Variation in ruminal in situ degradation of crude protein and starch from maize grains compared to in vitro gas production kinetics and physical and chemical characteristics

The objectives of this study were (1) to evaluate in situ ruminal dry matter (DM), crude protein (CP) and starch degradation characteristics and in vitro gas production (GP) kinetics using a set of 20 different maize grain genotypes and (2) to predict the effective degradation (ED) of CP and starch from chemical and physical characteristics alone or in combination with in vitro GP measurements. Maize grains were characterised by different chemical and physical characteristics. Ruminal in situ degradation was measured in three lactating Jersey cows. Ground grains (sieve size: 2 mm) were incubated in bags for 1, 2, 4, 8, 16, 24, 48 and 72 h. Bag residues were analysed for CP and starch content. Degradation kinetics was determined and the ED of DM, CP and starch calculated using a ruminal passage rate of 5%/h and 8%/h. The GP of the grains (sieve size: 1 mm) was recorded after 2, 4, 6, 8, 12, 24, 48 and 72 h incubation in buffered rumen fluid and fitted to an exponential equation to determine GP kinetics. Correlations and stepwise multiple linear regressions were evaluated for the prediction of ED calculated for a passage rate of 5%/h (ED5) for CP (EDCP5) and starch (EDST5). The in situ parameters and ED5 varied widely between genotypes with average values (±SD) of 64% ± 4.2, 62% ± 4.1 and 65% ± 5.2 for ED5 of DM, EDCP5 and EDST5 and were on average 10 percentage points lower for a passage rate of 8%/h. Degradation rates varied between 4.8%/h and 7.4%/h, 4.1%/h and 6.5%/h and 5.3%/h and 8.9%/h for DM, CP and starch, respectively. These rates were in the same range as GP rates (6.0–8.3%/h). The EDCP5 and EDST5 were related to CP concentration and could be evaluated in detail using CP fractions and specific amino acids. In vitro GP measurements and GP rates correlated well with EDCP5 and EDST5 and predicted EDCP5 and EDST5 in combination with the chemical characteristics of the samples. Equations can be used to obtain quick and cost effective information on ruminal degradation of CP and starch from maize grains.     

Variation of lupin protein degradation in ruminants studied in situ and using chemical protein fractions

The main objective of this study was to evaluate the variability in in situ CP degradation characteristics of 15 batches lupin grains from nine genotypes in a standardised approach. This study also investigated whether differences in CP degradation can be described by protein fractionation using the Cornell Net Carbohydrate and Protein System (CNCPS) and also whether thermal processing of lupins has an effect on CP degradation in the rumen and analysed protein fractions. The rising political and consumer demand for milk products from dairy production systems based on domestic protein sources and the wide range of lupin types and varieties that can be chosen as protein feed in dairy nutrition requires research to determine the variability in CP degradation characteristics in the rumen. For CP degradation measurements, ground grains were incubated in the rumen of three lactating Jersey cows fitted with a ruminal cannula for different times from 2 to 48 h, and the washing loss of non-incubated samples was also measured. Protein fractions were analysed according to CNCPS and used for the estimation of ruminally degraded protein. In situ CP degradation parameters varied widely between untreated samples. The mean value for the washout fraction was 29.3% (from 16.4% to 43.6%). The potentially degradable fraction averaged 70.5% (from 55.6% to 83.7%), hence maximal degradation of CP was close to completeness. Mean degradation rate was 16.6%/h (from 12.6 to 21.0%/h). Variation in estimated parameters led to variation in the effective degradation (ED) averaging 76.6% (from 67.3% to 83.0%) when calculated assuming a ruminal outflow of 8%/h. Thermal treatment of lupins induced changes in degradation characteristics, primarily by lowering degradation rates, and also led to a significant reduction in ED. The ED calculated from analysed protein fractions averaged 10 percentage points higher than ED calculated from in situ parameters for untreated grains. The ED based on protein fractionation was also reduced by heat treatment, but the correlation with in situ based ED was poor. It can be concluded that the variation in ED indicates a potential to increase the amount of rumen undegraded protein without additional chemical or physical treatment and the effect of genetic factors and agronomic practices on ED of lupin grains should be investigated in systematic studies in the future.     

Relationship between chemical composition and in situ rumen degradation characteristics of maize silages in dairy cows

Several in situ studies have been conducted on maize silages to determine the effect of individual factors such as maturity stage, chop length and ensiling of maize crop on the rumen degradation but the information on the relationship between chemical composition and in situ rumen degradation characteristics remains scarce. The objectives of this study were to determine and describe relationships between the chemical composition and the rumen degradation characteristics of dry matter (DM), organic matter (OM), CP, starch and aNDFom (NDF assayed with a heat stable amylase and expressed exclusive of residual ash) of maize silages. In all, 75 maize silage samples were selected, with a broad range in chemical composition and quality parameters. The samples were incubated in the rumen for 2, 4, 8, 16, 32, 72 and 336 h, using the nylon bag technique. Large range was found in the rumen degradable fractions of DM, OM, CP, starch and aNDFom because of the broad range in chemical composition and quality parameters. The new database with in situ rumen degradation characteristics of DM, OM, CP, starch and aNDFom of the maize silages was obtained under uniform experimental conditions; same cows, same incubation protocol and same chemical analysis procedures. Regression equations were developed with significant predictors (P<0.05) describing moderate and weak relationships between the chemical composition and the washout fraction, rumen undegradable fraction, potentially rumen degradable fraction, fractional degradation rate and effective rumen degradable fraction of DM, OM, CP, starch and aNDFom.     

Degradability characteristics of dry matter and crude protein of forages in ruminants

Twelve corn silages, 22 grass silages and 14 grass hays, obtained from various farms located in the lower Fraser Valley region of British Columbia, and 16 alfalfa hays, grown primarily in the Columbia basin of central Washington State, were evaluated using both the rumen and the mobile nylon bag in situ techniques. Nylon bags containing each forage were incubated in duplicate for 0, 2, 4, 8, 12, 24, 48, 72, or 96 h in two of six non-lactating Holstein cows fitted with rumen and duodenal cannulae. All forage types were evaluated in terms of the following dry matter (DM) and crude protein (CP) digestion characteristics: soluble fraction A, degradable fraction B, degradation rate, lag phase, and effective degradability. The mobile nylon bag technique was used to determine intestinal disappearance of DM and CP from the forages following pre-incubation in the rumen for 12 h. Significant (P < 0.05) differences in degradation characteristics occurred within all forages with regard to the soluble and potentially degradable DM and CP fractions. Soluble CP content in the rumen varied from 44.08 to 75.37% and from 18.74 to 65.38% in the corn and grass silages, respectively, and from 48.27 to 75.43% and from 30.13 to 65.95% in the alfalfa and grass hays, respectively. Significant differences within each forage type were also observed for the degradable CP in fraction B: 10.89 to 45.28% for corn silage, 20.72 to 82.77% for grass silage, 16.67 to 44.88% for grass hay and 25.44 to 62.93% for alfalfa hays. Significant differences (P > 0.05) were observed in fractional rates of ruminal DM degradation of the grass hays and corn silages. Significant differences did exist in the fractional rates of ruminal CP degradation within all forage types with the exception of alfalfa hays. Effective degradabilities of DM and CP were also significantly different between samples of a particular forage type. The mobile nylon bag data indicated that approximately 20% of the original CP in the grass silage, grass hay and alfalfa hay samples disappeared in the intestine and that there was significant variation between individual samples. On average, in the corn silage samples more than 10% of the original nitrogenous material disappeared in the intestine. The results presented in this study clearly demonstrate that the use of tabulated values for describing individual batches of forages in terms of their degradability characteristics is inaccurate since they may not reflect the particular forage being used in the ration and thus may lead to errors in diet formulation.     

Effects of ensiling on in situ ruminal degradability and intestinal digestibility of corn forage

The effective degradability of dry matter (DM), crude protein (CP) and amino acids (AA), and the intestinal effective digestibility (IED) of DM and CP of a green forage corn (GC) and its silage (EC) were determined on freeze-dried samples using three rumen and duodenum cannulated wethers. Two rumen incubations with duplicate bags were performed for each feed. Rumen degradation was determined on one series of bags from each incubation. The other series was freeze-dried and used to determine IED using mobile nylon bags. Microbial contamination of rumen incubated residues (determined with ¹⁵N techniques) fitted exponential functions, which showed a greater microbial contribution in EC than in GC in the undegradable DM (18.6% vs. 13.5%) and CP (81.7% vs. 69.4%). Degradability was calculated considering the particle rumen outflow rate (k_p : 0.056/h) of the EC (ED_p) or additionally the rate of comminution and mixing (k_c : 0.130/h) of these particles (ED_cp). Ensiling increased ED_p (9.33%, p < 0.01) or ED_cp (5.30%, p = 0.062) of DM and was associated with losses of nitrogen and with large changes in the AA profile. It is necessary to correct the microbial contamination, because it represents 32.0% (GC) and 42.5% (EC) of the undegraded CP when using k_p and k_c . Ensiling caused higher degradabilities for some AA as well as large differences in the changes due to the rumen fermentation on the AA profile. However, it had only limited effects on the undegraded protein profile. Ensiling also reduced the IED of DM (23.3% vs. 14.6%; p = 0.057). In conclusion, results do not show losses of nutritive value by ensiling corn cut at vitreous grain stage.     

Pelleting and extrusion can ameliorate negative effects of toasting of rapeseed meal on protein digestibility in growing pigs

Toasting time (TT) of rapeseed meal (RSM), the diet processing (DP) method and the interaction between both on the apparent CP digestion along the gastrointestinal tract and the apparent ileal digestibility (AID) of amino acids of growing pigs were investigated. The experiment consisted of a 3×3 factorial design of TT of RSM (0, 60 and 120 min) and DP method (mash, pelleting and extrusion). In total, 81 boars with a starting BW of 20 kg were euthanized 4 h after their last feeding. The gastrointestinal tract was dissected and the small intestine divided in three sections of similar length. Samples were collected from the stomach, 1.5 m from the ends of each of the three sections of the small intestine, and the rectum. The apparent digestibility (AD) of CP for each of the small intestine sections was used to calculate the rate of CP digestion. Increasing the TT of RSM resulted in lower protein solubility, lower lysine/reactive lysine contents and higher protein denaturation, indicative of the occurrence of protein aggregation and Maillard reactions. There were significant effects (P⩽0.01) of TT on the AD of CP in the different sections of the gastrointestinal tract. The rate of CP digestion of the 0 min toasted RSM diets was 23% and 35% higher than that of the 60 and 120 min toasted RSM diets, respectively. There was a significant interaction (P=0.04) between TT and DP for the AID of CP. Although pelleting of the 0 and 60 min toasted RSM diets did not change the AID of CP with respect to the mash diets, pelleting of the 120 min toasted RSM diet increased the AID of CP by 9.3% units. Extrusion increased the AID of CP of the 0 and 60 min toasted RSM diets by 3.4% and 4.3% units with respect to the mash diets, whereas extrusion of the 120 min toasted RSM diet increased the AID of CP by 6.9% units. Similar positive effects of pelleting and extrusion were obtained for the AID of lysine and reactive lysine, especially in the diets with higher TT. In conclusion, processing (pelleting and extrusion) of RSM containing diets can ameliorate the negative effects of RSM toasting on protein and amino acid digestibility; these effects were larger for the RSM toasted for longer times.     

Prediction of CP and starch concentrations in ruminal in situ studies and ruminal degradation of cereal grains using NIRS

Ruminal in situ incubations are widely used to assess the nutritional value of feedstuffs for ruminants. In in situ methods, feed samples are ruminally incubated in indigestible bags over a predefined timespan and the disappearance of nutrients from the bags is recorded. To describe the degradation of specific nutrients, information on the concentration of feed samples and undegraded feed after in situ incubation (‘bag residues’) is needed. For cereal and pea grains, CP and starch (ST) analyses are of interest. The numerous analyses of residues following ruminal incubation contribute greatly to the substantial investments in labour and money, and faster methods would be beneficial. Therefore, calibrations were developed to estimate CP and ST concentrations in grains and bag residues following in situ incubations by using their near-infrared spectra recorded from 680 to 2500 nm. The samples comprised rye, triticale, barley, wheat, and maize grains (20 genotypes each), and 15 durum wheat and 13 pea grains. In addition, residues after ruminal incubation were included (at least from four samples per species for various incubation times). To establish CP and ST calibrations, 620 and 610 samples (grains and bag residues after incubation, respectively) were chemically analysed for their CP and ST concentration. Calibrations using wavelengths from 1250 to 2450 nm and the first derivative of the spectra produced the best results (R²_Validation=0.99 for CP and ST; standard error of prediction=0.47 and 2.10% DM for CP and ST, respectively). Hence, CP and ST concentration in cereal grains and peas and their bag residues could be predicted with high precision by NIRS for use in in situ studies. No differences were found between the effective ruminal degradation calculated from NIRS estimations and those calculated from chemical analyses (P>0.70). Calibrations were also calculated to predict ruminal degradation kinetics of cereal grains from the spectra of ground grains. Estimation of the effective ruminal degradation of CP and ST from the near-infrared spectra of cereal grains showed promising results (R²>0.90), but the database needs to be extended to obtain more stable calibrations for routine use.     

Effect of moist heat treatment on in-vitro degradability and ruminal escape protein and amino acids of mustard meal

A study was conducted to determine the effects of moist heat treatment (127°C, 117 kPa steam pressure) for 10 min on protein fractions and in-vitro crude protein (CP) degradability of mustard meal. Rumen undegraded protein (RUP) and amino acid disappearance of unheated, and heated, mustard meal were measured following 12 h of rumen incubation using two ruminally fistulated cows. Intestinal availability of RUP was estimated using an enzymatic (pepsin–pancreatin) procedure. Heat treatment reduced (p<0.05) protein solubility and increased (p<0.05) neutral detergent insoluble CP without affecting acid detergent insoluble CP of mustard meal. Relative to the control, heated mustard meal had a lower (p<0.05) effective in-vitro CP degradability (445.2 vs. 746.8 g kg⁻¹ of CP) and a higher (p<0.05) ruminal escape CP (615.1 vs. 120.2 g kg⁻¹ of CP) value. Amino acid composition was not affected by heat treatment except for the concentration of arginine and lysine which was lower (p<0.05) in heated than in unheated mustard meal. Disappearance of all amino acids following 12 h of rumen incubation was lower (p<0.05) in unheated than in heated mustard meal. Heat treatment increased (p<0.05) the amount of protein available for digestion in the small intestine from 75.7 to 518.1 g kg⁻¹ of CP. It was concluded that moist heating of mustard meal for 10 min will reduce ruminal CP and amino acid degradability without compromising the intestinal availability of ruminal undegraded protein.     

Estimation of intestinal protein digestibility of protein supplements for ruminants using a three-step enzymatic in vitro procedure

This study included 33 samples with main focus on unprotected or rumen-protected rapeseed and soybean feedstuffs, which were analysed using an enzymatic in vitro procedure (EIVP) in order to determine intestinal crude protein (CP) digestibility (IPD) of ruminally undegraded CP. The EIVP involved the sequential digestion of samples with a protease from Streptomyces griseus, pepsin-HCl and pancreatin. Briefly, the EIVP started with determination of true protein. Feeds were incubated for 18 h in a buffer solution at a constant ratio (41 U/g) of S. griseus protease activity to feed true protein. The dried residues were incubated in pepsin-HCl solution for 1 h, and residues from this step were incubated in pancreatin solution for 24 h. Results appeared to have lower IPD dimensions than literature data of previous studies. In addition, a negative correlation became apparent between acid detergent fibre and IPD, as well as a positive correlation between CP, true protein and IPD. The EIVP in its current, strictly standardised form can be applied to develop a database that can be used for protein evaluation systems for establishing tabular values of IPD. Nevertheless, future studies may be hindered since sufficient reference values, i.e. in vivo data, are completely missing.     

In situ ruminal degradation of amino acids and in vitro protein digestibility of undegraded CP of dried distillers’ grains with solubles from European ethanol plants

The objectives of this study were to compare the in situ ruminal degradation of CP and amino acids (AAs) of dried distillers’ grains with solubles (DDGS), and to estimate intestinal digestibility (ID) of undegradable crude protein (UDP) with the in vitro pepsin–pancreatin solubility of CP (PPS), using either DDGS samples (DDGS-s) or DDGS residues (DDGS-r) obtained after 16 h ruminal incubation. Thirteen samples originating from wheat, corn, barley and blends were studied. Lysine and methionine content of DDGS-s varied from 1.4 to 4.0 and 1.3 to 2.0 g/16 g N, respectively. The milk protein score (MPS) of DDGS-s was low and ranged from 0.36 to 0.51, and lysine and isoleucine were estimated to be the most limiting AAs in DDGS-s and DDGS-r. DDGS-r contained slightly more essential AAs (EAAs) than did the DDGS-s. Rumen degradation after 16 h varied from 44% to 94% for CP, from 39% to 90% for lysine and from 35% to 92% for methionine. Linear regressions showed that the ruminal degradation of individual AAs can be predicted from CP degradation. The PPS of DDGS-s was higher than that of DDGS-r and it varied from 70% to 89% and from 47% to 81%, respectively. There was no significant correlation between the PPS of DDGS-s and PPS of DDGS-r (R²=0.31). The estimated intestinally absorbable dietary protein (IADP) averaged 21%. Moderate correlation was found between the crude fibre (CF) content and PPS of DDGS-r (R²=0.43). This study suggests an overestimation of the contribution of UDP of DDGS to digestible protein supply in the duodenum in some currently used protein evaluation systems. More research is required and recommended to assess the intestinal digestibility of AAs from DDGS.     

A simplified management of the in situ evaluation of feedstuffs in ruminants: Application to the study of the digestive availability of protein and amino acids corrected for the ruminal microbial contamination

The ruminal effective degradability (RED) and intestinal effective digestibility (IED) for dry matter, crude protein (CP) and amino acids (AA) were estimated by a simplified in situ method using pooled samples from rumen-incubated residues, which represented the ruminal outflow of undegraded feed. The effect of microbial contamination in the rumen was corrected using ¹⁵N infusion techniques. Studies were carried out for soybean meal (SBM), barley grain (BG) and lucerne hay (LH) in three wethers cannulated in the rumen and the duodenum. Uncorrected values of RED for CP obtained either by mathematical integration or our simplified method were similar in all feeds. Microbial N in the pooled samples of SBM, BG and LH were 2%, 11% and 24% of total N, respectively. However, intestinal incubation eliminated this microbial charge by 100%, 99% and 88%, respectively. With microbial corrections, RED showed an increase, and IED showed a decrease, except for SBM. With this correction, intestinal digested CP was reduced by 2% in SBM, 13% in BG and 34% in LH. Corrected IED of AA was relatively similar in SBM (97–99%). However, large variations were observed in BG (74–93%) and in LH (10–88%). Digestion in the rumen and intestine changed the essential AA pattern. Overall, our results support that AA digestion is affected by the characteristics of their radicals and their contents in plant cell wall proteins. The accurate estimation of feed metabolisable AA or protein requires effective measures that are corrected by ruminal microbial contamination. The proposed in situ method largely simplifies these tasks and allows a more complete and less expensive feed evaluation.     

Degradation of methionine by rumen contents in vitro and efficiency of its protection

Degradation of methionine (M), soya isolate (S) and casein hydrolysate (C) has been evaluated by incubation of these substrates (100 mg) with sheep rumen contents in vitro, in the presence of starch (250 mg). Five incubations were performed using one adult rumen fistulated sheep fed 300 g of hay and 300 g of concentrate daily. Total NH₃ production at different sampling times (after 2, 4, 6, 8 and 24 h of incubation) was calculated by subtracting the net NH₃-N production observed in the incubation containing starch only from that produced in the incubation containing the substrate. Protected M preparations, Smartamine (Sm) and Mepron (Mp), were also used. During two incubations of M, using four sheep on permanent pasture or fed four different hays, it was shown that the net disappearance of free M matches net NH₃ production at both low (2 mM) and high (20 mM) M concentration. The results indicate that the initial M degradation rate (3 h of incubation) was 12–14% that of C and never exceeded 1.5 mmol h⁻¹ l⁻¹ of rumen contents. Adaptation of the sheep rumen by daily introduction of 5 or 20 g of DL-methionine for 21 and 8 days, respectively, did not change this result (three to four incubations with rumen contents of three sheep fed 300 g of hay and 300 g of two different concentrates). The results also indicate that protection against rumen degradation was effective for Sm but not for Mp. The ‘effective degradation rate’ of M was estimated as 0.30 that of protein. Considering the high price of protected M (four to five fold the price of non protected M), and the low degradation rate of M, it is suggested that the latter be used at 1.43 of the amount normally added as rumen protected M, to obtain the same result.     

Grass cells ingested by ruminants undergo autolysis which differs from senescence: implications for grass breeding targets and livestock production

It is widely believed that the initial degradation of proteins contained in grazed forage is mediated by rumen micro‐organisms, but the authors’ recent work suggests that the plant cells themselves contribute to their own demise. In the present study the responses of Lolium perenne leaves to the rumen environment were investigated by using an in vitro system which simulates the main stresses of the rumen but from which rumen micro‐organisms were excluded. Degradation of leaf protein and the accumulation of amino acids in tissue and bathing medium occurred over a time‐scale that is relevant to rumen function, and in a near 1 : 1 ratio. Significant loss of nuclear material was observed after 6 h incubation and chloroplasts became morphologically more spherical as the incubation progressed. In situ localization suggested that ribulose 1,5 bisphosphate carboxylase/oxygenase was broken down within chloroplasts which from cytology were judged to be intact. We conclude from these data that plant metabolism may play a significant role in breaking down plant proteins within relatively intact organelles in the rumen. The determinations of chlorophyll content and cell viability revealed that the plant processes occurring in the simulated rumen were similar but not identical to those of natural senescence.     

In situ intestinal digestibility of dry matter and crude protein of cereal grains and rapeseed in sheep

The ruminal degradation and intestinal digestibility (ID) of dry matter (DM) and crude protein (CP) of different feed samples were measured in two trials by using nylon bag and rumen outflow rate techniques in three wethers cannulated in the rumen and in the duodenum. In trial 1, three samples of grains of wheat, barley, and corn treated by cooking (TW, TB, and TC, respectively) were studied together with a sample of untreated corn grains (CG) of different origin. In trial 2, these studies were carried out on a sample of rapeseed (RS) and on a mix of this same sample and rapeseed meal (in proportions 70:30) treated by cooking (TR). In both trials, the animals were fed at the same intake level (40 g DM x kg(-1) LW0.75) with 2:1 (DM basis) forage to concentrate diets. Rumen degradation rates of DM were high in the treated cereals (between 11.0 and 14.2% x h(-1)) and low in the CG (6.35% x h(-1)), whereas for CP these rates were low in all cereals. For DM, in all cereals, ID decreased linearly as the ruminal incubation time increased. The values of intestinal effective digestibility (IED), calculated from these functions and from the rumen outflow, were respectively: 86.4, 62.1, 51.5, and 67.9%. For CP, ID was unaffected by the ruminal incubation time in corn samples, whereas in TW and TB a reduction of these values was only observed for the time of 48 h. The values of IED of CP for CG, TW, TB and TC were: 82.6, 88.9,82.5, and 91.6%, respectively. Rumen degradation rates of the RS and TR samples were 8.35 and 8.23% x h(-1) for DM and 12.0 and 9.59% x h(-1) for CP. In RS, the ID of DM and CP showed a downward trend with an increase of the ruminal incubation time, as modelled according to an exponential function. This same trend was observed for TR after a lag period estimated at 7.53 and 6.51 h for DM and CP, respectively. The values of IED of RS and TR were respectively 56.5 and 50.8% for DM and 71.9 and 80.1% for CP. These same results were also determined by a simplified method using a sample pooled to be representative of the rumen outflow of undegraded feed. The respective values for RS and TR were 54.8 and 51.6 for DM and 65.8 and 78.9% for CP. This method seems to be a promising technique to estimate IED, although more studies are needed to improve its accuracy.     

Microbial colonisation of tannin-rich tropical plants: Interplay between degradability,methane production and tannin disappearance in the rumen

Condensed tannins in plants are found free and attached to protein and fibre but it is not known whether these fractions influence rumen degradation and microbial colonisation. This study explored the rumen degradation of tropical tannin-rich plants and the relationship between the disappearance of free and bound condensed tannin fractions and microbial communities colonising plant particles using in situ and in vitro experiments. Leaves from Calliandra calothyrsus, Gliricidia sepium, and Leucaena leucocephala, pods from Acacia nilotica and the leaves of two agricultural by-products: Manihot esculenta and Musa spp. were incubated in situ in the rumen of three dairy cows to determine their degradability for up to 96 h. Tannin disappearance was determined at 24 h of incubation, and adherent microbial communities were examined at 3 and 12 h of incubation using a metataxonomic approach. An in vitro approach was also used to assess the effects of these plants on rumen fermentation parameters. All plants contained more than 100 g/kg of condensed tannins with a large proportion (32–61%) bound to proteins. Calliandra calothyrsus had the highest concentration of condensed tannins at 361 g/kg, whereas Acacia nilotica was particularly rich in hydrolysable tannins (350 g/kg). Free condensed tannins from all plants completely disappeared after 24-h incubation in the rumen. Disappearance of protein-bound condensed tannins was variable with values ranging from 93% for Gliricidia sepium to 21% for Acacia nilotica. In contrast, fibre-bound condensed tannin disappearance averaged ～ 82% and did not vary between plants. Disappearance of bound fractions of condensed tannins was not associated with the degradability of plant fractions. The presence of tannins interfered with the microbial colonisation of plants. Each plant had distinct bacterial and archaeal communities after 3 and 12 h of incubation in the rumen and distinct protozoal communities at 3 h. Adherent communities in tannin-rich plants had a lower relative abundance of fibrolytic microbes, notably Fibrobacter spp. whereas, archaea diversity was reduced in high-tannin-containing Calliandra calothyrsus and Acacia nilotica at 12 h of incubation. Concurrently, in vitro methane production was lower for Calliandra calothyrsus, Acacia nilotica and Leucaena leucocephala although for the latter total volatile fatty acids production was not affected and was similar to control. Here, we show that the total amount of hydrolysable and condensed tannins contained in a plant govern the interaction with rumen microbes affecting degradability and fermentation. The effect of protein- and fibre-bound condensed tannins on degradability is less important.     

Restoration of in situ fiber degradation and the role of fibrolytic microbes and ruminal pH in cows fed grain-rich diets transiently or continuously

In this study, we used two different grain-rich feeding models (continuous or transient) to determine their effects on in situ fiber degradation and abundances of important rumen fibrolytic microbes in the rumen. The role of the magnitude of ruminal pH drop during grain feeding in the fiber degradation was also determined. The study was performed in eight rumen-fistulated dry cows. They were fed forage-only diet (baseline), and then challenged with a 60% concentrate diet for 4 weeks, either continuously (n=4 cows) or transiently (n=4 cows). The cows of transient feeding had 1 week off concentrate in between. Ruminal degradation of grass silage and fiber-rich hay was determined by the in situ technique, and microbial abundances attached to incubated samples were analyzed by quantitative PCR. The in situ trials were performed at the baseline and in the 1^st and the last week of concentrate feeding in the continuous model. The in situ trials were done in cows of the transient model at the baseline and in the 1^st week of the re-challenge with concentrate. In situ degradation of NDF and ADF of the forage samples, and microbial abundances were determined at 0, 4, 8, 24 and 48 h of the incubation. Ruminal pH and temperature during the incubation were recorded using indwelling pH sensors. Compared with the respective baseline, both grain-rich feeding models lowered ruminal pH and increased the duration of pH below 5.5 and 5.8. Results of the grass silage incubation showed that in the continuous model the extent of NDF and ADF degradation was lower in the 1^st, but not in the last week compared with the baseline. For the transient model, degradation of NDF of the silage was lower during the re-challenge compared with the baseline. Degradation of NDF and ADF of the hay was suppressed by both feeding models compared with the respective baseline. Changes in fiber degradation of either grass silage or hay were not related to the magnitude of ruminal pH depression during grain-rich feeding. In both feeding models total fungal numbers and relative abundance of Butyrivibrio fibrisolvens attached to the incubated forages were decreased by the challenge. Overall, Fibrobacter succinogenes was more sensitive to the grain challenge compared with Ruminococcus albus and Ruminococcus flavefaciens. The study provided evidence for a restored ruminal fiber degradation after prolonged time of grain-rich feeding, however depending on physical and chemical characteristics of forages.     

Digestibility of in rumen undergraded crude protein of treated protein feeds in postruminal part of digestive tract of ruminants

The effective degradability and intestinal digestibility of CP of untreated and with formaldehyde (F) treated sunflower press ‐ cakes (SF), lucerne meal (LM) and field beans (FB) were measured on polycannulated bulls by “in sacco”; and “mobile bag”; methods. The feeds were treated by F solution in doses from 0.2; 0.4. . . to 2.0 g F per 100 g CP.

The effective CP degradability after treatment was decreased significantly (for SF from 78 to 33%, LM from 73 to 62%, FB from 70 to 47% with max. dose of F). The effect of F was various on individual feeds.

The intestinal digestibility of treated feeds, without previous incubation in the rumen, passed from abomasum to feaces has been influenced with doses of F non significantly. The digestibility of FB treated with max. dose of F was lower about 20% in the part duodenum feaces than in abomasum feaces. The digestibility in the part caecum ‐ feaces for all tested feeds has been decreasing with doses of F, similar as in the rumen. The intestinal digestibility of in rumen undegraded crude protein residues of SF has been influenced by the treatment positively. It increased from 43 to 82%. The effect of F on LM was very low. The digestibility has been changed from 75 to 80%.     

Comparison of protein fermentation characteristics in rumen fluid determined with the gas production technique and the nylon bag technique

In this study, a modified version of the gas production technique was used to determine protein fermentation characteristics in rumen fluid of 19 feedstuffs. Performing the incubations in a N-free environment, and with an excess of rapidly fermentable carbohydrates, made N the limiting factor to microbial growth, and so gas production profiles reflected the availability of N from the feed samples. Results showed that fermentation of protein in rumen fluid can be determined with this modified gas production technique, and that there were distinct differences in protein fermentation between the feed samples. Availability of protein for fermentation was highest in wheat, potato pieces and lupin, and lowest in Rumiraap, a formaldehyde treated rapeseed meal, palm kernel expeller and brewery grains. The protein degradation characteristics of the 19 feed ingredients were also determined with the in situ nylon bag technique. With the obtained results, the amount of rumen escape protein (REP) was calculated for each feedstuff. The results showed that the rate of degradation ranged from 0.010/h for Rumiraap to 0.151/h for wheat. The amount of REP ranged from 197 g/kg CP for lupin to 840 g/kg CP for Rumiraap. Comparing the gas production results with the results obtained with the nylon bag technique showed that there was a good relationship between the gas production after 12–25 h of incubation and the calculated amount of REP (r² = 0.83–0.85). The results show that the adapted gas production technique, being depleted of N and using an excess of rapidly fermentable carbohydrates, is suitable to recognize differences in N availability between feed samples and can be used as an alternative to the nylon bag technique and other in vitro techniques.     

Effects of stage of harvest on the protein value of fresh lucerne for ruminants

The ruminal degradation of dry matter (DM) and crude protein (CP) and the intestinal availability of CP of four fresh lucerne (Medicago sativa L.) samples, corresponding to a 3rd growing cycle and harvested at 2-week intervals, were determined. Rumen degradability, measured by the nylon bag technique, and rumen outflow rates were determined on three rumen-cannulated wethers. Intestinal digestibility was determined by the mobile bag technique on three duodenal fistulated wethers. Both groups of animals were fed a 2:1 lucerne hay to concentrate diet at an intake level of 40 g DM x kg(-1) BW0.75. The effective degradability (ED) of DM decreased with maturity in linear and quadratic form, as a consequence of a decrease in the soluble fraction and a similar increase in the undegradable materials. The resultant values were 0.795, 0.661, 0.600, and 0.576 for harvests at 2, 4, 6, and 8 weeks. The ED of CP showed the same trend. However, the variations (values of 0.896, 0.832, 0.791, and 0.817, respectively), were moderate and mainly due to the reduction of the proportion of soluble CP. The intestinal digestibility of CP of all samples showed a downward trend with the increase in the ruminal incubation time, as modelled according to a logistic function. The undegraded CP digested in the gut (Di) and therefore the effective intestinal digestibility (EID) were derived from this function according to the rumen outflow of undegraded CP. The effects of maturity on the mean values of Di, expressed as a proportion of the original CP content, were the opposite of those recorded for the ED of CP. These values were 0.067, 0.102, 0.115, and 0.089 for samples harvested at 2, 4, 6, and 8 weeks, respectively. Nevertheless, when Di was expressed as g CP x kg(-1) DM, these values (18.0, 17.4, 17.1, and 14.3, respectively) decreased in linear form. The same trend was observed for EID values, which represent 0.641, 0.609, 0.549, and 0.488, respectively. The change of the digestion site produced by the reduction of ED of CP was also associated with an increase in the undigested CP (values of 0.037, 0.066, 0.094, and 0.094, at the four harvesting times).     

Reducing protein content in the diet of growing goats: implications for nitrogen balance,intestinal nutrient digestion and absorption,and rumen microbiota

Reducing dietary CP content is an effective approach to reduce animal nitrogen excretion and save protein feed resources. However, it is not clear how reducing dietary CP content affects the nutrient digestion and absorption in the gut of ruminants, therefore it is difficult to accurately determine how much reduction in dietary CP content is appropriate. This study was conducted to investigate the effects of reduced dietary CP content on N balance, intestinal nutrient digestion and absorption, and rumen microbiota in growing goats. To determine N balance, 18 growing wether goats (25.0 ± 0.5 kg) were randomly assigned to one of three diets: 13.0% (control), 11.5% and 10.0% CP. Another 18 growing wether goats (25.0 ± 0.5 kg) were surgically fitted with ruminal, proximate duodenal, and terminal ileal fistulae and were randomly assigned to one of the three diets to investigate intestinal amino acid (AA) absorption and rumen microbiota. The results showed that fecal and urinary N excretion of goats fed diets containing 11.5% and 10.0% CP were lower than those of goats fed the control diet (P < 0.05). When compared with goats fed the control diet, N retention was decreased and apparent N digestibility in the entire gastrointestinal tract was increased in goats fed the 10% CP diet (P < 0.05). When compared with goats fed the control diet, the duodenal flow of lysine, tryptophan and phenylalanine was decreased in goats fed the 11.5% CP diet (P < 0.05) and that of lysine, methionine, tryptophan, phenylalanine, leucine, glutamic acid, tyrosine, essential AAs (EAAs) and total AAs (TAAs) was decreased in goats fed the 10.0% CP diet (P < 0.05). When compared with goats fed the control diet, the apparent absorption of TAAs in the small intestine was increased in goats fed the 11.5% CP diet (P < 0.05) and that of isoleucine, serine, cysteine, EAAs, non-essential AAs, and TAAs in the small intestine was increased in goats fed the 10.0% CP diet (P < 0.05). When compared with goats fed the control diet, the relative richness of Bacteroidetes and Fibrobacteres was increased and that of Proteobacteria and Synergistetes was decreased in the rumen of goats fed a diet with 10.0% CP. In conclusion, reducing dietary CP content reduced N excretion and increased nutrient utilization by improving rumen fermentation, enhancing nutrient digestion and absorption, and altering rumen microbiota in growing goats.