Effect of supplementation with pelleted citrus pulp on digestibility and intake in beef cattle fed a tropical grass-based diet (Cynodon nlemfuensis)

Citrus pulp is an important by-product for sub-tropical and tropical ruminant animal production. In this study, three steers (average body weight = 324 ± 16 kg) were randomly assigned to three levels of pelleted citrus pulp (PCP) supplementation (0, 1.25, and 2.5 kg animal⁻¹ d⁻¹; as-fed) in a 3 × 3 Latin square design to evaluate its effects on forage intake, digestion, and ruminal pH. The basal diet was stargrass (Cynodon nlemfuensis) harvested and chopped every day and fed fresh. Supplementation with increasing amounts of PCP tended (P≤0.10) to result in a linear increase in digestibility of total diet dry matter (DM) and organic matter (OM), but no effects were noticed for digestibility of forage DM or total diet neutral detergent fiber. Forage DM intake decreased linearly (P=0.03) with increasing PCP supplementation, although the decrease tended (quadratic; P=0.08) to be of greater magnitude at the highest level of supplementation. Both a linear increase (P<0.01) and a quadratic trend (greatest increase with first level of supplementation; P=0.09) were also observed for intake of total digestible OM. Average ruminal pH was between 6.6 and 7.2 and was not affected (P=0.29) by supplementation treatment. Although supplementation with PCP depressed forage consumption somewhat, little effect on forage digestion was observed. The provision of digestible OM in the form of supplement was greater than that lost via depressed forage consumption, resulting in an overall increase in energy supply. Our results suggest that high levels of citrus pulp to beef cattle can lower forage intake, but increase total energy intake. High levels of citrus pulp supplementation could be beneficial in combination with forages high in rumen dagradable protein. Systems using grasses with higher ruminally degradable protein content than we used, may benefit from this extra supply of energy which should be tested in a further experiment.     

Varying endophyte status and energy supplementation of fresh tall fescue in continuous culture

Eight dual-flow continuous culture vessels (700 ml) were used to compare in vitro effects of toxic, endophyte-infected (E+), endophyte-free (E−), and non-toxic, endophyte-infected (EN) Jesup tall fescue (vegetative stage) on ruminal fermentation at 4 levels (0, 150, 300, and 450 g kg⁻¹ DM) of concentrate supplementation (ground corn) for a total of 12 experimental diets in a randomized incomplete block design with 2 replicates. Each culture vessel was offered a total of 15 g DM d⁻¹. Forage was fed in four equal portions (fed at 03:00, 09:00, 15:00, and 21:00 h); and corn was fed in two equal portions (fed at 09:00 and 21:00 h). Headspace gas and liquid samples were analyzed for methane, ruminal culture pH, ammonia–N, and volatile fatty acid production. Ammonia–N output (g d⁻¹) varied by grass; EN had lower values compared to those of E+ and E−. Increasing the level of grain linearly decreased ruminal culture pH, ammonia–N, acetate production, and the acetate-to-propionate ratio, whereas propionate and butyrate production increased with higher grain supplementation. Ruminal fermentation was minimally altered by the presence of the endophyte; however, for the highest level of grain fed (450 g kg⁻¹ DM fed) the methane production pattern for all three grasses was altered. In addition to having the lowest ruminal ammonia–N accumulation, the non-toxic, endophyte-infected fescue resulted in the lowest methane production measured.     

Utility of buckwheat (Fagopyrum esculentum Moench) as feed: Effects of forage and grain on in vitro ruminal fermentation and performance of dairy cows

Buckwheat is of high value in crop rotations and overall agricultural ecology because of strong rooting and intensive flowering properties, but it is rarely cultivated and information on its nutritional value to ruminants is scarce. The contents of net energy for lactation (NEL), as estimated with the Hohenheim Gas Test (n = 3), were 4.3, 4.9 and 7.5 MJ NEL/kg dry matter (DM) for fresh and ensiled whole buckwheat plants and buckwheat grain, respectively. In two experiments with the Rumen Simulation Technique (Rusitec), ruminal fermentation characteristics of buckwheat forages and buckwheat grain (n = 4/diet) were evaluated. In the first experiment, 0, 300 or 600 g/kg of a pure hay diet were replaced by either fresh or ensiled buckwheat to create five diets. Neither form of buckwheat forages had effects on in vitro ruminal degradability and short chain fatty acid (SCFA) concentrations and composition. The use of fresh buckwheat reduced ruminal ammonia concentrations and enhanced estimated microbial N growth efficiency. These differences did not occur with silage, indicating a change in nutritional value by ensiling. Fresh buckwheat reduced the number of bacteria in the incubated fluid, while ensiled buckwheat reduced that of holotrich protozoa. Methane formation was not influenced by the buckwheat forages. In the second experiment, wheat meal (400 g/kg dietary DM), was replaced stepwise (0.5 and 1.0) by buckwheat grain meal. This did not cause differences in parameters of nutrient degradability, relative N efficiency and total amount and composition of SCFA. Holotrich protozoa counts increased, but total gas formation decreased with increasing dietary level of buckwheat grain. In a final experiment, cows yielding about 40 kg milk/day were fed mixed silage-concentrate diets (n = 4). A control diet contained no buckwheat. In a second diet, maize silage was partly substituted by buckwheat silage (98 g/kg dietary DM). In a third group, part of the energy concentrate was substituted by buckwheat grain meal (94 g/kg). There were no effects on feed intake, milk yield and milk composition. Buckwheat proved to be a plant that offers different feeds of a quality sufficient to be considered suitable in ruminant nutrition.     

Fecal nitrogen to estimate intake and digestibility in grazing ruminants

This study aimed at evaluating forage intake and digestibility in ruminants using fecal nitrogen content, as well as validating a non-linear model to estimate digestibility in ruminants. A total of 58 conventional metabolism trials, carried out with sheep fed 27 forages (offered pure or in mixture) used in Rio Grande do Sul (RS) during the period 1969–1989 was analyzed. OM intake and OM digestibility (OMD) results were regressed linearly against fecal N, and OMD was also estimated from fecal crude protein (N × 6.25) content by a non-linear regression model. Fecal nitrogen excretion estimated forage intake in sheep with an R² = 0.73, whereas a low R² value of 0.36 was observed for OMD estimates. The equation obtained using the non-linear model was OMD = 0.7326 ? 0.3598 exp [(?0.9052 CP (g/kg OM))/100]. The parameters a (0.7326) and b (0.3598) estimated by the equation for all forages were significant (P<0.00001) and there was no effect of type of forage (P=0.38). The mean prediction error (MSPE), was 0.2379, indicating that the equation fit well to the data. The difference between estimated and observed organic matter digestibility was mainly caused by random variation (0.9765). The results indicated that the equation using the non-linear model developed with all forages can be used with enough precision to estimate the OM digestibility of forage consumed by sheep in Rio Grande do Sul.     

Ruminal large and small particle kinetics in dairy cows fed red clover and grass silages harvested at two stages of growth

Passage, comminution and digestion rates of large and small particles were estimated using a rumen evacuation technique and total faecal collection with five lactating dairy cows in a 5 × 5 Latin square experiment. Two grass and two red clover silages harvested at early and late primary growth stages and a 1:1 mixture of late harvest grass and early harvest red clover were the dietary treatments. Cows received 9.0 kg supplementary concentrate per day. Ruminal contents and faeces were divided into large (>1.25 mm) and small (1.25–0.038 mm) particles by wet sieving. Indigestible neutral detergent fibre (iNDF) was determined by 12 days ruminal in situ incubation followed by neutral detergent extraction. Plant species did not affect ruminal particle size distribution, whereas advancing forage maturity decreased the proportion of large particles for both grass and red clover silage diets. Ruminal pool size of iNDF was higher (P<0.001) with red clover compared to grass silage diets. Ruminal passage rates of iNDF and potentially digestible NDF (pdNDF) increased with decreasing particle size (P<0.01). Passage rate of iNDF for small particles was slower (P<0.01) when red clover compared to grass silage diets were fed. Particle comminution rate in the rumen was slower (P<0.001) with red clover compared to grass silage diets and it increased (P<0.01) with advancing forage maturity. The contribution of particle comminution to ruminal mean retention time of iNDF in the ruminal large particle pool was smaller (P<0.01) in red clover compared to grass silage diets and it increased (P<0.05) with the mixed silage compared to the separate silages. Passage rate of pdNDF for both large and small particles was not affected by dietary treatments. Digestion rate of pdNDF for large particles was faster (P<0.001) with red clover compared to grass silage diets. Differences in ruminal passage and digestion rates of the large and small particles, in addition to differences in the passage and digestion rates of red clover compared to grass silage diets, emphasize the need to consider particle size and forage type in metabolic models predicting feed intake and fibre digestibility in ruminants.     

Ecosystem functions as indicators for heathland responses to nitrogen fertilisation

Anthropogenic deposition of reactive nitrogen (N) has increased during the 20th century, and is considered an important driver of shifts in ecosystem functions and biodiversity loss. The objective of the present study was to identify those ecosystem functions that best evidence a target ecosystem’s sensitivity to N deposition, taking coastal heathlands as an example. We conducted a three-year field experiment in heathlands of the island Fehmarn (Baltic Sea, North Germany), which currently are subject to a background deposition of 9 kg N ha⁻¹ yr⁻¹. We experimentally applied six levels of N fertilisation (application of 0, 2.5, 5, 10, 20, and 50 kg N ha⁻¹ yr⁻¹), and quantified the growth responses of different plant species of different life forms (dwarf shrubs, graminoids, bryophytes, lichens) as well as shifts in the C:N ratios of plant tissue and humus horizons. For an applicability of the experimental findings (in terms of heathland management and critical load assessment) fertilisation effects on response variables were visualised by calculating the treatment ‘effect sizes’. The current year’s shoot increment of the dominant dwarf shrub Calluna vulgaris proved to be the most sensitive indicator to N fertilisation. Shoot increment significantly responded to additions of ≥ 5 kg N ha⁻¹ yr⁻¹ already in the first year, whereas flower formation of Calluna vulgaris increased only in the high-N treatments. Similarly, tissue C:N ratios of vascular plants (Calluna vulgaris and the graminoids Carex arenaria and Festuca ovina agg.) only decreased in the highest N treatments (50 and 20 kg N ha⁻¹ yr⁻¹, respectively). In contrast, tissue C:N ratios of cryptogams responded more quickly and sensitively than vascular plants. For example, Cladonia spp. tissue C:N ratios responded to N additions ≥ 5 kg N ha⁻¹ yr⁻¹ in the second study year. After three years we observed an increase in cover of graminoids and a corresponding decrease of cryptogams at N fertilisation rates of ≥ 10 kg N ha⁻¹ yr⁻¹. Soil C:N ratios proved to be an inappropriate indicator for N fertilisation at least within our three-year study period. Although current critical N loads for heathlands (10−20 kg N ha⁻¹ yr⁻¹) were confirmed in our experiment, the immediate and highly sensitive response of the current year’s shoots of Calluna vulgaris suggests that at least some ecosystem functions (e.g. dwarf shrub growth) also might respond to low (i.e. < 10 kg N ha⁻¹ yr⁻¹) but chronic inputs of N.     

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.     

Chara hispida beds as a sink of nitrogen: Evidence from growth,nitrogen uptake and decomposition

Chara hispida forms dense beds (0.78–0.95 kg DW m⁻²) in Colgada Lake. The ability of Chara meadows to act as a nitrogen source or sink was evaluated by the following methods: (1) investigating Chara growth, (2) nitrogen incorporation and decomposition laboratory experiments and (3) relating experimental results to field conditions. Sediment oospores were germinated in large aquaria and observed growth rates were 0.001 m day⁻¹ (shoot length) and 0.0002 g day⁻¹ (dry weight). Nitrogen uptake rates were determined by addition of K¹⁵NO₃ during two different periods of Chara growth and the rates were 1.21 and 3.86 μM g DW⁻¹ h⁻¹ when charophytes were 166 days old (not sexually mature) and 323 days old (sexually mature), respectively. After the uptake experiments, the same charophytes were allowed to decompose within two types of litter bags (3 mm-pore litter bags and entire, non-porous plastic litter bags). Decomposition rates of Ch. hispida were 0.016 and 0.009 day⁻¹ in perforated and non-perforated bags, respectively, and fit a negative exponential model. The nitrogen release rate, calculated as the disappearance of N content from Chara tissues, was 0.012 day⁻¹ and there were no statistically significant differences between the values from the two different bag types. The dissolved organic nitrogen concentrations in aquarium and non-perforated litter bags waters increased linearly with time due to the leaching of soluble compounds from Chara. The rate of N loss from Chara tissues, total nitrogen and dissolved organic nitrogen release rates and the decrease in initial dry weight rate were all lower than the daily rate of Chara N uptake. By extrapolating laboratory data to field situations, we determined that approximately 38% of the N taken up by charophytes in Colgada Lake during the growth period is retained. Given the high charophyte biomass in the lake, its ability to incorporate nitrogen, its low decomposition rate and its ability to over-winter, we conclude that Chara beds could be acting as nitrogen sinks in this ecosystem.     

The effects of NH4+ and NO3− on growth,resource allocation and nitrogen uptake kinetics of Phragmites australis and Glyceria maxima

The effects of NH₄⁺ or NO₃⁻ on growth, resource allocation and nitrogen (N) uptake kinetics of two common helophytes Phragmites australis (Cav.) Trin. ex Steudel and Glyceria maxima (Hartm.) Holmb. were studied in semi steady-state hydroponic cultures. At a steady-state nitrogen availability of 34 μM the growth rate of Phragmites was not affected by the N form (mean RGR = 35.4 mg g⁻¹ d⁻¹), whereas the growth rate of Glyceria was 16% higher in NH₄⁺-N cultures than in NO₃⁻-N cultures (mean = 66.7 and 57.4 mg g⁻¹ d⁻¹ of NH₄⁺ and NO₃⁻ treated plants, respectively). Phragmites and Glyceria had higher S/R ratio in NH₄⁺ cultures than in NO₃⁻ cultures, 123.5 and 129.7%, respectively.Species differed in the nitrogen utilisation. In Glyceria, the relative tissue N content was higher than in Phragmites and was increased in NH₄⁺ treated plants by 16%. The tissue NH₄⁺ concentration (mean = 1.6 μmol g fresh wt⁻¹) was not affected by N treatment, whereas NO₃⁻ contents were higher in NO₃⁻ (mean = 1.5 μmol g fresh wt⁻¹) than in NH₄⁺ (mean = 0.4 μmol g fresh wt⁻¹) treated plants. In Phragmites, NH₄⁺ (mean = 1.6 μmol g fresh wt⁻¹) and NO₃⁻ (mean = 0.2 μmol g fresh wt⁻¹) contents were not affected by the N regime. Species did not differ in NH₄⁺ (mean = 56.5 μmol g⁻¹ root dry wt h⁻¹) and NO₃⁻ (mean = 34.5 μmol g⁻¹ root dry wt h⁻¹) maximum uptake rates (V_max), and V_max for NH₄⁺ uptake was not affected by N treatment. The uptake rate of NO₃⁻ was low in NH₄⁺ treated plants, and an induction phase for NO₃⁻ was observed in NH₄⁺ treated Phragmites but not in Glyceria. Phragmites had low K_m (mean = 4.5 μM) and high affinity (10.3 l g⁻¹ root dry wt h⁻¹) for both ions compared to Glyceria (K_m = 6.3 μM, affinity = 8.0 l g⁻¹ root dry wt h⁻¹). The results showed different plasticity of Phragmites and Glyceria toward N source. The positive response to NH₄⁺-N source may participates in the observed success of Glyceria at NH₄⁺ rich sites, although other factors have to be considered. Higher plasticity of Phragmites toward low nutrient availability may favour this species at oligotrophic sites.     

In vivo and in situ digestibilities and nitrogen balance of Buddleia skutchii as a sole component and mixed with Pennisetum clandestinum in sheep diets

The objective of this work was to evaluate the intake (I) of all Buddleia skutchii foliage (BSF), collected from three different sites (places: A, B and C) in feeding sheep (phase 1), and in combination with Pennisetum clandestinum (Pc) (phase 2). Trials of feed intake, in vivo dry matter digestibility (IVDMD), and digestibilities of crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), and nitrogen balance were carried out during phase 1. Diet was given to nine Creole male lambs of 23(±3) kg body weight (BW), located in individual metabolism crates. During phase 2, four treatments were evaluated (T1 = 100% Pc, T2 = 20% BSF + 80% Pc, T3 = 40% BSF + 60% Pc and T4 = 60% BSF + 40% Pc) in a 4 × 4 Latin square design, using four ruminal cannulated Creole male rams of 50 ± 2 kg BW and remained in individual metabolism crates. In vivo digestibility (DM, CP and gross energy (GE)) and kinetics of in situ disappearance of DM were evaluated. The results in phase 1 indicated that BSF from Site B had relatively higher CP (14.9%), ADF (50.6%) content and nitrogen retention (1.93 g d⁻¹). On the other hand, the lambs showed intake levels of 376.29 g d⁻¹ DM, 56.21 g d⁻¹ CP, 206.24 g d⁻¹ ADF and 1418.21 kcal gross energy (P > 0.05); and digestibilities of 54.23% DM, 47.17% CP and 39.31% NDF. Therefore, BSF from Site B was selected for the second phase of this work as the best result. We observed that the nutrition quality of the diets was higher as a result of increasing BSF concentration in the diet. When sheep were fed on 40% BSF–60% Pc, DM intake levels of 900.6 g d⁻¹, and DM, CP and GE digestibility of 70.0, 52.82 and 55.1%, respectively, were observed. There were not significant differences among diets, and in situ disappearance, K_d and K_p, but the diet with 60% of BSF presented higher ruminal digestibility (42.3%). The results allowed to validate the local knowledge on BSF as a promising forage species, and showed that BSF should be incorporated in a sheep production system.     

Effects of phosphorus and nitrogen amendments on the growth of Egeria najas

The effect of nutrient addition on the growth of E. najas was evaluated in a dose response experiment using sand amended with phosphorus (P) and nitrogen (N), and in enrichment trials with N and P amendments to natural sediments. Plants, water and sediment came from lagoons of the Upper Paraná River Floodplain and from Itaipu Reservoir (Brazil). Relative growth rates (RGRs) of E. najas shoots, based on dry mass (DM), varied from 0.03 to 0.060 d⁻¹ for both nutrients. Root:shoot biomass ratios were related to sediment exchangeable P (r = −0.419; P = 0.03) and N (r = −0.54; P = 0.006), however root RGR was not related to sediment nutrient concentrations. When natural sediments were amended with N and P, neither shoot nor root RGRs differed among treatments for substrata from either the reservoir or the floodplain lagoons (P > 0.05). Comparison of nutrient concentrations measured in natural sediments collected from several sites in both the Upper Paraná River Floodplain (range 49–213 μg P g⁻¹ DM; 36–373 μg N g⁻¹ DM) and Itaipu Reservoir (range 43–402 μg P g⁻¹ DM; 7.9–238 μg N g⁻¹ DM) showed that sediment N and P from these systems usually exceeded minimum requirements necessary for E. najas growth, as measured in the dose response experiment. Together, these results indicate that E. najas, at least in early stages of development, responds to sediment nutrient amendments and relies upon bottom sediments to meet its N and P requirements and that for at least two Brazilian ecosystems, growth of this species is not limited by insufficient sediment N or P. Thus, reducing N and P in water is not enough to control E. najas growth in short time periods in these ecosystems.     

Intake and digestion by lambs of dwarf elephant grass (Pennisetum purpureum Schum. cv. Mott) hay or hay supplemented with urea and different levels of cracked corn grain

This study was carried out to evaluate intake, digestibility, ruminal fermentation, nitrogen (N) retention and ruminal microbial protein synthesis in lambs fed dwarf elephant grass (Pennisetum purpureum Schum. cv. Mott) hay or hay supplemented with urea and 0, 5, 10 or 15 g/kg of live weight (LW) of cracked corn grain. Ten lambs (mean LW of 28 ± 0.9 kg), housed in metabolic cages, were used in a double 5 × 5 Latin Square experiment. Except fibre intake and digestibility, which was higher, the intake and digestibility of the others feed components, as well as ruminal microbial protein synthesis and N retention were lower in non-supplemented lambs. Corn supplementation increased total dry matter (DM) (P<0.05), organic matter (OM), non-structural carbohydrate (NSC) and energy intake (P<0.01) but decreased total neutral detergent fibre (aNDFom) (P<0.01) intake, as well as OM and aNDFom intake from the hay (P<0.01). Apparent DM, OM and energy digestibility, as well as OM true digestibility (OMTD) increased (P<0.01), and aNDFom digestibility decreased linearly (P<0.01) as corn supplementation increased. Total N intake was not influenced but, apparent and true N digestibility, as well as urinary N excretion decreased (P<0.01), and ruminal microbial N entering the small intestine increased linearly (P<0.01) as corn supplementation increased. However, the efficiency of ruminal microbial protein synthesis was similar for all treatments. Mean ruminal pH values and ammonia N concentrations decreased linearly (P<0.01) with level of corn supplementation. Ammonia N and amino acid, as well as peptide concentrations in ruminal fluid were quadratically related (P<0.01) with the time after feeding. Corn supplementation had a linear additive effect on total dry matter and digestible energy intake, as well as on N retention, but a linear negative effect on hay intake and on fibre digestibility. However, decreased forage digestibility by animals was probably neither related to lower ruminal pH, which values were always higher than 7.0, nor related to ruminal sugar concentrations, which were similar for all treatments.     

Performance of West African dwarf goats fed Guinea grass–Verano stylo mixture,N-fertilized and unfertilized Guinea grass

The supplementary values of Verano stylo in a mixed Guinea grass (Panicum maximum cv. Ntchisi)–Verano stylo (Stylosanthes hamata cv. Verano) diet from a sown grass–legume mixture and N fertilized grass were compared in West African dwarf (WAD) goats. Liveweight (LW) gain, feed intake, digestibility and N utilization were determined using 15 goats in two trials lasting for 98 days. Goats were fed Guinea grass–Verano stylo mixture (GSM), N-fertilized (NFG) and unfertilized grass (UFG). The goats were divided into three groups of five animals each and randomly allocated to the dietary treatments in a randomized complete block design. Total DM and OM intakes of the goats did not vary significantly among the forage diets and averaged 55.1 and 50.4 g kg⁻¹ W^0.75 per day, respectively. CP intake (g kg⁻¹ W^0.75 per day) was highest with NFG (5.6) followed by GSM (4.8) and the UFG (3.5). Total N excreted followed the same trend as the CP intake. There was no significant difference between N-retention of GSM and NFG (28.5 and 26.7%), but goats on UFG had a negative N balance (−9.16%). Animals on GSM had significantly higher liveweight gain (31.9 g per day) than those of NFG (25.1 g per day) and UFG (21.9 g per day) which also differed significantly. The digestibilities of total DM, OM, CP, NDF were higher with GSM than NFG or UFG. It is concluded that growing Verano stylo in mixture with Guinea grass is a better option for improving the feed quality of forage diets for goats than direct application of inorganic fertilizer at 200 kg N ha⁻¹ to the pure grass.     

Light intensity increases the susceptibility of Vallisneria natans to snail herbivory

Palatability to snail herbivory (Radix swinhoei H. Adams) and C/N ratios were assessed for Vallisneria natans (Lour.) Hara, in three different experimental light regimes (midday fluxes respectively 280 μmol m⁻² s⁻¹, 15 μmol m⁻² s⁻¹, and a variable intensity between these two). Higher light intensity as well as prolonged photoperiods increased palatability and growth, and improved C/N ratio by decreasing N content. Snail growth was slightly increased but juvenile survivorship decreased under higher light. The results suggest that the availability of light may affects intraspecific variation in palatability of V. natans.     

Enhancement of polysaccharide production in suspension cultures of protocorm-like bodies from Dendrobium huoshanense by optimization of medium compositions and feeding of sucrose

A strategy that optimization of medium compositions for maximum biomass followed by feeding of sucrose for maximum polysaccharide synthesis was developed for enhancing polysaccharide production in suspension culture of protocorm-like bodies (PLBs) of Dendrobium huoshanense C.Z. Tang et S.J. Cheng. In growth stage, the original half-strength MS medium was optimized with carbon sources, nitrogen sources and metal ion combinations. The effects of different carbon sources on PLBs growth were remarkable and sucrose at 35 g l⁻¹ was the most suitable. Sole nitrate nitrogen of 30 mmol l⁻¹ was the best for PLBs growth. Metal ions (Ca²⁺, Fe²⁺, Mn²⁺ and Zn²⁺) showed different influences on PLBs growth. The optimal concentration of Ca²⁺, Fe²⁺, Mn²⁺ and Zn²⁺ was 4.5 mmol l⁻¹, 0.1 mmol l⁻¹, 0.5 mmol l⁻¹ and 0.06 mmol l⁻¹, respectively. In the optimized medium (sucrose, nitrate, Ca²⁺, Fe²⁺, Mn²⁺ and Zn²⁺ concentration as described above, the other component concentration seen in half-strength MS), 33.9 g DW l⁻¹ PLBs were harvested after 30 days of culture and biomass increase was improved 245% as compared with that in the original medium. In production stage, polysaccharide synthesis was significantly improved by the feeding sucrose. The maximum polysaccharide production (22 g l⁻¹) was obtained in the case of 50 g l⁻¹ sucrose feeding at day 30 of culture, which was about 109-fold higher than that in the original medium without feeding of sucrose.     

Mixotrophy in the newly described dinoflagellate Yihiella yeosuensis: A small,fast dinoflagellate predator that grows mixotrophically,but not autotrophically

To investigate tropical roles of the newly described Yihiella yeosuensis (ca. 8 μm in cell size), one of the smallest phototrophic dinoflagellates in marine ecosystems, its trophic mode and the types of prey species that Y. yeosuensis can feed upon were explored. Growth and ingestion rates of Y. yeosuensis on its optimal prey, Pyramimonas sp. (Prasinophyceae), as a function of prey concentration were measured. Additionally, growth and ingestion rates of Y. yeosuensis on the other edible prey, Teleaulax sp. (Cryptophyceae), were also determined for a single prey concentration at which both these rates of Y. yeosuensis on Pyramimonas sp. were saturated. Among bacteria and diverse algal prey tested, Y. yeosuensis fed only on small Pyramimonas sp. and Teleaulax sp. (both cell sizes = 5.6 μm). With increasing mean prey concentrations, both specific growth and ingestion rates of Y. yeosuensis increased rapidly before saturating at a mean Pyramimonas concentration of 109 ng C mL⁻¹ (2725 cells mL⁻¹). The maximum growth rate (mixotrophic growth) of Y. yeosuensis fed with Pyramimonas sp. at 20 °C under a 14:10-h light-dark cycle of 20 μE m⁻² s⁻¹ was 1.32 d⁻¹, whereas the growth rate of Y. yeosuensis without added prey was 0.026 d⁻¹. The maximum ingestion rate of Y. yeosuensis fed with Pyramimonas sp. was 0.37 ng C predator⁻¹ d⁻¹ (9.3 cells predator⁻¹ d⁻¹). At a Teleaulax concentration of 1130 ng C mL⁻¹ (66,240 cells mL⁻¹), growth and ingestion rates of Y. yeosuensis fed with Teleaulax sp. were 1.285 d⁻¹ and 0.38 ng C predator⁻¹ d⁻¹ (22.4 cells predator⁻¹ d⁻¹), respectively. Thus, Y. yeosuensis rarely grows without mixotrophy, and mixotrophy supports high growth rates in Y. yeosuensis. Y. yeosuensis has the highest maximum mixotrophic growth rate with the exception of Ansanella graniferaamong engulfment feeding mixotrophic dinoflagellates. However, the high swimming speed of Y. yeosuensis (1572 μm s⁻¹), almost the highest among phototrophic dinoflagellates, may prevent autotrophic growth. This evidence suggests that Y. yeosuensis may be an effective mixotrophic dinoflagellate predator on Pyramimonas and Teleaulax, and occurs abundantly during or after blooms of these two prey species.     

Effect of by-product gypsum application rate to grass pasture,grass hay,and corn silage on fermentation by rumen microorganisms in continuous culture

A dual-flow continuous culture fermenter system was used to investigate ruminal fermentation in response to increased by-product gypsum application rate of three forages. The treatments included 0, 22, 45, and 90 tonnes/ha by-product gypsum applied to grass plots and 0, 22, and 45 tonnes/ha by-product gypsum applied to corn plots. Forage was harvested to represent grass pasture (GP), grass hay (GH), and corn silage (CS), dried, ground, and fed to fermenters at a rate of 60 g dry matter (DM)/day. Organic matter (OM) and neutral detergent fiber (aNDF) digestibilities, rumen pH, total volatile fatty acid (VFA) production, and N metabolism were not affected by gypsum application rate for all forage types. The GH had greater sulfur content than recommended as the maximum tolerable level by the National Research Council (NRC). The results of this study indicate that ruminal fermentation was not compromised when by-product gypsum was applied to GP, GH, or CS at rates up to 90 tonnes/ha. By-product gypsum application to pastures and crops shows promise as an economical soil amendment to reduce dissolved phosphorus loss in runoff, although potential animal health issues should be further evaluated.     

Reducing nutrient loss from farms through silvopastoral practices in coarse-textured soils of Florida,USA

Trees integrated into the range- and pasturelands of Florida could remove nutrients from deeper soil profiles that would otherwise be transported to water bodies and cause pollution. Soil nitrogen (N) and phosphorus (P) concentrations were monitored in three pastures: a treeless pasture of bahiagrass (Paspalum notatum); a pasture of bahiagrass under 20-year-old slash pine (Pinus elliotti) trees (silvopasture); and a pasture of native vegetation under pine trees (native silvopasture). Soil analysis from 10 profiles within each pasture showed that P concentrations were higher in treeless pasture (mean: 9.11 mg kg⁻¹ in the surface to 0.23 mg kg⁻¹ at 1.0 m depth) compared to silvopastures (mean: 2.51 and 0.087 mg kg⁻¹, respectively), and ammonium–N and nitrate–N concentrations were higher in the surface horizon of treeless pasture. The more extensive rooting zones of the combined stand of tree + forage may have caused higher nutrient uptake from silvopastures than treeless system. Further, compared to treeless system, soils under silvopasture showed higher P storage capacity. The results suggest that, compared to treeless pasture, silvopastoral association enhances nutrient retention in the system and thus reduces chances for nutrient transport to surface water. The study reflects the scope for applying ecological-engineering and ecosystem-restoration principles to silvopastoral-system design.     

Effects of Yucca schidigera extract on fermentation and degradation of steroidal saponins in the rumen simulation technique (RUSITEC)

A rumen simulation technique (RUSITEC) apparatus with eight 940 ml fermentation vessels was used to study the effects of the steroidal saponins in Yucca schidigera extract (YE) on ruminal microbial activity and saponin degradation. The YE contained approximately 4.4% (w/w) saponin, as smilagenin equivalents, and was included at 0 (control) or 0.5 mg ml⁻¹ (n=4) in the McDougall's buffer infused continuously into the vessels (dilution rate=0.75 day⁻¹). Each vessel received 5 g chopped alfalfa hay and 5 g concentrate (as-fed basis) daily for 22 days. Ammonia concentrations were lower (P<0.05) in effluent from vessels receiving YE than from controls for the first half of the study, but did not differ thereafter. Total amounts of VFA in effluent were not affected (P>0.05) by YE, but molar proportions of iso-butyric and iso-valeric acids were lower (P<0.05) in the YE vessels than in the controls in the first half of the experiment. Yucca extract at 0.5 mg ml⁻¹ did not affect (P>0.05) dry matter disappearance (DMD) from hay or from concentrate, nor did it affect total gas or methane production, or bacterial numbers (total or cellulolytic populations) in homogenates prepared from fermenter vessel liquid and feed particles. Protozoal numbers in the homogenates were substantially reduced (P<0.01) by YE (at 0.5 mg ml⁻¹), protease activity was increased (P<0.05), deaminase activity and activity against Ala₂ were unaffected (P>0.05) and activity against Ala₅ was reduced by 25% (P>0.05). When the homogenates from control and YE-supplemented (0.5 mg ml⁻¹) vessels were used to inoculate roll tubes containing 0 or 5 mg ml⁻¹ of YE, fewer colonies developed (P<0.01) in roll tubes containing YE than in those without YE, irrespective of the source of inoculum. Homogenates were also assayed for saponin degradation and for protease, peptidase and deaminase activities. Inoculum from the vessels receiving YE degraded saponin slightly during a 2 h incubation. Yucca extract at 0.5 mg ml⁻¹ altered proteolytic activity and reduced protozoal numbers, but did not affect DMD or bacterial activity, and did not induce resistance to YE at a concentration of 5 mg ml⁻¹.     

Growth limitation of Lemna minor due to high plant density

The effect of high population densities on the growth rate of Lemna minor (L.) was studied under laboratory conditions at 23 °C in a medium with sufficient nutrients. At high population densities, we found a non-linear decreasing growth rate with increasing L. minor density. Above a L. minor biomass of ca. 180 g dry weight (DW) m⁻², the net growth rate became negative. At a density of 9 g DW m⁻², a maximum relative growth rate of ca. 0.3 d⁻¹ was found. At very low densities (<9 g m⁻²), we observed an inverse density dependence (or Allee effect). Probably, this lower growth rate was due to lower local temperatures within such partly covered L. minor decks. On the basis of these experimental results and literature data, a simple model was created. To test the model, the density of duckweed in three different Dutch ditches was monitored for 9 weeks in spring. Within this period, full coverage of the ditches by duckweed was reached. The maximum density increased with rising air temperature. The model described the field data well, suggesting that crowding is an important factor in limitation of duckweed growth.