Perennial Ryegrass Swards Research Articles

A comparison of diploid and tetraploid perennial ryegrass and tetraploid ryegrass/white clover swards under continuous sheep stocking at controlled sward heights. 3. Sward characteristics and animal output, years 4–8

Results for years 4–8 of a long‐term grazing experiment on swards of a diploid perennial ryegrass (Lolium perenne), var. Contender (D swards), a tetraploid ryegrass, var. Condesa (T swards) and Condesa with S184 white clover (Trifolium repens) (TC swards), direct sown in May 1987, are presented. The swards were continuously stocked with sheep from 1988 to 1990, as previously reported, and for a further 5 years, 1991–95, at a target sward surface height (SSH) of 4–6 cm. Control of sward height was successfully achieved by variable stocking, except in 1993 when paddocks were set stocked and the resulting mean SSH was 9·3 cm. Grass swards received on average 160 kg N ha−1 year−1; grass/clover swards were mainly not fertilized with N with the exception that they were given 30 kg N ha−1 as a remedial mid‐summer application during a period of low herbage mass on offer in 1994 and 1995.Mean white clover content of the swards fell from 18·2% of herbage dry‐matter (DM) in 1992 to 8·5% in 1993, whereas stolon lengths fell from 120 to 58 m m−2. A return to lower sward heights in 1994–95 resulted in an increase in white clover content to 12·8% by the final sampling in August 1995. Perennial ryegrass content of the grass swards remained high throughout (mean 96·7% in 1995). Perennial ryegrass tiller densities recorded in August 1991, 1993 and 1994 showed consistently significant (P < 0·001) sward differences (3‐year mean 16 600, 13 700 and 10 100 perennial ryegrass tillers m−2 for the D, T and TC swards). In 1994, the year after lax grazing, a low perennial ryegrass tiller density (9100 m−2) and low white clover content (mean 4·3%) in the TC swards resulted in a much lower herbage bulk density than in the grass swards (April–July means 72, 94 and 44 kg OM ha−1 cm−1 for the D, T and TC swards). There was a consistent 40 g d−1 increase in lamb liveweight gain on the TC swards over the T swards, except in 1994. In that year there was a reduction in lamb liveweight gain of 33 g d−1 on the TC swards and a significant increase in ewe liveweight loss (117 g d−1) associated with low herbage bulk density despite optimal sward height. Lamb output (kg liveweight ha−1) on TC swards reflected white clover content, falling from a similar output to that produced from grass given 160 kg N ha−1, at 18% white clover DM content, down to 60% of grass + N swards with around 5% clover. A 6% greater output from the T than the D swards was achieved mainly through higher stocking rate. The experiment demonstrated a rapid, loss in white clover under lax grazing, and showed that the relationship between performance and sward height is also dependent on herbage density. High lamb output from a grass/clover sward was only achieved when the clover content was maintained at 15–20% of the herbage DM.

The effects of treating low dry matter herbage with a bacterial inoculant or formic acid on the intake and performance of lactating dairy cattle

AbstractA randomized block design experiment involving 64 lactating dairy cattle was carried out to evaluate a bacterial inoculant and two rates of formic acid as silage additives. Herbage from the primary growth of a predominantly perennial ryegrass sward was ensiled unwilted using two precision-chop harvesters. Alternate loads of herbage were either untreated (UT) or treated with formic acid applied at the rate of 2·7 l/t grass (LF) and 5·7 l/t grass (HF) or an inoculant enzyme preparation applied at the rate of 2·2 l/t grass (I). The mean dry matter (DM) and water-soluble carbohydrate (WSC) concentrations and buffering capacity of the UT herbage were 148 g/kg, 151 g/kg DM and 638 mEq/kg DM. Inoculant treatment had no effect on the rate of silage fermentation post ensiling relative to the UT silage whereas HF treatment produced a restricted fermented silage. For silages UT, LF, I and HF, pH values were 4·53, 3·89, 4·32 and 4·05 (s.e.d. = 0·061); ammonia nitrogen (N) concentrations were 179, 89, 150 and 73 g/kg total N (s.e.d. = 10·4); butyrate concentrations were 6·0,1·9, 5·1 and 2·0 g/kg DM (s.e.d. = 1·24); and WSC concentrations were 14·4, 35·2, 18·0 and 100·7 g/kg DM (s.e.d. = 1·24), respectively. The silages were offeredad libitum. The UT silage was supplemented with either 2 (UT2), 4 (UT4) or 6 (UT6) kg concentrates per head daily while the LF, I and HF silages were supplemented with 4 kg (LF4,14, HF4) of concentrates. For treatments UT4, LF4, 14 and HF4, silage DM intakes were 9·69, 10·89, 9·93 and 10·89 (average s.e.d. = 0·465) kg/day; fat plus protein yields 1·39,1·44,1·32 and 1·49 (average s.e.d. = 0·057) kg/day; protein concentrations 29·2, 31·1, 29·9 and 30·2 (average s.e.d. = 1·01) g/kg. Inoculant treatment increased N apparent digestibility (P < 0·05) of the total diets relative to UT. The apparent digestibilities of neutral-detergent fibre (P < 0·05) and hemicellulose (P < 0·01) were decreased due to HF treatment. For the production of a constant milk fat plus protein yield it was estimated that an extra 0·63 kg per head per day and 1·04 and 1·77 kg per head per day less concentrate would be required for the I, LF and HF treatments, respectively. It is concluded that relative to the UT treatment, I treatment had no beneficial effects on silage fermentation, total diet apparent digestibility (other than N apparent digestibility) or animal performance. The LF treatment improve lage fermentation and intake, and tended to increase the yield of fat plus protein (P > 0·05) whereas HF treatment restricted silage preservation and increased silage intake and the yields of protein and fat plus protein.

Long-term effects of CO2enrichment and temperature increase on the carbon balance of a temperate grass sward

Perennial ryegrass swards were grown in large containers on a soil, at two N fertilizer supplies and were exposed during two years in highly ventilated plastic tunnels to elevated (700 μl l−1 [CO2) or ambient atmospheric CO2 concentration at outdoor temperature and to a 3°C increase in air temperature in elevated CO2. The irrigation was adjusted to obtain a soil water deficit during summer. The daily net C assimilation was increased in elevated CO2 by 29 and 36% at the low and high N supplies, respectively. Canopies grown in elevated CO2 for 14 to 27 months photosynthetized significantly less rapidly, in both elevated and normal CO2 concentrations, than their counterparts developed in ambient CO2 but the magnitude of this effect was small (−8% to −13%). Elevated CO2 resulted in a large increase in the fructan concentration in the pseudostems and laminae (+46% and +189%, respectively). In elevated CO2, the hexose and sucrose pool increased by 28% in the laminae, whereas it did not vary significantly in the pseudo-stems. A 3°C temperature increase in elevated CO2 did not affect significantly the average WSC concentrations in the pseudostems and laminae. The elevated CO2 effects on the net C assimilation and on the nocturnal shoot respiration were greater in summer than in spring. On average, a 35% increase in the below-ground respiration was measured in elevated CO2. At the high N supply, a 3°C increase in air temperature led to a decline in the below-ground respiration due to a low soil moisture. The below-ground carbon storage was increased by 32% and 96% in elevated CO2 at the low and high N supplies, respectively, with no significant increased temperature effect. The role for the below-ground carbon storage of CO2-induced changes in the root fraction of the grass and of temperature-induced changes in the moisture content of the soil are discussed.

The response of perennial ryegrass/white clover swards to elevated atmospheric CO2 concentrations 1. Effects on competition and species composition and interaction with N supply.

The effects of long-term carbon dioxide enrichment on competition for nutrients and light in a ryegrass/clover association were determined for simulated swards of perennial ryegrass (Lolium perenne L. cv. Parcour) and white clover (Trifolium repens L. cv. Karina), which were grown as monocultures and in three mixtures (25/75, 50/50, 75/25), according to the replacement design, at two levels of nitrogen (N) supply (no additional N and 200 kg N ha-1 ) and at season-long ambient (380 ppm) and elevated (670 ppm) CO2 concentrations, in open-top chambers. Stands were cut four times, at about monthly intervals, to a height of 5 cm. Plant material was separated into different species, fresh and dry weights were determined and the content of macroelements (N, P, K, S, Mg) in both species was measured. In addition, plant height of both species at harvest dates and during several regrowth periods was monitored. Results indicate that both species made demand on different resources and profited from growth in a mixed sward. Co2 related yield increase amounted to 16-4-2 % for white clover whereas the effect of high CO2 on ryegrass yield ranged between -33% and +9% depending on N supply, mixture and year. As a result the contribution of white clover to total yield in mixed swards was significantly enhanced by CO2 enrichment at many harvests in both N supply treatments. Without additional N supply, shoot competition for light was intensified by CO2 enrichment to the disadvantage of ryegrass, since clover petioles grew longer and ryegrass was shorter at elevated CO2 With N fertilization, no marked effect of CO2 enrichment on interspecific competition could be observed. Since clover and total yield were increased by CO2 enrichment, nutrient requirements were also increased and potassium deficiency and increased intraspecific competition of clover for K was observed in the mixtures under elevated CO2 which had the highest nutrient withdrawal. Although white clover profited much more from CO2 enrichment in both N fertilization treatments, the suppression of ryegrass in mixed swards could only be observed under low N conditions. Generally, the effect of N fertilization on competitive interference between both species was much greater than the effect of CO2 enrichment and it is suggested that the effect of elevated CO2 on the balance of species and the outcome of competition in a grass/clover sward is mainly dependent on the N status.

The effects of offering sucrose and fishmeal to dairy cows receiving different levels of concentrates on food intake and animal performance

Quota restricts the volume and butterfat content of milk at farm level. However there is no restriction on milk protein concentration. In a previous study in the present series, sucrose supplementation of cows in late lactation offered grass silage based diets increased milk protein concentration, while supplementation with sucrose and fishmeal increased protein concentration and the yields of milk, protein and fat plus protein equivalent to, or greater than, that obtained from the parent herbage. The present study was undertaken to evaluate the effects of partially replacing a concentrate supplement with sucrose and/or fishmeal, over a range of concentrate feed levels, on forage intake, milk production and composition.Herbage was harvested from the primary growth of a predominantly perennial ryegrass sward, unwilted, precision chopped and treated with a formic acid based additive (Add-Safe, Trouw Nutrition) at 2.85 l/t. A concentrate was formulated consisting of unmolassed sugar beet pulp, barley, soyabean meal and minerals and vitamins. Four complete diets were prepared consisting of the silage and either concentrate (20 g/kg fresh silage) (SC), concentrate and sucrose (each at 10 g/kg fresh silage) (SCS) concentrate and fishmeal (each at 10 g/kg fresh silage) (SCF) or sucrose and fishmeal (each at 10 g/kg fresh silage) (SSF).

The diagnosis and recommendation integrated system (DRIS) for diagnosing the nutrient status of grassland swards : I. Model establishment

Herbage analysis offers a definitive means of determining the N, P, K and S status of perennial ryegrass swards. Unfortunately, the results of such analyses can be difficult to interpret, simply because the minimum or 'critical' concentration of a nutrient in plant tissue for optimum growth, varies both with crop age and with changes in the concentrations of other nutrients. The Diagnosis and Recommendation Integrated System (DRIS) could help to improve the reliability of such interpretations. Diagnoses made using DRIS are based on relative rather than on absolute concentrations of nutrients in plant tissue, and as such should be comparatively independent of crop age.

The effects of regrowth and maintenance height on a grass sward with a high density of tillers

AbstractA perennial ryegrass sward was grazed by sheep in April 1993 to a target sward surface height (SSH) of 3 cm to create a high density of grass tillers. From 3 May, the sheep were removed and small plots were established on the sward, when the average tiller density (± s.e.) was 35 900 ± 420 live tillers m−2. Different regrowth treatments were then imposed by allowing plots to regrow to target SSHs of 6 cm (18 g dry matter (DM) M−2), 9 cm (78 g DM m−2), 12 cm (132 g DM m−2) or 15 cm (197 g DM m−2). The plots were then maintained by cutting at either 6 or 9 cm SSH until the end of the experiment on 30 September. Live tiller density was reduced by regrowth beyond 8.9 cm (78 g DM m−2, P<0.001) and leaf‐stem ratio and in vitro organic matter digestibility were reduced by regrowth beyond 6.1 cm (18 g DM m−2, P < 0.05). The effect on live tiller density was sustained through the remainder of the season. From the beginning of June to the end of September, maintenance of SSH at an average of 9.1 cm compared with 6.4 cm also resulted in lower live tiller density, live‐dead tiller ratio and leaf‐stem ratio and higher herbage mass (at least P< 0. 05). There were significant interactions between regrowth SSH and maintenance SSH, so that leaf‐stem ratio, live‐dead tiller ratio and live tiller density were reduced by regrowth to a SSH of 16–4 cm followed by maintenance at 9.1 cm, compared with regrowth to 6.1 cm and maintenance at 6.4 cm.

Grass silage as a basic feed for store lambs. 2. Effect of harvesting system and chop length of grass silage on silage intake and performance of store lambs

AbstractA perennial ryegrass sward was cut at a leafy stage of growth and harvested with different harvesters to produce silages differing in chop length to evaluate the effect of silage chop length on silage intake and on the performance of store Iambs when silage was fed as the sole diet. The silage was harvested in late May either as long silage (L), single‐chopped (S). double‐chopped (D). long precision‐chopped (LP) or medium precision‐chopped (MP) silage with (he appropriate machinery. The silages were treated with formic acid at 2.5 1 t−1. were well preserved (pH 3.7–3.8) and were of high dry‐matter digestibility [749–810 g DMD kg−1 dry‐matter (DM)]. The silages were fed ad libitum as the sole diet to Suffolk crossbred store lambs over a period of 11 weeks.Silage intake and lamb performance progressively increased as silage chop length declined from 32.4 cm (L) to 6.8 cm (MP). Silage intakes were 572, 661, 750, 893 and 1129 (± 21) g DM d−1 for silages L, S, D, LP and MP respectively. The corresponding daily liveweight gains were ‐3, 40, 53, 85 and 151 (± 7.6) g d−l. Similar increases in empty body weight gain and carcass weight gain were obtained as silage chop length declined.Rumen retention time (RRT), estimated from the rumen contents of the lambs at slaughter and their silage intake in the week before slaughter, was much shorter for silages LP and MP compared with silages L or S. Silage intake was negatively related to RRT(b= ‐24.5 ± 6.1 gDM h−l RRT).The results of this study showed that high intakes of grass silage and liveweight gains were achieved when grass was cut at a leafy stage of growth and harvested with a precision‐chop harvester set to produce a moderate chop length (7 cm). The feeding of long or flail‐chopped silages resulted in lower intakes and lower liveweight gains.

Intra-ruminal particle size reduction in deer fed fresh perennial ryegrass (Lolium perenne) or chicory (Cichorium intybus)

SUMMARYPure swards of chicory (Cichorium intybus) and perennial ryegrass{Lolium perenne)were grown at Palmerston North, New Zealand. They were cut daily and fed fresh at 2 kg dry matter (DM)/day to ten hand-reared rumen fistulated castrated red deer stags kept in metabolism crates in April and October 1994. The efficiency of particle breakdown during the time allowed for rumination (<C.PART>) to below the critical size required to leave the rumen (passage through a 1 mm sieve) and jaw activities (i.e. eating and ruminating) were measured. Total eating time and the number of eating bouts were similar for deer fed each forage, but deer fed chicory had a greater chewing rate during eating (97·4 v. 81·0 chews/min), and a higher number of chews/g DM eaten (36·2 v. 31·5). Deer fed chicory had lower total ruminating time (30 v. 257 min/22·5 h), lower number of boli ruminated (38 v. 440/22·5 h), lower number of rumination bouts (5·4 v. 16·2/22·5 h) and less chews per minute ruminating (16·5 v. 44·3) than those fed perennial ryegrass. Of the ten deer used to measure (<C.PART>), only four ruminated when fed chicory compared with nine when fed perennial ryegrass.Deer fed chicory had a higher efficiency of particle breakdown (<C.PART>; 0-64 v. 0·42), higher fractional degradation of particles > 1 mm (9·2 v. 5·1 %/h) and faster fractional disappearance of total DM from the rumen (10·2 v. 5·3 %/h). All three measurements for chicory were similar in deer that did or did not ruminate, but with perennial ryegrass, all values were considerably reduced in the deer that did not ruminate.It was concluded that chicory can be broken down faster in the rumen, with less rumination being required than for perennial ryegrass, and that some deer (60%) could break down swallowed chicory to below the critical particle size without ruminating at all. The faster clearance of DM from the rumen explains the high voluntary feed intake (VFI) of deer grazing chicory. Future research needs to be done to partition rumen fractional disappearance rate into its components, rumen fractional degradation rate and rumen fractional outflow rate in deer fed chicory and perennial ryegrass.

Effects of inoculant treatment on ryegrass silage fermentation, digestibility, rumen fementation, intake and performance of lactating dairy cattle

AbstractA randomized block experiment involving thirty‐six lactating dairy cattle was carried out to evaluate a bacterial inoculant (Grazyme Grobac, Agritech), containing bacteria, enzymes and a rumen enhancer, as a silage additive. Herbage from the primary regrowth of predominantly perennial ryegrass swards was ensiled unwilted and precision‐chopped after a 51‐d growth interval on 4 and 5 August. Alternate loads of herbage were ensiled either untreated (C) or treated with formic acid at a rate of 2.65 1 (t herbage)−1 (F) or the inoculant at a rate of 0.64 kg (t grass)−1 (I). The treatments were harvested using the same harvester in the rotation of I, F and C treatments. Mean dry‐matter (DM), water‐soluble carbohydrate and nitrate nitrogen (N) concentrations and buffering capacity of the C herbages at ensiling were 198 g kg−1, 18 2 g kg−1, 290 mg (1 juice)−1 and 379 mequiv. (kg DM)−1 respectively. For silages C, F and I pH values were 3.7, 3.8 and 3.8 and ammonia N concentrations 61, 43 and 58 g (kg total N)−1 respectively. Inoculant treatment did not alter aerobic stability of the silages, whereas formic acid treatment increased it. The silages were offered ad libitum and supplemented with 5 kg of concentrates per head daily. For treatments C, F and I silage DM intakes were 10.8, 11.2 and 10.8 (s.e. 0–33) kg d−1, milk yields 21.3, 20.9 and 20.7 (s.e. 0.52) kg d−1, fat concentrations 38.3, 40.3 and 37.2 (s.e. 0.83) g kg−1 and protein concentrations 30.8, 32.6 and 32.6 (s.e. 0.49) g kg−1 respectively. Inoculant treatment did not alter (P0.05) the digestibility coefficients of the total diets, whereas formic acid treatment decreased DM (P0.05), organic matter (P0.05), neutral detergent fibre (P0.01) and hemicellulose (P0.01) digestibilities. Formic acid treatment altered rumen fermentation patterns, whereas inoculant treatment had no effect. It is concluded that, relative to a well‐preserved untreated silage, additive treatment did not alter DM intake, milk yield or fat plus protein yield. However, both additive treatments increased milk protein concentrations and formic acid treatment increased milk fat concentration relative to the well‐preserved, untreated silage.

The effects of sward characteristics and supplement type on the herbage intake and milk production of summer‐calving cows

AbstractHigh (H; 27 350 m−1:) or low (L. 13 300 m‐1) tiller density perennial ryegrass swards were created in the mid‐ and late grazing season by imposing different sward heights in the spring. Summer‐calving cows then grazed these swards from 6 June to 2 September 1992 and were offered 5 kg fresh weight hd−1 d−1 of either a barley (S) or a molassed sugar beet pulp (F) based supplement. The factorial combination of sward and supplement types resulted in four experimental swards being grazed by thirteen Holstein/Friesian cows each.Supplement F contained more crude fibre (110 vs. 58 g kg−1) and less metabolizable energy [12–5 vs. 13–2 MJ kg−1 dry matter (DM)] than supplement S. Herbage on the H sward contained more metabolizable energy (11–9 vs. 104 MJ kg−1 DM) and crude protein (232 vs. 205 g kg−1 DM), had fewer rejected areas f 16–5 vs. 26–9%) and a higher live‐dead tiller ratio (4–6 vs. 2–1) than that on the L sward.Sward, but not supplement type, significantly affected the intake of grazed herbage (P<0–001). On average, the herbage intakes of cows grazing II swards were higher than for L swards (14–5 vs. 11 6kg DM d−1) and those of cows on the S and F supplements were 12–6 and 13–5 kg DM d−1 respectively. Averaged over the grazing period, sward and supplement had no significant effects on milk yield, milk composition or yield of constituents. When expressed on an average weekly basis, cows grazing an L sward and offered the F supplement on occasions had significantly lower milk yields and higher milk fat contents (P<005) than those grazing an H sward and offered the S supplement. There were no significant effects on cow live weight or condition score change. The results suggested that grazing swards with a high density of live tillers increased herbage intakes and on occasions milk yield, relative to low density swards. However, small increases in energy intake from sward and supplement effects were used primarily to ameliorate liveweight loss.

Effects of applying a bacterial inoculant to silage immediately before feeding on silage intake, digestibility, degradability and rumen volatile fatty acid concentrations in growing beef cattle

AbstractIn an experiment, involving twelve male cattle (initially 235 kg live weight), the effects of applying lactic acid bacteria [Lactobacillus plantarum; 109 colony‐forming units (g fresh silage)−1] to grass silage, immediately prior to that silage being fed, on dry‐matter (DM) intake of the silage, degradability of nitrogen (N) and fibre in the rumen, total tract digestibility and composition of rumen fluid in the animals were examined. A grass silage, which had been made from the primary growth of a predominantly perennial ryegrass sward, was offered as the sole diet. The inoculant was applied to the silage at the rate of 2 g of freeze‐dried powder reconstituted in 12 ml of water (kg fresh silage)−1 immediately prior to that silage being fed and an equivalent amount of water was applied to the silage in the control treatment. The two diets were compared in a change‐over design. The silage was well preserved, having a pH and concentrations of ammonia N and butyrate of 3.72, 74 g (kg total N)−1 and 0.11 g (kg DM)−1 respectively. Application of the inoculant significantly increased true protein, acid‐insoluble N and water‐soluble carbohydrate concentrations (P < 0.001) in the diet. Silage DM intake was not significantly increased (P= 0.072) by this of inoculant treatment, which had no significant effect (P > 0.05) on rumen degradability or total tract digestibility of DM, N, neutral detergent fibre or modified acid detergent fibre. Rumen pH, ammonia concentration or the molar proportions of volatile fatty acids were not altered (P>0.05) by inoculant treatment. It is concluded that application of the inoculant to the silage prior to silage being fed did not significantly affect silage DM intake, total tract digestibility, or degradability or fermentation in the rumen of cattle offered grass silage as the sole diet. It is also concluded that the results of this experiment provide no evidence that the mode of action of L plantarum, applied as an additive to grass at ensiling in previous studies, is through ‘direct’ effects in the rumen.

Long-term effects of CO2 enrichment and temperature increase on a temperate grass sward

Perennial ryegrass swards were grown in large containers on a soil and were exposed during two years to elevated (700 μL L-1) or ambient atmospheric CO2 concentration at outdoor temperature and to a 3 °C increase in air temperature in elevated CO2. The nitrogen nutrition of the grass sward was studied at two sub-optimal (160 and 530 kg N ha-1 y-1) and one non-limiting (1000 kg N ha-1 y-1) N fertilizer supplies. At cutting date, elevated CO2 reduced by 25 to 33%, on average, the leaf N concentration per unit mass. Due to an increase in the leaf blade weight per unit area in elevated CO2, this decline did not translate for all cuts in a lower N concentration per unit leaf blade area. With the non-limiting N fertilizer supply, the leaf N concentration (% N) declined with the shoot dry-matter (DM) according to highly significant power models in ambient (% N=4.9 DM-0.38) and in elevated (%N=5.3 DM-0.52) CO2. The difference between both regressions was significant and indicated a lower critical leaf N concentration in elevated than in ambient CO2 for high, but not for low values of shoot biomass. With the sub-optimal N fertilizer supplies, the nitrogen nutrition index of the grass sward, calculated as the ratio of the actual to the critical leaf N concentration, was significantly lowered in elevated CO2. This indicated a lower inorganic N availability for the grass plants in elevated CO2, which was also apparent from the significant declines in the annual nitrogen yield of the grass sward and in the nitrate leaching during winter. For most cuts, the harvested fraction of the plant dry-matter decreased in elevated CO2 due, on average, to a 45–52% increase in the root phytomass. In the same way, a smaller share of the plant total nitrogen was harvested by cutting, due, on average, to a 25–41% increase in the N content of roots. The annual means of the DM and N harvest indices were highly correlated to the annual means of the nitrogen nutrition index. Changes in the harvest index and in the nitrogen nutrition index between ambient and elevated CO2 were also positively correlated. The possible implication of changes in the soil introgen cycle and of a limitation in the shoot growth potential of the grass in elevated. CO2 is discussed.

Effects of elevated carbon dioxide concentrations on agricultural grassland production

Open-top chambers have been used on a field-grown perennial ryegrass ( Lolium perenne) sward to investigate the long-term responses to elevated CO 2 concentrations. A concentration of 2 × ambient CO 2 increased annual harvestable yield by about 20%, but the proportional stimulation was not constant throughout the growing season nor from one season to the next. Other effects of elevated CO 2 were an increase in carbon/nitrogen ratio of tissues and a decrease in specific leaf area and canopy conductance. There was no effect of CO 2 on the digestibility of the harvested grass. It is likely that climate change during the next century will lead to significant increases in agricultural grassland production in northern Europe. Production will be stimulated by a direct fertiliser effect due to the increasing CO 2 concentration of the atmosphere.

Effects of inoculant treatment on silage fermentation and digestibility and on rumen fermentation, dry matter intake and performance of lactating dairy cattle

Recent studies have shown that the use of an effective bacterial inoculant as a silage additive results in improvements in animal performance of dairy and beef cattle. Treatment with an inoculant based on a single strain of L. plantarum has increased silage digestibility and altered the composition of rumen fluid in beef cattle (Keady and Steen, 1994 and 1995). Inoculant products vary in composition, containing different bacteria species and numbers, possibly with the addition of enzymes, clostridiaphages and rumen enhancers. The present study was designed to evaluate an inoculant containing mixed strains of bacteria, enzymes, bacteriophages and a rumen enhancer through lactating dairy cattle and to study its effects on diet digestibility and rumen fermentation patterns.Herbage was harvested from the primary regrowth of a predominantly perennial ryegrass sward, which had received 99 kg nitrogen (N) per ha after the previous harvest, after a fifty-one day regrowth interval. Herbage was mown down using a mower conditioner and picked up immediately, unwilled, using a precision chop harvester.

An examination of the effect of concentrate energy source on milk production of dairy cows offered grass silages with differing intake characteristics

Considerable progress has been made recently at this Institute in improving the accuracy of prediction of silage intake when offered as the sole diet. However in most farm situations, silage is usually supplemented with varying levels and types of concentrate when offered to dairy cattle. The aim of the present study was to examine the effects of concentrate energy source on the voluntary food intake and milk yield and composition of lactating dairy cattle when offered a diverse range of grass silages.A total of five grass silages were used in the study, silages A, B and D were produced from primary regrowths, while silages C and E were produced from second regrowths of perennial ryegrass swards. Silages A, B, C, D and E were ensiled after 48, 24, 0, 0 and 24 hour wilting periods. Silages A and C were ensiled untreated, B and D treated with an inoculant, and silage E treated with a formic acid based additive.

Effects of inoculant treatment on silage fermentation and digestibility and on rumen fermentation, dry matter intake and performance of lactating dairy cattle

Recent studies have shown that the use of an effective bacterial inoculant as a silage additive results in improvements in animal performance of dairy and beef cattle. Treatment with an inoculant based on a single strain of L. plantarum has increased silage digestibility and altered the composition of rumen fluid in beef cattle (Keady and Steen, 1994 and 1995). Inoculant products vary in composition, containing different bacteria species and numbers, possibly with the addition of enzymes, clostridiaphages and rumen enhancers. The present study was designed to evaluate an inoculant containing mixed strains of bacteria, enzymes, bacteriophages and a rumen enhancer through lactating dairy cattle and to study its effects on diet digestibility and rumen fermentation patterns.Herbage was harvested from the primary regrowth of a predominantly perennial ryegrass sward, which had received 99 kg nitrogen (N) per ha after the previous harvest, after a fifty-one day regrowth interval. Herbage was mown down using a mower conditioner and picked up immediately, unwilled, using a precision chop harvester.

An examination of the effect of concentrate energy source on milk production of dairy cows offered grass silages with differing intake characteristics

Considerable progress has been made recently at this Institute in improving the accuracy of prediction of silage intake when offered as the sole diet. However in most farm situations, silage is usually supplemented with varying levels and types of concentrate when offered to dairy cattle. The aim of the present study was to examine the effects of concentrate energy source on the voluntary food intake and milk yield and composition of lactating dairy cattle when offered a diverse range of grass silages.A total of five grass silages were used in the study, silages A, B and D were produced from primary regrowths, while silages C and E were produced from second regrowths of perennial ryegrass swards. Silages A, B, C, D and E were ensiled after 48, 24, 0, 0 and 24 hour wilting periods. Silages A and C were ensiled untreated, B and D treated with an inoculant, and silage E treated with a formic acid based additive.

The effect of tractor wheel passes on herbage production from diploid and tetraploid ryegrass swards

AbstractDiploid and tetraploid perennial ryegrass swards were managed under an intensive silage system over 3 years. The swards were subjected to five tractor wheel pass treatments to simulate combinations of silage operations in the field from cutting, tedding, lifting and fertilizing. Wheel tracking was applied uniformly over the swards after June, July, August and October cuts each year.Tractor wheel passes caused mean reductions in herbage dry matter (DM) yield during successive years of 14%, 6% and 9% compared with their absence, and frequent or delayed wheel passes affected yield more adversely than infrequent or undelayed wheel passes. Nitrogen and mineral concentrations in herbage and nutrient offtakes were also generally reduced but organic matter digestibility (OMD) was unaffected. Soil assessments each autumn showed that soil bulk density increased in the wheel‐pass treatments, particularly when frequently applied. The two sward types responded in a similar manner to the wheel‐tracking treatments, probably because they had similar cushioning capability, the disadvantage of the tetraploid in terms of fewer tillers in relation to the diploid being compensated for by larger tiller size. Soil compaction, with its adverse effect on sward growth vigour, and direct wheel damage to young regrowth will be lessened by minimizing wheel traffic on silage swards and undertaking operations over short rather than long periods.

The effect of propiconazole on foliar fungal diseases, herbage yield and quality of perennial ryegrass

The fungicide propiconazole, applied as a foliar spray to swards of perennial ryegrass ( Lolium perenne) at four sites in England from 1990 to 1992, reduced the incidence of powdery mildew ( Blumeria graminis), Drechslera leaf spot ( Drechslera spp.) and Rhynchosporium leaf blotch ( Rhynchosporium spp.), increased the number of leaves per tiller and reduced the proportion of dead leaves. Propiconazole increased yield, by 6–7%, at harvests in mid-May, but had no effect at harvests in late June, when the cut herbage was dried to produce hay, although in one hay crop, in vitro organic matter digestibility was increased from 575.6 to 588.5 g kg −1 ( P < 0.05). Further research is required to determine the rationale and optimum timing of fungicide application to grassland.