coarser grinding (4-mm screen) and correction for particulate matter loss.

A study was carried out to examine the effects of method of grass conservation on intake and apparent digestibility by sheep and rate of degradation in the rumen of cattle. Thirty-six hoggets were arranged in a three-period partial change-over design involving nine treatments. The treatments consisted of fresh herbage or herbage from the same pasture which was ensiled for 2, 4, 7, 10, 20 and 41 days in round bales or herbage from the same pasture conserved as hay or ensiled in a bunker silo for 51 days. In addition the rate of dry-matter disappearance in the rumen for each treatment was determined using three rumen fistulated steers. The fresh and ensiled treatments had been frozen prior to feeding. Results from the study showed that the dry-matter intakes, corrected for losses of volatile compounds, of material ensiled in round bales, was increasingly depressed with period of ensiling up to 20 days after ensiling. Intakes of digestible energy followed a similar trend. Regression analysis indicated that reductions in intake with ensiling were mainly due to increases in ammonia N and n-butyric acid concentration, while changes in pH, water-soluble carbohydrate and acetic acid concentration also influenced intake. The differences in intakes of dry matter and digestible energy between fresh herbage and herbage from the bunker silo were not significant. The ensiling of herbage in round bales had little effect on organic matter apparent digestibility but led to an increase in nitrogen apparent digestibility and effective degradability when calculated at rumen outflow rates of 0·05 per h and 0·08 per h. Conservation of grass as hay led to a reduction in the intake, apparent digestibility and effective degradability of dry matter.

Two experiments were designed to examine the effects of ammonia treatment of barley straw on rumen environmental conditions for fibre degradation, and to determine the effect of treatment on the soluble and insoluble fractions of straw. In experiment 1, rumen pH, and ammonia-nitrogen and volatile fatty acid concentrations in the rumen of sheep receiving untreated (US1) or ammonia-treated (TS1) straw were recorded. Also, both straws were incubated in the rumen of both groups of animals. There were no significant differences (P > 0·05) within rumen parameters, except for butyrate proportion, which was higher (P < 0·01) with TS1. Dry matter and neutraldetergent fibre disappearances of TS1 were higher (P < 0·001) than those of US1 at all the incubation times. Degradation of both straws in US1-fed sheep was not smaller, and in some periods of incubation was even greater, than in TS1-fed animals. In experiment 2, samples of untreated (US2) and treated (TS2) straw were incubated in wethers offered a mixture (50:50) of alfalfa hay and straw. Samples of US2 and TS2 were soaked in autoclaved rumen fluid to measure their solubility. It was clear that, although treatment increased the soluble fraction of US2 and TS2 by 52 and 65 g/kg respectively, from 0 to 72 h of incubation, increasing the differences between straws from 45 to 58 g/kg in that period, actual microbial action on the treated roughage was the more important factor, accounting for a difference between US2 and TS2 of 131 g/kg after 72 h incubation.

Ten hays harvested at three stages (early bloom MB, mid bloom MB or in seed) made from lucerne (Medicago sativaj, sweet clover (Melilotus segetalis), Persian clover (Trifolium resupinatum) and pre-bloom (PB) Italian ryegrass (Lolium multiflorum var.), were offered ad libitum to four Merino male sheep and daily intake (g dry matter (DM) per kg M0·75) and DM apparent digestibility (DMD) were measured. In sacco DM degradation (g per 100 g DM), gas production (ml per 200 mg DM), in vitro digestibility and fibre composition (g/kg DM) of the hays were also studied. Gas production or DM degradation were calculated at 6, 12, 24, 48, 72 or 96 h and their kinetics were described using the equation p = a + b(1 - e-ct). Intake and in vivo DMD of the hays were variable (P < 0·01). Lucerne EB and Persian clover (all stages) had the highest nutritive value, whereas sweet clover (all stages) had the lowest. Apart from neutral-detergent fibre, which was only related to intake (r = -0·68; P < 0·05), chemical components and in vitro digestibility were poorly (P > 0·05) related to animal performance. Between 12 and 96 h incubation, intake and in vivo DMD were better related to DM degradation (r = 0·79 to 0·83; r = 0·61 to 0·77) than to gas production (r = 0·73 to 0·80; r = 0·58 to 0·78). Prediction of intake and in vivo DMD from the (a + b) values did not provide a great advantage over using some of the static values of gas production or DM degradation.

Multiple regression using separated kinetics of degradation resulted in highest accuracy for predicting intake and apparent digestibility from gas production (R2 = 0·63; R2 = 0·78) and nylon bag degradability (R2 = 0·77; R2 = 0·89). It was concluded that the gas test has good potentiality as it was capable of predicting not only apparent digestibility, but also intake to a level close to that of the nylon bag technique.

Leaves of Leucaena leucocephala, Sesbania sesban and Calliandra callothyrsus were harvested in Rwanda from young shoots at 8 weeks after the first cutting. They were dried, ground and incubated at the same time in polyester bags in three non-lactating Holstein-Friesian cows each fitted with a ruminal cannula. The bags were removed at 0, 2, 4, 8, 24, 48, 72 and 144 h after the start of incubations. The different parameters characterizing extent and rate of ruminal degradation of organic matter (OM), neutral-detergent fibre (NDF), and crude protein (CP) were calculated. In vitro digestibility of residual protein after 24 h and 48 h incubation was also determined. Sesbania sesban had lowest cell wall contents and gave highest ruminal degradability for OM, NDF and CP. Leucaena leucocephala was degraded to a lesser extent, but its undegraded protein had a somewhat higher in vitro digestibility. In contrast, protein of Calliandra callothyrsus was poorly degraded and digested. The proportion and composition of cell wall could not explain these differences in digestion characteristics and other measurements, such as tannins, were incriminated. Increased ruminal incubation time augmented the extent of ruminal degradation and reduced in vitro digestibility of undegraded protein but did not affect the undigestible protein fraction.