Effect of the level of dry matter and protein and degradation rate of starch on in vitro ruminal fermentation

Effects of starch type, feeding level and level of a mixed N source upon rumen fermentation were examined using an in vitro rumen simulation system (i.e., SIMCO) with a fluid volume of 1100 ml and liquid dilution rate of approximately 0.07/h. Two sources of starch, two feeding levels and two levels of N were examined in an experiment following a 2 × 2 × 2 factorial arrangement of treatments. The starch sources were raw slowly degrading (R), and cooked fast degrading (C), potato starch and constituted 450 g/kg diet dry matter (DM). The remaining was supplied in the form of a grass hay mixture. The feeding levels were 20 (DM20) and 40 (DM40) g DM/d and the diet N level was either low (N1) or high (N2), using peptone and ammonia salt additions in the buffer. Two simulations of 10 days each were completed. The amount of bicarbonate in buffer was varied according to feeding level, and pH (average 6.3) did not differ between treatments. An increased degradation rate of starch (R vs. C) depressed neutral detergent fibre (aNDFom) digestibility (0.46 vs. 0.36) and organic matter true digestibility (OMTD; 0.73 vs. 0.68), but there were no other treatment effects on digestibility. The VFA production efficiency (average 0.47 g VFA/g OMTD) was not affected by the main treatments, although an interaction between starch type and feeding level occurred. A decline in protozoa rating over the 10 day simulations was more apparent at the lower feeding level (DM20), indicating poor growth conditions for protozoa. Higher microbial efficiency (11.0 vs. 8.9 mg microbial N/g OMTD) and a higher proportion of propionate (272 vs. 207 mmol/mol VFA) occurred at DM20 compared to DM40. Increased degradation rate of starch (i.e., R vs. C) resulted in an improved microbial N efficiency (8.8 vs. 11.2 mg/g OMTD) and an increase in the proportion of propionate (226 vs. 253 mmol/mol VFA) at the expense of acetate (610 vs. 591 mmol/mol VFA). Increasing the level of N (i.e., N1 vs. N2) improved the microbial N efficiency (9.2 vs. 10.7 mg/g OMTD) and increased the proportion of propionate (230 vs. 249 mmol/mol VFA) and butyrate (100 vs. 119 mmol/mol VFA) at the expense of acetate (629 vs. 572 mmol/mol VFA). Interactions between starch type and N level upon VFA patterns were apparent. Results support earlier findings in that carbohydrate degradation rate is an important factor determining microbial growth rates and VFA distribution.     

The influence of addition of gallic acid, tannic acid, or quebracho tannins to alfalfa hay on in vitro rumen fermentation and microbial protein synthesis

Tannins may reduce rumen degradability of protein, increase the proportion of feed protein reaching the lower digestive tract for enzymatic digestion and thereby increase the efficiency of protein utilization. The objective was to assess the effects of different types and levels of tannins on rumen in vitro gas production and its kinetics, in vitro true degradability (IVTD) and rumen degradability of protein (IVRDP), and microbial protein synthesis by incubating alfalfa (Medicago sativa L.) hay in buffered rumen fluid. Alfalfa was incubated in buffered rumen fluid with and without the addition of different levels of gallic acid (GA), quebracho tannin (QT), or tannic acid (TA). Tannins at the lower inclusion levels had minimal effects on fermentation products compared to the higher levels. Addition of QT and TA reduced ammonium-N (NH₄⁺-N) concentration. Addition of QT at 20, 40, and 60 g/kg DM decreased NH₄⁺-N by 2, 7, and 12% compared with control whereas addition of TA reduced NH₄⁺-N by 5, 6, and 12% when added at 20, 40 and 60 g/kg DM, respectively. In experiment 2, addition of QT at 50, 100, and 150 g/kg DM, resulted in reduction of NH₄⁺-N by 12, 30, and 51%, respectively, compared with the control. Addition of TA at 50, 100, and 150 g/kd DM reduced NH₄⁺-N by 14, 26, and 47% compared with control. Inclusion of QT at 50, 100, 150 DM reduced IVRDP by 13, 30, and 36% compared with control whereas at these levels of inclusion, TA resulted in reduction of IVRDP by 14, 25, and 48%. Rate of gas production decreased (P<0.001), while asymptotic gas production increased (P<0.0001) with increasing level of GA and TA. Quebracho tannin decreased (P<0.0001) both the rate and asymptotic of gas production. Gallic acid had a positive effect on fermentation as indicated by increased gas production and total short chain fatty acids (SCFA) production. Quebracho tannin decreased 24 h gas production, IVTD, and total SCFA production. Acetate to propionate ratio increased with the addition of GA and but decreased when QT was added. Addition of tannins did not markedly increase total purines but numerical values tended to be higher in the presence of tannins compared with the control. Efficiency of microbial growth was lower in the presence of GA and unaltered by TA, but higher in the presence of QT compared with the control. The effect of tannins on rumen fermentation and protein degradation varied with type and level of tannins. In vivo studies will be conducted to validate the in vitro results.     

Effects of dietary forage particle size and concentrate level on fermentation profile, in vitro degradation characteristics and concentration of liquid- or solid-associated bacterial mass in the rumen of dairy cows

This study investigated effects of dietary forage particle size (PS) and concentrate level (CL) on fermentation profiles of particle-associated rumen liquid (PARL) and free rumen liquid (FRL), in vitro degradation characteristics and concentration of bacterial mass attached to the solid or fluid rumen digesta phase in dairy cows. The experiment was a 4 × 4 Latin square design with four late-lactation dairy cows in four 23 day periods. Cows were restrictively fed (17 kg dry matter (DM)/d) one of four diets varying in the theoretical PS (6 and 30 mm) of grass hay and in the levels (approximately 200 and 550 g/kg, DM basis) of a cereal-based concentrate. Proportion of large particles (>6 mm) and the content of structural fibre in the diet increased by reducing dietary CL and, particularly, by increasing hay PS. This effect was not reflected by changes in mean total volatile fatty acid concentration or pH in the rumen. However, cows fed high concentrate diets had pH of 5.28 and 5.37 in PARL at 3 h after the last meal, when fine or long chopped hay was offered. The low pH may indicate a depression of the capacity of PARL to degrade fibre in vitro. Gas production in vitro of concentrate increased with the high concentrate diet at 12 h, suggesting that amylolytic capacity was affected only in early phases of fermentation. In addition, elevating dietary CL appeared to shift ruminal fermentation outputs from propionate to butyrate and valerate. Inclusion of coarsely chopped hay to a high concentrate diet does not appear to bring advantages due to increased structure in restrictively fed dairy cows. In addition, results suggest that the response of pH in PARL is more sensitive to dietary changes (i.e., forage PS and CL) than the response in FRL, and so PARL might be better to evaluate the risk of ruminal disfunction in dairy cows.     

Effects of exogenous fibrolytic enzymes on ruminal fermentation and digestibility of total mixed rations fed to lambs

This experiment was designed to study effects of exogenous fibrolytic enzymes on digestibility and ruminal fermentation of total mixed rations (TMR) with different forage:concentrate (F:C) ratios. The experimental design was a 6×6 Latin square with six ruminally cannulated Ramboulliet lambs (58 ± 7.4 kg body weight) used in a 3×2 factorial arrangement of treatments using three forage:concentrate (F:C) ratios (400:600, 500:500, 600:400 kg/kg) and two (0 or 2 g) levels of fibrolytic enzymes/kg TMR dry matter (DM). Exogenous fibrolytic enzymes increased the soluble fraction of DM (P<0.01) and ruminal in situ disappearance rate of DM and neutral detergent fibre (aNDF; P<0.001). However, there were no differences among treatments in DM and aNDF in vivo digestibility due to enzyme addition to the diet. Feed intake and N balance were also not affected by enzymes, and ruminal fermentation patterns were unchanged. Exogenous fibrolytic enzymes improved ruminal disappearance rates of DM and aNDF, but had no impact on lamb performance or ruminal fermentation.     

Effect of different drying procedures on the nutritive value of olive (Olea europaea var. europaea) leaves for ruminants

Fresh, freeze-, air- and oven-dried at 60 °C and 100 °C olive leaves (OL) were studied in order to determine the effect of different drying procedures on OL chemical composition, in vitro digestibility, ruminal degradability, and intestinal digestibility. The drying procedure affected all the parameters measured except for gross energy (GE; P=0.194). Protein-bound condensed tannins (CT) decreased (P=0.001) with freeze-, air- and 60 °C drying (from 1.25 up to 0.82 g/kg dry matter, DM). Total CT were only decreased (P=0.001) by drying at 60 °C (from 10.0 to 6.24 g/kg DM). The in vitro crude protein (CP) digestibility increased (P<0.001) with drying except for oven-drying at 100 °C up to 58%. Values for CP digestibility found in freeze- and air-dried OL were not different (P>0.05). No differences (P>0.05) were observed between CP digestibility in air- and oven-dried at 60 °C OL. Effective degradability of DM and CP increased from 0.53 to 0.62 (P=0.005) and from 0.46 to 0.64 (P=0.002), respectively after treatment. The apparent intestinal digestibility of undegraded CP in the rumen was only affected (P=0.046) by oven-drying, which increased it from 0.33 to 0.39. As air-drying did not have detrimental effects on the OL nutritive value it could be an appropriate, simple and low-cost procedure for olive-leaves preservation.     

Relationships between kernel vitreousness and dry matter degradability for diverse corn germplasm: II. Ruminal and post-ruminal degradabilities

Correlations between kernel vitreousness and ruminal in situ (RDMD) and total tract dry matter (TDMD; sum of ruminal in situ and post-ruminal in vitro measurements) degradabilities were determined for 33 diverse corn germplasm sources. These included a wide range of endosperm characteristics from opaque 2 (o2) types to densely packed flint types, and a number of intermediates. Harvests were done at two growth stages; 1/2 milk-line (ML) and black-layer (BL). Kernels from middle portion of ears were oven dried at 40 °C for 72 h and ground through a Wiley mill (6 mm screen) for measurement of in situ RDMD after 0 and 14 h of incubation using two steers (1.5 g/bag × 8 replicates per time point per steer in 5 cm × 5 cm bags of 50 μm pore size). Residue from the 14 h bags proceeded to an 8 h in vitro enzymatic post-ruminal digestion after which the residue was oven dried at 62 °C for 48 h and dry matter content determined. Inbred by harvest-stage interactions were observed for 0-h disappearance and TDMD. Vitreousness had strong negative correlations with degradability measurements, particularly for more mature (BL) samples (−0.728, −0.770 and −0.603) versus ML (−0.569, −0.541 and −0.338) for 0 h disappearance, RDMD and TDMD, respectively. Vitreousness was highly correlated with corn degradability, especially at a black-layer stage of harvest, in this diverse corn germplasm.     

Effects of feeding supplemental palmitic acid (C16:0) on performance and milk fatty acid profile of lactating dairy cows under summer heat

The objective was to determine performance and milk fatty acid changes of high producing dairy cows in early lactation, under summer heat, by adding a supplemental rumen inert fat in the form of a saturated free fatty acid (856 g/kg C16:0/kg of total fatty acids) to the total mixed ration (TMR). Early lactation multiparous Holstein cows in two similar pens of 99 and 115 cows were used in a 2 × 2 Latin Square design experiment with 35 d periods during a period when daily high and low temperatures averaged 34.3 and 15.9 °C, the relative humidity averaged 51% and there were no rain events. The TMR was the same for both groups, consisting of approximately 435 g/kg forage and 565 g/kg concentrate, except that the vitamin/mineral premix had no added fat (control, C) or added fat (C16:0) at a level designed to deliver approximately 450 g/cow/d of supplemental fat if cows consumed 26.5 kg/d of dry matter (DM). The two TMR averaged 905 g/kg organic matter (OM), 318 g/kg neutral detergent fiber (aNDF), and 186 g/kg crude protein (CP). The ‘C’ TMR had 58 g/kg total fatty acids with an estimated net energy for lactation (NE_l) of 7.3 MJ/kg (DM), while the C16:0 TMR had 72 g/kg total fatty acids and 7.5 MJ/kg NE_l (DM). Whole tract digestibility of DM, OM, aNDF and CP tended (P<0.10) to increase, and that of fatty acids increased substantially (P<0.01), with C16:0 feeding, whereas, DM intake was not affected. Milk fat content decreased (P<0.01) with C16:0 feeding (37.5 versus 36.0 g/kg), whereas, true protein content tended (P=0.09) to increase. There was a tendency (P=0.07) for increased milk yield (36.69 versus 38.04 kg/d), while milk protein yield increased (P=0.03) with C16:0 supplementation (1.08 versus 1.13 kg/d). Milk fat yield was unaffected by treatment. Concentrations of short and medium chain milk fatty acids (C6:0–C15:0), decreased, or tended to decrease, with C16:0 addition (C13:0 and C15:0, P<0.10; all others, P≤0.05). The concentration of C16:0 increased (P<0.001) in milk triglycerides from cows fed C16:0 (27.10 versus 31.57 g/kg), the longer chain saturated fatty acids C17:0 and C18:0 decreased (P≤0.05) and other long chain unsaturated fatty acids were unaffected. Benefits of C16:0 feeding on cow productivity must be balanced against negative effects on the nutritive value of the milk (i.e., increased C16:0 in milk fatty acids) produced for human consumption. However, relatively low amounts of supplemental C16:0 (27.10 versus 31.57 g/kg in milk triglycerides for C and C16:0 supplemented cows, respectively) were actually secreted in milk, in spite of them being essentially fully digested in the digestive tract. Strategies to divide cows into production groups based on milk yield and/or milk fat proportions could further limit C16:0 secretion in milk. Supplemental dietary C16:0 may have positive effects on milk production that outweigh the negative health effects of the increased C16:0 content in the milk fat.     

The interaction between lactose level and enzyme supplementation and form of barley processing on performance, digestibility and faecal volatile fatty acid concentration of weanling pigs fed barley-based diets

A 2×3 factorial arrangement was used to investigate the interaction between lactose level (170 g/kg versus 275 g/kg), enzyme supplementation (with or without endo-1,3 (4)-β-glucanase) and toasting (raw barley versus toasted barley) in barley-based diets (250 g/kg) on piglet performance and diet digestibility postweaning. One hundred and forty-four weaned piglets (24 days old, 6.5 kg live weight) were blocked on the basis of live weight and were assigned to one of six dietary treatments (n = 6) for 21 days as follows: (1) 170 g lactose/kg and barley (250 g/kg), (2) 275 g lactose/kg and barley (250 g/kg), (3) 170 g lactose/kg and toasted-flaked barley (250 g/kg), (4) 275 g lactose/kg and toasted-flaked barley (250 g/kg), (5) 170 g lactose/kg and barley (250 g/kg) plus β-glucanase, (6) 275 g lactose/kg and barley (250 g/kg) plus β-glucanase. There was an interaction (P<0.05) between lactose level and β-glucanase supplementation on average daily gain (ADG), food conversion ratio (FCR) and coefficient of total tract apparent digestibilities (CTTAD) of dry matter (DMD), organic matter (OMD) and nitrogen (N). Pigs offered 170 g lactose/kg and β-glucanase supplementation had an improved FCR and ADG compared to the treatment based on 170 g lactose/kg and unsupplemented barley. However, β-glucanase supplementation at 275 g lactose/kg had no significant effect on FCR and ADG compared to the 275 g lactose/kg and unsupplemented barley. Pigs offered diets containing 170 g lactose/kg plus β-glucanase had a significantly higher CTTAD for DMD, OMD and nitrogen compared to the 275 g lactose/kg plus β-glucanase diet. However, there was no significant effect of lactose level in the unsupplemented diets. Pigs offered high lactose diets showed significantly increased total VFA concentration, molar proportions of butyric acid and reduced acetic acid compared to those offered low lactose diets. Pigs offered β-glucanase supplemented diets showed reduced (P<0.05) total VFA concentration compared to unsupplemented diets. In conclusion, β-glucanase supplementation improved diet digestibility and pig performance compared to the unsupplemented diet at the low lactose level only. There was no response of β-glucanase supplementation at the high level of lactose.     

Effects of formaldehyde treated mustard cake and molasses supplementation on nutrient utilization, microbial protein supply and feed efficiency in growing kids

Twenty healthy growing male kids (Sannen × Beetal and Alpine × Beetal) of 2–3 months of age, weighing 12 ± 0.61 kg, were randomly assigned to one to four dietary treatments in a 2 × 2 factorial design. Two types of isonitrogenous and isocaloric concentrate mixtures were fed to kids in four treatments being: untreated mustard cake, untreated mustard cake with molasses, formaldehyde treated mustard cake and formaldehyde treated mustard cake with molasses. Both concentrate mixtures were similar in composition with the only difference in RDP and UDP due to replacement of untreated mustard cake by formaldehyde (FA) treated mustard cake. Kids were fed concentrate and forage (berseem hay:wheat straw = 2:1) in a 50:50 ratio. A metabolism experiment of 7 days duration was conducted before the end of the experiment. Kids were housed in individual pens and fed experimental diets for 120 days. No differences occurred in digestibility of DM, OM, CP and NDF_om, but ether extract digestion in kids fed FA treated mustard cake was higher (P<0.05). Supplementation of molasses increased apparent nutrient digestibility, without influencing digestion of CP and NDF_om. Intake of DM, CP and ME did not differ among treatments. The CP content of the diet actually consumed that was supplemented with molasses was lower (P<0.01), with a higher (P<0.01) ME content, without influence of FA treatment on nutritive level of the diet consumed. N balance was higher (P<0.01) in kids fed FA treated MC and supplemental molasses. Microbial protein yield, calculated from purine derivatives excreted in urine, was similar among treatments. The DM intake in the growth experiment was higher by feeding both FA treated MC and molasses. Average daily gain was influenced by feeding FA treated MC, without any effect of supplemental molasses on growth rate of the kids. The higher DM intake and improved growth rate in kids fed FA treated MC resulted better feed efficiency. Higher UDP intake improved growth performance in kids and supplementation of molasses, with or without ruminal escape CP, has no added advantage.     

Chemical composition and in vitro fermentation of tannin-rich tree fruits

Dry and mature tree fruits are a potential source of protein for goats in the semi-arid areas of southern Africa, but their chemical composition and feeding value is largely unknown. This study presents the chemical composition and in vitro fermentation of indehiscent whole fruits and separated seed and hull fractions from Acacia nilotica, Acacia erubescens, Acacia sieberiana, Acacia erioloba, Piliostigma thonningii and Dichrostachys cinerea trees. Results indicate that the N contents of whole fruits ranged between 13.5 g/kg DM (A. nilotica) and 27.1 g/kg DM (A. erubescens). Seeds had a higher N content than hulls for all tree species. A. nilotica, D. cinerea and P. thonningii fruits had high levels of extractable phenolics (758, 458 and 299 g/kg DM, respectively). Soluble phenolics (SPh) and ytterbium precipitable phenolics (YbPh) levels were negatively correlated to in vitro gas production but positively correlated to in vitro organic matter degradability (iOMD). Partition factors for whole fruits at 48 h ranged between 3.6 mg/ml for A. erioloba and 7.8 mg/ml for A. nilotica. Seeds of A. erioloba, A. erubescens and P. thonningii were consistently fermented more efficiently throughout the incubation period compared to their whole fruits or hulls. Estimating in vitro degradability of phenolic-rich substrates through filtration procedures can give erroneous results due to the loss of soluble phenolics, which are not necessarily degradable. The feeding value of fruits from D. cinerea and A. nilotica tree species may be reduced due to the presence of high levels of phenolics.     

Effects of a slow-release urea source on absorption of ammonia and endogenous production of urea by cattle

Three experiments were conducted with Angus or Holstein steers to evaluate effects of dietary urea–calcium (a slow rumen-release urea source) on absorption of ammonia N from the gut and urea N production in the liver. Steers were fed a high-grain diet (Experiment 1) or an all-forage diet (Experiments 2 and 3). Urea or urea–calcium (0.25 g/kg body weight) was dosed into the esophagus (Experiments 1 and 2) or rumen (Experiment 3), and blood samples were serially collected for 180 min. Blood concentrations of ammonia N and urea N were measured in all experiments, and net flux of metabolites across splanchnic tissues was measured in Experiment 3. Compared to urea, urea–calcium reduced (P<0.05) plasma concentrations of ammonia N in steers fed all-forage diets, and tended (P<0.06) to reduce arterial glucose concentrations in Experiment 3. Plasma concentrations of urea N were not affected by treatment in any experiment. Treatment and time post-dosing interactions (P<0.05) in Experiment 3 were due to increased ruminal fluid concentrations of ammonia N, net release of ammonia N by portal-drained viscera and total splanchnic tissues with urea versus urea–calcium treatment shortly after dosing. Similar interactions (P<0.05) indicated that urea caused higher hepatic glucose release and increased l-lactate release by total splanchnic tissues after dosing than urea–calcium. Urea–calcium was effective in mitigating rapid ammonia release in the rumen and subsequent effects on glucose and lactate metabolism.     

The digestion of dietary protein bound by condensed tannins in the gastro-intestinal tract of sheep

The digestion of dietary protein bound by condensed tannins (CTs) in ruminants was investigated by determining the extent of dissociation of insoluble ¹²⁵I-BSA + CT complexes administered to abomasally and intestinally fistulated sheep. The extent of dissociation was registered as the true digestibility of iodinated bovine serum albumin (¹²⁵I-BSA). The true digestibility of ¹²⁵I-BSA originally bound to Leucaena pallida CT (0.721) was lower (P<0.05) than that of ¹²⁵I-BSA originally bound to L. leucocephala CT (0.880) between the abomasum and terminal ileum. These results indicate that differences in the ability of CT to inhibit ¹²⁵I-BSA digestion in vivo matched the relative abilities of the same CT to bind BSA in vitro, indicating that the in vitro BSA-binding assay for ranking CT behaviour was biologically relevant in vivo. Furthermore, the true digestibility of CT-bound ¹²⁵I-BSA between the mouth and faeces permitted the prediction of the quantitative contribution that CT-bound dietary proteins make to improved nitrogen supply to the small intestines.     

Effects of Tasco (a seaweed extract) and heat stress on N metabolism and meat fatty acids in wether lambs fed hays containing endophyte-infected fescue

Wether lambs (n = 27, average BW = 40 kg) were used to test response to forage treated with Tasco-Forage (an extract of the brown kelp Ascophyllum nodosum) prior to conserving, or to direct feeding of the extract (Tasco-EX). Hays made from endophyte (Neoyphodium coenophialum)-infested tall fescue (Festuca arundinacea)-based pasture received 0 or 3 kg of Tasco/ha prior to harvest. Lambs, blocked by weight, were randomly allotted to three diets: (1) control hay, (2) treated hay, and (3) #1 + Tasco-EX fed at 1% of the diet. Hays were low in CP (<7%) so all lambs were fed soybean meal (12% of the diet) in addition to trace mineralized salt. Diets were fed at 1.5% BW to prevent refusals. Total collections (7 d) were made during periods without or with applied heat stress. After each period, rumen contents were obtained to determine pH, NH₃ and VFA. Lambs were sacrificed post-trial. A subset was used to evaluate sensory traits and muscle fatty acids. Lambs were in negative N balance during the study and Tasco treatments did not affect N metabolism. Fecal N tended (P < 0.10) to increase with short duration heat stress causing a concomitant decrease (P < 0.05) in apparent N digestibility (58.6 versus 56.1%; S.E. = 0.7). Urinary N loss decreased (P < 0.001) with heat stress (8.0 versus 5.9 g/d; S.E. = 0.2), resulting in increased (P < 0.001) N retention (−2.1 versus −0.3 g/d; S.E. = 0.2). Apparent OM digestibility was not affected by heat stress but was greater (P < 0.05) for lambs fed Tasco-EX treatment than those fed treated hay. Treatment diets decreased (P < 0.05) ruminal butyrate. Heat stress increased (P < 0.05) acetate and total VFA and decreased (P < 0.01) ruminal pH. A tendency (P < 0.11) of increased 14:1ω5, decreased (P < 0.05) 18:0 and total saturated fatty acids in muscle was observed with Tasco diets. Meat sensory characteristics were not affected by treatment. Tasco may alter some aspects of rumen or lipid metabolism but has no effect on N metabolism or meat sensory characteristics of sheep fed restricted, low-quality diets.     

Characteristics of microbial fermentation and potential digestibility of fiber in the hindgut of dugongs (Dugong dugon)

The number of microorganisms in the hindgut of dugongs (Dugong dugon) were estimated and their in vitro volatile fatty acid (VFA) production and degradation of eelgrass measured. Scanning electron microscopy showed that some rod bacteria attached to the surface of plant tissue degraded and eroded the cell walls. Number of starch-, lactate-, cellobiose-, pectin-, xylan- and cellulose-utilizing bacteria, sulfate-reducing bacteria and methane-producing bacteria were estimated at 10⁹ ∼ 10¹⁰ colony forming units g^-1. Microorganisms degraded the cellulose and noncellulolytic components of the eelgrass, and about 47.3% of dry matter was degraded after 36 h in vitro incubation. The total VFA concentration was 10.5 mmol dL^-1 at 36 h incubation, which included 55.7 mol% acetate, 18.0 mol% n-butyrate and 15.1 mol% propionate. The gas composition of in vitro fermentation was 68.4% carbon dioxide, 22.2% methane and 9.4% hydrogen.     

Effects of oilseed meal and grain-urea supplements fed infrequently on digestion in sheep: 1. Low quality grass hay diets

An experiment examined intake, growth response and rumen digestion of young sheep fed ad libitum low quality grass hay alone or supplemented with approximately isonitrogenous amounts of barley grain and urea (Bar/N), safflower meal (SAF) or linseed meal (LIN) provided at 3 days intervals. Supplements comprised 13–20% of total DM intake. Sheep fed grass hay alone consumed 60.2 g DM/kg LW^0.75/day of hay and an estimated 6.09 MJ metabolizable energy (ME)/day, and were in liveweight (LW) maintenance. Hay intake was decreased (P<0.05) by the Bar/N supplement with a substitution rate of 0.9, but was not changed by the oilseed meal supplements. Each of the supplements increased (P<0.05) estimated ME intake to a similar extent, but LW gain and wool growth were lower (P<0.05) in sheep supplemented with Bar/N than those supplemented with LIN. Rumen degradabilities of the SAF and LIN CP were estimated to be 0.72 and 0.62, respectively. Rumen ammonia concentrations in sheep fed hay alone (average 97 mg NH₃/l) were expected to be adequate for microbial activity. Fractional outflow rate (FOR) of liquid from the rumen measured with Co-EDTA (mean 0.109 h⁻¹) was greater than that of Cr-mordanted supplements (mean 0.056 h⁻¹), which was in turn greater than the FOR of Cr-mordanted hay (mean 0.031 h⁻¹). Diet did not affect these FOR. Supplemented sheep accommodated increased DM intake on Day 1 of the 3 day supplementation cycle by increasing rumen digesta load rather than by increasing rate of passage of digesta. Results show that the LW gain of young sheep fed low quality hay was increased more by either oilseed meal than by equivalent amounts of barley grain/urea supplement, apparently due to more efficient utilization of ME for LW gain.     

Effects of glutamate on microbial efficiency and metabolism in continuous culture of ruminal contents and on performance of mid-lactation dairy cows

Three experiments were conducted to determine (1) the dose of glutamate needed to alter fermentation and nitrogen (N) partitioning in a continuous culture system, (2) the effect of supplemental glutamate in diets varying in rumen-undegradable protein on fermentation and N partitioning in a continuous culture system, and (3) the effect of dietary supplemental glutamate on the lactational performance of mid-lactation dairy cows, total tract nutrient digestibility, and ruminal microbial N synthesis. In experiment 1, the equivalent of 0, 40, or 80 g of supplemental glutamate per cow per day was added to a basal diet. The dietary treatments were evaluated in a continuous culture system. Glutamate decreased protein digestion and microbial growth while increasing non-ammonia, non-microbial N. Within the doses tested, the equivalent of 80 g glutamate per cow per day most effectively increased non-ammonia, non-microbial N. In experiment 2, dietary treatments consisted of diets formulated to have low rumen-undegradable protein (LRUP; 62 g/kg DM), low rumen-undegradable protein plus the equivalent of 80 g glutamate per cow per day (LRUP + G), and high rumen-undegradable protein [HRUP; 68 g/kg dry matter (DM)]. The dietary treatments were evaluated in a continuous culture system. When added to a diet low in rumen-undegradable protein, glutamate tended to decrease DM and organic matter (OM) digestibility, decreased total volatile fatty acid (VFA) production, increased fermenter pH, increased feed N converted to microbial N, and had no effect on microbial N production. The LRUP + G diet was similar to the HRUP diet and different from the LRUP diet in feed N converted to microbial N and ammonia N concentration. In experiment 3, 40 Holstein cows were utilized in a crossover study to test the effects of two dietary treatments: 0 or 80 g of supplemental glutamate per cow per day. The addition of glutamate to the diet of lactating dairy cows did not improve lactational performance or nutrient digestibility. Based on the results from these in vitro and in vivo experiments, the addition of glutamate to lactating cow diets is not recommended.     

Round versus flat: bone cell morphology, elasticity, and mechanosensing

There is increasing evidence that cell function and mechanical properties are closely related to morphology. However, most in vitro studies investigate flat adherent cells, which might not reflect physiological geometries in vivo. Osteocytes, the mechanosensors in bone, reside within ellipsoid containment, while osteoblasts adhere to flatter bone surfaces. It is unknown whether morphology difference, dictated by the geometry of attachment is important for cell rheology and mechanosensing. We developed a novel methodology for investigating the rheology and mechanosensitivity of bone cells under different morphologies using atomic force microscopy and our two-particle assay for optical tweezers. We found that the elastic constant of MLO-Y4 osteocytes when flat and adherent (>1 kPa) largely differed when round but partially adherent (<1 kPa). The elastic constant of round suspended MLO-Y4 osteocytes, MC3T3-E1 osteoblasts, and primary osteoblasts were similarly <1 kPa. The mechanosensitivity of round suspended MLO-Y4 osteocytes was investigated by monitoring nitric oxide (NO) release, an essential signaling molecule in bone. A preliminary observation of high NO release from round suspended MLO-Y4 osteocytes in response to 5 pN force is reported here, in contrast with previous studies where flat cells routinely release lesser NO while being stimulated with higher force. Our results suggest that a round cellular morphology supports a less stiff cytoskeleton configuration compared with flat cellular morphology. This implies that osteocytes take advantage of their ellipsoid morphology in vivo to sense small strains benefiting bone health. Our assay provides novel opportunities for in vitro studies under a controlled suspended morphology versus commonly studied adherent morphologies.     

Comparative studies on the degradation and mean retention time of solid and liquid phases in the forestomachs of dromedaries and sheep fed on low-quality roughages from Tunisia

The digestion of the acid detergent fiber (ADF) fraction of vetch-oat hay was studied in two dromedaries and three sheep, all rumen-fistulated and fed vetch-oat hay with a concentrate. Dromedaries and sheep consumed similar amounts of feed dry matter (DM) per kilogram of metabolic weight, but dromedaries drank less water than sheep. There were no differences in the volatile fatty acid (VFA) and ammonia concentrations in the rumen between dromedaries and sheep, but pH was higher in the dromedaries than in the sheep (P < 0.05). The mixture of VFA contained more propionate and butyrate and less acetate in dromedaries than in sheep (P < 0.05). The protozoal concentration was higher in the rumen of sheep than of dromedaries. This result was consistent with the higher N---NH₃, concentration in sheep. Entodinium was the most abundant species in both dromedaries and sheep. Specific rates of rumen liquid (PEG) and particle (chromium-mordanted hay) outflow were higher and lower, respectively, in dromedaries than in sheep. Also, dromedaries had higher in sacco, in vitro, and fecal digestibilities of vetch-oat hay dry matter (DM) and ADF than sheep. In sacco, the potential degradable fraction was higher, but the rate of degradation was not. The greater utilization of ADF in the rumen by dromedaries is discussed in relation to the higher cellulolytic activity of the rumen microorganisms, the longer retention time of feed particles and/or the greater buffering capacity of the rumen contents of the dromedary against fermentation acids.     

Assessment of a brown midrib (BMR) mutant gene on the nutritive value of sudangrass using in vitro and in vivo techniques

The brown midrib (BMR) gene has been reported to reduce the lignin concentration in plants, which contributed to increased fiber digestion in ruminants. Three studies were completed to compare the digestibility of a BMR mutant of sudangrass (sorghum bicolor subsp. Drummondii) versus a non-BMR (‘Piper’) variety when included in diets fed to sheep (Study 1), to complete a rumen in vitro assessment of sheep and lactating cow diets (Study 2), and to compare digestibility when included in the diet fed to lactating dairy cows (Study 3). Four wether sheep were used in a 2 × 2 Latin square experiment (Study 1) with total fecal collection to determine total tract apparent digestibility of pelleted Piper (P) and BMR (P-BMR) sudangrass hays. Forage pellets consisted of either P-BMR or P hay with added urea to meet the maintenance crude protein (CP) requirement of the sheep. Digestibility of organic matter (OM; P<0.01), dry matter (DM; P<0.01), acid detergent fiber (ADF; P<0.05), and neutral detergent fiber (aNDFom; P<0.07) was higher for P-BMR than P sudangrass. In vitro rumen digestibility of aNDFom using cattle rumen fluid was higher at 24 (P<0.01), 48 (P<0.01) and 72 h (P<0.01) of fermentation for P-BMR versus P (Study 2). Four lactating Holstein dairy cows (251 ± 30 days in milk) and fitted with ruminal and duodenal cannulae were used in a 4 × 4 Latin square experiment. Total mixed rations (TMR) contained 180 g/kg DM shredded sudangrass hay and 180 g/kg sliced alfalfa hay, but the proportion of P to P-BMR sudangrass varied as 100:0, 66:34, 34:66, or 0:100. Yields of milk and milk protein were highest at the 66:34 level (Quadratic: P=0.06 and 0.07, respectively), but composition of milk fat, protein and lactose, as well as DM intake, did not differ (Study 3), probably because forestomach and total tract apparent digestion of aNDFom and OM did not differ due to sudangrass source.     

Effects of Acacia nilotica, A. polyacantha and Leucaena leucocephala leaf meal supplementation on performance of Small East African goats fed native pasture hay basal forages

Optimal utilisation of tannin-rich browse tree fodders including Acacia spp. foliages as crude protein (CP) supplements to ruminants in the tropics is limited by less available information on their feed nutritive potential. Two studies were conducted to: (1) determine rate and extent of ruminal dry matter (DM) degradability (DMD) and (2) investigate effect of sun-dried Acacia nilotica (NLM), A. polyacantha (PLM) and Leucaena leucocephala leaf meal (LLM) supplementation on growth performance of 20 growing (7–9 months old) Small East African male goats (14.6 ± 0.68 kg) fed on native pasture hay (NPH) basal diet for 84 days in a completely randomised design experiment in north-western Tanzania. The goats were randomised into four treatment groups consisting of five animals each. Three supplement diets: 115.3 g NLM (T₂), 125.9 g PLM (T₃) and 124.1 g LLM (T₄), which was used as a positive control, were supplemented at 20% of the expected DM intake (DMI; i.e., 3% body weight) to the three animal groups fed on NPH (basal diet) compared to the animals in a control group that were fed on NPH without browse supplementation (T₁).

NPH had significantly the lowest (P < 0.05) CP of 45.5 g kg⁻¹ DM compared to NLM, PLM and LLM (159, 195 and 187 g kg⁻¹ DM, respectively). NPH had higher (P < 0.05) fibre fractions; lower ruminal DM degradability characteristics and ME than NLM, PLM and LLM. Supplementation of the animals with browse resulted to (P < 0.05) higher average daily weight gains (ADG) of 157.1 g day⁻¹ in T₄ than the animals fed on T₂ (114.3 g day⁻¹) and T₃ (42.9 g day⁻¹), and even to those fed on T₁ (control), which lost weight (−71.4 g day⁻¹). Improved weight gains were mainly due to corrected feed nitrogen (N) or CP due to supplementation of the animals with browse fodder. Too low CP of the NPH would not meet the normal requirements of CP (80 g CP kg⁻¹ DM) for optimal rumen microbial function in ruminants. Higher ADG due to LLM (T₄) and NLM (T₂) supplementation suggest optimised weight gains due to browse supplementation (20% of expected DMI); while lower weight gains from supplementation with PLM (T₃) indicate the possible utilisation of A. polyacantha leaves to overcome weight losses especially during dry seasons.