Sucrose supplements in cattle given grass silage-based diet. 2. Digestion of cell wall carbohydrates

Impact of Molasses on Ruminal Volatile Fatty Acid Production and Microbiota Composition In Vitro

The aim of this study was to assess if molasses could modify VFA production and the rumen microbial community in vitro. Three beet (treatment Beet) and three cane (treatment Cane) molasses preparations were randomly selected from a variety of samples collected worldwide and incubated in vitro with rumen fluid along with a control sample (treatment CTR, in which no molasses was used). Flasks for VFA analysis were sampled at 0, 1, 2, 3, 4, 6, 8, and 24 h of each incubation. For microbiota analysis, samples from each fermentation flask after 12 and 24 h were subjected to microbial DNA extraction and V3-V4 16S rRNA gene sequencing on an Illumina MiSeq platform. Total net VFA production was higher in the beet and cane preparations than in the control (CTR) group at 24 h (33 mmol/L, 34 mmol/L, and 24.8 mmol/L, respectively), and the composition of VFAs was affected by the inclusion of molasses: acetic acid increased in the CTR group (73.5 mol%), while propionic acid increased in the beet and cane molasses (19.6 mol% and 18.6 mol%, respectively), and butyric acid increased, especially in the cane group (23.2 mol%). Molasses even influenced the composition of the rumen microbiota, and particularly the relative abundance of the most dominant family in the rumen, Prevotellaceae, which decreased compared to CTR (37.13%, 28.88%, and 49.6%, respectively). In contrast, Streptococcaceae (19.62% and 28.10% in molasses compared to 6.23% in CTR), Veillonellaceae (6.48% and 8.67% in molasses compared to 4.54% in CTR), and Fibrobacteraceae (0.90% and 0.88% in molasses compared to 0.62% in CTR) increased in the beet and cane groups compared to the CTR group. Another important finding is the lower proportion of Methanobacteriaceae following the addition of molasses compared to CTR (0.26%, 0.28%, and 0.43%, respectively). This study showed the impact of molasses in influencing VFA production and composition as a result of a modified rumen microbial composition.

Granulated Cane Sugar as a Partial Replacement for Steam-Flaked Corn in Diets for Feedlot Cattle: Ruminal Fermentation and Microbial Protein Synthesis

The aim of this study was to evaluate the influence of supplemental granulated cane sugar (GCS) levels (0, 13.3, 26.6, and 39.9% on a dry matter basis) in a steam-flaked corn-based finishing diet on measures of ruminal fermentation and the site and extent of nutrient digestion. Four Holstein steers (251 ± 3.6 kg live weight) with “T” type cannulas in the rumen and proximal duodenum were used in a 4 × 4 Latin square experiment to evaluate the treatments. The experiment lasted 84 d. Replacing steam-flaked corn (SFC) with GCS linearly decreased the flow of ammonia-N (NH3-N) to the small intestine, increasing the flow of microbial nitrogen (MN; quadratic effect, p = 0.02), ruminal N efficiency (linear effect, p = 0.03) and MN efficiency (quadratic effect, p = 0.04). The ruminal digestion of starch and neutral detergent fiber (NDF) decreased (linear effect, p ≤ 0.02) as the level of GCS increased. The postruminal digestion of organic matter (OM), neutral detergent fiber (NDF), and starch were not affected by the GCS inclusion. However, postruminal N digestion decreased (linear effect, p = 0.02) as the level of GCS increased. There were no treatment effects on total tract OM digestion. However, total tract NDF and N digestion decreased (linear effect, p ≤ 0.02) as the level of GCS increased. The ruminal pH decreased (linear effect, p < 0.01) as the GCS increased in the diet. The ruminal acetate molar proportion decreased (linear effect, p = 0.02) and the ruminal valerate molar proportion tended to increase (linear effect, p = 0.08) as the level of GCS increased. It is concluded that replacing as much as 13% of SFC with GCS in a finishing diet will enhance the efficiency of N utilization (g non-ammonia-N entering the small intestine/g N intake) without detrimental effects on total tract OM digestion. The inclusion of GCS decreased the ruminal proportion of acetate linearly without an effect on the acetate-to-propionate ratio or estimated methane production. Some of the effects on N utilization at a high level of GCS inclusion (27 and 40%) can be magnified by the differences in the CP content between diets. A higher level of GCS supplementation in the diet decreased the ruminal pH below 5.5, increasing the risk of ruminal acidosis.

Increased intake of mono- and disaccharides by Reeves's muntjac (Muntiacus reevesi). Effect on gastrointestinal tract structure and function and blood parameters

The aim of this study was to determine the effect of an increased mono- and disaccharide (MD) intake on selected functions and structure of the gastrointestinal tract (GIT), and selected blood parameters in Reeves's muntjac (Muntiacus reevesi), a small browsing ruminant. Eighteen male muntjacs were fed diets consisting of lucerne (ad libitum), a high fibre pellet (100 g/day) and wheat bran (30 g/day) without (MD0) or with addition of 10 or 20 g of glucose, fructose and sucrose mixture/day (MD10 and MD20, respectively) for 14 days. MD dosages were set to increase intake of these saccharides by 25% and 50% relative to MD0, which resulted in a range of water-soluble carbohydrate content in the consumed dry matter from 7% to 12%. Compared to MD0 animals, MD20 animals had a lower dry matter intake, a higher MD concentrations in the reticulorumen (RR), abomasal and small intestinal digesta, higher ruminal butyrate concentration, higher SGLT1 expression in the epithelium of proximal jejunum, higher plasma glucose, lower RR tissue weight but greater caecal tissue weight (p ≤ 0.05), and had or tended to have shorter papillae and lower mucosa surface area in the Atrium ruminis (by 44%; p = 0.02 and p = 0.10, respectively); MD10 animals tended to have higher MD concentrations in the abomasal and small intestinal digesta (p ≤ 0.10), and a higher amylolytic activity (p = 0.02) as well as a tendency to lower xylanolytic activity in the RR digesta (p = 0.06). MD supplementation did not affect ruminal pH. In conclusion, low to moderate increase of MD intake increased MD concentrations in the RR, abomasal and intestinal digesta, and SGLT1 expression in intestinal epithelium, suggesting incomplete fermentation of those saccharides in the RR. MD supplementation dose-dependently affects structure of GIT in Reeves's muntjac.

Effects of addition of different sources and doses of sugars on in vitro digestibilities of dry matter, fibre and cell wall monosaccharides of corn silage in ruminants

In ruminant diets, soluble sugar is an important factor in the digestive process. The objective of this study was to evaluate the effects of the source and dose of soluble sugars, under controlled pH conditions, on the in vitro digestibility of DM, fibre fractions (NDF and ADF) and cell wall neutral monosaccharides of corn silage. Silage was collected from several points in a silage mass from a bunker silo, oven-dried at 55°C and ground through a 1-mm screen. Sub-samples were combined with sugars to compose the treatments, in a 5 × 5 factorial arrangement, as a combination of five soluble sugar sources (glucose, fructose, arabinose, xylose and sucrose) and five sugar doses (0, 100, 200, 300 and 400 g/kg sugar in DM corn silage), respecting the following proportions of sugar : corn silage, 0 : 100, 10 : 90, 20 : 80, 30 : 70, 40 : 60 represented by the sugar doses, respectively. An in vitro test was performed to determine the true digestibility (D) of the chemical entities (DM, NDF and ADF) and cell wall monosaccharides (glucose = gluc, arabinose = arab and xylose = xyl). During the first 12 h of incubation, the pH was maintained above 6.0 by the addition of 2.5 N NaOH. The concentrations of neutral monosaccharides (arabinose, xylose and glucose) were determined by GLC. The soluble sugars decreased the digestibility of corn silage followed by pH reduction, especially at doses higher than 200 g/kg sugar. Overall, xylose, followed by sucrose, fructose and arabinose, had greater impacts on DM digestibility, whereas fibre digestibility was impaired by sucrose at all doses. Xylose and fructose had greater impacts on NDF digestibility at 300 and 400 g/kg sugar. Although xylose impaired the Dgluc in the cell wall in all doses. All doses of glucose improved the Dgluc and Dxyl in the cell wall.

Liquid molasses interacts with buffers to affect ruminal fermentation, milk fatty acid profile, and milk fat synthesis in dairy cows fed high-concentrate diets

We aimed to evaluate the effects of feeding sugarcane liquid molasses (LM) with or without a commercial buffer mix (BFM) on ruminal fermentation parameters, milk fatty acid (FA) profile, and milk yield and composition in dairy cows fed high-concentrate diets (35:65 forage-to-concentrate ratio). Eight multiparous Holstein cows (4 ruminally cannulated) averaging 165 ± 12 d in milk at the beginning of the study were randomly assigned to a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Each period lasted 21 d with 14 d for diet adaptation and 7 d for data and sample collection. Cows were fed the following diets: (1) no LM or BFM supplementation (CTRL), (2) LM without BFM supplementation (MOL), (3) BFM without LM supplementation (BUF), and (4) LM plus BFM supplementation (COMBO). These 4 isonitrogenous and isoenergetic diets were formulated by replacing (dry matter basis) 5% ground corn with LM, whereas BFM replaced wheat bran at 0.8% of the diet. Significant LM × BFM interactions were observed for the duration of ruminal pH below 5.8, molar proportion of propionate, acetate-to-propionate ratio, milk proportions of trans-10 18:1 and total trans FA, and concentration and yield of milk fat. Feeding MOL and BUF alone were effective on reducing the time that ruminal pH remained below 5.8 compared with the CTRL treatment, and the COMBO diet decreased it further. A similar pattern was observed for the ruminal molar proportion of propionate. The milk proportions of trans-10 18:1 and total trans FA dropped significantly with BFM or LM supplementation versus cows fed CTRL, and the COMBO diet decreased these variables further. Note, however, that these changes elicited by the COMBO diet were not in the same magnitude as those caused by MOL or BUF fed alone. The ruminal molar proportion of acetate increased with the BUF diet and that of butyrate increased in cows fed MOL, but mean ruminal pH was not affected by treatments. Diets with LM resulted in increased concentrations of short- and medium-chain FA in milk fat. The yield of 3.5% fat-corrected milk increased significantly in cows fed MOL or BUF due to the improved concentration of milk fat. A trend and a significant increase for energy-corrected milk were observed with feeding MOL or BUF, respectively. Overall, inclusion of LM and BFM appears to reduce milk trans-10 18:1 FA and total trans FA by modulating ruminal pH and volatile FA profile in cows fed high-concentrate diets.

Enteric methane emission and digestion in dairy cows fed wheat or molasses

The aim of this experiment was to measure enteric methane (CH₄) emission and its relation with rumen digestion in dairy cows fed diets rich in 1 of the 2 carbohydrate sources, starch or sugar. The rations were based on late first-cut grass-clover silage supplemented with wheat (Wh), NaOH-treated wheat (Wh+NaOH), sugar beet molasses (Mo), or sugar beet molasses with addition of sodium bicarbonate (Mo+Bic). Wheat and molasses made up 35% of dry matter in the 2 diets with molasses and wheat, respectively. Four cows fitted with ruminal, duodenal, and ileal canulae were used in a 4 × 4 Latin square design. Nutrient digestibility was measured using chromium oxide and titanium oxide as flow markers, and emissions of CH₄ and hydrogen were measured via open-circuit indirect calorimetry on 4 consecutive days. Data were analyzed using PROC MIXED of SAS (version 9.4; SAS Institute Inc., Cary, NC) with treatment and period as fixed effects and cow as random effect. Furthermore, orthogonal contrasts were calculated. The cows produced 32.5, 33.6, 36.2, and 35.1 L of CH₄/kg of dry matter intake (DMI) on diets Wh, Wh+NaOH, Mo, and Mo+Bic, respectively. The emission of CH₄ per day, per kilogram of DMI, and per kilogram of energy-corrected milk as well as daily hydrogen emission were higher on the Mo diet compared with the Wh diet. With the present inclusion of wheat and molasses in the diet, no effects of NaOH treatment of wheat or of sodium bicarbonate supplementation to the Mo diet could be demonstrated on CH₄ emission expressed per kilogram of DMI or per kilogram of energy-corrected milk. The duodenal flow of starch was higher when wheat was treated with NaOH. Under the conditions in the present experiment, ruminal NDF digestibility was not affected by carbohydrate source, NaOH treatment of wheat, or bicarbonate supplementation. Total volatile fatty acid concentration in the rumen and the proportions of acetate and propionate were not affected by carbohydrate source, NaOH treatment of wheat, or bicarbonate supplementation. Likewise, we could not show any influence of diet on microbial protein synthesis or efficiency of microbial protein synthesis expressed as grams of microbial protein synthesis per kilogram of true rumen-digested organic matter. We concluded that CH₄ emission was increased when wheat was replaced by molasses, whereas no effect of manipulating rumen fermentation by NaOH treatment of wheat or addition of bicarbonate to molasses could be found with a level of approximately 25% of dry matter from starch and sugar, respectively.

The effect of fructose supplementation on feed intake, nutrient digestibility and digesta retention time in Reeves's muntjac (Muntiacus reevesi)

The aim of the study was to determine the effect of fructose supplementation in the diet on feed intake, nutrient digestibility and digesta retention time in Reeves's muntjac (Muntiacus reevesi), a browsing cervid. In Experiment 1, six adult males of Reeves's muntjac were used in a replicated 3 × 3 Latin square design and fed a diet consisting of dehydrated chopped lucerne (ad libitum), high-fibre pellet (120 g/day) and wheat bran (30 g/day) without (F0) or with addition of 12 and 24 g fructose/day (F12 and F24, respectively). In Experiment 2, the same six adult muntjacs were used in crossover design and fed F0 or F12. Doses of supplemental fructose were set to increase intake of water-soluble carbohydrates (WSC; ≈40 g/day; ≈8% of WSC in consumed dry matter [DM]) by 25 and 50% relative to F0. Feed intake was controlled daily (Experiment 1 and 2) and total tract digestibility and digesta retention time were determined (Experiment 2). In Experiment 1, DM intake of chopped dehydrated lucerne decreased with fructose supplementation (F0 vs. F12 and F24; p = .01) but was not different between F12 and F24 (p = .76). Total DM intake was also not different between treatments (p ≥ .13). In Experiment 2, DM intake of lucerne, total DM intake and nutrient digestibility was not affected by fructose supplementation (p ≥ .17), but mean retention time of long particles in the whole GIT tended to be longer for F12 compared to F0 (p = .09). Under conditions of the current study, additional fructose intake (resulting in a range of WSC content in consumed DM from 8.6% to 13%) had only minor impact on feed intake and investigated functions of the gastrointestinal tract of Reeves's muntjac.

Effects of carbohydrate and nitrogen supplementation on fermentation of cheatgrass () in a dual-flow continuous culture system

Cheatgrass (CG; ), an introduced winter annual grass, is an aggressive invader of the sagebrush community in the Western United States. Because of its greater flammability, mature CG constitutes a fire hazard leading to repeated wildfires. One fuel-reduction strategy is livestock grazing. The objective of this study was to evaluate the effects of urea, molasses, or a combination of urea and molasses supplementation of a CG-based diet on digestibility, microbial fermentation, bacterial protein synthesis, and nutrient flow using a dual-flow continuous culture system. Eight fermenters were used in a replicate 4 × 4 Latin square design with four 10-d experimental periods. Experimental treatments (DM basis) were 1) forage only (CON), 2) CG plus urea alone (URE; 1.36% urea), 3) CG plus molasses alone (MOL; 15.9% molasses), and 4) CG plus urea and molasses combined (URE+MOL; 1.28% urea plus 19.3% molasses). Each fermenter was fed 72 g/d of DM, and data were analyzed using the GLIMMIX procedure of SAS (SAS Inst. Inc., Cary, NC). The true digestibilities of NDF and ADF were not affected by diets ( > 0.05). Molasses-containing diets had greater true digestibility of OM ( = 0.02). However, true digestibility of CP was increased when molasses was fed alone ( < 0.01). Molasses-containing diets had lower pH ( < 0.01) and greater VFA concentrations ( < 0.01) compared to those of the other diets. The URE+MOL diet resulted in a greater VFA concentration ( < 0.01). Propionate concentration increased ( < 0.01), whereas acetate concentration decreased ( < 0.01) when molasses alone or in combination with urea was added to the diets. Supplying molasses alone resulted in greater ( = 0.03) total branched-chain VFA compared to the other diets. The concentration of NH-N and total N flow increased ( < 0.01) in response to urea supplementation and was greater ( < 0.01) when urea alone was supplemented in the diet. On the other hand, molasses-supplemented diets yielded more non-ammonia N ( < 0.01) and bacterial N ( = 0.04). Supplementation had no effect ( = 0.83) on bacterial efficiency. Results from this study indicate that the addition of urea and molasses in a CG-based diet could improve nutrient supply to animals, notably VFA supply and microbial N supply; however, in the levels tested in this study, it did not improve CG utilization as assessed by NDF digestion.

Review: Sugar beets as a substitute for grain for lactating dairy cattle

Dairy cows are customarily given grains and highly digestible byproduct ingredients as additions to forage to support milk production. In many parts of the world growing seasons are short, and the grain crops that can be grown may not provide adequate yields. Sugar beets, on the other hand are relatively hardy, and dry matter yields surpass the yields of most grain crops. There are however, perceptions that beets may not be suitable as a feed ingredient due to the fact that the storage form of carbohydrate is sugar rather than starch. With little analytical support, sugar has been rejected in many feeding programs with the view that sugar reduces rumen pH, fiber digestion and microbial yield. This review explores available facts revolving around these concerns. Information regarding the feeding of sugar beets is provided and the use of sugar beets as a partial replacement for grain is proposed.

The effects of synchronizing the rate of dietary energy and nitrogen supply to the rumen on milk production and metabolism of ewes offered grass silage based diets

Twenty-four multiparous ewes were used to test the hypothesis that synchronizing the hourly rate of release of energy and nitrogen in the rumen would optimize milk production. Three diets were formulated using the in situ degradability of the food ingredients, to differ in their rate of organic matter (OM) and nitrogen (N) release in the rumen. All diets contained 400 g grass silage per kg dry matter (DM) and were predicted to have a similar content of metabolizable energy (11·8 MJ/kg DM), metabolizable protein (102 g/kg DM), neutral-detergent fibre (365 g/kg DM) and daily ratio of N: OM supply to the rumen but differ in their hourly pattern of nutrient release to be either synchronous (S), asynchronous (A) or intermediate (I). The diets were offered ad libitum as a complete feed in a 3 × 3 Latin-square design consisting of three periods each of 28 days duration. Synchronizing the hourly supply of energy and N to the rumen did not significantly alter milk or milk fat yield (g/d), milk protein content (g/kg), DM intake (kg/day), total time spent eating or the number of meals per day. However, compared with ewes offered diets I or A, those offered diet S had a lower milk fat content (g/kg; P < 0·05) whilst protein yield (g/day) tended to be increased (P = 0·05). Animals offered the synchronous diet (S) had lower plasma urea concentrations throughout the day and significantly higher beta-hydroxybutyrate concentrations at 14:00 and 18:00 h than those offered diets I or A. In conclusion, synchronizing dietary energy and N supply to the rumen did not have a major effect on milk production in ewes.

The effects of ensiling and supplementation with sucrose and fish meal on forage intake and milk production of lactating dairy cows

The effect of ensiling grass and supplementing the resulting silage with water-soluble carbohydrate in the form of sucrose and undegradable dietary protein (UDP) in the form offish meal on forage intake and milk production and composition were evaluated in an experiment involving 63 mid-lactation Holstein-Friesian cows. Herbage from the primary growth of a predominantly perennial ryegrass sward was zero-grazed (ZG) from 19 April to 16 May 1993. The herbage was mown and picked up with a precision-chop harvester and offered as the sole diet, twice daily, to 18 cows which were on average 186 days into lactation. On 13 May, herbage from the same sward was harvested identically to the ZG herbage and ensiled, treated with formic acid at a rate of 2·85 lit grass. At 53 days after ensiling the silage was offered either as the sole diet (SO) or supplemented with sucrose at 10·3 g/kg fresh silage (SS) or supplemented with sucrose and fish meal each at 10·3 g/kg fresh silage (SSF) to 15 cows per treatment which were on average 164 days into lactation. The feeding period was 28 days for ZG and 21 days for the SO, SS and SSF treatments, and the last 7 days were the main recording interval. Prior to going on to the experimental diets all animals were offered a common silage ad libitum and supplemented with 5 kg of a 180 g/kg crude protein concentrate. Dry-matter intakes (DMI), milk yields and milk composition were recorded during the pre-experimental period and subsequently used as covariates in the statistical analysis. For diets ZG, SO, SS and SSF, forage DMI (kg/day), total DMI (kg/day), milk yields (kg/day), fat concentration (g/kg) and protein concentration (g/kg) were 14·4,14·0,13·7 and 13·9 (average s.e.d. = 0·55); 14·4,14·0,14·5 and 15·4 (average s.e.d. = 0·59); 15·4, 14·4, 14·5 and 16·7 (average s.e.d. = 0·42); 36·6, 38·6, 38·6 and 37·5 (average s.e.d. = 2·67); 33·0, 30·7, 32·2 and 32·8 (average s.e.d. = 0·75). Nitrogen (N) digestibility was higher on SO and SSF (P < 0·05) relative to ZG with SS being intermediate, otherwise treatment did not alter (P > 0·05) diet apparent digestibility. Ensilage increased the immediately soluble N fraction (a value) and degradability of N (P < 0·001) relative to ZG. It is concluded that ensilage had no effect on forage DMI but decreased milk yield and protein concentration relative to the parent herbage. The positive response in milk yield due to supplementation of the silage-based diet with sucrose and fish meal and the lack of response to sucrose supplementation alone suggests that nutrients absorbed from the digestive tract of cows offered silage-based diets are more limiting in protein or specific amino acids supplied by fish meal than in energy. The decrease in animal performance due to ensiling may be overcome by supplementation of silage-based diets with UDP at sufficient levels to equate that of the parent herbage.

Determination of reticulo-rumen and whole-stomach digestion in lactating cows by omasal canal or duodenal sampling

Four ruminally and duodenally cannulated multiparous Finnish Ayrshire cows were fed on diets consisting of grass silage (0·6 kg/kg DM) and one of four concentrates: barley, barley + urea, barley + rapeseed meal and barley + rapeseed cake. The objective of the present study was to compare omasal canal and duodenal digesta flows. Values for digesta flow into the omasal canal and duodenum were determined using a triple-marker method based on Co-EDTA, Yb-acetate and indigestible neutral-detergent fibre (NDF) markers. Microbial non-NH3 N (NAN) flow was assessed by purine flow. Microbial samples to determine the bacterial purine: N ratio were harvested from the rumen, omasum and duodenum. Organic matter flow was significantly lower into the omasum than the duodenum, indicating an endogenous organic matter secretion into the abomasum. In contrast, NDF and acid-detergent fibre flows were significantly higher into the omasum indicating digestion of fibre in the omasum. Microbial NAN flows were significantly different (P < 0·001) when estimates were based on bacterial samples harvested from different sites. Differences in total NAN, microbial NAN and dietary NAN flows entering the omasal canal and duodenum were non-significant. The results indicated that the omasal sampling technique provides a promising alternative to the duodenal sampling technique to investigate forestomach digestion in dairy cows and offers an alternative means to study rumen N metabolism.

Integration of Ruminal Metabolism in Dairy Cattle

An important objective is to identify nutrients or dietary factors that are most critical for advancing our knowledge of, and improving our ability to predict, milk protein production. The Dairy NRC (2001) model is sensitive to prediction of microbial protein synthesis, which is among the most important component of models integrating requirement and corresponding supply of metabolizable protein or amino acids. There are a variety of important considerations when assessing appropriate use of microbial marker methodology. Statistical formulas and examples are included to document and explain limitations in using a calibration equation from a source publication to predict duodenal flow of purine bases from measured urinary purine derivatives in a future study, and an improved approach was derived. Sources of specific carbohydrate rumen-degraded protein components probably explain microbial interactions and differences among studies. Changes in microbial populations might explain the variation in ruminal outflow of biohydrogenation intermediates that modify milk fat secretion. Finally, microbial protein synthesis can be better integrated with the production of volatile fatty acids, which do not necessarily reflect volatile fatty acid molar proportions in the rumen. The gut and splanchnic tissues metabolize varying amounts of volatile fatty acids, and propionate has important hormonal responses influencing milk protein percentage. Integration of ruminal metabolism with that in the mammary and peripheral tissues can be improved to increase the efficiency of conversion of dietary nutrients into milk components for more efficient milk production with decreased environmental impact.

Effect of the carbohydrate composition of feed concentratates on methane emission from dairy cows and their slurry

Dietary carbohydrate effects on methane emission from cows and their slurry were measured on an individual animal basis. Twelve dairy cows were fed three of six diets each (n = 6 per diet) of a forage-to-concentrate ratio of 1 : 1 (dry matter basis), and designed to cover the cows' requirements. The forages consisted of maize and grass silage, and hay. Variations were exclusively accomplished in the concentrates which were either rich in lignified or non-lignified fiber, pectin, fructan, sugar or starch. To measure methane emission, cows were placed into open-circuit respiration chambers and slurry was stored for 14 weeks in 60-L barrels with slurry being intermittently connected to this system. The enteric and slurry organic matter digestibility and degradation was highest when offering Jerusalem artichoke tubers rich in fructan, while acid-detergent fiber digestibility and degradation were highest in cows and slurries with the soybean hulls diet rich in non-lignified fiber. Multiple regression analysis, based on nutrients either offered or digested, suggested that, when carbohydrate variation is done in concentrate, sugar enhances enteric methanogenesis. The methane emission from the slurry accounted for 16.0 to 21.9% of total system methane emission. Despite a high individual variation, the methane emission from the slurry showed a trend toward lower values, when the diet was characterized by lignified fiber, a diet where enteric methane release also had been lowest. The study disproved the assumption that a lower enteric methanogenesis, associated with a higher excretion of fiber, will inevitably lead to compensatory increases in methane emission during slurry storage.

Effects of Replacing Dietary Starch with Sucrose on Ruminal Fermentation and Nitrogen Metabolism in Continuous Culture

A dual-effluent continuous-culture system was used to evaluate the effects of partially replacing cornstarch with sucrose in a total mixed ration on ruminal fermentation and N metabolism. The 4 treatments were 0 (control), 2.5, 5.0, and 7.5% sucrose and, respectively, 7.5 (control), 5.0, 2.5, and 0% cornstarch in a total mixed ration containing 20% corn silage and 40% alfalfa silage. Fermenters were fed 4 times a day during four 9-d periods with sampling beginning on d 6. Replacing cornstarch with sucrose did not alter ruminal pH (5.97), total volatile fatty acids (VFA) (104.4 mmol/L), or the acetate to propionate ratio (2.16); however, branched-chain volatile fatty acids were higher for the control treatment compared with the 7.5% sucrose treatment. Five hours postfeeding, sucrose treatments significantly altered molar proportions of all volatile fatty acids, and acetate-to-propionate and glucogenic-to-lipogenic ratios. Digestibility of dry matter and N were not affected by treatment, but digestibility of total non-structural carbohydrates was increased with sucrose treatments. A quadratic effect was noted for neutral detergent fiber (NDF) digestibility as sucrose replaced starch. A higher NDF digestibility (66.1 vs. 59.9%) was observed for the 7.5% sucrose treatment compared with the other 2 sucrose treatments. Levels of ammonia N were within an acceptable range to support microbial protein synthesis and did not differ among treatments (mean=9.23 mg/dL). Sucrose inclusion in the total mixed ration did not affect bacterial N synthesis. Results indicate that (at the levels tested in this study) inclusion of sucrose in the diet when rumen-degradable protein is adequate does not affect ruminal fermentation.

Ruminal and total plant cell-wall digestibility estimated by a combined in situ method utilizing mathematical models

Three ruminally and duodenally cannulated non-lactating Finnish Ayrshire cows were used to investigate ruminal and intestinal digestion of cell-wall carbohydrates by a combined in situ method. Five grasses cut at 10 d intervals were incubated in the rumen for 0, 6, 12, 24, 48, 72 and 96 h, and the undegraded residues were exposed to intestinal digestion. With advancing maturity of grass both the rate and extent of cell-wall digestion decreased. At early stages of growth the decreases were faster for the rate of digestion and at late stages of growth for the extent of digestion. Applying a passage rate of 0.02/h in one compartmental rumen model resulted in digestibility values markedly lower than typically observed in vivo. However, applying a rumen model incorporating a selective retention of particles and time-dependent release of particles from the non-escapable pool resulted in much higher digestibility values. Recovery of lignin after 96 h ruminal incubation with a subsequent mobile-bag incubation was very low (from 244 to 460 mg/g). Intestinal disappearance of neutral-detergent fibre (NDF) and hemicellulose decreased with advancing maturity of grass and with increasing length of preceding ruminal incubation period, i.e. with decreasing potential digestibility of the material. Disappearance of hemicellulose was much greater than that of cellulose for intact grasses but the difference diminished with increasing length of preceding rumen incubation period. On average, 195 mg/g of potentially digestible NDF disappeared from the mobile bags in the intestines. The post-ruminal digestion as a proportion of the total NDF digestibility varied between 0.034 and 0.058. Despite methodological problems both in ruminal in situ and intestinal mobile bag techniques, these methods can be used to investigate ruminal and intestinal cell-wall digestion and to partition cell-wall digestibility between ruminal and post-ruminal digestion providing that appropriate rumen models are used.

Influence of barley and buffer supplements on quantitative aspects of ruminal fiber digestion of cows

Four Jersey cows, fitted with ruminal and duodenal cannulas, were used to assess the specific effects of changes in ruminal pH that were induced by barley addition to a hay diet on ruminal fiber digestion. Cows received successively 100% unchopped cocksfoot hay (diet H), 65% hay and 35% pelleted ground barley (diet HB), and HB plus a continuous intraruminal infusion of bicarbonate salt solution (diet HBB). Cows were limit-fed once daily at 7 kg of DM day-1. The ruminal fractional passage rate of the liquid and hay was respectively estimated from a single administration of Cr-EDTA and Eu labeled on hay fiber. Duodenal fiber flow was estimated both by the double marker method (Yb-acetate/Cr-EDTA) and by multiplying the fractional passage rate of Eu-labeled hay by ruminal pool size. Barley supplement decreased ruminal NDF and ADF digestion compared with diet H, but passage rates of the solid and fluid fractions in the rumen were not affected. The depressive effect of barley supplement on in situ degradability of hay NDF and ADF decreased the degradation rates and increased the 72-h undegradable fraction. Compared with diet HB, ruminal NDF and ADF digestion was improved with buffer supplementation but was less than that of diet H, even though ruminal pH was similar to that of diet H. Passage rates of the fluid and particle fractions were depressed and unaffected, respectively, with buffer addition. Higher in situ degradability of hay with the buffer supplement resulted in an increase in the 72-h undegradable fraction, but the fractional degradation rate was unaffected.

Sucrose supplementation and feed intake of dairy cows in early lactation

Based on results from previous 14-d sequential elimination trials, which indicated that cows in early lactation preferred a sucrose-sweetened diet, a 12-wk lactation trial was conducted to evaluate further the effects of sucrose supplementation. Twenty-four cows (16 multiparous Jerseys and 8 primiparous Holsteins) were assigned at parturition to a control or sucrose-sweetened (1.5% of dietary DM) TMR in a randomized complete block design. The diet included 10% corn silage, 30% alfalfa haylage, and 60% concentrate based on corn and soybean meal on a DM basis and was fed to ensure 10% orts. An additional 2.3 kg of alfalfa hay were fed for the first 5 d postpartum. Covariant-adjusted (BW on the day of parturition) mean DMI, milk yields, 3.5% FCM yields, and percentages of milk fat, milk protein, and SNF were unaffected by treatment and averaged 19.0 and 19.1 kg/d, 28.4 and 29.3 kg/d, 28.4 and 28.4 kg/d, and 3.40 and 3.30%, 3.51 and 3.28%, and 8.4 and 8.3%, respectively, for cows on control and sucrose-supplemented diets. In the absence of a choice of diets, sucrose at 1.5% of dietary DM did not enhance mean DMI over the first 12 wk postpartum; however, a transient increase in consumption of the sucrose-supplemented diet may have occurred over the a 2-wk period after parturition. Variation in feed consumption during early lactation suggests that additional data are needed to examine this potential effect.

[Simulation of nutrient dynamics in the rumen of sheep and cattle considering the feed composition, level of feed intake and feeding frequency. 1. Model description]

The aim of this work was to develop a dynamic, mechanistic computer-model, which can be used to simulate digestion, outflow and pools of different nutrients in the rumen of sheep and cattle and which reacts on changes of the feed composition, on the level and the frequency of feeding. The model consists of 35 flux- and 17 differential equations and works under cyclic steady-state conditions. The following mechanism are integrated into the model: The three substrates protein, neutral detergent fibre (NDF) and non-fibre-carbohydrates are degraded by three specific groups of microbes. A fourth group degrades NDF and non-fibre-carbohydrates following the principle of competitive inhibition. The fermentation in the rumen serves for supply of energy for growth and for the maintenance of microbes. The rates of degradation are calculated from the turnover-time of the specific substrate and the amount of microbes. Recycling of N occurs through recycling of the microbial protein and the ruminohepatic pathway. If concentration of ammonia in rumen fluid decreases below 50 mg/l then the growth of microbes declines.

[Simulation of nutrient dynamics in the rumen of sheep and cattle considering the feed composition, level of feed intake and feeding frequency. 2. Model validation]

A mathematical model of rumen fermentation processes was validated with 65 sheep experiments and 45 cattle experiments, respectively. Further, it was shown how the model reacts when the feed composition, the level of feed intake and the feeding frequency was changed. The model predictions were satisfactory for the digestibility of organic matter and neutral detergent fibre (NDF) in rumen, the production of volatile fatty acids and the non-ammonia-N (NAN) flow to duodenum. The partition of NAN in microbial and feed N was estimated with lower reliability. The effects of variation of feeding level, feeding frequency and roughage quality (crude protein, lignin) on digestion processes have been simulated correctly. On the other hand, the effects of the proportion of roughage to concentrate have not been reproduced sufficiently with the mechanisms included in the model. To make correct predictions in this area too, it is necessary to integrate the rumen pH and its effects on rumen processes into the model. A mechanistic approach for estimation of the velocity constants for passage of substances out of the rumen would improve the model.

Digestion in the rumen and total tract of forage-based diets with starch or dextrose supplements fed to Holstein heifers

Three diets were fed to six cannulated heifers in a replicated 3 x 3 Latin square design. Diets were a high forage control, a high forage diet with dextrose (5.6% of DM), and a medium concentrate (39.7% of DM) diet. Diets contained 13.3% CP and 1% NaHCO3 and were fed as a TMR twice daily. Mean ruminal pH (6.47), glucose concentration (.55 mM), and reducing sugar concentration (.64 mM) in heifers were similar across diets. Rate of orchardgrass NDF digestion in situ was faster for heifers fed the dextrose than for those fed the medium concentrate diet, but both were similar to that for heifers fed the control diet. Heifers fed the medium concentrate and dextrose diets had faster ruminal particulate fractional passage rates than those fed the control diet. True ruminal and apparent total tract digestion of OM and NDF were similar among diets, but ruminal NDF digestion tended to be higher with the control than with the medium concentrate diet. Total NAN and bacterial N flow to the duodenum and efficiency of bacterial protein synthesis in the rumen were greater with the medium concentrate diet than with the control and dextrose diets. The results were consistent with others that demonstrated that factors related to nonstructural carbohydrates in the diet other than just low ruminal pH affect ruminal fiber digestion; however, these results were not as strong as those of our previous in vitro work.

The effect of sucrose supplements on particle-associated carboxymethylcellulase (EC 3.2.1.4) and xylanase (EC 3.2.1.8) activities in cattle given grass-silage-based diet

Carboxymethylcellulase (EC 3.2.1.4; CMCase) and xylanase (EC 3.2.1.8) activities were assayed in rumen fluid and from microbes closely associated either with rumen particulate material or with feed particles incubated in nylon bags in the rumen of cattle. The cattle were fitted with a permanent rumen cannula and a simple 'T'-piece duodenal cannula and were given four diets in a 4 x 4 Latin Square experiment. The basal diet (diet C) consisted of grass silage, barley and rapeseed meal (700, 240 and 60 g/kg total dry matter (DM)) given at the rate of 5.3 kg/d or supplemented with 1.0 kg sucrose/d given twice daily (diet S), twice daily with 0.25 kg sodium bicarbonate/d (diet B) or as a continuous intrarumen infusion (diet I). Giving sucrose supplements decreased CMCase and xylanase activities extracted from microbes associated with rumen particulate material or feed particles incubated in nylon bags as compared with diet C. Supplementation of the sucrose diet with sodium bicarbonate resulted in higher CMCase and xylanase activities than other sucrose diets (S and I). Particle-associated CMCase and xylanase activities were found to be very sensitive in detecting differences in the rumen environment and were related to changes in cell wall digestion. The activities were highly correlated with disappearance of DM and neutral-detergent fibre from nylon bags incubated in the rumen, rumen and total digestion of cell-wall carbohydrates and rumen pool size of cell-wall carbohydrates. It was concluded that the attachment of fibrinolytic enzymes is involved in the depression of fibre digestion. Particle-associated CMCase and xylanase activities were much higher when measured from rumen particulate material than from feed particles incubated in nylon bags.