A simulation model of a dairy forage system to evaluate feeding management strategies with spring rotational grazing

Abstract To counteract a decrease in the availability of grazing for feeding dairy cows in France, a simulation model is proposed in the paper, which combines decision and agronomic submodels to study forage system management strategies compatible with spring grazing use. Nine strategies were tested with the model using a sequence of 16 climatic years. Three of these strategies come from a survey in south‐west France and six others were designed with research scientists or farm advisors. The strategies differ in the duration of maize silage feeding, the area dedicated to maize silage and the area dedicated to grass silage. Results from simulation models show that the consequence of a large and constant maize silage area is a high maize silage overstock if there is an early turnout or a high grass silage overstock if turnout is late. The consequence of a low maize area is a high grazing duration combined in some years with feeding shortages. Strategies that have no feeding shortage and a low level of maize and grass silage overstock have a high grazing duration and have no constant maize or grass silage areas. The solution proposed to avoid climatic risk, and its consequences on feeding, is based on two procedures: use of reserve areas for production and allowing the production programme to be modified to take into account fresh information, especially weather records.     

Performance and environmental effects of forage production on sandy soils. III. Energy efficiency in forage production from grassland and maize for silage

Based on experimental data gathered in a research project on nitrogen fluxes in intensive dairy farming in Northern Germany, an analysis of fossil energy input and energy efficiency in forage production from permanent grassland and maize for silage was conducted. Field experiments comprised different defoliation systems and different rates of mineral N fertilizer and slurry application. Each change from grazing to cutting in grassland systems reduced the energy efficiency. Energy efficiency consistently decreased with increasing rates of mineral N application. In the production of maize for silage, maximum energy efficiency was obtained with an application of 50 kg N ha^?1 from slurry only. Net energy yields of maize for silage were much higher than that of grassland when compared at the same level of fossil energy and nitrogen fertilizer input. Considering both nitrate‐leaching losses and a necessary minimum quantity of grass herbage in a well‐balanced ration, it is suggested that a high proportion of maize for silage in combination with N‐unfertilized grass/clover swards used in a mixed cutting/grazing system represents a good trade‐off between the leaching of nitrates and energy efficiency.     

The use of conserved forage as a supplement for grazing dairy cows

The difficulty in matching the herbage requirements of grazing dairy cows to herbage production, due mainly to the unpredictability of the latter., causes stocking rates to be too low for maximum per hectare production and, thus, cows to be underfed at certain times in the grazing season. Conserved forage may be used as a supplement for grazing dairy cows in order to reduce variation in forage intake by the cow, to allow pasture stocking rates to be increased and to increase the efficiency of land use. The effect of offering conserved forage with herbage on intakes and production is reviewed in comparison to both ad libitum and restricted herbage. Total nutrient intakes and milk fat + protein yields are reduced for cows offered herbage and supplementary forage compared with cows offered ad libitum herbage, but increased compared with cows offered a restricted herbage level. Increasing pasture stocking rates may allow increases in utilized metabolizable energy levels from grassland but further research is needed in this area. Both grass and maize silage supplements offer potential for increasing the efficiency of land use, but in the case of grass silage this is only achieved in the best management practices.     

Economic modelling of an integrated grazed and conserved perennial ryegrass forage production system

The Grange Feed Costing Model was modified to simulate the economic implications of grassland management strategies for a grass‐based suckler beef calf‐to‐weanling system at the whole‐farm level. The modified model enabled costing of annual grass consumed as grazed grass and silage when the farm grazing and conservation areas are integrated. Grass growth data from sites in the south, east and north of Ireland were used. Sixty‐three scenarios were simulated, enabling analysis of site, stocking rate and silage strategy effects on total annual feed cost for the grass forage production system. Total annual feed cost (of grazed grass and grass silage) ranged from €96 to €111 per 1000 UFL (Unité Fourragère Lait) and €411 to €456 per beef cow unit (CU). The silage strategy with respect to the number of harvests and whether the silage area was grazed in the spring had negligible impact on annual total feed cost per CU. However, a tendency towards reduced annual feed cost under a two harvest, relative to a one harvest, silage strategy was observed. The lowest cost stocking rate was 2 CU ha^?1. Site‐specific differences such as seasonal growth distribution and nitrogen fertilizer response rate had the greatest influence on the annual cost of the grass‐based feeding system.     

FACTORS LIMITING ANIMAL PRODUCTION FROM GRAZED PASTURE*

Animal production from intensively managed pasture (240 units N/ac or 300 kg N/ha applied annually) should in theory reach 11,000 Ib/ac (12,500 kg/ha) of milk or 1550 lb/ac (1750 kg/ha) of liveweight gain per year. The figure for theoretical milk production is achieved in experiments, although rarely approached in commercial practice; the figure for liveweight gain is never approached, either experimentally or commercially. On commereial farms in Britain, the average stocking rate for grazed lowland pasture in 1971 was about 0·74 cow equivalents/ac (l±82/ha), compared with a theoretical target of 1·9/ac; in 1969 fertilizer N application was about 48 units/ae (60 kg/ha). The main purpose of this paper is to suggest reasons for the differences between practical, experimental and theoretical levels of production. Economic factors may deter farmers from intensifying their grassland management, but the deterrent to high stocking rates may be the fear of running out of grass. In practice, ungrazed herbage is used as a buffer, but other feeds might be used for this purpose. Concentrates, pelleted roughages and even long dried grass and silage are too attractive to grazing beef cattle to be offered to appetite; but silage might be used as a long-term buffer. Fouling of pasture reduces efficiency of harvesting, but attempts to overcome this effect, by conditioning of grazing animals, spreading excreta or by alternation of grazing and cutting, have largely been unsuccessful. High production per unit area cannot be achieved without high production per animal. Legumes have often been found to increase production per animal, and a technique has been developed for growing red-clover and grass in adjoining areas and grazing them together. The clover was grazed satisfactorily by dairy cows (and caused no bloat) but failed to increase milk yield per animal. Recent calorimetric studies of grass have shown that the net energy value of digestible organic matter is variable, and in particular is low for late-season herbage.     

Herbage growth and utilized output from grassland on dairy farms in southwest England: case studies of five farms, 1982 and 1983. II. Herbage utilization

Utilized Metabolizable Energy output was calculated and herbage utilization evaluated in two contrasting years on five profitable farms representing a range of soil types.
Annual UME output was 72 GJ ha^-1 on average, with a range from 47 to 91 GJ ha^-1. Grazed grass provided 66% of the utilized metabolizable energy, and conserved grass 34%. Higher utilized metabolizable energy output was not always obtained at higher fertilizer N inputs, even when soil moisture conditions favoured herbage growth.
The efficiency of utilization of herbage conserved (almost always as silage rather than hay) was calculated by expressing utilized metabolizable energy output as a proportion of the quantity of herbage cut, measured by swath weighings; the mean value was 64%, with a range from 55 to 73%. Cellulose analyses indicated that mean dry matter losses via CO₂ and effluent were 10%; the remaining 26% loss appeared to be due to physical losses in the field, surface waste and wastage at feedout.
For grazed herbage the utilized metabolizable energy output was expressed as a proportion of herbage accumulation measured over 28-day periods. The resultant apparent efficiency of utilization averaged 67%, with a wide range from 51 to 83%. The lowest values were on badly drained farms.
It is suggested that:
(i) there is considerable potential for increasing output from grazing on dairy farms; higher grazing pressure and more flexible management would be needed. Targets should probably be set lower on badly drained soils;
(ii) there is great potential for increasing the efficiency of utilization of conserved forage, by careful application of existing technology;
(iii) on the farms studied the utilized metabolizable energy output from grazed and conserved fields appeared to be similar.     

A REVIEW OF NUTRIENT LOSSES AND EFFICIENCY OF CONSERVING HERBAGE AS SILAGE, BARN-DRIED HAY AND FIELD-CURED HAY

A review of American literature indicates that barn drying of hay and silage making are both greatly superior to the field curing of hay in preserving nutrients. This is true of total dry matter, crude protein, ether extract and ash; crude-fibre losses are greater in silage making. Energy losses run parallel with dry matter. Bam drying of hay with heat preserves a rather greater proportion of nutrients than does silage making.
Chemical composition and digestibility are mostly a function of stage of maturity of the crop at the time of cutting. Actual carbohydrate (energy) losses are greater than protein losses in all methods. The influence of method of conservation is unimportant if conservation is properly carried out, but considerable deterioration can result from bad application. Field-cured hay usually suffers most in this respect, due to weather damage.
The conservation processes reviewed have no influence per se on feeding value where each is applied under ideal conditions. Differences found in practice are usually linked to the stage of maturity or to weather damage, which explains the usually superior feeding value of silage and barn-dried hay over field-cured hay.
When the efficiency of each method is compared by determining the quantity of milk produced from equal areas of forage, conserved in the three different ways, barn-dried hay is somewhat superior to silage, but both are greatly superior to field-cured hay.     

GRASSLAND SYSTEMS*

Reference is made to the contrast between actual and potential yields from grassland, to the main factors affecting the development of effective grassland systems for dairy cows and to the technical developments which are now available. The unrealized potential for simplification and increased output from grazing systems is stressed. The available information on the effect of mechanical grazing and storage feeding systems is reviewed and the practical advantages and problems of these systems summarized. Simple calculations are made of the capital involved in large herd organization and the increases in herbage yield or efficiency of use needed to justify this additional expenditure. For large herds a relatively small increase (10%) in output per acre would justify the annual capital charge and feed cost for mechanical harvesting or tower silage; greater increases would be needed for grass drying (22%) or for tower silos in smaller (100-cow) herds (16%). Other important but less tangible factors influencing the choice of system are referred to. It is considered that unless herbage yields can be greatly increased by the use of mechanical grazing compared with normal grazing, the practical difficulties of this method outweigh its advantages. If tower silos allow more efficient conservation and easier feeding, they may be worthwhile, but the search should continue for cheaper alternatives. Only in very large-scale enterprises can grass drying, solely to produce cattle feed, be justified, although this method offers the greatest potential. In view of the complexities, it is suggested that computer models may help to resolve such problems and one such study is briefly described.     

A comparison of milk yields and methane production from three contrasting high‐yielding dairy cattle feeding regimes: Cut‐and‐carry,partial grazing and total mixed ration

There have been reductions in grazing cattle and corresponding increases in mixed diets across many regions. Mixed diets consist of silage, grains, legumes and other herbaceous plants (termed total mixed ration, TMR). TMR has been associated with increased milk yields but has also been linked to increased enteric methane production. We measured milk yields and methane production from high‐yielding Holstein‐Friesian cattle after substituting 29%–36% of a TMR diet with grass. Two feeding treatments were compared with a diet of TMR: grass grazed at pasture and grass cut in the field and delivered to housed cattle (termed cut‐and‐carry). Each feeding treatment was fed to 15 cattle, and the experiment was conducted in South‐west Scotland. Using a laser methane detector, we measured a twofold and fourfold decline in enteric methane production for the cut‐and‐carry and grazing groups, respectively, when the animals consumed grass. TMR was consumed by both grass‐fed groups overnight, so daily values were adjusted to include elevated methane production during this period. This revealed that methane production for the cut‐and‐carry and grazing groups was 17% and 39% lower than for the TMR‐fed group respectively. Milk yields were maintained for all three groups, and the efficiency of milk production per unit of methane was substantially greater for the two grass‐fed groups. A shift away from exclusively feeding TMR by adding fresh grass to the diets of cattle could contribute to meeting emissions targets and could also represent an economically sustainable climate change mitigation strategy.     

The effects of offering a range of forage and concentrate supplements on milk production and dry matter intake of grazing dairy cows

An experiment was undertaken to examine the effect of supplement type on herbage intake, total dry matter (DM) intake, animal performance and nitrogen utilization with grazing dairy cows. Twenty‐four spring‐calving dairy cows were allocated to one of six treatments in a partially balanced changeover design with five periods of four weeks. The six treatments were no supplement (NONE), or supplementation with either grass silage (GS), whole‐crop wheat silage (WS), maize silage (MS), rapidly degradable concentrate (RC) or slowly degradable concentrate (SC). Cows were rotationally grazed with a mean herbage allowance of 20·5 kg DM per cow per day, measured above 4 cm. Forage supplements were offered for approximately 2 h immediately after each morning milking, with cows on NONE, RC and SC treatments returning to the grazing paddock immediately after milking. Cows on treatment MS had a significantly higher supplement DM intake than the other treatments but a significantly lower grass DM intake than the other treatments, resulting in no significant difference in total DM intake when compared with cows on treatments WS, RC and SC. Concentrate type had no significant effect on herbage intake, milk yield, milk composition or yield of milk components. The yield of milk fat and milk protein was significantly higher on treatments MS, RC and SC compared with treatments NONE, GS and WS. The results indicate that despite a relatively high substitution rate, maize silage can be a useful supplement for the grazing dairy cow.     

THE EFFECT OF STAGE OF GROWTH AT DEFOLIATION ON WHITE CLOVER IN MIXED SWARDS

Four experiments are described in which various defoliation methods and frequencies were imposed on grass/white-clover swards. Clover was not reduced in any of these hy increasing the length of growth period or hy cutting at a late stage of growth, but intensive sheep grazing reduced clover compared nitb cutting and taking a silage cut in a grazing sequence improved clover yield. These results do not support the contention that cutting a mixed sward for hay or silage suppresses clover because of competition for light: with a ‘big white’ type of clover infrequent defoliation may cause no more shading than frequent. Alternatively, any additional shading may be compensated for by an increase in clover growth, stimulated hy the longer growth period. It is suggested that, in practice, competition for nutrients and moisture also contrihute towards clover suppression when swards are cut for hay or silage.     

An evaluation of the effects of grazing management systems involving preferential treatment of high-yielding dairy cows on animal performance and sward utilization

Two systems of grazing management involving preferential treatment of high- yielding dairy cows were compared with a grazing system in which both high- and low-yielders received uniform treatment. Cows were rotationally grazed across I-day paddocks without concentrate supplementation from 23 April to 8 October 1985, with a mean stocking rate over the season of 5-4 cows ha^?1. Preferential treatment of high-yielding cows was achieved either by using a leader/follower approach (LF) with high-yielding cows in the leader group, or by preferential forage feeding (PFF) where high-yielding cows were allowed access to grass silage for 1 -5 h daily and grazed alongside low-yielders. Control (C) cows grazed together as a single group. The high grazing stocking rates used on all three treatments resulted in good grass utilization with residual sward heights, assessed by a rising-plate sward stick, of 45, 50 and 48 mm for the LF, PFF and C treatments respectively. Animal performance data for the LF, PFF and C treatments respectively were: milk yield (kg d^?1) 15middot;1, 15middot;6 and 14middot;7 (s.e. 0middot;78); milk fat yield (g d^?1) 598, 606 and 567 (s.e. 34); milk protein yield (g d^?1) 500, 519 and 480 (s.e. 31); and live weight gain (kg d^?1) 0middot;12, 0middot;23 and 0middot;25 (s.e. 0·05). These results indicate that leader/follower grazing had little overall effect on animal performance when high grazing severity was imposed, with the improvement in animal performance of high-yielding cows in the leader group being offset by the reduced performance of the follower group. Buffer-feeding of high-yielding, rotationally-grazed cows with high-quality grass silage had little effect on animal performance and resulted in a decrease in the efficiency of grassland utilization. Silage appeared to substitute for herbage, with a reduction in herbage DM intake of 0middot;55 kg per kg silage DM consumed.     

GRAZING MANAGEMENT FOR DAIRY CATTLE

Many studies in recent years have stressed that grassland provides the greater part of the feed requirements of ruminant livestock in temperate lands, that a large proportion of this is supplied as grazing (83, 122) and that in this form it is the cheapest source of feed for ruminants (25, 38, 40). Several authors have contrasted the production estimated to be available from pasture with the much lower proportion—about 50% (74, 116)—harvested by the animal. For these reasons the efficiency of grass utilization under grazing conditions has received intensive study in the past 20 years and many of the principles of grazing management have been elucidated. Consideration of grazing management involves a study of the needs of the animals to be catered for, the sequence of grass crops which may be grown over the season, including the influence of special-purpose pastures and of fertilizer treatment on the yield and seasonal distribution of production, and the effective conservation of surplus herbage. In this review, however, attention is concentrated on the problems concerned in grazing management for the dairy cow during the main growing period of the year. The object of grazing management may be defined as 'to ensure a large supply of nutritious grazing over the growing season at a low cost and to utilize it in such a manner that physical waste of herbage and inefficient utilization by the animal are minimized and the productive capacity of the sward is maintained'. It is a complex subject, involving many interrelated factors including botanical, animal and per-acre considerations. These are briefly outlined before the available experimental data in grazing management practices are considered.     

Integrated analysis of profitable stocking‐rate decisions in pasture‐based dairy systems

A nonlinear optimization model of a pasture‐based dairy farm, located in the Waikato region of New Zealand, is used to provide an integrated analysis of profitable stocking‐rate decisions for pasture‐based dairy production, across a range of alternative milk and nitrogen fertilizer prices. Previous research has identified that operating profit increases either in a linear or concave fashion as stocking rate is lifted. This study shows that both views are relevant, depending on the magnitude of milk and nitrogen fertilizer prices. A lower milk price and/or higher per‐unit cost for nitrogen fertilizer reduces profit at higher stocking rates, as the cost of maintaining a larger herd through pronounced feed deficits is magnified. In contrast to previous research, nitrogen fertilizer and imported supplement are shown to be highly complementary strategies under profitable farm management. Model output demonstrates that decreasing stocking rates to reduce leaching, in most cases, will impose a cost in terms of both production and profit. Overall, this work indicates the key importance of stocking‐rate decisions to profitable grazing strategies, relative to those concerning milk per cow. Nevertheless, it is the inherent linkages between stocking rate and the multiple elements of a grazing system that infers this importance, highlighting the need to carefully consider all management levers.     

The effect of subsequent mangement on the success of introducing white clover to an existing sward

Two experiments, each lasting approximately 12 months, were carried out at North Wyke, Devon, in 1982-83 (A) and 1983-84 (B), to investigate various sward managements following oversowing of white clover (Trifolium repens, cv. Grasslands Huia) at 4 kg ha^-1 with a Hunter Rotary Strip-Seeder in June or July into the stubble of a permanent grass sward following conservation. Experimental managements comprised cutting, grazing with wether sheep or grass suppression by herbicide, as appropriate, in late summer/autumn (Phase I), winter (Phase II) and spring/early summer (Phase III). During Phase I, there was no differential effect on clover stolon development of lenient grazing at approximately 4-weekly intervals or topping at the same frequency to a similar height. Early in Phase II of Experiment A, grazed paddocks became so badly poached that no differences occurred between grazing either to early January or throughout the winter. Under drier conditions in Phase II of Experiment B, continuous grazing at either five (L) or ten (H) sheep ha^-1 had no immediate effect on clover stolon development, but in a silage cut in June, paddocks formerly stocked at the lower rate yielded 40% more DM than those at the higher rate. Experiment A compared the use of a grass-suppressing herbicide, propyzamide, applied at 0.6 kg a.i. ha^-1 in either October or February; in Experiment B it was applied in October. Prophyzamide applied at either time in Experiment A increased the clover content of herbage regrowing after the end of the experimental period from 16% to 36% (s.e.d. ± 3.9). In Experiment B, October application raised the clover contents of herbage cut in June 1984 from 10% (H) and 17% (L) to 32% (s.e.d.±5.9), and stolon lengths per m² at the end of the summer period from 33 (H) and 56 (L) to 86m (s.e.d. ± 11.7). However, the effect of spraying propyzamide on subsequent herbage yields was erratic, and appeared to depend on the incidence of frost after application. In Phase III of Experiment A, continuous grazing was compared with a silage cut in June. At the end of the experiment there were 31 m m^-2 of clover stolon in silaged areas compared with only 2.5 m m^-2 following grazing (s.e.d.±6.6). Clover content and herbage yields were also significantly higher following conservation. In Experiment B in the same period, rotational grazing with a 14- or 35-day recovery interval was compared with a silage cut in June, with or without 100 kg N ha^-1 applied in March. Application of N to the conservation treatment reduced clover stolon length per unit area, and in the regrowth in the post-experimental period the conservation treatment without N had the largest clover content (31% compared with 16-23% for other treatments, s.e.d. ± 3.6)     

The practical and economic consequences of integrating maize with grass production on dairy farms in southern England: a computer simulation

A mathematical model of the production, harvesting and utilization of maize and grass silage on a dairy farm with an autumn-calving herd is described. Using the model the comparative costs and benefits of growing and feeding maize in place of grass silage are examined for three sites in southern England. It is concluded that a winter milk production system based on maize rather than grass should improve profits by at least £30, and possibly by as much as £80 cow^-1. This financial improvement is attributable to higher feed intakes and lower harvesting and fertilizer costs with maize silage. Simulating the results over a 10-year period also revealed that the switch from grass to maize should lower the risks in terms of the annual variability of silage yields and herd profits. Furthermore, it would appear unnecessary to completely turn over from grass to maize production to realize a significant financial benefit. Setting aside just 25% of the conservation area to maize and feeding a mixture of maize and grass silage is projected to increase profits from winter milk production by £30 to £45 cow^-1.     

Effect of early turnout to grass in spring on dairy cow performance

This experiment examined the effects of grazing severity and degree of silage restriction during early turnout of dairy cows to pasture in spring on animal performance. Forty late‐winter‐calving Holstein Friesian dairy cows were allocated to one of five treatments between 7 March and 17 April 1997. The treatments involved early turnout of cows to grass for 2 h per day at two residual sward heights and two silage allowances, plus a control treatment, in a randomized block design. Dairy cows on the control treatment remained indoors throughout the experiment and were offered grass silage ad libitum. Dairy cows on all treatments were also offered 6 kg d^–1 of a concentrate on a flat‐rate basis, split equally between the morning and afternoon milkings. Offering cows access to pasture in early spring for 2 h per day resulted in increases in both milk (P < 0·001) and protein yield (P < 0·01). On average, over all grazing treatments, cows produced an additional 2·6 kg milk per day compared with the control treatment (28·5 vs. 25·9 kg d^–1, s.e.m. 0·43). Furthermore, these increases in milk yield were obtained even when silage was restricted indoors (28·4 vs. 25·9 kg d^–1) and cows grazed down to a residual sward height of 40 mm (28·1 vs. 25·9 kg d^–1). Protein yield was higher (P < 0·01) with dairy cows grazing pasture compared with cows indoors (848 vs. 707 g d^–1, s.e.m. 28·9). Silage intake was significantly (P < 0·001) reduced when cows were turned out to pasture. In conclusion, early turnout of dairy cows to pasture in spring for 2 h per day reduced silage intake and increased milk yield and protein yield relative to those fully housed and offered grass silage with a low level of concentrates.     

Effect of offering silage during housing at night on the performance of grazing dairy cows and on labour requirements

In the UK, dairy cows are increasingly housed at night throughout the grazing season. However, there is limited information on cow performance and the impact on labour requirements when a forage supplement is offered during housing at night throughout the entire grazing season. The effects of housing at night were studied in two experiments, in which two treatments were compared. On treatment part‐grazing (PG), dairy cows were given access to grazing by day and were offered grass silage while housed at night, and, on treatment continuous grazing (CG), dairy cows were given access to grazing both by day and by night. Experiments 1 (138‐d duration) and 2 (127‐d duration) involved sixty (primiparous) and seventy‐six (primiparous and multiparous) Holstein‐Friesian dairy cows respectively. Concentrates were offered during milking at 4·0 and 3·0 kg per cow per day in Experiments 1 and 2 respectively. In Experiment 1, total milk output was significantly higher with treatment PG than treatment CG (P < 0·01) while the reverse occurred in Experiment 2 (P < 0·001). Milk protein concentration was significantly higher with treatment CG in Experiments 1 and 2 (P < 0·001). Cows on treatment CG in Experiment 2 had significantly higher body condition scores and live weights at the end of experiment than those on treatment PG (P < 0·05). Weekly labour requirements were calculated to be proportionally 0·04 lower on treatment PG than on treatment CG. When offered silage during housing at night, the response of grazing dairy cows was largely determined by the grazing conditions encountered and the quality of the forage offered.     

Effects of two mixtures of perennial ryegrass cultivars with contrasting heading dates, and differing in spring-grazing frequency and silage harvest date, on characteristics of silage from first-cut swards

This experiment quantified the effects of: (i) heading date of perennial ryegrass, (ii) grazing frequency in spring and (iii) date of silage harvest, on the ensilability of herbages harvested for silage, and on the conservation and estimated nutritive value of the resultant silages. Replicated field plots with two perennial ryegrass mixtures (intermediate‐ and late‐heading cultivars) were subjected to three spring‐grazing regimes (no grazing, grazing in late March and grazing in both late March and late April) and were harvested on four first‐cut harvest dates between 20 May and 21 June. Herbage from each of the four replicates of these 24 treatments was precision‐chopped and ensiled unwilted and with no additive in laboratory silos. Herbage from the sward with the intermediate‐heading cultivar had a higher (P < 0·001) dry‐matter (DM) content and buffering capacity than that from the late‐heading cultivar, whereas water‐soluble carbohydrate concentrations increased (P < 0·001) with more frequent grazing in spring. Later harvesting enhanced herbage ensilability through an increased (P < 0·001) DM content and reduced (P < 0·001) buffering capacity and pH. Fermentation profiles of the silage were not markedly influenced by the cultivar mixture used but grazing in both late March and late April resulted in a more extensive fermentation with the acids produced increasingly dominated by lactic acid. The concentrations of acetic acid, and to a lesser extent, ethanol declined as silage harvest date was delayed. Overall, the relative effects of grass cultivar mixture were smaller than those of spring‐grazing treatment or silage‐harvesting date although on any given harvest date the herbage from the intermediate‐heading cultivar mixture was easier to preserve as silage than herbage from the late‐heading cultivar mixture. Delaying the harvesting of the late‐heading swards by 8 d removed the differences related to growth stage in buffering capacity, pH and DM content.