Effects of the colour and thickness of polyethylene film on ensiling conditions and silage quality of chopped maize, as investigated under ambient conditions and in mini-silos

Abstract The influences of variations in thickness and colour of agricultural plastic film on silage preservation conditions and silage quality were investigated. Thirty cylindrical plastic containers (mini‐silos; 0·3 m³) were filled with chopped maize and covered with five different types of film (90 µm white, 150 µm transparent, 150 µm white, 150 µm black, 200 µm white). Four mini‐silos of each variant were placed in the open air, and two were housed and subjected to a test procedure. The maximum storage period of silages was 104 d. The surface temperature of the films was found to be strongly dependent on the type of sheet. The temperatures inside the mini‐silos directly under the film differed significantly, whereas this effect was not recorded in the centre of the mini‐silos. In all, the differences were quantitatively small. Results of the chemical analysis of silages did not reveal any significant influence of film type. This was also the case when restricting the analysis to the uppermost silage layer. These findings are discussed against the background of the relatively small temperature differences and likely effects on gas permeability. On the basis of the results presented, it is concluded that, under the conditions of the experiment, well‐preserved forage of high nutritive value can be produced with silo sheets of differing colour, as well as with those of reduced thickness. Adequate mechanical robustness has to be ensured, if there is a reduction in film thickness.     

Effect of type of underlay film on fermentation profile,nutritional quality and estimated loss of organic matter in the outer layer of whole‐plant maize ensiled in large bunker silos

Losses of organic matter in the outer layers of bunker silos covered with conventional polyethylene (PE) plastic can be substantial due to oxygen transmission through the plastic top‐covering film during the post‐ensiling storage period. The effect of two silo covering materials, oxygen barrier (OB) film (45 μm thickness) and clear PE film (50 μm thickness), as underlays to a white‐on‐black PE plastic top cover (120 μm thickness), was assessed in the outer layer of whole‐plant maize silage stored in three large bunker silos in the People's Republic of China. Samples of the crop at harvest and of silage from the upper 45 cm layer at 5 months post‐ensiling, prior to removal of silage for feed‐out, were analysed for DM, fermentation profile and chemical composition. Loss of OM was estimated from concentrations of ash in the crop at harvest and in the silage. Differences between underlay films in silage fermentation profile were small. Silage protected with OB underlay film had higher mean concentration of starch (p < .008) and higher mean NDF digestibility (p < .003) than silage under PE underlay film. Concentrations of ash were lower (p < .001) for silage covered with OB film than for PE film in all three trials. Mean estimated losses of OM were 170 g/kg for OB underlay film and 232 g/kg for PE underlay film (p < .001), and whole‐silo estimated net economic benefits to OB underlay film ranged from 0.17 to 0.74 US $ per tonne fresh crop ensiled.     

Top spoilage losses in maize silage sealed with plastic films with different permeabilities to oxygen

The quality of plastic films used for horizontal silos is important to limit losses in the upper silage layer. The aim of this work was to study the effectiveness of different plastic films in reducing the top losses in maize silage. The following treatments were evaluated: (i) coextruded polyethylene/polyamide oxygen barrier film (OB), (ii) polyethylene film (PE), (iii) polyvinyl chloride film (PVC), and (iv) coextruded PE/polyvinyl alcohol film (PVOH). These treatments differed according to oxygen permeability with values of 75, 722, 982 and 289 cm³ m^?2 per 24 hour respectively. OB and PVOH films had better temperature and fermentation profiles than the more permeable films. The OB film was effective in reducing the dry‐matter (DM) losses during storage (82 g kg^?1), and the PVOH film had an intermediate value of DM loss (101 g kg^?1). PE and PVC films had higher losses (138 and 145 g kg^?1 respectively). Oxygen permeability of the films promoted a positive correlation with DM losses (P < 0·05; r² = 0·945). The results indicate that O₂ permeability through the plastic film is a crucial factor for maintaining silage quality in the upper layer of the silo when it is perfectly sealed.     

Gas composition of baled grass silage as influenced by the amount,stretch, colour and type of plastic stretch‐film used to wrap the bales,and by the frequency of bale handling

The effectiveness of the polyethylene stretch‐film barrier to air infiltration is the major factor affecting the preservation of silage in bales. Three separate experiments investigated the effects of the number of layers of stretch‐film cover, film colour, stretch extent, film type and frequency of bale handling on gas composition, surface mould growth and conservation characteristics of baled grass silages. Monitoring gas composition in bales during ensiling proved useful for assessing the success with which wrapped bales were stored anaerobically. Under good storage conditions the early stages of ensiling were characterized by the rapid reduction of O₂ concentration in the bale and the creation of a CO₂‐rich environment. However, wrapping bales in only two layers of stretch‐film failed to create the anaerobic conditions required for a successful fermentation and the inhibition of visible fungal growth. In contrast, a minimum of four layers of stretch‐film were required to achieve suitably anaerobic conditions, but the additional benefits of applying more layers were relatively small. Under temperate climatic conditions with moderate solar radiation, film colour had little effect on the gas composition in baled silage. Likewise, the extent of stretching applied to the film at wrapping and film type had no influence on gas composition, baled silage quality or mould development. However, frequent mechanical handling of bales after wrapping had a negative effect on gas composition and surface mould growth, and thus should be kept to a minimum.     

Modelling the comparative productivity and profitability of grass and legume systems of silage production in northern Europe

A pre‐existing mechanistic model of grass growth, developed to simulate grass production in the UK, was extended to include a variety of grass–legume mixtures and used to predict comparative yields across a range of sites in northern Europe, using experimental data from a series of experiments at fifteen sites. Specifically, predictions were made of the comparative yields of grass (Lolium perenne L.), white clover (Trifolium repens L.), red clover (T. pratense L.), lucerne (Medicago sativa L.), lotus (Lotus corniculatus L.) and galega (Galega orientalis Lam.). The results indicated that the model could generate simulated differences in yields between forage crops, which accorded with observed rankings. However, the predictions were more accurate for total yields than individual cuts, for a country than for an individual site, and for monocultures than for grass–legume mixtures. Nevertheless, the results appeared sufficiently robust to be used to prepare forecasts of yield productivity in different agro‐climatic zones in northern Europe. Using estimates of the production costs and economic values for the forages, it was also possible to assess their comparative profitability. The study indicated that red clover, whether grown singly or in a mixture with grass economically outperformed all silage systems based on pure grass swards, even those receiving 400 kg N ha^?1. White clover and lucerne were also consistently more profitable than grass‐based systems, receiving 200 kg N ha^?1. In relative terms, lucerne appeared to be more profitable in the south and east of the region, while white clover outperformed lucerne in the north and west. In the north and east of the region, there was some evidence that galega might also hold promise as a silage crop, but lotus was not found to be viable under north European environmental conditions.     

Effect of forage matting on rate of grass drying, rate of silage fermentation, silage intake and digestibility of silage by sheep

The effects of forage matting on rate of grass drying and silage fermentation, digestibility, and intake were examined using perennial ryegrass swards. Treatments compared were: forage mats, where grass was processed through a laboratory scale macerator prior to matting and wilting to 228 g dry matter (DM) kg^?1 (FM treatment); unconditioned grass which was direct ensiled at 163 g DM kg^?1 (DE treatment); unconditioned grass which was wilted for the same period as FM to 213 g DM kg^?1 (UC treatment); unconditioned grass which was wilted to 234 g DM kg^?1 (UC₂₅, treatment). All forages were dried on black plastic sheeting. For each treatment a total of approximately 80 kg grass DM was ensiled in seven 290 I plastic bins for 136 d prior to feeding to wether sheep. A further total of 14 kg grass DM from each treatment was ensiled in twenty-one plastic pipes (152 mm diameter, 762 mm long) to give a total of 84 pipes. Rate of silage fermentation was determined by destructively sampling pipes following 1, 2, 4, 6, 13, 20 and 50 d of ensilage. Over the mean wilting period of 6·9 h, grass from the FM treatment dried significantly faster (P < 0·001) and required less solar energy per unit of moisture loss than unconditioned grass. The rate of grass drying was highly correlated with solar radiation. The FM treatment did not influence the rate or extent of silage fermentation. The intakes and digestibilities of FM, UC and UC₂₅ were not significantly (P < 0·05) different from each other but were higher than for the DE treatment (P < 0·05 for digestibility and NS for intake). In Northern Ireland it is unlikely that there will be sufficient solar radiation to allow forage mats to be made, wilted to a level to prevent effluent production and harvested within one working day. Further work is required to optimize mat-making technology for more rapid drying and to determine the effect of adverse weather on nutrient losses from mats.     

A meta‐analysis comparing standard polyethylene and oxygen barrier film in terms of losses during storage and aerobic stability of silage

A meta‐analysis was undertaken of 51 comparisons of standard polyethylene film with oxygen barrier (OB) film in covering systems for bunker silos, unwalled clamp silos and bales. Mean losses of DM or OM during storage from the top 10 to 60 cm of bunker and clamp silos were 195 g kg^?1 for standard film and 114 g kg^?1 for OB film systems (41 sets of data, P < 0·001), while mean total losses of DM from baled silage were 76·8 g kg^?1 for standard film and 45·6 g kg^?1 for OB film systems (10 sets of data, P < 0·001). Top surface silage judged subjectively to be inedible was 107 and 29·6 g kg^?1 for standard film and OB film systems respectively (5 sets of data, P = 0·02). Aerobic stability was 75 h for silage stored under standard film system and 135 h for silage stored under OB film system (11 sets of data, P = 0·001). It is concluded that the OB film system reduces losses from the outer layers of silos and from bales and increases the aerobic stability of silage in the outer layers of silos.     

The effects of high-concentrate diets and pasture on the concentration of conjugated linoleic acid in beef muscle and subcutaneous fat

Abstract In view of the evidence indicating several potential benefits of high intakes of conjugated linoleic acid (CLA) on human health, an experiment was conducted to examine the effects of the diet of beef cattle on the total CLA concentration in muscle and subcutaneous fat. High‐concentrate [steers consumed 515 g concentrates and 485 g grass silage kg^?1 dry matter (DM) for 8 weeks followed by 887 g concentrates and 113 g grass silage kg^?1 DM for 14 weeks until slaughter] and high‐forage (steers consumed 803 g grass silage and 197 g concentrates kg^?1 for 8 weeks followed by grass silage only for 10 weeks and then grazed perennial ryegrass‐based pasture for 23 weeks until slaughter) treatments were imposed on 48 steers, which were crosses of continental beef breeds (initially 414 kg live weight) The concentrates were based on barley, extracted soyabean meal, molassed sugarbeet pulp and maize meal. The silages were of medium to low digestibility and contained 117–137 g crude protein kg^?1 DM and 83–158 g ammonia‐N kg^?1 total N. The pasture was of high quality and contained 168 g crude protein, 234 g acid‐detergent fibre and 222 g water‐soluble carbohydrate kg^?1 DM. Samples of muscle were taken post slaughter from the m. semimembranosus, m. gluteobiceps, m. longissimus and m. deltoideous muscles, and subcutaneous fat was taken from over the m. longissimus. Concentrations of total CLA in the tissues were for the high‐concentrate and high‐forage treatments, respectively (mg 100 g^?1 fresh tissue), m. gluteobiceps 18 and 47 (s.e. 3·5); m. semimembranosus 9 and 20 (s.e. 1·6); m. longissimus 15 and 35 (s.e. 3·2), m. deltoideous 20 and 59 (s.e. 4·3); subcutaneous fat 584 and 1975 (s.e. 138·7). It is concluded that muscle and subcutaneous fat tissue from grass‐fed cattle contained three times as much CLA as those from concentrate‐fed cattle, and that the consumption of beef from grass‐fed cattle should be effective in increasing the intake of CLA by humans.     

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

In 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.     

The influence of weather factors on the drying rate of cut perennial ryegrass herbage under controlled conditions

The rates of drying of cut perennial ryegrass (Lolium perenne L.) herbage over short periods of time were measured in four experiments in a controlled environment room. Standard weights of 33·7 g grass dry matter (DM) were placed in half the area of wire‐mesh trays (0·5 m long × 0·3 m wide × 0·07 m high with 11‐mm‐square mesh) which, so as to simulate conditions in a swath, were supported on wooden frames within dark plastic boxes 25 mm above 35‐mm‐thick wet sponges. The trays of grass in the controlled environment room were weighed hourly for 7 h, drying rate being assessed by the change in grass fresh weight. Light was supplied from 400‐W mercury vapour lamps, while an air conditioning unit within the controlled environment room allowed control of vapour pressure deficit (VPD). Only one particular VPD could be created on any one day and resource limitations restricted the study to one replicate per day. The first experiment correlated drying rates under the mercury vapour lamps with drying rates in the open air under sunshine over 3 d. This work showed that a distance of 200 mm between the tray and lamps equated to 1081 W m^–2, 400 mm to 432 W m^–2 and 600 mm to 281 W m^–2. Experiment 2, conducted with previously frozen grass, was a 4 × 4 factorial design with light intensity and VPD as factors. The third experiment (Experiment 3) compared the drying rate of freshly cut grass with grass that had previously been frozen in a 2 × 2 × 2 factorial design with the two grasses, two light intensities and two wind speeds as factors. The final experiment (Experiment 4) was a 3 × 2 × 2 factorial design with light intensity, VPD and wind speed as factors. A wind of approximately 3 m s^–1 was simulated using a 22‐mm, 30 W fan set in a fixed position 600 mm from each tray plus grass. Fresh grass was cut each morning of the experiment. There were six replicates of each treatment. The effect of the three radiation intensities on grass DM concentration in Experiment 2 was highly significant (P < 0·001). VPD had less effect (P < 0·05). Results from Experiment 3 showed that previously frozen material dried much more rapidly than fresh grass and as a result would not simulate actual grass drying in the field. Consequently in Experiment 2 fresh grass was used as opposed to previously frozen material. In Experiment 4, light intensity had the greatest influence on grass drying followed by VPD and wind speed. However, the influence of wind speed was variable. A wind speed of ≈3 m s^–1 increased the rate of water loss from grass with a low initial DM concentration (<160 g kg^–1) receiving low levels of solar radiation (281 W m^–2), while at higher initial DM concentrations (>210 g kg^–1) and higher solar radiation levels (432 W m^–2) the effect of wind was to slow grass drying. The results from Experiments 2 and 4 also indicated that high levels of either wind (3 m s^–1) or VPD (>6 mbars), when associated with low levels of solar radiation, resulted in large increases in grass DM concentration. However, these extreme weather conditions are unlikely to occur in practice.     

Effect of stage of maturity and chop length on the chemical composition and utilization of formic acid-treated ryegrass and formic acid silage by sheep

Two areas of an early-heading perennial ryegrass cv. Cropper were harvested by either a precision-chop or a flail harvester at around 50% ear emergence (15 May 1978) and 14d later (29 May). Formic acid (85%) was applied at the rate of 2·2 litres t^-1. Mature crossbred wethers were used in a 2 × 2 factorial design to determine the effect of stage of maturity and method of harvesting (chop length) on the in vivo digestibilities of formic acid-treated grass in experiment 1 and formic acid silage in experiment 2. Apparent digestibility coefficients were determined at a fixed level of feeding for both grass and silage and at ad libitum access to feed for silage only. There were no significant differences in the concentrations of crude protein (CP), ether extract (EE), acid-detergent fibre (ADF) or acid-detergent lignin (ADL) in grass or silages of differing chop lengths but the later cut forages had significantly higher ADF and ADL concentrations and lower CP concentrations than the early-cut forages. The ADF and ADL concentrations were also higher in the silages than in the corresponding grasses. In general, the fermentation characteristics of precision-chopped silage were better than for the corresponding flail-cut silage but date of harvest was a more important determinant of quality and the late, flail-cut silage had the highest butyrate and ammonia N concentrations and the highest pH (411) of any treatment. There was a significantly higher intake of precision-chopped as compared with flail-cut silage with both the early-and the late-cut silage but there were no significant differences attributable to stage of maturity (i.e. date of harvest) or significant interaction between chop length and maturity. The slightly increased intake of early harvested, precision-chopped silage as compared with late precision-chopped silage was not significant. Dry matter digestibility (DMD) of the grass decreased at a rate of 0004 units d^-1 post 50% ear emergence. The results of experiment 2 indicated a decrease of 0·207 units d^-1 in silage fed at a similar level. The late-cut silage (DMD 0·292, mean of both harvesting treatments) thus had a significantly lower digestibility than the corresponding grass (mean DMD 0·247). Chop length had a variable influence on the DMD of both grass and silage fed at a fixed level but treatment differences were non-significant. However, a trend towards higher digestibility of flail-cut as compared with precision-chopped silage was apparent and this became statistically significant when the animals were allowed ad libitum access to feed. This may be a response to the generally lower intake of flail-cut silage.     

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.     

A new sterilization and inoculation method in silage research

The study aimed at evaluating an effective sterilization–inoculation technique to facilitate silage research on the effect of forage microflora on fermentation variables. The sterilization effect of heating at 60°C for 3 h + 103°C for 15 h was tested on samples of grass, grass–clover, white clover and maize, pre‐dried at 60°C to a dry‐matter (DM) content >900 g kg^?1. The ensilability of treated samples, reconstituted to original DM concentration (250–390 g kg^?1), was assessed by inoculation with microfloras extracted from the original samples. Microfloral inoculants were obtained by a combination of centrifugation (15 500  g for 40 min) and filtration (0·45 and 0·22 μm pore sizes) of the supernatant. The sterilization treatment effectively sterilized the forage samples but decreased water soluble carbohydrates by 49% and N buffer solubility by 22% and increased the acid detergent insoluble N proportion of total N by 53% (P < 0·05). The reconstituted silages had 18% less lactic acid, 20% less ethanol and 37% less ammonia‐N (P < 0·05), but volatile fatty acids and 2,3‐butanediol did not differ from the untreated silages (P > 0·05). Counts of lactic acid bacteria, enterobacteria, clostridia, yeasts and moulds in the two silage treatments were also similar (P > 0·05). It is concluded that, despite causing chemical and physical alterations, the sterilization–inoculation technique evaluated could be a useful tool for future studies on the effects of microflora on ensiling results.     

Nitrogen metabolism and milk production in dairy cows fed semi‐restricted amounts of ryegrass–legume silage with birdsfoot trefoil (Lotus corniculatus L.) or white clover (Trifolium repens L.)

In change‐over trials, mid‐lactation dairy cows were fed concentrate‐supplemented, isonitrogenous and isofibrous perennial ryegrass–legume silage diets that satisfied energy requirements but were suboptimal with respect to metabolizable protein supply. Legumes were either birdsfoot trefoil with low levels of condensed tannins (typical for hemiboreal conditions), or white clover. Averaged over two experimental years, birdsfoot trefoil–based silage resulted in lower digestibility (P < 0·001) of dry matter (50 g kg^?1), organic matter (52 g kg^?1), neutral detergent fibre (120 g kg^?1) and nitrogen (24 g kg^?1) and lower rumen total volatile fatty acid concentration (7 mm ; P = 0·009). Milk protein yield was 36 g d^?1 higher with birdsfoot trefoil silage (P = 0·002), while raw milk yield tended to be 0·8 kg d^?1 higher (P = 0·06). Rumen ammonia concentration was similar between diets, but milk urea concentration (P < 0·001), urinary urea excretion (P = 0·002) and faecal‐N proportion (P = 0·001) were higher with birdsfoot trefoil silage. The results suggest that grass–birdsfoot trefoil silage produced in hemiboreal areas exhibits a protein‐sparing effect in dairy rations, despite a low condensed tannin content that is further diluted by companion grasses and ration concentrate proportion.     

Impact of spatial heterogeneity of plant species on herbage productivity,herbage quality and ewe and lamb performance of continuously stocked,perennial ryegrass–white clover swards

The benefits of white clover (Trifolium repens L.) in pastures are widely recognized. However, white clover is perceived as being unreliable due to its typically low content and spatial and temporal variability in mixed (grass‐legume) pastures. One solution to increase the clover proportion and quality of herbage available to grazing animals may be to spatially separate clover from grass within the same field. In a field experiment, perennial ryegrass (Lolium perenne L.) and white clover were sown as a mixture and compared with alternating strips of ryegrass and clover (at 1·5 and 3 m widths), or in adjacent monocultures (strips of 18 m width within a 36‐m‐wide field). Pastures were stocked by ewes and lambs for three 10‐month grazing periods. Over the 3 years of the experiment, spatial separation of grass and clover, compared with a grass–clover mixture, increased clover herbage production, although its proportion in the sward declined through time (0·49–0·54 vs 0·34 in the mixture in the first year, 0·28–0·33 vs 0·15 in the second year and 0·03–0·18 vs 0·01 in the third year). Total herbage production in the growing season in the spatially separated treatments decreased from 11384 kg DM ha^?1 in the first year to 8150 kg DM ha^?1 in the third year. Crude protein concentration of clover and grass components in the 18‐m adjacent monoculture treatment was greater than the mixture treatment for both clover (310 vs 280 g kg^?1 DM) and grass (200 vs 180 g kg^?1 DM). There was no clear benefit in liveweight gain beyond the first year in response to spatially separating grass and clover into monocultures within the same field.     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK: 7. Sustainability of white clover in grass/clover swards with reduced levels of fertilizer nitrogen

The sustainability of white clover in grass/clover swards of an upland sheep system, which included silage making, was studied over 5 years for four nitrogen fertilizer rates [0 (N₀), 50 (N₅₀), 100 (N₁₀₀) and 150 (N₁₅₀) kg N ha^?1]. A common stocking rate of 6 ewes ha^?1 was used at all rates of N fertilizer with additional stocking rates at the N₀ fertilizer rate of 4 ewes ha^?1 and at the N₁₅₀ fertilizer rate of 10 ewes ha^?1. Grazed sward height was controlled, for ewes with their lambs, from spring until weaning in late summer by adjusting the proportions of the total area to be grazed in response to changes in herbage growth; surplus pasture areas were harvested for silage. Thereafter sward height was controlled on separate areas for ewes and weaned lambs. Areas of pasture continuously grazed in one year were used to make silage in the next year. For treatments N₀ and N₁₅₀, white clover stolon densities (s.e.m.) were 7670 (205·4) and 2296 (99·8) cm m^?2, growing point densities were 4459 (148·9) and 1584 (76·0) m^?2 and growing point densities per unit length of stolon were 0·71 (0·015) and 0·67 (0·026) cm^?1 respectively, while grass tiller densities were 13 765 (209·1) and 18 825 (269·9) m^?2 for treatments N₀ and N₁₅₀ respectively. White clover stolon density increased over the first year from 780 (91·7) cm m^?2 and was maintained thereafter until year 5, reaching 8234 (814·3) and 2787 (570·8) cm m^?2 for treatments N₀ and N₁₅₀ respectively. Growing point density of white clover increased on treatment N₀ from 705 (123·1) m^?2 to 2734 (260·7) m^?2 in year 5 and it returned to the initial level on treatment N₁₅₀ having peaked in the intermediate years. Stolon density of white clover was maintained when the management involved the annual interchange of continuously grazed and ensiled areas. The non‐grazing period during ensiling reduced grass tiller density during the late spring and summer, when white clover has the most competitive advantage in relation to grass. The increase in stolon length of white clover in this period appears to compensate for the loss of stolon during periods when the sward is grazed and over winter when white clover is at a competitive disadvantage in relation to grass. The implications for the management of sheep systems and the sustainability of white clover are discussed.     

The influence of grass and maize silage quality on apparent diet digestibility, metabolizable energy concentration and intake of finishing beef cattle

The effects of offering a range of grass silages and mixtures of grass and maize silages on the intake of beef cattle were studied. Four grass silages (GS1, GS2, GS3 and GS4) were used. Grass silage 1 was ensiled from a second regrowth in mid‐late September and treated with an inoculant additive. Grass silages 2, 3 and 4 were ensiled, without additive, from a primary regrowth harvested in early July, late May and mid‐June respectively. Wilting periods were 8, 30, 36 and 36 h for GS1, GS2, GS3 and GS4 respectively. Grass silages 1, 2 and 3 were precision chopped and ensiled in bunker silos, while GS4 was ensiled in round bales. The DM content (g kg^?1) and starch concentration (g kg^?1 DM) of the three maize silages (MS1, MS2 and MS3) used were 256 and 128, 256 and 184, and 402 and 328 for MS1, MS2 and MS3 respectively. Seventy‐two Charolais and Limousin cross‐bred steers were used in a changeover design with two 4‐week periods. The study consisted of sixteen treatments incorporating the four grass silages fed alone and with the three maize silages arranged as a 4 × 4 factorial design. The grass silage and maize silage mixtures were offered in a ratio of 0·60:0·40 (DM basis) once daily using individual Calan gates. All silages were offered ad libitum with 3 kg per head per day of a concentrate supplement. Dry matter and metabolizable energy (ME) intakes were highest with diets based on grass silage GS4 compared with diets containing the other grass silages. Metabolizable energy intakes of diets containing no maize silage, and those based on MS1 and MS2, were similar (P > 0·05) but lower than that of diets containing MS3. Only limited increases were found in DM and ME intakes with the inclusion of maize silage in grass silage‐based diets while offering high‐quality grass silage (assessed in terms of DM content, and fibre and N concentrations) promoted high voluntary intakes.     

Kinetics of bubble growth in wheat flour dough during proofing studied by computed X-ray micro-tomography

Bread doughs of various compositions were prepared and studied by computed X-ray microtomography (XRT) with high resolution (5 μm). Their cellular structure was followed during the last stage of proofing, from 40 min to 180 min, to focus on the films separating bubbles and their possible coalescence. Image analysis allowed to determine the porosity, the connectivity index, the bubble size and the cell walls thickness distributions which were fitted by usual mathematical functions. Images showed that different compositions led to different cellular structures. The kinetics of porosity and connectivity had sigmoid shapes with 0.7 and 1 as asymptotic values, respectively. For an average formula, mean cell width grew from 410 μm to 675 μm and the mean cell wall thickness grew from 200 μm to 230 μm. At the end of proofing, most bubbles were interconnected, i.e. they were separated by films of thickness lower than 5 μm. Changes of recipe led to different structures, which were discussed through the influence of the liquid fraction and of the sugar content on the coalescence of bubbles. These results suggested that at the end of fermentation, the dough could be considered as a three phase co-continuous medium: gas/liquid/viscoelastic matrix.     

The effect of system of silage harvesting and feeding on milk production

Two silages were produced by harvesting grass either unwilted, using a direct cutting flail forage harvester (flail-direct), or wilted following precut-ting and being picked up using a meter-chop harvester (precision-wilted). Formic acid was applied at the rates of 2·45 and 2·9 1 t^-1 for the flail-direct and precision-wilted silages, respectively. Weather conditions were difficult, both before and during harvesting with a total of 27 mm rainfall falling on the wilted herbage before ensiling. The in-silo dry matter losses were 199 and 68 g kg^-1 for the flail-direct and precision-wilted silages, respectively. The resulting silages had mean particle lengths of 49 and 24 mm, dry matter contents of 186 and 276 g kg-^-1 and D-values of 068 and 062 for the flail-direct and precision-wilted silages, respectively. During a 141-day feeding period commencing on 19 November, the two silages were offered to 88 British Friesian cows with a mean calving date of 21 January and divided into four groups in a 2×2 factorial design experiment. The silos were divided longitudinally and two groups of cows were self-fed the silages in situ, one for each silage type, while the other two groups were easy-fed the same silages along a feed fence. There were no significant interactions between system of silage harvesting and feeding on any of the measurements of animal performance. Animals on the flail-direct silage consumed 16% less silage dry matter and produced 10% more milk per cow than those on the precision-wilted silage treatment. The overall effect was a 12% greater milk output for each unit of grass dry matter ensiled with the flail-direct than with the precision-wilted harvesting system. System of silage feeding did not significantly influence silage intake or milk output, with the mean milk yields during the final 21 days of the study being 234 and 236 kg d^-1 (±0.30) for the self- and easy-feed systems, respectively. The effects of the treatments on milk composition, liveweight change, body condition score and total ration digestibility are also reported.     

Comparison of the fermentation quality and nutritive value of sulphuric and formic acid-treated silages fed to beef cattle

Five experiments were carried out in the years 1980-1983 and 1986 to study the effect of treating grass at ensiling with sulphuric acid (850 g kg^?1) and formic acid (850 g kg^?1) additives alone, and in mixtures with or without formalin on the preservation of grass, in vivo digestibility in sheep, in-silo loss, intake and performance of finishing cattle. Primary growth grass was ensiled in experiments 1 (3–4 June 1980), 2 (12-15 June 1981) and 3 (31 May-2 June 1982), primary regrowth grass in experiment 4 (1-2 August 1983) and secondary regrowth grass in experiment 5 (7-10 October 1986). During the ensiling period within each experiment, approximately 60 t of unwilted, double-chopped, additive-treated or untreated grass was packed into covered concrete-walled 60-t capacity silos. The dry matter (DM) contents of the ensiled grass in experiments 1, 2 and 5 ranged from 155-180 g kg^?1 and were lower than those recorded in experiments 3 and 4 (214 g kg^?1). With the exception of grass ensiled in experiment 2, where water-soluble carbohydrate (WSC) contents were low, at 104 g kg^?1 DM, grass in all other experiments contained relatively high WSC contents ranging from 140-154 g kg^?1 DM. In experiments 1, 3 and 4 all silages were well-preserved. However, in experiment 2 the 450 g kg^?1 sulphuric acid-treated and formic acid-treated silages displayed significantly lower pH, buffering capacity (Bc) and ammonia nitrogen contents than the untreated silage. In experiment 5, the sulphuric acid-treated and formic acid-treated silages displayed significantly lower pH, Bc, ammonia nitrogen, butyrate and volatile fatty acid (VFA) contents than the untreated silage. Each of the silages was offered daily with various levels of a supplementary concentrate for approximately 70-d periods to twelve animals of mixed breed in experiments 1, 3, 4 and 5 and to fifteen animals in experiment 2. All animals weighed between 380-470 kg at the start of the experiments. In experiments 1, 2 and 3 there were no significant differences between silages for any of the intake or animal performance parameters. In experiment 4, cattle fed the formic acid-treated silage displayed significantly higher silage DM intakes and daily liveweight gains than those fed the sulphuric acid-treated and untreated silages; in experiment 5, cattle fed the formic acid-treated silage displayed significantly higher silage DM intakes than those fed the untreated silage. It was concluded that formic acid was a more effective silage additive than sulphuric acid. Increasing the level of supplementation significantly decreased silage DM intakes in cattle in experiments 3 and 4, and significantly increased daily liveweight gains and daily carcass in cattle in experiments 1, 3 and 4.