Herbage Chemical Composition Research Articles

Grazed rain-fed small-grain cereals as a forage option for small-scale dairy systems in central Mexico.

Small-scale dairy systems face reduced availability of water for irrigation of pastures and disruption in the amount or pattern of rains due to climate change, so research on alternative short-cycle rain-fed forages is needed. Grazing reduces feeding costs and small-grain cereals may be an option. The objective was to assess on-farm the performance of dairy cows grazing 6h/day of three small-grain cereals: rye (RYE), wheat (WHT), and triticale (TRT), and supplemented 4.5kg dry matter (DM)/cow/day of concentrate. Twelve Holstein cows were used in repeated 3 × 3 Latin squares with 14-day experimental periods. Pasture variables were analysed with a split-plot design, and economic analysis was performed with partial budgets. Sampling of forage (sward height, net herbage accumulation, botanical and chemical composition of herbage) and animal variables (milk yield and composition, live weight, and body condition score) were at the end of each period. The RYE showed a trend (P > 0.05) for higher net herbage accumulation (NHA) with highly significant differences (P < 0.001) among periods. The RYE had higher DM, a lower crude protein (CP) content (P < 0.05), and no differences for other chemical components between treatments (P > 0.05). The RYE proportion in pasture was consistently higher, whilst the lowest cereal proportion was in WHT. There were no differences (P > 0.05) for any animal variable. The RYE and TRT treatments proved useful as rain-fed forage alternatives under grazing. WHT showed lower crop and economic performance. However, given the higher cereal component in pastures, regrowth potential, and post-grazing herbage mass, as well as better economic performance, the RYE treatment was better ranked by the participating farmer.

Protein and Carbohydrate Fractions in Warm-Season Pastures: Effects of Nitrogen Management Strategies

Nitrogen (N) management affects herbage production and chemical composition; however, information on the impact of tropical herbage on N and carbohydrate fractions is scarce. A two-year study was conducted to investigate the potential use of pintoi peanut (Arachis pintoi) compared with N fertilization of palisade grass (Brachiariabrizantha cv. Marandu) by evaluating the herbage chemical composition (fractionation of protein and carbohydrate), herbage mass and accumulation rate, herbage disappearance rate, and stocking rate of pastures. The experiment was conducted in a completely randomized design with three treatments, and four replications (paddocks) were used with twenty-one non-lactating crossbred dairy heifers. Treatments consisted of pastures of palisade grass without a N source (control), fertilized with urea (150 kg/ha/year; fertilized), or mixed with pintoi peanut (mixed). Inclusion of the legume increased concentrations of fractions A (p = 0.009), which is the soluble N compound, and B3 (p &lt; 0.001), which is slowly degraded true protein, compared with pastures fertilized with N and non-fertilized pastures. Nitrogen fertilization increased fraction B1 + B2 (p = 0.046), mainly true proteins, and decreased fraction C (p = 0.0007), indigestible protein, and neutral detergent fiber concentrations (p = 0.0003), contributing to increasing the nutritive value of the herbage. Additionally, N fertilization increased herbage mass (p = 0.004) and herbage allowance (p = 0.0001). Both N fertilization and biologically fixed N increased herbage allowance (p = 0.02) and accumulation rate (p = 0.02), as well as the crude protein content of herbage (p &lt; 0.0001) compared with non-fertilized pastures. Nitrogen fertilization increased true protein and decreased indigestible protein of herbage and promoted a greater herbage mass production, while the inclusion of legumes increased soluble protein and decreased the slowly degraded true protein of herbage. Both N management strategies increased herbage allowance and accumulation rate.

Milk production and estimated enteric methane emission from cows grazing ryegrass pastures in small-scale dairy systems in Mexico.

The work assessed the productive response and estimated enteric methane (CH4) emissions of dairy cows grazing in small-scale dairy systems. Treatments were grazing annual pasture (AP) mainly of annual ryegrass and perennial pasture (PP) mainly of perennial ryegrass, complemented daily with 3.72kg DM/cow of commercial concentrate. Eight Holstein cows were used in a double cross-over design with three 14-day-each experimental periods for animal variables and CH4 emissions. Pasture variables were analysed with a split-plot design. AP showed higher sward height (P < 0.05) with no differences (P > 0.05) in net herbage accumulation or in herbage chemical composition. Cows on AP yielded 24.6% more milk (P < 0.001) than grazing PP, but there were no differences in milk fat and protein content. There were differences (P ≤ 0.05) among periods for milk yields, but no differences among periods for milk fat and protein. Milk urea nitrogen was significantly higher (P < 0.001) in PP than in AP with no differences among periods. There was higher (P < 0.001) DMI for AP than PP with a significant decline (P < 0.05) as periods progressed. There was a trend (P = 0.08) for higher daily CH4/cow in AP, but significantly lower emissions (7.2%) in AP/kg DMI, and 20.1% lower emission intensity of g CH4/kg milk. The proportion of gross energy lost as CH4 for AP was lower (P < 0.01). Higher milk yields in AP resulted in a 26% higher margin over feed costs than for PP. Results show that grazing annual pastures with moderate concentrate supplementation results in higher milk yields, higher incomes, and reduces the intensity of CH4 emissions.

Digestion and nitrogen metabolism in beef cattle and in vitro rumen fermentation of autumn grass differing in fertilizer nitrogen application rate

AbstractBeef cattle partition dietary nitrogen (N) into meat or excrete it mainly in faeces and urine, which can contribute significantly to water and air pollution. The effects of two inorganic nitrogen (N) fertilizer application rates—15 (LN) or 80 (HN) kg N/ha—to Lolium perenne‐dominant swards in autumn, on herbage chemical composition, intake, digestion and N balance in beef cattle, and in vitro fermentation and methane production were studied. Four growing beef steers used in a 2 × 2 crossover design experiment were offered zero‐grazed grass harvested 21 days post‐N application between July and October. The same grasses were incubated in an eight‐vessel rumen simulation technique in a randomized complete block experiment. Grass dry‐matter (DM) concentration was 26 g/kg lower and crude protein (CP) concentration was 35 g/kg DM higher for HN compared to LN. There was no difference in herbage DM intake or in vivo DM digestibility between treatments. Nitrogen intake and the digestibility of N were higher for HN compared to LN. Total and urine N loss were 41 and 45 g/day greater, respectively, for HN compared to LN, but faecal N loss did not differ between treatments. The quantity of N retained and therefore N‐use efficiency did not differ between LN and HN (25% vs. 22%). In vitro rumen pH and ammonia‐N concentrations were higher for HN compared to LN, whereas volatile fatty acid concentrations and molar proportions did not differ between treatments. In vitro methane and total gas production were 0.9 mmol/day and 280 ml/day lower for HN than LN respectively. Under the particular conditions of this experiment, reducing fertilizer N application rate reduced total and urinary N excretion, which has potential environmental benefits; however, methane output measured in vitro was increased.

Temporal fermentation and microbial community dynamics in rumens of sheep grazing a ryegrass-based pasture offered either in the morning or in the afternoon

Eight ruminally-fistulated wethers were used to examine the temporal effects of afternoon (PM; 1600h) v. morning (AM; 0800 h) allocation of fresh spring herbage from a perennial ryegrass (Lolium perenne L.)-based pasture on fermentation and microbial community dynamics. Herbage chemical composition was minimally affected by time of allocation, but daily mean ammonia concentrations were greater for the PM group. The 24-h pattern of ruminal fermentation (i.e. time of sampling relative to time of allocation), however, varied considerably for all fermentation variables (P⩽0.001). Most notably amongst ruminal fermentation characteristics, ammonia concentrations showed a substantial temporal variation; concentrations of ammonia were 1.7-, 2.0- and 2.2-fold greater in rumens of PM wethers at 4, 6 and 8h after allocation, respectively, compared with AM wethers. The relative abundances of archaeal and ciliate protozoal taxa were similar across allocation groups. In contrast, the relative abundances of members of the rumen bacterial community, like Prevotella 1 (P=0.04), Bacteroidales RF16 group (P=0.005) and Fibrobacter spp. (P=0.008) were greater for the AM group, whereas the relative abundance of Kandleria spp. was greater (P=0.04) for the PM group. Of these taxa, only Prevotella 1 (P=0.04) and Kandleria (P<0.001) showed a significant interaction between time of allocation and time of sampling relative to feed allocation. Relative abundances of Prevotella 1 were greater at 2h (P=0.05), 4h (P=0.003) and 6h (P=0.01) after AM allocation of new herbage, whereas relative abundances of Kandleria were greater at 2h (P=0.003) and 4h (P<0.001) after PM allocation. The early post-allocation rise in ammonia concentrations in PM rumens occurred simultaneously with sharp increases in the relative abundance of Kandleria spp. and with a decline in the relative abundance of Prevotella. All measures of fermentation and most microbial community composition data showed highly dynamic changes in concentrations and genus abundances, respectively, with substantial temporal changes occurring within the first 8h of allocating a new strip of herbage. The dynamic changes in the relative abundances of certain bacterial groups, in synchrony with a substantial diurnal variation in ammonia concentrations, has potential effects on the efficiency by which N is utilised by the grazing ruminant.

Pasture condition and milk production by grazing dairy cows as affected by daily herbage-allowance restriction

Daily herbage allowance is recognised as the main tool to control pasture utilisation and milk production per cow. The aim of the present study was to evaluate the long-term effects of daily herbage allowance (DHA) on pasture characteristics and milk production of dairy cows. Forty-four dairy cows were randomly assigned to one of four treatments in a 2 × 2 factorial design by considering two levels of DHA (20 and 30 kg DM/cow.day) and two types of supplements (high-moisture maize and maize silage) over a 77-day period. Pre- and post-grazing herbage masses, vertical distribution of herbage mass, species density, botanical and chemical composition, sward depletion and changes in morphological components of the pasture were measured. The effect of DHA on soil compaction was evaluated on the basis of the penetration resistance. Milk production and composition levels, bodyweights and body condition scores were recorded. Post-grazing residual declined as the level of DHA decreased, while grazing efficiency increased from 39.8% to 44.8%. We found no effects of DHA on any pasture characteristics, pasture regrowth or soil compaction. Low-DHA conditions induced a faster sward-height reduction, while the herbage mass remained unaffected. Individual milk production decreased with DHA. However, milk outputs per hectare increased by 2772 L/ha. Milk composition, bodyweight and body condition score were not affected by DHA. The results showed that DHA restriction decreases milk production per cow while increasing both herbage utilisation and milk production per hectare, without affecting long-term pasture condition.

Dynamics of forage ingestion, oral processing and digesta outflow from the rumen: a development in a mechanistic model of a grazing ruminant, MINDY

AbstractDetailed representation of ingesta inflow to and digesta outflow from the rumen is critical for improving the modelling of rumen function and herbage intake of grazing ruminants. The objective of the current work was to extend a mechanistic model of a grazing ruminant, MINDY, to simulate the dynamic links between ingestive and digestive processes as affected by forage and sward features (e.g. sward structure, herbage chemical composition) as well as the internal state of the animal. The work integrates existing aspects of forage ingestion, oral physiology and rumen digestion that influence ingesta characteristics and digesta outflows from the rumen, respectively. The paper describes the structure and function of the new development, assessing the new model in terms of dynamic changes of oral processing of ingesta and rumen dilution rate under different grazing contexts. MINDY reproduces characteristics of ingesta inflow to and digesta outflow from the rumen of grazing ruminants, achieving temporal patterns of occurrence within and between meals, similar to those for grazing animals reported in the literature. The model realistically simulates changes in particle size distribution of the ingestive bolus, bolus weight and rumen dilution rate in response to contrasting grazing management regimes. The new concepts encoded in MINDY capture the underlying biological mechanisms that drive the dynamic link between ingestion and digestion patterns. This development advances in the understanding and modelling of grazing and digestive behaviour patterns of free-ranging ruminants.

Rotatinuous stocking: A grazing management innovation that has high potential to mitigate methane emissions by sheep

To test the hypothesis that the best sward structure in the grazing management strategy based on animal behaviour, called ?Rotatinuous? stocking, results in higher nutrient intake and lower methane emission and intensity by sheep grazing Italian ryegrass pastures, two grazing management strategies were studied: the traditional rotational stocking (RT) with pre- and post-grazing sward target heights of 25 and 5 cm, respectively and, ?Rotatinuous? stocking (RN) with pre- and post-grazing sward target heights of 18 and 11 cm, respectively. Male castrated sheep were used. The experiment was carried out in 2014 and 2015 in southern Brazil. The experimental design was a randomized complete block with four replicates. The RN treatment had better herbage chemical composition in terms of quality than that of the RT treatment, with greater (P < 0.05) crude protein and lower neutral and acidic detergent fibre. The ideal sward structure and greater chemical composition of Italian ryegrass pastures found under RN treatment resulted in greater herbage digestibility and intake of organic matter and metabolizable energy by grazing sheep than under the RT treatment. Our study highlights that management is the key strategy to reduce the environmental impact of grazing through lower CH4 emissions in livestock grazing systems. Rotatinuous: stocking was the more efficient grazing management strategy for mitigation of CH4 emissions and intensity by grazing sheep, with 64% less CH4 production per area and 170% less CH4 emission per unit of animal product when compared to the RT treatment.

Nitrogen utilization efficiency and prediction of nitrogen excretion in sheep offered fresh perennial ryegrass ().

Nitrogen excretion from sheep production systems is an important source of nitrate, ammonia, and nitrous oxide responsible for groundwater pollution and global warming. The present study aimed to identify key parameters influencing N utilization efficiency and develop prediction equations for manure N, feces N, and urine N outputs in sheep. Data used were collected from 82 sheep offered fresh perennial ryegrass () as the sole diet in 6 metabolism experiments (data from non-grass-only diets were not used). Sheep were from breeds of Highlander, Texel, Scottish Blackface, and Swaledale at the age of 5 to 18 mo and weighing from 24.5 to 62.7 kg. Herbage was harvested daily from 6 swards of contrasting harvest dates (May to December), offering wide variation in feed value to cover the range that would be offered in most practical farm situations. Before the commencement of each study, the experimental sward was harvested at a residual height of 4 cm and allowed to grow for 2 to 4 wk to target an average pregrazing sward height in a range of 8 to 15 cm depending on the time of year. Sheep were housed in individual pens for 14 d and then transferred to individual metabolism crates for 4 d with feed intake and feces and urine outputs measured. Data were analyzed using the linear mixed model procedure to develop prediction equations for feces N, urine N, and manure N outputs using N intake, herbage chemical composition, and digestibility with effects of sex, breed, and experimental periods removed. Nitrogen intake was the best single predictor for N output in feces, urine, and manure, and the value for prediction of manure N output was greater than those for feces N and urine N (0.86 vs. 0.70 and 0.77, respectively; < 0.001). Animal BW and herbage DM, ether extract, NDF, ADF, water soluble carbohydrate, and DE concentrations and N digestibility were also used to predict N outputs because N intake may not be available in commercial practice. The prediction equations for N utilization efficiency indicated that increasing feeding level and ME concentration and reducing N concentration could improve N utilization efficiency and shift N excretion into feces rather than urine ( < 0.001). The equations developed in the current study provide an approach for sheep producers to quantify N excretion against production and, consequently, to develop their own mitigation strategies to reduce the environmental impact of sheep production systems.

Effect of replacing organic grass-clover silage from primary growth with regrowth on N digestion in dairy cows

Clover proportions, and thereby chemical composition of herbage, differ between primary growth (PG) and regrowth (RG) in organic managed grass-clover fields. The characteristics of PG and RG silages suggest different supplementary feeding strategies to sustain an efficient milk production in dairy cows. Silage made of the RG generally offers more crude protein (CP) in the diet than silage made of the PG because of an increasing proportion of clover later in the season. Additionally, grass and clover have different amino acid (AA) profiles. His has been suggested to be the first limiting AA in grass silage, while Met has been suggested to be the primarily limiting AA in red clover silage. Eight rumen cannulated Norwegian Red cows were used in two replicated 4×4 Latin squares with 21-days periods. Organic PG and RG silages were fed ad libitum in four diets with RG replacing PG silage in ratios of 0, 0.33, 0.67 and 1 on dry matter (DM) basis. Changing RG silage proportions from 0 to 1 increased daily CP intake from 2.90 to 3.08kg and rumen NH3-concentrations from 4.9 to 8.4mmol/L, but did not promote a better protein supply. Neither total ruminal outflow of AA nor the AA profile in the small intestine differed between dietary treatments. Met and His were probably the most limiting AA for a higher milk production. Limitations by His may be more related to diets based on PG, while production by cows fed diets based on more RG herbage were more likely limited by Met.

Effect of timing of pasture allocation on production, behavior, rumen function, and metabolism of early lactating dairy cows during autumn

The objective of the present study was to evaluate the effect of timing of pasture allocation on performance, feeding behavior, rumen function and plasma and urine metabolites of early-lactation dairy cows in autumn, strip-grazing a perennial ryegrass sward. Forty-two Holstein Friesian cows were randomly allocated to one of the following treatments: Pasture strips allocated daily at either 10:00h (AM-ALL), 16:50h (PM-ALL) or twice a day at 10:00 and 16:50h (AM–PM). Herbage allowance was 21kg DM/cow/day for all treatments. All cows received a daily allocation of concentrate and grass silage, 3.0 and 3.2kg DM per cow, respectively. Herbage chemical composition differed amongst treatments, as dry matter and WSC contents were greater in PM-ALL than in AM-ALL and AM–PM. Milk yield tended to be greater with PM-ALL (P=0.06) compared with AM-ALL and AM–PM. The concentration of protein tended to be greater with AM–PM (P=0.09) compared with PM-ALL and AM-ALL. Protein and urea concentrations in milk did not differ among treatments. Daily grazing, ruminating and idling times were similar among treatments (P>0.05). During the first 2h, cows in AM-ALL grazed 30 and 15min longer than cows in AM–PM and PM-ALL treatments (P<0.05). Herbage disappearance was greater (P=0.003) in PM-ALL compared with AM-ALL and AM–PM. Treatment did not affect rumen fermentation metabolites, except for the concentration of propionic acid, which was 3% lower for cows in AM–PM compared with AM-ALL and PM-ALL cows. Cows in PM-ALL had lower concentration of urea in plasma 0.88 and 0.68mmol/L less compared with cows in AM-ALL and AM–PM (P=0.04). Concentrations of urinary metabolites were not affected by treatment. These results suggest that timing of pasture strip allocation alters nutrients supplied by herbage to cows, but has only a small effect on herbage dry matter intake. Consequently, allocating the daily pasture strips in the afternoon would tend to increase milk production compared with allocations during the morning (~3) and twice a day (4.4%).

Comparison of specific methane yield of perennial ryegrass prepared by thermal drying versus non-thermal drying in small-scale batch digestion tests

Dried milled biomass samples are frequently utilised in small-scale batch digestion tests. However, herbage chemical composition can be altered by thermal drying, and this may affect specific methane (CH4) yields. Thus, the specific CH4 yield of herbage pre- and post-ensiling, prepared by two preparation methods were compared. Perennial ryegrass samples were either non-thermally dried (i.e. subject to cryogenic conditions, −196°C) or thermally dried (40°C), prior to milling. Specific CH4 yield was subsequently determined in a small-scale batch digestion test. Herbage pre-ensiling yielded 204 and 243LCH4kg−1VSadded and herbage post-ensiling yielded 212 and 188LCH4kg−1VSadded with non-thermal dried and thermal dried sample preparation methods, respectively. Due to opposing effects of thermal drying on CH4 yields of herbage either pre- or post-ensiling, it is not recommended to use thermal drying. Instead, it is recommended that non-thermal dried herbage samples are used in small-scale batch digestion tests.

Cocksfoot, tall fescue and reed canary grass: Dry matter yield, chemical composition and biomass convertibility to methane

The study was aimed to select productive accessions of tall fescue (Festuca arundinacea), cocksfoot (Dactylis glomerata) and reed canary grass (Phalaris arundinacea) by screening germplasm collection, as well as to ascertain the influence of grass maturity on quality of the biomass and it convertibility to the methane. In spaced stand trial, according to the dry matter yield (DMY) per plant (sum of 3 cuts per 2 years) the Lithuanian cvs. Aukštuolė and Navas DS proved to be the most high-yielding accessions (407.7 g and 396.0 g) among the cocksfoot, and tall fescue, respectively, while American cv. Palaton (382.1 g) – among reed canary grass. In the dense stand trial, the annual DMY of Palaton was 12.79 t ha−1 and that of the cvs. Navas DS and Aukštuolė amounted to 10.32 t ha−1 and 10.22 t ha−1. Advancing maturity from the early heading until full flowering increased total solids in the biomass of all the three species by 50.6%–55.6%, the values of NDF digestion by cellulolytic enzymes changed by (−48.0)% to (−58.0) %. The specific methane yields of all grass species and at all development stages varied from 266 L kg−1 VS to 426 L kg−1 VS. The alteration in the bioenergy potential and quality of cocksfoot biomass with advanced maturity stage occurred not as sharply as that of reed canary grass and tall fescue. The dependence of methane yield and energy value of biomass on the chemical composition of herbage was examined.

Morning and afternoon sampling and herbage chemical composition of rotationally stocked elephant grass cv. Napier

Nutrient intake by grazing animals depends on the amount of dry matter consumed and its chemical composition. Forage grasses produce assimilates during the day via photosynthesis to sustain live tissues, plant growth and organic reserves (Taiz and Zeiger 2013). In that context, herbage chemical composition may vary according to variations in the photosynthesis-respiration balance throughout the day. From dawn to dusk photosynthesis predominates and herbage dry matter content and concentration of soluble carbohydrates increase; the reverse happens from dusk to dawn. That could influence nutritive value and nutrient intake of grazing animals (Delagarde et al. 2000), since for a given bite volume the amount of herbage and its composition could vary depending on the time of the day. This phenomenon could have implications for rotationally managed pastures, with time of changing animals from one paddock to the other assuming greater importance. Against that background, the objective of this experiment was to evaluate dry matter (DM) content and the concentrations of soluble carbohydrates (SC), crude protein (CP), neutral (NDF) and acid (ADF) detergent fiber in herbage samples harvested during the morning and afternoon periods from rotationally stocked elephant grass (Pennisetum purpureum) cv. Napier.

A modified method for assessment of the morphological stage of development as a predictor of alfalfa herbage chemical composition and nutritive value

SUMMARYThe aim of the current work was to investigate the possibility of modifying the existing mean stage by weight (MSW) system for evaluating the average development stage in alfalfa. The modification was performed with the aim of providing a simplified system that may be used to evaluate the alfalfa development stage and to predict its nutritive value for ruminants. The suggested modification consists of designating an MSW value on the basis of the fresh weight of all morphological stages in a fresh green plant, as opposed to the original method which is based on weighing all morphological stages dried at 65 °C. The investigation was done on 141 samples of one alfalfa cultivar, collected from the same location during the first three growth cycles: spring growth, the first and the second regrowth. On all collected samples the following characteristics were determined: MSW, modified MSW (mean stage by fresh weight (MSFW)), crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), crude ash (CA) and in vitro organic matter digestibility (IVOMD). For these characteristics of chemical composition (apart from CA) and nutritive value the regressions were calculated for their prediction based on MSW and MSFW. The regressions were derived for individual growth cycles and all cycles combined. A trend for an increase in the coefficient of determination (R2) was identified as well as a decrease in root-mean-square error (RMSE) for all equations derived for all investigated characteristics from the spring growth to the second regrowth. A deviation from this trend was observed only in equations derived for IVOMD. A very high correlation was observed between MSW and MSFW (r=0·999). The determined R2 and RMSE were very similar within the same growth cycle in all regressions for prediction of chemical composition and nutritive value derived for MSW and MSFW. Based on the results of this investigation the MSFW appears to be a quick and accurate method for determining the average development stage in alfalfa which can therefore be recommended for both scientific research and practical field use, as well as for prediction of its chemical composition and nutritive value.

Silage fermentation characteristics of grass species grown under two nitrogen fertilizer inputs and harvested at advancing maturity in the spring growth

AbstractThree of the main management factors affecting herbage chemical composition pre‐ensiling are plant species, rate of nitrogen (N) fertilizer application and stage of maturity at harvest. This study investigated the effects of N fertilizer input and harvest date in the spring growth on the fermentation characteristics, dry matter recovery and aerobic stability of silages prepared from five common grass species. Perennial ryegrass (Lolium perenne cv. Gandalf), Italian ryegrass (Lolium multiflorum cv. Prospect), tall fescue (Festuca arundinacea cv. Fuego), cocksfoot (orchardgrass, Dactylis glomerata cv. Pizza) and timothy (Phleum pratense cv. Erecta) were grown under two inorganic N fertilizer inputs (0 and 125 kg N ha−1), harvested at five dates in the spring growth (fortnightly from 12 May to 7 July; Harvests 1 to 5, respectively) and subsequently ensiled in laboratory pipe silos for a period of 100 days. The ryegrass and tall fescue silages exhibited a lactic acid dominant fermentation and showed little evidence of secondary clostridial activity. In contrast, the challenge to preservation proved greater for the timothy (Harvests 1 and 2) and cocksfoot (Harvests 1 and 5) herbages, with the high pH (&gt;4.2) and high butyric acid (&gt;10 g kg−1 dry matter) and ammonia‐N (&gt;100 g kg−1 N) concentrations being indicative of secondary clostridial activity during storage. Despite the effects on herbage chemical composition prior to ensiling being indicative of a greater challenge to preservation, there was little effect of fertilizer N on the extent or direction of fermentation. Although the Italian ryegrass herbage avoided significant clostridial activity, this herbage incurred the greatest dry matter losses during ensiling. This was particularly evident at early harvest dates suggesting yeast fermentation of sugars, which were surplus to the requirement for a lactic acid dominant fermentation.

In vitro rumen methane output of forb species sampled in spring and summer

The chemical composition, in vitro rumen fermentation variables and methane (CH4) output of a range of common forb species sampled in spring and summer, and grass silage (14 treatments in total), were determined in this study. Dried, milled herbage samples were incubated in an in vitro rumen batch culture with rumen microbial inoculum (rumen fluid) and buffered mineral solution (artificial saliva) at 39 °C for 24 hours. All herbage chemical composition and in vitro rumen fermentation variables were affected (p&lt;0.001) by treatment. Rumex obtusifolius (in spring and summer), Urtica dioica (summer) and Senecio jacobaea (summer) had lower (p&lt;0.05) CH4 outputs relative to feed dry matter incubated compared with grass silage, reflecting their lower extent of in vitro rumen fermentation.

In vitro rumen methane output of perennial ryegrass varieties and perennial grass species harvested throughout the growing season

AbstractThe selection and feeding of perennial ryegrass (Lolium perenne L.) varieties (PRV) or perennial grass species (PGS) may affect enteric methane (CH4) output because of changes in the fermentation dynamics in the rumen as a result of differences in herbage chemical composition. The objective of this study was to determine the effects of PRV and PGS harvested throughout the growing season on herbage chemical composition, and in vitro rumen fermentation variables and CH4 output per unit of feed using a batch culture technique. Seven PRV (Experiment 1: Alto, Arrow, Bealey, Dunluce, Greengold, Malone, Tyrella) and six perennial grasses [Experiment 2: perennial ryegrass (Navan), perennial ryegrass (Portstewart), cocksfoot, meadow fescue, tall fescue, timothy; defined as PGS], managed under a simulated grazing regime, were incubated for 24 h with buffered rumen fluid in two separate experiments. The CH4 output per unit of feed dry‐matter (DM) incubated was not affected (P &gt; 0·05) by PRV (range of mean values across PRV of 23·9–25·3 (SEM 0·41) mL g−1 DM) or by PGS (25·6–26·6 (SEM 0·37) mL g−1 DM). The CH4 output per unit feed DM disappearing during the in vitro rumen incubation was not affected by PRV (33·9–35·1 (SEM 0·70) mL g−1 DM), and although there was an overall PGS effect (P &lt; 0·05; 37·2–40·3 (SEM 0·71) mL g−1 DM), none of the paired contrasts between PGS were significant when analysed using Tukey adjusted comparisons. This outcome reflected either small‐scale or a lack of treatment effects on individual herbage chemical composition (e.g. 454–483 g NDF kg−1 DM, 215–224 g CP kg−1 DM and 94–122 g water‐soluble carbohydrate (WSC) kg−1 DM across PRV; 452–506 g NDF kg−1 DM, 208–243 g CP kg−1 DM and 73–131 g WSC kg−1 DM across PGS) and in vitro rumen fermentation variables. Hence, these results provide no encouragement that choices among the grasses examined, produced within the management regimes operated, would reduce enteric CH4 output per unit of feed in vivo. However, the technique utilized did not take account of animal × PRV or PGS interactions, such as potential differences in intake between animals, that may occur under farm conditions.

Technical note: A simple model to estimate changes in dietary composition of strip-grazed cattle during progressive pasture defoliations

Methodological problems occur in measuring herbage intake and diet quality during short-term (4–24h) progressive defoliations by grazing. Several models were developed to describe pasture component selection by grazing ruminants, particularly sheep. These models contain empirical coefficients to determine preferences that require laborious and data-demanding calibration. The objective was to develop a simple and practical model of changes in diet composition (green:dead) of pastures strip-grazed by dairy cows. The model was based on 3 premises when cows are strip-grazed in relatively homogeneous swards: 1) cows eat dead material only when green leaf and uncontaminated material have been removed; 2) dead material increases toward the bottom of the sward canopy; and 3) cows progressively defoliate pasture in layers. The main simplification in this model was assuming a linear decrease of green mass from the top to the bottom of the sward canopy. Thus, the proportion of green mass in the stratum eaten depended on the proportion of green in the entire sward canopy and its vertical profile. The model offers a simple solution to estimate changes in dietary compositions in pastures strip-grazed by dairy cattle during progressive pasture defoliations. It uses 2 inputs, the green mass proportion of the total herbage mass and the proportion of total herbage mass eaten during grazing. This can be optionally complemented with inputs of herbage chemical composition. The main outputs of the model are the proportions of green and dead herbage mass in the diet. For example, if the green proportion in the sward was 0.5 and the proportion of herbage mass eaten was 0.5, then the diet would be 0.75 green:0.25 dead; assuming 0.8 and 0.4 digestibility for green and dead material, respectively, the diet digestibility would be 0.7.

Short‐term impact of grazing by sheep on vegetation dynamics in a newly created salt‐marsh site

AbstractThe effects of grazing by sheep at a stocking density of c. 1 sheep ha−1 from August to April on total vegetation cover, diversity of plant species, above‐ground plant biomass and concentration of crude protein, neutral‐detergent fibre and acid‐detergent fibre of salt‐marsh vegetation was assessed over a 2‐year period on a newly created salt‐marsh area on the Belgian coast. Assessments were made in both grazed and ungrazed areas in four elevation zones: low, intermediate, high and floodmark zone. The cover of dominant salt‐marsh species (Salicornia europaea, Limonium vulgare and Elymus athericus), plant diversity, plant biomass and chemical composition of herbage were compared between grazed and ungrazed plots, and between 2005 (initial state) and 2007 (after a 2‐year grazing period) using paired t‐tests. Grazing by sheep maintained plant diversity in the high zone, whereas diversity decreased in the ungrazed plots. Grazing had no apparent effect on total vegetation cover and composition of the vegetation. Concentration of crude protein in herbage increased and that of neutral‐detergent fibre decreased in the high and intermediate zones. Expansion of the dominant species of the high zone, E. athericus, was not affected by the stocking density used in the study.