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Effect of stage of growth on the chemical composition, nutritive value and ensilability of whole-crop barley
Animal Feed Science and Technology 152 (2009) 50–61
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Effect of stage of growth on the chemical composition, nutritive value and ensilability of whole-crop barley A. Hargreaves a,∗, J. Hill b, J.D. Leaver c a
Pontificia Universidad Católica de Chile, Facultad de Agronomía e Ingeniería Forestal, P.O. Box 306, 22 Santiago, Chile Department of Agriculture and Food Systems, Melbourne School of Land and Environment, University of Melbourne, Parkville, Victoria 3010, Australia c Royal Agricultural College, Cirencester, GL7 6JS, United Kingdom b
a r t i c l e
i n f o
Article history: Received 10 April 2008 Received in revised form 12 February 2009 Accepted 16 March 2009 Keywords: Cereal silage Chemical composition Nutritive value Deterioration
a b s t r a c t Chemical composition, nutritive value and ensilability of wholecrop barley as a supplementary feed for dairy cows was investigated using a range of maturities of barley (seed coat ripe—GS 69, early dough stage—GS 82, soft dough—GS 87 and grain ripe—GS 90) in small scale silos. The ensiling experiment was based on a complete randomised design with three replicate silos per harvest date. Twelve 0.225 m3 plastic silo (were used in the experiment and silo were sampled on opening for chemical composition and nutritive value. The fermentation process reduced the concentrations of water-soluble carbohydrate in the ensiled forage compared to the fresh forage. The proportion of residual WSC in silage did however increase with increasing crop maturity (0.051, 0.077, 0.167 and 0.560 of WSC retained in the silage after the process of fermentation from forages cut at GS 69, 82, 87 and 90 respectively). Silages that were made from forage cut at the most mature stage of growth had a substantially lower production (P<0.001) of total fermentation acids (38.9 g/kg DM for GS 90) compared to those made from the least mature forage (203.4 g/kg DM for GS 69). The pH and concentrations of the various fermentation acids for silages made with the least mature forage (GS 69) were typical of acetic acid dominated fermentation. These silages contained little or no butyric acid and had a pH of 4.5 and contained high concentrations of ammoniaN (186 g/kg total N). Silages produced from forages cut at growth
Abbreviations: DM, oven dry matter; GS, growth stage; NDFom, neutral detergent fibre; ADFom, acid detergent fibre; N, nitrogen; WSC, water soluble carbohydrate; NDCD, neutral detergent cellulose digestibility; MOG, material other than grain. ∗ Corresponding author. E-mail address: [email protected] (A. Hargreaves). 0377-8401/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2009.03.007
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stage 82 were similar to those conserved from immature forages, having acetic acid dominated fermentation (lactic acid to acetic acid ratio of 1:1.22), relatively high pH (4.85) and high concentrations of ammonia-N (141 g/kg total N). These silages differed from those made from the most immature forage insofar that they contained high concentrations of butyric acid (50.5 g/kg DM). The processes of fermentation were affected by the stage of growth of the forage at ensiling and hence the economics of silage production. If the forage was too immature at ensiling, the yield of crop would be compromised but the silage produced may have moderate to high nutritive value and reasonable aerobic stability during the feed out phase. If the whole-crop forage was grown as a crop to secure high levels of supplementary feed from an alternative forage source (other than grass), the trade-off between yield, nutritive value and losses of feed immediately after silo opening would suggest the crop should be harvested between 350 and 450 g DM/kg dry matter. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Traditionally, the dairy and beef sectors have conserved surpluses in pasture production to alleviate feed shortages during periods of low pasture productivity or drought. Recently, there has been increasing interest in the use of alternative forage crops in pasture-based systems with small grain cereal crops (including maize) being preferred. Whole-crop cereals as a forage for dairy cows can provide several advantages to the dairy sector. For instance the cereal cropping system can be incorporated into a programme of pasture renovation (De Ruiter and Hanson, 2004), it can provide a source of supplementary feed with characteristics of high digestibility and substantial levels of starch (Adesogan et al., 1999) and cereal crops can be grown in areas where maize silage is limited by climatic conditions (Weller et al., 1992). The use of whole-crop cereal systems also provides an ideal opportunity to integrate arable cropping and the dairy sector leading to greater opportunities for each sector to transfer expertise and improve financial returns. One of the important issues that has to be considered for the exploitation of whole-crop cereals in pasture-based dairy systems is the “trade-off” between harvestable yield and the nutritive value of the cereal crop. This situation is not well defined but an understanding of this balance is essential for the subsequent utilisation of cereal crops in dairy systems. From a practical point of view the dairy farmer requires precise information on harvest date, a method to evaluate date of harvest (growth stage or grain characteristics) potential yield and subsequent losses of DM during storage and feedout, and nutritive value to achieve high financial returns from an alternative cropping system. If maximum yield of dry matter per hectare is to be achieved under northern European conditions, winter-sown whole-crop barley must be harvested at about 500 g DM/kg of dry matter (DM) content (Tetlow and Mason, 1987). However there is evidence that the relationship between growth stage of the crop and DM content is poor and it is therefore difficult to predict precisely physiological maturity and hence maximum yield (Fisher et al., 1972; Juskiw et al., 2001). If the “trade-off” between yield and nutritive value is considered and a target of 80–90% of the maximum yield is identified for winter-sown wholecrop barley, the crop could be harvested at growth stages concomitant to 300–350 g DM/kg (Tetlow and Mason, 1987; O’Kiely and Moloney, 1991). Delaying harvest for maximum yield of cereal crops for forage production (mature stages of growth) has been demonstrated to lead to extensive lignification of the stem, leaf sheath and lemma/palea reducing the digestibility of the straw and chaff fraction. Grain testa permeability is also reduced leading to a reduction in the availability of starch to digestion in the rumen. Therefore it has been suggested that whole-crop barley should be harvested for silage no later than early dough or soft dough stage of growth to ensure that the forage has high intake characteristics, maintains a moderate to high digestibility of nutrients (Polan et al., 1968; Fisher et al., 1972) and an economic yield of forage per hectare.
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The objectives of the study reported in this paper were to examine the effect of harvest date on yield of forage, chemical composition and ensilability of whole-crop barley for subsequent feeding to dairy cows as a supplement to grazed grass.
2. Material and methods 2.1. Forage agronomy Winter barley crops (vars. Pipkin and Puffin) were grown on a field scale under a conventional cropping pattern (prophylactic spray programme to control weed, fungal and aphid populations). The crops were drilled into a prepared seed-bed (Argillic brown earth; Hamble series) on in mid September of each growing season at a seed rate of 235 kg/ha and 80 kg N/ha was applied in the spring of each year. The total crop area established each year was 11 ha of which 1.1 ha were harvested for whole-crop cereal production. Each crop was sampled weekly with the first sample taken immediately after the early booting stage of growth (growth stage (GS) 41–42; Zadoks et al., 1974) from mid-April onwards until harvest for forage conservation. At each harvest date, stage of growth was recorded using the Zadoks cereal growth stage key (Zadoks et al., 1974). Eight 0.25 m2 quadrat samples were cut randomly from the area destined for whole-crop forage production. Each sample was cut to ground level using hand shears (stainless steel) at 1200 h, collected for subsequent assessment of the harvested crop for components of yield and biomass. All plants in the sub sample were cut at 10 cm from the base to simulate the stubble height after cutting. Both the upper portion of the plant and the 10 cm-stubble, were weighed separately and then dried at 100 ◦ C for 24 h to estimate DM content and yield of harvested crop and total biomass. Samples of crops were taken every fortnight from the samples from the upper portion of the crop and stubble fraction (200 and 50 g fresh matter respectively), dried at 65 ◦ C to constant weight, ground to 1 mm and stored for subsequent chemical analysis. After the emergence of the inflorescence (GS: 60–65), whole plants (n = 15) were taken at random from the samples cut for yield estimation and separated into inflorescence (ear), stem (excluding the leaf sheath) and leaf fractions. Each component of yield was weighed and dried to constant weight at 100 ◦ C to calculate the contribution of each fraction to total biomass yield. Grains were threshed from the ear fraction, counted, weighed and the harvest index calculated (contribution of grain mass to total biomass. Thousand grain weights were also calculated from the grain samples to examine grain fill during the period of ear emergence to final harvest.
2.2. Ensiling experiment In the second year of the three years of crop monitoring an ensiling experiment was conducted. The ensiling experiment was based on the techniques reported by Hill and Leaver (1999). A winter barley crop (var. Pipkin) was swathed to 10 cm stubble height at four stages of growth (GS 69 (seed coat water ripe), 82 (early dough development), 87 (soft dough), and 90 (grain ripe); Zadoks et al., 1974) using an oilseed rape swather (1.5 m reciprocating blade, reel and side unloading belt). The objective of the experiment was to cut the crop at dry matter contents of 250, 350, 450, and 550 g/kg but use the growth stage of the crop as an on-farm tool to estimate the cutting date. The crops for ensiling were harvested immediately using a self-propelled precision chop forage harvester with a pick up reel and chop length set at 25 mm. The ensiling experiment was based on a complete randomised design with three replicate silos per harvest date. Twelve 0.225 m3 plastic silo (see Hill and Leaver, 1999 for details of construction) were used in the experiment and silo sampling were conducted using the methods reported in Hill and Leaver (2002). The calculated packing densities for forages harvested at GS 69, 82, 87 and 90 were 103, 164, 162 and 178 kg DM/m3 respectively (P<0.001). The samples of conserved forages were taken from each silo at opening and stored at −20 ◦ C for chemical analysis.
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2.3. Chemical analysis Samples of forage were analysed for oven DM (100 ◦ C for 24 h; MAFF, 1986) however, the dry matter content of samples of silage was assessed using the toluene extraction technique (MAFF, 1986). Subsamples of forages and silages for chemical compositional analysis were dried at 65 ◦ C for 48 h and milled to 1 mm. Cell wall fractions (NDFom and ADFom) of all forages and silages were assessed using the method of Van Soest et al. (1991) which included sequential extraction of each fraction, the use of sodium sulphite in the extraction solution but without ␣ amylase and cell wall contents expressed with residual ash. Crude hemicellulose content was calculated by subtraction (NDFom–ADFom) after the sequential extraction of NDF and ADF. Digestibility of samples of forages and silages were assessed using the neutral detergent cellulase digestion method of Dowman and Collins (1982). Starch (Keppler and Decker, 1984) and total ash (MAFF, 1986) were assessed in all forages and conserved feeds. Total N content of the forages and conserved products was determined using a micro-Kjeldahl method (MAFF, 1986) with a copper–selenium catalyst. The concentration of crude protein in the feed was estimated as 6.25 × N content. Ammonium N of conserved forages was assessed by micro distillation (MAFF, 1986). Aqueous extracts from the samples of forage and whole-crop silages were analysed for pH and watersoluble carbohydrate (MAFF, 1986). Concentrations of fermentation acids and ethanol of samples of silages (lactic acid, acetic acid, propionic acid and butyric acid) were assessed using the method of (Fussell and McCalley, 1987). The concentrations of calcium, magnesium, potassium and sodium in forages and silages were determined using atomic absorption spectrometry after digestion of samples in concentrated nitric acid (15.8 mol/l). Total phosphorus content of the feeds was assessed using the method of Allen (1989). 2.4. Statistical analysis The data from the field experiments was fitted to an exponential function (Y = aeb ) and rate of change in DM content (g/day) was calculated with associated standard errors (s.e.). No significant differences between years were observed for individual coefficients of regression and the data was pooled to develop a ‘unified’ between year exponential function. Linear regression was applied to determine the relationships between dry matter content and growth stage (Zadoks et al., 1974) and dry matter yield and growth stage using pooled data from all three years. Chemical compositional data (including DM losses) from the ensiling experiment in the second year of the study was subjected to analysis of variance (ANOVA) with the main effects of growth stage (3 d.f.) were assessed. Statistical analyses were conducted using SAS version 3 (SAS Institute, 1985). 3. Results 3.1. Agronomic characteristics of forage barley crops The predictive equations for harvestable DM yield of the barley crops for forage during the three years of the experiment are shown in Fig. 1. The cubic model was chosen to fit DM yield data over time, the mean square of the error being lower for the cubic model (m.s.e. = 0.36) than for the quadratic model (m.s.e. = 0.95). In Year 2 of the experiment, the forage barley crop was harvested for the ensiling experiment. The yields of forage harvested for each ensiling experiment were 10.1, 13.2, 13.3 and 13.1 t DM/ha. The efficiency of harvesting of the crops reduced substantially in relation to the more mature stages of growth from 0.98 to 0.61 for the first and last cutting dates respectively in relation to theoretical yield of biomass predicted. The variation in yield between years for the four cutting dates was estimated as 2.40, 3.54, 3.72 and 4.84 t DM/ha. The results from the analysis of the drying curves for the forage crops are summarised in Table 1. The overall rates of drying (linear) were under 5.0 g/day on average but higher rates were observed for more mature crops (greater than growth stage 80). If the forage barley crop is to be harvested between 350 and 400 g DM/kg, the “window” for harvest was estimated as 15 days providing an adequate period of time to harvest the crop efficiently. The relationships between growth stage analysis (Zadoks et al., 1974) and dry matter and yield of dry matter were investigated. The relationship between instanta-
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Fig. 1. Yield of DM (t/ha) of forage barley crop in relation to crop growth characteristics over three typical growing seasons in SE England. The arrows represent the actual cutting dates in Year 2 of the barley crop for the ensiling experiment.
Table 1 Dry matter content of winter barley harvested for whole-crop forage production. The data was fitted to an exponential function (Y = aebt ) and calculated rate of change in DM (g DM/day) with associated standard errors (s.e.).
a
b
Intercept
Exponential Rate of change of DM content
Year 1
Year 2
Year 3
Overall
111.5 (s.e. 10.4) (11 April) 0.015 (s.e. 0.007) 3.5 (s.e. 0.14)
85.7 (s.e. 9.7) (11 April) 0.016 (s.e.0.008) 2.1 (s.e. 0.09)
99.5 (s.e. 11.5) (16 April) 0.018 (s.e. 0.006) 4.1 (s.e.0.12)
108.6 (s.e. 10.1) (13 April) 0.016 (s.e. 0.007) 3.6 (s.e. 0.11)
Y = predicted DM content of winter barley at time t (days); a = DM content at time (t) = 0; b (exponential; unitless) = rate of change of DM content over the whole period; calculated rate of change of DM content reported as g DM/day.
neous drying rate and growth stage was reasonably strong (R = 0.472; P<0.05) with a predicted change in dry matter of 6.5 g/unit of growth stage. The relationship between dry matter accumulation and growth stage was again reasonably strong (R = 0.619; P<0.05) with a predictive change in dry matter yield per unit of growth stage of 0.2 t DM/ha. The aims of the crop DM compositional analysis and calculation of the harvest index were to understand how the proportion of grain and material other than grain (straw) changed during the period for harvesting the crop for forage production (Table 2). The partitioning of DM into stem, leaf and ear demonstrated repartitioning of dry matter from stem to the developing ear. The harvest index (ratio of economic yield of grain to total biomass) increased in a curvilinear fashion as the grain deposited starch. As expected, the highest harvest index (551 g/kg DM) was observed at the final harvest date suggesting the yield of grain from the harvested crop was approximately 7.2 t/ha. The changes in the proportions of the various crop fractions would alter the chemical composition of the forage for ensiling and also, potentially, alter the intake characteristics of the feeds for ruminants. The chemical compositions of harvested whole-crop barley forages are outlined in Table 2. 3.2. Chemical composition of forage before ensiling The chemical composition of the barley forage cut at the four stages of growth before ensiling is presented in Table 2. The concentrations of crude protein, water-soluble carbohydrate, phosphorus and calcium, and the estimated digestibility (NDCD) of the forage declined with increasing growth stage index and the onset of grain maturity. The average linear decline in concentration of crude protein
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Table 2 Mean crop fractionation and chemical composition of fresh forage (g/kg DM unless otherwise stated) ensiled from the crop in the second year of the experiment. Standard error of mean derived on 3, 8 d.f. Harvest date 1 Crop fractionation Growth stage (according to Zadoks et al., 1974) Harvest index (g grain/kg plant DM biomass) Chemical composition Dry matter (g/kg) Crude protein Water soluble carbohydrate Starch Neutral detergent cellulase digestibility Neutral detergent fibre Acid detergent fibre Calcium Phosphorus ns * ** ***
69 94 260 103 197 116 705 412 287 5.1 3.5
Harvest date 2
Harvest date 3
Harvest date 4
82 391
87 524
90 551
320 83 157 223 680 467 288 4.6 3.1
437 74 96 243 566 508 287 4.0 2.6
530 64 50 267 522 568 243 3.8 2.3
s.e.m
7.4*** 3.93* 6.7*** 7.5*** 6.8** 8.8* 8.1ns 0.36ns 0.32ns
P>0.05. P<0.05. P<0.01. P<0.001.
was 1.34 g/kg DM/day over the period of increasing crop maturity from growth stage 69 to 90. During the same period of crop development, there was a decrease in digestibility (NDCD) of 3.9 g/kg DM/day reflecting concomitant increases in lignification of the crop. The concentration of starch increased from 116 to 267 g/kg DM in the whole-crop during the period growth stage 69 –90. This increase (linear increase of 3.4 g starch/kg DM/day) suggested continued deposition of starch in the developing grain during the potential harvesting period of the crop for forage production. The decline in the concentrations of calcium and phosphorus were similar to those observed by other authors examining cereal forages (Edwards et al., 1968; Cherney and Marten, 1982; Acosta et al., 1991). The rates of decline for both minerals were similar (approximately 0.03 g/kg DM/day) and therefore there were no substantial changes in the Ca:P ratio during crop maturity. The only substantial increase in the Ca:P ratio was for crops harvested at growth stage 90 where the ratio increased from an average of 1.48 (from GS 69 to 87) to 1.90. 3.3. Chemical composition of ensiled whole-crop barley The chemical compositions of the whole-crop barley silages immediately after silo opening are presented in Table 3. As expected the toluene DM of the silages increased (P<0.001) with stages of maturity of the crop with a range of DM contents of 250–530 g DM/kg. Increasing crop maturity leads to an increase in concentrations of starch (P<0.001) in the silages with relatively high concentrations (>200 g/kg of dry matter) being observed in forages cut at growth stages 87 and 90. However, there was an overall decline in the digestibility (NDCD; P<0.001) of conserved silages with increasing crop maturity. The linear rate of decline in digestibility over the whole range of crop maturities was estimated as 2.6 g/kg DM/day, less than that observed for the fresh forage suggesting a restricted fermentation in forages above 400 g DM/kg (Fig. 2). The fermentation process reduced substantially the concentrations of water-soluble carbohydrate in the ensiled forage compared to the fresh forage. The proportion of residual WSC in silage did however increase with increasing crop maturity (0.051, 0.077, 0.167 and 0.560 of WSC retained in silage after the processes of fermentation from forages cut at GS 69, 82, 87 and 90 respectively). These changes are typical of a so-called restricted fermentation reflecting the relatively high dry matter content (or more strictly the lower moisture content) of mature cereal forages used for silage production. These observations were further supported by the pH, yield of total fermentation acids and individual volatile fatty acid concentrations. Silages that were made from forage cut at the most mature stage of growth had a substantially lower production (P<0.001) of total fermentation acids (38.9 g/kg DM for
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Table 3 Chemical composition of silages (g/kg DM unless otherwise stated) at opening of the silos made from barley whole-crop forage cut at four stages of growth. Standard error of mean derived on 3, 8 d.f.
Toluene dry matter (g/kg) Crude protein Water soluble carbohydrate Starch Neutral detergent cellulase digestibility pH Ammonia-N (g/kg total N) Ethanol Lactic acid Acetic acid Butyric acid DM losses ns * ** ***
Harvest date 1
Harvest date 2
Harvest date 3
Harvest date 4
s.e.m
251 98 10 92 680 4.50 186 28.9 80.6 122.0 0.8 109
322 74 12 218 614 4.85 141 61.0 91.6 112.0 50.5 82
432 76 16 234 575 5.29 71 25.4 23.9 24.0 34.0 96
530 67 28 287 559 5.75 55 3.1 1.7 7.7 29.5 110
8.8*** 4.10ns 0.90*** 11.9*** 3.28** 0.31** 19.2* 1.56*** 7.49** 10.1*** 1.90*** 3.18**
P>0.05. P<0.05. P<0.01. P<0.001.
GS 90) compared to those made from the least mature forage (203.4 g/kg DM for GS 69). The pH and concentrations of the various fermentation acids for silages made with the least mature forage (GS 69) were typical of acetic acid dominated fermentation (lactic acid to acetic ratio of 1:1.5. These silages contained little or no butyric acid and had a pH of 4.5. However, these silages did however contain high concentrations of ammonia-N (186 g/kg total N). Silages produced from forages cut at growth stage 82 were similar to those conserved from immature forages, having acetic acid dominated fermentation (lactic acid to acetic acid ratio of 1:1.22), relatively high pH (4.85) and high concentrations of ammoniaN (141 g/kg total N). However, these silages differed from those made from the most immature forage insofar that they contained high concentrations of butyric acid (50.5 g/kg DM). When the dry matter content of the forage exceeded 400 g/kg, the processes of fermentation were restricted. The silages made from forage of approximately 435 g DM/kg was characterised by pH 5.3, total fermentation acids of 81.9 g/kg DM of which lactic and acetic acids contributed 0.584 of total fermentation acids. The concentration of butyric acid was again elevated to 34 g/kg DM, however the concentration of ammonia-N was lower than the two immature silages being 71 g/kg total N. When the dry matter content of the fresh forage exceeded 500 g DM/kg, the restriction in fermentation was substantial. The yield of total fermentation acids was 38.9 g/kg DM of which butyric acid comprised over 0.750 (29.5 g/kg DM) of total acid production. The pH of these silages was 5.75 and concentration of ammonia-N was 55 g/kg total N.
Fig. 2. Digestibility (neutral detergent cellulase digestibility; NDCD g/kg DM) of fresh () and ensiled () whole-crop barley cut at four stages of growth.
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3.4. Dry matter losses during storage Losses of DM during fermentation are shown in Table 3. Unusually, total DM losses were lowest in silages made from barley cut at growth stage 82 (P<0.01) compared to other treatments. The highest losses were in the silages made from the most immature whole-crop forage. 4. Discussion 4.1. Development of DM yield The DM yield of winter barley crops for forage production cut at similar stages of crop maturity are lower than those observed for winter wheat crops cut for silage production (Hill and Leaver, 1999). This reduction in yield suggests the crop may initially seem to reduce economic output from arable land integrated into dairy systems, but the earlier harvest date of barley crops for forage production makes such crops attractive from dual summer cropping system (e.g. integration of turnips or forage brassica into grazing systems in rain-fed dryland pasture systems). For cereal crops to be acceptable as alternative forage crops in dairy production systems they must have moderate to high harvestable yield of dry matter per hectare which is subsequently conserved as hay or silage. These conserved wholecrop forages must also have the attributes of moderate to high energy value and high intake potential. This paper examines in detail the former attributes (composition of yield and nutritive value). One of the most important factors that determine the successful utilisation of cereal crops for forage in dairy systems is the prediction of harvest date. The decision-making processes to identify if a crop is suitable for harvesting are complex and are outlined in Fig. 3. The relationship between harvest date is informed by several factors, for instance if the crop is being used for chemical treatment or ensiling, the classification of livestock being offered the feed after conservation and the climatic and environmental factors associated with the development of yield. The key “on-farm” factor that has to be identified and monitored is the drying rate of the crop. For ensiling the target dry matter of the crop should be between 350 and 450 g DM/kg. The rate of drying between 350 and 450 g DM/kg was estimated as below 5 g DM/kg/day (similar to observations by Corrall et al., 1977). The estimated harvest window for the crop for ensiling is approximately 20 days, however periods of hot dry weather during this period can shorten the harvest window to about 10 days (Harvey, 1992). In the experiments reported in this paper, the DM yield of the crop would range between 7 and 13 t DM/ha harvestable forage with a harvest index of approximately 500 g/kg DM (Rasmusson and Gengenbach, 1984). These were comparable to observations by Corrall et al. (1977), Tetlow and Mason (1987) and Kristensen (1992), however the range is considerable from an economic yield point of view as well as a whole farm feed supply. A far simpler method of appraising the optimum harvesting date for cereal forages is the use of growth stage key of Zadoks et al. (1974). The relationship between growth stage and instantaneous drying rate was reasonably strong (approximately 0.47 of variance accounted for; P<0.05) with a predicted change in dry matter of 6.5 g/unit of growth stage. The use of growth stages analysis to predict instantaneous drying rate is however contentious. For instance, Harvey (1992) reported that growth stage by itself was a poor predictor for forecasting DM content and DM yield in winter wheat crops for forage. Local climatic conditions and crop water deficits during the development of floral primordia has been demonstrated to delay the onset of anthesis and development of grain in cereal crops. Furthermore, if the crop water deficit occurs immediately after anthesis, the development of the grain and deposition of starch can be compromised, thus reducing the harvest index or total biomass yield. These changes would alter either total harvestable yield or the quantity of starch harvested per hectare—an important criteria for selection of cereal crops as a forage crop in dairy production systems. 4.2. Crop composition before harvesting and its possible impact on ensilability of cereal forages Hill and Leaver (1999) examined the re-partitioning of non-structural carbohydrate and mobilisation of nitrogenous compounds from leaf and stem fractions to develop grain in winter wheat crops for forage production. The data presented in this paper is similar to those reported in Hill and Leaver
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Fig. 3. Decision support process for harvesting cereal crops in dairy production systems.
(1999) but there are some important differences that have to be identified. The overall contribution of grain to total biomass is generally higher in winter barley compared to winter wheat however the starch content of barley grain is lower than that of wheat. This apparent compensation—higher overall contribution of grain but lower starch content per grain leads to similar concentrations of starch in harvested forage from wheat and barley crops (Bonnett and Incoll, 1992, 1993). The partitioning of the “material other than grain” fraction (MOG) does however highlight the reasons why the digestibility (NDCD) of barley forage is lower than that of wheat forage cut at the same stage of maturity. The contribution of leaf biomass to total MOG is lower in barley than wheat and therefore the MOG fraction has a lower digestibility in barley than wheat crops. These factors, and the previously identified compensatory effects during grain development, are critical factors in the determination of the overall chemical compositional analysis of whole-crop cereal forage prior to ensiling. Furthermore, the apparent changes in the concentrations of readily degradable substrates (e.g. WSC and starch) during crop development and grain fill also provide a mechanism to identify the reasons
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for the underlying processes that restrict the fermentation observed in the silages reported in this paper. Two important chemical compositional attributes of cereal forage for silage production are crude protein and WSC. The crude protein content was low (approximately 100 g/kg DM) in the least mature forage at harvest and there was a progressive decline in the crop to less than 70 g/kg DM in the most mature forage. These concentrations fall within the ranges predicted by Bruno-Soares et al. (1998) and Acosta et al. (1991) for green cereal crops. The decline in crude protein content during crop maturation has been reported previously. Edwards et al. (1968) reported the average crude protein content of eight varieties of barley declined from 103 g/kg DM (heading completed) to 66 g/kg DM (ripe for cutting). Furthermore the nitrogen content of spring barley crops monitored by Corrall et al. (1977) also had a similar decline in crude protein content. The concentration of WSC in cereal forage is lower than that observed in many other grass species (McDonald et al., 1991; MacGregor and Edwards, 1968). The impact of lower concentrations of WSC and the concomitant increasing concentration of starch in the forage as the crop matures reduces the potential production of fermentation acids during the ensiling period. Typically, if the forage for silage production is immature at harvest, the fermentation is dominated by lactic acid production with moderate concentrations of acetic acid—a situation typical of a heterofermentative microflora. In this paper we report a situation where the ratio of lactic acid to acetic acid diverged from the typical > 2.5:1 ratio to 1:1.5 or more. The shift in the concentrations of lactic and acetic acids may reflect a fermentation process dominated by acetic acid bacteria for instance Acetobacter. The changes in the ratio reflect several factors, principally silo packing density, concentrations of WSC and other substrates available for fermentation. The silo packing densities reported in this experiment are lower (by about 0.15) than those reported by Hill and Leaver (2002). The reduction in silo packing density also reflects the degree of consolidation of the crop and therefore the amount of air trapped in the harvested forage during silo loading. The fresh weight packing densities of the various silage treatments ranged from 335 to 513 kg/m3 (396, 513, 370 and 335 kg/m3 for GS 69, 82, 87 and 90 respectively). Microaerophilic conditions in the silage would lead to an increase in dominance of acetic acid bacteria compared to lactic acid bacteria (McDonald et al., 1991). The formation of butyric acid in silages made at intermediate cutting dates reflect two processes, the conversion of lactic acid to butyric acid presumably reflecting the presence of Clostridia and the process of proteolysis releasing ammonia and butyric acid. These processes alter pH by the effect of ammonia release and loss of free acidity. The concentrations of butyric acid in silages of 350–450 g DM/kg are approaching the theoretical maximum concentration for silages dominated by heterofermentative microflora. The implications of the heterofermentative fermentation or conservation processes dominated by the formation of acetic or butyric acid are that the silages have variable aerobic stability (Woolford, 1984) and their intake potential may be compromised (Tetlow and Mason, 1987). 4.3. Aerobic stability of silages Feed wastage prior to harvest, during conservation and at feedout has been poorly characterised in farming systems. Wastage is the Achilles’ heal of economic profitability of a feeding system and if not considered, claims concerning the integration of new alternative feeding systems at pasture can be questioned. One of the main problems identified by many authors investigating whole-crop cereal silages is the poor stability of the silage once exposed to the air. Anecdotal evidence suggests losses of ensiled feed can be as high at 0.30 (dry matter basis), thus rendering the crop as a forage for dairy production uneconomic. The highest dry matter losses were observed in silages of 437 g DM/kg and the lowest observed in silages of 320 g DM/kg. These observations reflect two processes. In wet silages (those made of immature forage) the presence of water in the forage mass acts as a heat sink, thus reducing the overall silo temperature when exposed to air. These immature silages do however contain moderate to high concentrations of lactic acid (a partially volatile fermentation acid) which under the correct aerobic conditions can be converted to butyric acid (a potent inhibitor of yeast and microfungi—the principal organisms controlling aerobic deterioration in silage). This process is partially demonstrated in the silages made of the most immature cereal forage. Silages containing
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the highest concentrations of butyric acid are generally highly stable under aerobic conditions. This was highlighted by the low rise in temperature immediately after opening of the whole-crop barley silage made with forage cut at about 350 g DM/kg. The most rapid deterioration was observed in silage made from forage cut at 450 g DM/kg. This is the worst-case situation insofar as silage production. The forage has poor consolidation characteristics, a reasonable supply of rapidly fermentable substrates but a restricted fermentation. Silages of these characteristics heat and deteriorate rapidly; a process mediated by yeast and microfungi. 5. Conclusions The processes of fermentation were affected by the stage of growth of the forage at ensiling and hence the economics of silage production. If the forage was too immature at ensiling, the yield of crop would be compromised but the silage produced may have moderate to high nutritive value and reasonable aerobic stability during the feed out phase. This situation may be acceptable if the dryland dairy system received adequate rainfall and forage supplies were plentiful. If however, the whole-crop forage was grown as a crop to secure high levels of supplementary feed from an alternative forage source (other than grass), the trade-off between yield, nutritive value and losses of feed immediately after silo opening would suggest the crop should be harvested between 350 and 450 g DM/kg. Decisions to harvest the crop at dry matter contents of greater than 450 g DM/kg should be based on options to either chemically treat the forage (e.g. urea treatment) or utilise the grain and straw as individual feed components on farm or sold into other markets. Acknowledgements The authors wish to thank P. Drury and J. Greenland for technical assistance. References Acosta, Y.M., Stallings, C.N., Polan, C.E., 1991. Evaluation of barley silage harvested at boot and soft dough stages. J. Dairy Sci. 74, 167. Adesogan, A.T., Owen, E., Givens, D.I., 1999. Prediction of the metabolisable energy value of whole-crop wheat from laboratorybased measurements. Anim. Sci. 68, 427–439. Allen, S., 1989. Chemical Analysis of Ecological Materials. Blackwell Scientific Publications. Bonnett, G.D., Incoll, L.D., 1992. The potential pre-anthesis and post-anthesis contributions of stem internodes to grain yield in crops of winter barley. Ann. Bot. 69, 219–225. Bonnet, G.D., Incoll, L.D., 1993. Effects on the stem of winter barley of manipulating the source and sink during grain filling, II. Changes in the composition of water-soluble carbohydrates of internodes. J. Exp. Bot. 44, 83–91. Bruno-Soares, A.M., Murray, I., Paterson, R.M., Abreu, J.M.F., 1998. Use of near infrared reflectance spectroscopy (NIRS) for the prediction of the chemical composition and nutritional attributes of green crop cereals. Anim. Feed Sci. Technol. 75, 15–25. Cherney, J.H., Marten, G.C., 1982. Small grain crop forage potential: II. Interrelationships among biological, chemical, morphological and anatomical determinants of quality. Crop Sci. 22, 240–245. Corrall, A.J., Heard, A.J., Fenlon, J.S., Terry, C.P., Lewis, G.C., 1977. Whole-crop forages. In: Relationship Between Stage of Growth, Yield and Forage Quality in Small Grain Cereal and Maize. Grassland Research Institute, Hurley, U.K, Technical Report N◦ 22. De Ruiter, J.M., Hanson, R., 2004. Whole-crop cereal silage. In: Production and Use in Dairy, Beef, Sheep and Deer Farming. New Zealand Institute for Crop and Food Research Limited, Christchurch, NZ, p.33. Dowman, M.G., Collins, F.C., 1982. The use of enzymes to predict the digestibility of animal feeds. J. Sci. Fd. Agric. 33, 689–696. Edwards, R.A., Donaldson, E., MacGregor, A.W., 1968. Ensilage of whole-crop barley, I. Effects of variety and stage of growth. J. Sci. Fd. Agric. 19, 656–660. Fisher, L.J., Lessard, J.R., Lodge, G.A., 1972. Whole-crop barley as conserved forage for lactating cows. Can. J. Anim. Sci. 52, 497–504. Fussell, R.J., McCalley, D.V., 1987. Determination of volatile fatty acids (C2 –C5 ) and lactic acid in silage by gas chromatography. Analyst 112, 1213–1216. Harvey, J.J., 1992. Assessing whole-crop cereal maturity in the field. In: Stark, B.A., Wilkinson, J.M. (Eds.), Whole-crop Cereals. Chalcombe Publications, Canterbury, UK, pp.39–50. Hill, J., Leaver, J.D., 1999. Effect of stage of growth at harvest and level of urea application on chemical changes during storage of whole-crop wheat. Anim. Feed Sci. Technol. 77, 281–301. Hill, J., Leaver, J.D., 2002. Changes in chemical composition and nutritive value of urea treated whole-crop wheat during exposure to air. Anim Feed Sci. Technol. 102, 181–195. Juskiw, E., Patricia, Jame, Y.W., Kryzanowski, L., 2001. Phenological development of spring barley in a short-season growing area. Agron. J. 93, 370–379. Keppler, D., Decker, K., 1984. In: Bergmeyer, H.U. (Ed.), Methoden der enzymetischen Analyse, 2. Verlag, Weinheim, Germany, pp. 1171–1176.
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Kristensen, V.F., 1992. The production and feeding of whole-crop cereals and legumes in Denmark. In: Stark, B.A., Wilkinson, J.M. (Eds.), Whole-crop Cereals. Chalcombe Publications, Canterbury, UK, pp. 21–37. McDonald, P., Henderson, A.R., Heron, S.J.E., 1991. The Biochemistry of Silage, Second Edition. Chalcombe, p. 340. MacGregor, A.Q., Edwards, R.A., 1968. Ensilage of whole-crop barley, 2. Composition of barley and barley silage at different stages of growth. J. Sci. Fd. Agric. 19, 661–666. 1986. The Analysis of Agricultural Materials. HMSO, London, UK. O’Kiely, P., Moloney, A.P., 1991. 1991 Live and carcass weight grains of cattle offered whole-crop barley silage harvested at an immature growth stage. BSAP Winter Meeting, 149. Polan, C.E., Starling, T.M., Huber, J.T., Miller, C.N., Sandy, R.A., 1968. Yields, compositions and nutritive evaluation of barley silages at three stages of maturity for lactating cows. J. Dairy Sci. 51, 1801–1805. Rasmusson, C.D., Gengenbach, B.G., 1984. Genetics and use of physiological variability in crop breeding. In: Tesar, M.B. (Ed.), Physiological Basis of Crop Growth and Development. The American Society of Agronomy, Madison, Wisconsin, USA, pp. 291–320. SAS Institute Inc., 1985. Statistical Analysis with SAS. SAS Institute, Cary, USA. Tetlow, R.M., Mason, V.C., 1987. Treatment of whole-crop cereals with alkali. 1. The influence of sodium hydroxide and ensiling on the chemical composition and in vitro digestibility of rye, barley and wheat harvested at increasing maturity and dry matter content. Anim. Feed. Sci. Technol. 18, 257–271. Van Soest, P.J., Robertson, J.B., Lewis, R.A., 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74, 3583–3597. Weller, R.F., Cooper, A., Dhanoa, M.S., 1992. The National Whole-Crop Cereals survey. In: Stark, B.A., Wilkinson, J.M. (Eds.), Whole-crop Cereals. Chalcombe Publications, Canterbury, UK, pp. 137–156. Woolford, M.K., 1984. The Silage Fermentation. Marcel Dekker, NY, US. Zadoks, J.C., Chang, T.T., Konzak, C.F., 1974. A decimal code for the growth stage of cereals. Weed Res. 14, 415–421.
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Animal Feed Science and Technology journal homepage: www.elsevier.com/locate/anifeedsci
Effect of stage of growth on the chemical composition, nutritive value and ensilability of whole-crop barley A. Hargreaves a,∗, J. Hill b, J.D. Leaver c a
Pontificia Universidad Católica de Chile, Facultad de Agronomía e Ingeniería Forestal, P.O. Box 306, 22 Santiago, Chile Department of Agriculture and Food Systems, Melbourne School of Land and Environment, University of Melbourne, Parkville, Victoria 3010, Australia c Royal Agricultural College, Cirencester, GL7 6JS, United Kingdom b
a r t i c l e
i n f o
Article history: Received 10 April 2008 Received in revised form 12 February 2009 Accepted 16 March 2009 Keywords: Cereal silage Chemical composition Nutritive value Deterioration
a b s t r a c t Chemical composition, nutritive value and ensilability of wholecrop barley as a supplementary feed for dairy cows was investigated using a range of maturities of barley (seed coat ripe—GS 69, early dough stage—GS 82, soft dough—GS 87 and grain ripe—GS 90) in small scale silos. The ensiling experiment was based on a complete randomised design with three replicate silos per harvest date. Twelve 0.225 m3 plastic silo (were used in the experiment and silo were sampled on opening for chemical composition and nutritive value. The fermentation process reduced the concentrations of water-soluble carbohydrate in the ensiled forage compared to the fresh forage. The proportion of residual WSC in silage did however increase with increasing crop maturity (0.051, 0.077, 0.167 and 0.560 of WSC retained in the silage after the process of fermentation from forages cut at GS 69, 82, 87 and 90 respectively). Silages that were made from forage cut at the most mature stage of growth had a substantially lower production (P<0.001) of total fermentation acids (38.9 g/kg DM for GS 90) compared to those made from the least mature forage (203.4 g/kg DM for GS 69). The pH and concentrations of the various fermentation acids for silages made with the least mature forage (GS 69) were typical of acetic acid dominated fermentation. These silages contained little or no butyric acid and had a pH of 4.5 and contained high concentrations of ammoniaN (186 g/kg total N). Silages produced from forages cut at growth
Abbreviations: DM, oven dry matter; GS, growth stage; NDFom, neutral detergent fibre; ADFom, acid detergent fibre; N, nitrogen; WSC, water soluble carbohydrate; NDCD, neutral detergent cellulose digestibility; MOG, material other than grain. ∗ Corresponding author. E-mail address: [email protected] (A. Hargreaves). 0377-8401/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2009.03.007
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stage 82 were similar to those conserved from immature forages, having acetic acid dominated fermentation (lactic acid to acetic acid ratio of 1:1.22), relatively high pH (4.85) and high concentrations of ammonia-N (141 g/kg total N). These silages differed from those made from the most immature forage insofar that they contained high concentrations of butyric acid (50.5 g/kg DM). The processes of fermentation were affected by the stage of growth of the forage at ensiling and hence the economics of silage production. If the forage was too immature at ensiling, the yield of crop would be compromised but the silage produced may have moderate to high nutritive value and reasonable aerobic stability during the feed out phase. If the whole-crop forage was grown as a crop to secure high levels of supplementary feed from an alternative forage source (other than grass), the trade-off between yield, nutritive value and losses of feed immediately after silo opening would suggest the crop should be harvested between 350 and 450 g DM/kg dry matter. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Traditionally, the dairy and beef sectors have conserved surpluses in pasture production to alleviate feed shortages during periods of low pasture productivity or drought. Recently, there has been increasing interest in the use of alternative forage crops in pasture-based systems with small grain cereal crops (including maize) being preferred. Whole-crop cereals as a forage for dairy cows can provide several advantages to the dairy sector. For instance the cereal cropping system can be incorporated into a programme of pasture renovation (De Ruiter and Hanson, 2004), it can provide a source of supplementary feed with characteristics of high digestibility and substantial levels of starch (Adesogan et al., 1999) and cereal crops can be grown in areas where maize silage is limited by climatic conditions (Weller et al., 1992). The use of whole-crop cereal systems also provides an ideal opportunity to integrate arable cropping and the dairy sector leading to greater opportunities for each sector to transfer expertise and improve financial returns. One of the important issues that has to be considered for the exploitation of whole-crop cereals in pasture-based dairy systems is the “trade-off” between harvestable yield and the nutritive value of the cereal crop. This situation is not well defined but an understanding of this balance is essential for the subsequent utilisation of cereal crops in dairy systems. From a practical point of view the dairy farmer requires precise information on harvest date, a method to evaluate date of harvest (growth stage or grain characteristics) potential yield and subsequent losses of DM during storage and feedout, and nutritive value to achieve high financial returns from an alternative cropping system. If maximum yield of dry matter per hectare is to be achieved under northern European conditions, winter-sown whole-crop barley must be harvested at about 500 g DM/kg of dry matter (DM) content (Tetlow and Mason, 1987). However there is evidence that the relationship between growth stage of the crop and DM content is poor and it is therefore difficult to predict precisely physiological maturity and hence maximum yield (Fisher et al., 1972; Juskiw et al., 2001). If the “trade-off” between yield and nutritive value is considered and a target of 80–90% of the maximum yield is identified for winter-sown wholecrop barley, the crop could be harvested at growth stages concomitant to 300–350 g DM/kg (Tetlow and Mason, 1987; O’Kiely and Moloney, 1991). Delaying harvest for maximum yield of cereal crops for forage production (mature stages of growth) has been demonstrated to lead to extensive lignification of the stem, leaf sheath and lemma/palea reducing the digestibility of the straw and chaff fraction. Grain testa permeability is also reduced leading to a reduction in the availability of starch to digestion in the rumen. Therefore it has been suggested that whole-crop barley should be harvested for silage no later than early dough or soft dough stage of growth to ensure that the forage has high intake characteristics, maintains a moderate to high digestibility of nutrients (Polan et al., 1968; Fisher et al., 1972) and an economic yield of forage per hectare.
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The objectives of the study reported in this paper were to examine the effect of harvest date on yield of forage, chemical composition and ensilability of whole-crop barley for subsequent feeding to dairy cows as a supplement to grazed grass.
2. Material and methods 2.1. Forage agronomy Winter barley crops (vars. Pipkin and Puffin) were grown on a field scale under a conventional cropping pattern (prophylactic spray programme to control weed, fungal and aphid populations). The crops were drilled into a prepared seed-bed (Argillic brown earth; Hamble series) on in mid September of each growing season at a seed rate of 235 kg/ha and 80 kg N/ha was applied in the spring of each year. The total crop area established each year was 11 ha of which 1.1 ha were harvested for whole-crop cereal production. Each crop was sampled weekly with the first sample taken immediately after the early booting stage of growth (growth stage (GS) 41–42; Zadoks et al., 1974) from mid-April onwards until harvest for forage conservation. At each harvest date, stage of growth was recorded using the Zadoks cereal growth stage key (Zadoks et al., 1974). Eight 0.25 m2 quadrat samples were cut randomly from the area destined for whole-crop forage production. Each sample was cut to ground level using hand shears (stainless steel) at 1200 h, collected for subsequent assessment of the harvested crop for components of yield and biomass. All plants in the sub sample were cut at 10 cm from the base to simulate the stubble height after cutting. Both the upper portion of the plant and the 10 cm-stubble, were weighed separately and then dried at 100 ◦ C for 24 h to estimate DM content and yield of harvested crop and total biomass. Samples of crops were taken every fortnight from the samples from the upper portion of the crop and stubble fraction (200 and 50 g fresh matter respectively), dried at 65 ◦ C to constant weight, ground to 1 mm and stored for subsequent chemical analysis. After the emergence of the inflorescence (GS: 60–65), whole plants (n = 15) were taken at random from the samples cut for yield estimation and separated into inflorescence (ear), stem (excluding the leaf sheath) and leaf fractions. Each component of yield was weighed and dried to constant weight at 100 ◦ C to calculate the contribution of each fraction to total biomass yield. Grains were threshed from the ear fraction, counted, weighed and the harvest index calculated (contribution of grain mass to total biomass. Thousand grain weights were also calculated from the grain samples to examine grain fill during the period of ear emergence to final harvest.
2.2. Ensiling experiment In the second year of the three years of crop monitoring an ensiling experiment was conducted. The ensiling experiment was based on the techniques reported by Hill and Leaver (1999). A winter barley crop (var. Pipkin) was swathed to 10 cm stubble height at four stages of growth (GS 69 (seed coat water ripe), 82 (early dough development), 87 (soft dough), and 90 (grain ripe); Zadoks et al., 1974) using an oilseed rape swather (1.5 m reciprocating blade, reel and side unloading belt). The objective of the experiment was to cut the crop at dry matter contents of 250, 350, 450, and 550 g/kg but use the growth stage of the crop as an on-farm tool to estimate the cutting date. The crops for ensiling were harvested immediately using a self-propelled precision chop forage harvester with a pick up reel and chop length set at 25 mm. The ensiling experiment was based on a complete randomised design with three replicate silos per harvest date. Twelve 0.225 m3 plastic silo (see Hill and Leaver, 1999 for details of construction) were used in the experiment and silo sampling were conducted using the methods reported in Hill and Leaver (2002). The calculated packing densities for forages harvested at GS 69, 82, 87 and 90 were 103, 164, 162 and 178 kg DM/m3 respectively (P<0.001). The samples of conserved forages were taken from each silo at opening and stored at −20 ◦ C for chemical analysis.
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2.3. Chemical analysis Samples of forage were analysed for oven DM (100 ◦ C for 24 h; MAFF, 1986) however, the dry matter content of samples of silage was assessed using the toluene extraction technique (MAFF, 1986). Subsamples of forages and silages for chemical compositional analysis were dried at 65 ◦ C for 48 h and milled to 1 mm. Cell wall fractions (NDFom and ADFom) of all forages and silages were assessed using the method of Van Soest et al. (1991) which included sequential extraction of each fraction, the use of sodium sulphite in the extraction solution but without ␣ amylase and cell wall contents expressed with residual ash. Crude hemicellulose content was calculated by subtraction (NDFom–ADFom) after the sequential extraction of NDF and ADF. Digestibility of samples of forages and silages were assessed using the neutral detergent cellulase digestion method of Dowman and Collins (1982). Starch (Keppler and Decker, 1984) and total ash (MAFF, 1986) were assessed in all forages and conserved feeds. Total N content of the forages and conserved products was determined using a micro-Kjeldahl method (MAFF, 1986) with a copper–selenium catalyst. The concentration of crude protein in the feed was estimated as 6.25 × N content. Ammonium N of conserved forages was assessed by micro distillation (MAFF, 1986). Aqueous extracts from the samples of forage and whole-crop silages were analysed for pH and watersoluble carbohydrate (MAFF, 1986). Concentrations of fermentation acids and ethanol of samples of silages (lactic acid, acetic acid, propionic acid and butyric acid) were assessed using the method of (Fussell and McCalley, 1987). The concentrations of calcium, magnesium, potassium and sodium in forages and silages were determined using atomic absorption spectrometry after digestion of samples in concentrated nitric acid (15.8 mol/l). Total phosphorus content of the feeds was assessed using the method of Allen (1989). 2.4. Statistical analysis The data from the field experiments was fitted to an exponential function (Y = aeb ) and rate of change in DM content (g/day) was calculated with associated standard errors (s.e.). No significant differences between years were observed for individual coefficients of regression and the data was pooled to develop a ‘unified’ between year exponential function. Linear regression was applied to determine the relationships between dry matter content and growth stage (Zadoks et al., 1974) and dry matter yield and growth stage using pooled data from all three years. Chemical compositional data (including DM losses) from the ensiling experiment in the second year of the study was subjected to analysis of variance (ANOVA) with the main effects of growth stage (3 d.f.) were assessed. Statistical analyses were conducted using SAS version 3 (SAS Institute, 1985). 3. Results 3.1. Agronomic characteristics of forage barley crops The predictive equations for harvestable DM yield of the barley crops for forage during the three years of the experiment are shown in Fig. 1. The cubic model was chosen to fit DM yield data over time, the mean square of the error being lower for the cubic model (m.s.e. = 0.36) than for the quadratic model (m.s.e. = 0.95). In Year 2 of the experiment, the forage barley crop was harvested for the ensiling experiment. The yields of forage harvested for each ensiling experiment were 10.1, 13.2, 13.3 and 13.1 t DM/ha. The efficiency of harvesting of the crops reduced substantially in relation to the more mature stages of growth from 0.98 to 0.61 for the first and last cutting dates respectively in relation to theoretical yield of biomass predicted. The variation in yield between years for the four cutting dates was estimated as 2.40, 3.54, 3.72 and 4.84 t DM/ha. The results from the analysis of the drying curves for the forage crops are summarised in Table 1. The overall rates of drying (linear) were under 5.0 g/day on average but higher rates were observed for more mature crops (greater than growth stage 80). If the forage barley crop is to be harvested between 350 and 400 g DM/kg, the “window” for harvest was estimated as 15 days providing an adequate period of time to harvest the crop efficiently. The relationships between growth stage analysis (Zadoks et al., 1974) and dry matter and yield of dry matter were investigated. The relationship between instanta-
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Fig. 1. Yield of DM (t/ha) of forage barley crop in relation to crop growth characteristics over three typical growing seasons in SE England. The arrows represent the actual cutting dates in Year 2 of the barley crop for the ensiling experiment.
Table 1 Dry matter content of winter barley harvested for whole-crop forage production. The data was fitted to an exponential function (Y = aebt ) and calculated rate of change in DM (g DM/day) with associated standard errors (s.e.).
a
b
Intercept
Exponential Rate of change of DM content
Year 1
Year 2
Year 3
Overall
111.5 (s.e. 10.4) (11 April) 0.015 (s.e. 0.007) 3.5 (s.e. 0.14)
85.7 (s.e. 9.7) (11 April) 0.016 (s.e.0.008) 2.1 (s.e. 0.09)
99.5 (s.e. 11.5) (16 April) 0.018 (s.e. 0.006) 4.1 (s.e.0.12)
108.6 (s.e. 10.1) (13 April) 0.016 (s.e. 0.007) 3.6 (s.e. 0.11)
Y = predicted DM content of winter barley at time t (days); a = DM content at time (t) = 0; b (exponential; unitless) = rate of change of DM content over the whole period; calculated rate of change of DM content reported as g DM/day.
neous drying rate and growth stage was reasonably strong (R = 0.472; P<0.05) with a predicted change in dry matter of 6.5 g/unit of growth stage. The relationship between dry matter accumulation and growth stage was again reasonably strong (R = 0.619; P<0.05) with a predictive change in dry matter yield per unit of growth stage of 0.2 t DM/ha. The aims of the crop DM compositional analysis and calculation of the harvest index were to understand how the proportion of grain and material other than grain (straw) changed during the period for harvesting the crop for forage production (Table 2). The partitioning of DM into stem, leaf and ear demonstrated repartitioning of dry matter from stem to the developing ear. The harvest index (ratio of economic yield of grain to total biomass) increased in a curvilinear fashion as the grain deposited starch. As expected, the highest harvest index (551 g/kg DM) was observed at the final harvest date suggesting the yield of grain from the harvested crop was approximately 7.2 t/ha. The changes in the proportions of the various crop fractions would alter the chemical composition of the forage for ensiling and also, potentially, alter the intake characteristics of the feeds for ruminants. The chemical compositions of harvested whole-crop barley forages are outlined in Table 2. 3.2. Chemical composition of forage before ensiling The chemical composition of the barley forage cut at the four stages of growth before ensiling is presented in Table 2. The concentrations of crude protein, water-soluble carbohydrate, phosphorus and calcium, and the estimated digestibility (NDCD) of the forage declined with increasing growth stage index and the onset of grain maturity. The average linear decline in concentration of crude protein
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Table 2 Mean crop fractionation and chemical composition of fresh forage (g/kg DM unless otherwise stated) ensiled from the crop in the second year of the experiment. Standard error of mean derived on 3, 8 d.f. Harvest date 1 Crop fractionation Growth stage (according to Zadoks et al., 1974) Harvest index (g grain/kg plant DM biomass) Chemical composition Dry matter (g/kg) Crude protein Water soluble carbohydrate Starch Neutral detergent cellulase digestibility Neutral detergent fibre Acid detergent fibre Calcium Phosphorus ns * ** ***
69 94 260 103 197 116 705 412 287 5.1 3.5
Harvest date 2
Harvest date 3
Harvest date 4
82 391
87 524
90 551
320 83 157 223 680 467 288 4.6 3.1
437 74 96 243 566 508 287 4.0 2.6
530 64 50 267 522 568 243 3.8 2.3
s.e.m
7.4*** 3.93* 6.7*** 7.5*** 6.8** 8.8* 8.1ns 0.36ns 0.32ns
P>0.05. P<0.05. P<0.01. P<0.001.
was 1.34 g/kg DM/day over the period of increasing crop maturity from growth stage 69 to 90. During the same period of crop development, there was a decrease in digestibility (NDCD) of 3.9 g/kg DM/day reflecting concomitant increases in lignification of the crop. The concentration of starch increased from 116 to 267 g/kg DM in the whole-crop during the period growth stage 69 –90. This increase (linear increase of 3.4 g starch/kg DM/day) suggested continued deposition of starch in the developing grain during the potential harvesting period of the crop for forage production. The decline in the concentrations of calcium and phosphorus were similar to those observed by other authors examining cereal forages (Edwards et al., 1968; Cherney and Marten, 1982; Acosta et al., 1991). The rates of decline for both minerals were similar (approximately 0.03 g/kg DM/day) and therefore there were no substantial changes in the Ca:P ratio during crop maturity. The only substantial increase in the Ca:P ratio was for crops harvested at growth stage 90 where the ratio increased from an average of 1.48 (from GS 69 to 87) to 1.90. 3.3. Chemical composition of ensiled whole-crop barley The chemical compositions of the whole-crop barley silages immediately after silo opening are presented in Table 3. As expected the toluene DM of the silages increased (P<0.001) with stages of maturity of the crop with a range of DM contents of 250–530 g DM/kg. Increasing crop maturity leads to an increase in concentrations of starch (P<0.001) in the silages with relatively high concentrations (>200 g/kg of dry matter) being observed in forages cut at growth stages 87 and 90. However, there was an overall decline in the digestibility (NDCD; P<0.001) of conserved silages with increasing crop maturity. The linear rate of decline in digestibility over the whole range of crop maturities was estimated as 2.6 g/kg DM/day, less than that observed for the fresh forage suggesting a restricted fermentation in forages above 400 g DM/kg (Fig. 2). The fermentation process reduced substantially the concentrations of water-soluble carbohydrate in the ensiled forage compared to the fresh forage. The proportion of residual WSC in silage did however increase with increasing crop maturity (0.051, 0.077, 0.167 and 0.560 of WSC retained in silage after the processes of fermentation from forages cut at GS 69, 82, 87 and 90 respectively). These changes are typical of a so-called restricted fermentation reflecting the relatively high dry matter content (or more strictly the lower moisture content) of mature cereal forages used for silage production. These observations were further supported by the pH, yield of total fermentation acids and individual volatile fatty acid concentrations. Silages that were made from forage cut at the most mature stage of growth had a substantially lower production (P<0.001) of total fermentation acids (38.9 g/kg DM for
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Table 3 Chemical composition of silages (g/kg DM unless otherwise stated) at opening of the silos made from barley whole-crop forage cut at four stages of growth. Standard error of mean derived on 3, 8 d.f.
Toluene dry matter (g/kg) Crude protein Water soluble carbohydrate Starch Neutral detergent cellulase digestibility pH Ammonia-N (g/kg total N) Ethanol Lactic acid Acetic acid Butyric acid DM losses ns * ** ***
Harvest date 1
Harvest date 2
Harvest date 3
Harvest date 4
s.e.m
251 98 10 92 680 4.50 186 28.9 80.6 122.0 0.8 109
322 74 12 218 614 4.85 141 61.0 91.6 112.0 50.5 82
432 76 16 234 575 5.29 71 25.4 23.9 24.0 34.0 96
530 67 28 287 559 5.75 55 3.1 1.7 7.7 29.5 110
8.8*** 4.10ns 0.90*** 11.9*** 3.28** 0.31** 19.2* 1.56*** 7.49** 10.1*** 1.90*** 3.18**
P>0.05. P<0.05. P<0.01. P<0.001.
GS 90) compared to those made from the least mature forage (203.4 g/kg DM for GS 69). The pH and concentrations of the various fermentation acids for silages made with the least mature forage (GS 69) were typical of acetic acid dominated fermentation (lactic acid to acetic ratio of 1:1.5. These silages contained little or no butyric acid and had a pH of 4.5. However, these silages did however contain high concentrations of ammonia-N (186 g/kg total N). Silages produced from forages cut at growth stage 82 were similar to those conserved from immature forages, having acetic acid dominated fermentation (lactic acid to acetic acid ratio of 1:1.22), relatively high pH (4.85) and high concentrations of ammoniaN (141 g/kg total N). However, these silages differed from those made from the most immature forage insofar that they contained high concentrations of butyric acid (50.5 g/kg DM). When the dry matter content of the forage exceeded 400 g/kg, the processes of fermentation were restricted. The silages made from forage of approximately 435 g DM/kg was characterised by pH 5.3, total fermentation acids of 81.9 g/kg DM of which lactic and acetic acids contributed 0.584 of total fermentation acids. The concentration of butyric acid was again elevated to 34 g/kg DM, however the concentration of ammonia-N was lower than the two immature silages being 71 g/kg total N. When the dry matter content of the fresh forage exceeded 500 g DM/kg, the restriction in fermentation was substantial. The yield of total fermentation acids was 38.9 g/kg DM of which butyric acid comprised over 0.750 (29.5 g/kg DM) of total acid production. The pH of these silages was 5.75 and concentration of ammonia-N was 55 g/kg total N.
Fig. 2. Digestibility (neutral detergent cellulase digestibility; NDCD g/kg DM) of fresh () and ensiled () whole-crop barley cut at four stages of growth.
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3.4. Dry matter losses during storage Losses of DM during fermentation are shown in Table 3. Unusually, total DM losses were lowest in silages made from barley cut at growth stage 82 (P<0.01) compared to other treatments. The highest losses were in the silages made from the most immature whole-crop forage. 4. Discussion 4.1. Development of DM yield The DM yield of winter barley crops for forage production cut at similar stages of crop maturity are lower than those observed for winter wheat crops cut for silage production (Hill and Leaver, 1999). This reduction in yield suggests the crop may initially seem to reduce economic output from arable land integrated into dairy systems, but the earlier harvest date of barley crops for forage production makes such crops attractive from dual summer cropping system (e.g. integration of turnips or forage brassica into grazing systems in rain-fed dryland pasture systems). For cereal crops to be acceptable as alternative forage crops in dairy production systems they must have moderate to high harvestable yield of dry matter per hectare which is subsequently conserved as hay or silage. These conserved wholecrop forages must also have the attributes of moderate to high energy value and high intake potential. This paper examines in detail the former attributes (composition of yield and nutritive value). One of the most important factors that determine the successful utilisation of cereal crops for forage in dairy systems is the prediction of harvest date. The decision-making processes to identify if a crop is suitable for harvesting are complex and are outlined in Fig. 3. The relationship between harvest date is informed by several factors, for instance if the crop is being used for chemical treatment or ensiling, the classification of livestock being offered the feed after conservation and the climatic and environmental factors associated with the development of yield. The key “on-farm” factor that has to be identified and monitored is the drying rate of the crop. For ensiling the target dry matter of the crop should be between 350 and 450 g DM/kg. The rate of drying between 350 and 450 g DM/kg was estimated as below 5 g DM/kg/day (similar to observations by Corrall et al., 1977). The estimated harvest window for the crop for ensiling is approximately 20 days, however periods of hot dry weather during this period can shorten the harvest window to about 10 days (Harvey, 1992). In the experiments reported in this paper, the DM yield of the crop would range between 7 and 13 t DM/ha harvestable forage with a harvest index of approximately 500 g/kg DM (Rasmusson and Gengenbach, 1984). These were comparable to observations by Corrall et al. (1977), Tetlow and Mason (1987) and Kristensen (1992), however the range is considerable from an economic yield point of view as well as a whole farm feed supply. A far simpler method of appraising the optimum harvesting date for cereal forages is the use of growth stage key of Zadoks et al. (1974). The relationship between growth stage and instantaneous drying rate was reasonably strong (approximately 0.47 of variance accounted for; P<0.05) with a predicted change in dry matter of 6.5 g/unit of growth stage. The use of growth stages analysis to predict instantaneous drying rate is however contentious. For instance, Harvey (1992) reported that growth stage by itself was a poor predictor for forecasting DM content and DM yield in winter wheat crops for forage. Local climatic conditions and crop water deficits during the development of floral primordia has been demonstrated to delay the onset of anthesis and development of grain in cereal crops. Furthermore, if the crop water deficit occurs immediately after anthesis, the development of the grain and deposition of starch can be compromised, thus reducing the harvest index or total biomass yield. These changes would alter either total harvestable yield or the quantity of starch harvested per hectare—an important criteria for selection of cereal crops as a forage crop in dairy production systems. 4.2. Crop composition before harvesting and its possible impact on ensilability of cereal forages Hill and Leaver (1999) examined the re-partitioning of non-structural carbohydrate and mobilisation of nitrogenous compounds from leaf and stem fractions to develop grain in winter wheat crops for forage production. The data presented in this paper is similar to those reported in Hill and Leaver
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Fig. 3. Decision support process for harvesting cereal crops in dairy production systems.
(1999) but there are some important differences that have to be identified. The overall contribution of grain to total biomass is generally higher in winter barley compared to winter wheat however the starch content of barley grain is lower than that of wheat. This apparent compensation—higher overall contribution of grain but lower starch content per grain leads to similar concentrations of starch in harvested forage from wheat and barley crops (Bonnett and Incoll, 1992, 1993). The partitioning of the “material other than grain” fraction (MOG) does however highlight the reasons why the digestibility (NDCD) of barley forage is lower than that of wheat forage cut at the same stage of maturity. The contribution of leaf biomass to total MOG is lower in barley than wheat and therefore the MOG fraction has a lower digestibility in barley than wheat crops. These factors, and the previously identified compensatory effects during grain development, are critical factors in the determination of the overall chemical compositional analysis of whole-crop cereal forage prior to ensiling. Furthermore, the apparent changes in the concentrations of readily degradable substrates (e.g. WSC and starch) during crop development and grain fill also provide a mechanism to identify the reasons
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for the underlying processes that restrict the fermentation observed in the silages reported in this paper. Two important chemical compositional attributes of cereal forage for silage production are crude protein and WSC. The crude protein content was low (approximately 100 g/kg DM) in the least mature forage at harvest and there was a progressive decline in the crop to less than 70 g/kg DM in the most mature forage. These concentrations fall within the ranges predicted by Bruno-Soares et al. (1998) and Acosta et al. (1991) for green cereal crops. The decline in crude protein content during crop maturation has been reported previously. Edwards et al. (1968) reported the average crude protein content of eight varieties of barley declined from 103 g/kg DM (heading completed) to 66 g/kg DM (ripe for cutting). Furthermore the nitrogen content of spring barley crops monitored by Corrall et al. (1977) also had a similar decline in crude protein content. The concentration of WSC in cereal forage is lower than that observed in many other grass species (McDonald et al., 1991; MacGregor and Edwards, 1968). The impact of lower concentrations of WSC and the concomitant increasing concentration of starch in the forage as the crop matures reduces the potential production of fermentation acids during the ensiling period. Typically, if the forage for silage production is immature at harvest, the fermentation is dominated by lactic acid production with moderate concentrations of acetic acid—a situation typical of a heterofermentative microflora. In this paper we report a situation where the ratio of lactic acid to acetic acid diverged from the typical > 2.5:1 ratio to 1:1.5 or more. The shift in the concentrations of lactic and acetic acids may reflect a fermentation process dominated by acetic acid bacteria for instance Acetobacter. The changes in the ratio reflect several factors, principally silo packing density, concentrations of WSC and other substrates available for fermentation. The silo packing densities reported in this experiment are lower (by about 0.15) than those reported by Hill and Leaver (2002). The reduction in silo packing density also reflects the degree of consolidation of the crop and therefore the amount of air trapped in the harvested forage during silo loading. The fresh weight packing densities of the various silage treatments ranged from 335 to 513 kg/m3 (396, 513, 370 and 335 kg/m3 for GS 69, 82, 87 and 90 respectively). Microaerophilic conditions in the silage would lead to an increase in dominance of acetic acid bacteria compared to lactic acid bacteria (McDonald et al., 1991). The formation of butyric acid in silages made at intermediate cutting dates reflect two processes, the conversion of lactic acid to butyric acid presumably reflecting the presence of Clostridia and the process of proteolysis releasing ammonia and butyric acid. These processes alter pH by the effect of ammonia release and loss of free acidity. The concentrations of butyric acid in silages of 350–450 g DM/kg are approaching the theoretical maximum concentration for silages dominated by heterofermentative microflora. The implications of the heterofermentative fermentation or conservation processes dominated by the formation of acetic or butyric acid are that the silages have variable aerobic stability (Woolford, 1984) and their intake potential may be compromised (Tetlow and Mason, 1987). 4.3. Aerobic stability of silages Feed wastage prior to harvest, during conservation and at feedout has been poorly characterised in farming systems. Wastage is the Achilles’ heal of economic profitability of a feeding system and if not considered, claims concerning the integration of new alternative feeding systems at pasture can be questioned. One of the main problems identified by many authors investigating whole-crop cereal silages is the poor stability of the silage once exposed to the air. Anecdotal evidence suggests losses of ensiled feed can be as high at 0.30 (dry matter basis), thus rendering the crop as a forage for dairy production uneconomic. The highest dry matter losses were observed in silages of 437 g DM/kg and the lowest observed in silages of 320 g DM/kg. These observations reflect two processes. In wet silages (those made of immature forage) the presence of water in the forage mass acts as a heat sink, thus reducing the overall silo temperature when exposed to air. These immature silages do however contain moderate to high concentrations of lactic acid (a partially volatile fermentation acid) which under the correct aerobic conditions can be converted to butyric acid (a potent inhibitor of yeast and microfungi—the principal organisms controlling aerobic deterioration in silage). This process is partially demonstrated in the silages made of the most immature cereal forage. Silages containing
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the highest concentrations of butyric acid are generally highly stable under aerobic conditions. This was highlighted by the low rise in temperature immediately after opening of the whole-crop barley silage made with forage cut at about 350 g DM/kg. The most rapid deterioration was observed in silage made from forage cut at 450 g DM/kg. This is the worst-case situation insofar as silage production. The forage has poor consolidation characteristics, a reasonable supply of rapidly fermentable substrates but a restricted fermentation. Silages of these characteristics heat and deteriorate rapidly; a process mediated by yeast and microfungi. 5. Conclusions The processes of fermentation were affected by the stage of growth of the forage at ensiling and hence the economics of silage production. If the forage was too immature at ensiling, the yield of crop would be compromised but the silage produced may have moderate to high nutritive value and reasonable aerobic stability during the feed out phase. This situation may be acceptable if the dryland dairy system received adequate rainfall and forage supplies were plentiful. If however, the whole-crop forage was grown as a crop to secure high levels of supplementary feed from an alternative forage source (other than grass), the trade-off between yield, nutritive value and losses of feed immediately after silo opening would suggest the crop should be harvested between 350 and 450 g DM/kg. Decisions to harvest the crop at dry matter contents of greater than 450 g DM/kg should be based on options to either chemically treat the forage (e.g. urea treatment) or utilise the grain and straw as individual feed components on farm or sold into other markets. Acknowledgements The authors wish to thank P. Drury and J. Greenland for technical assistance. References Acosta, Y.M., Stallings, C.N., Polan, C.E., 1991. Evaluation of barley silage harvested at boot and soft dough stages. J. Dairy Sci. 74, 167. Adesogan, A.T., Owen, E., Givens, D.I., 1999. Prediction of the metabolisable energy value of whole-crop wheat from laboratorybased measurements. Anim. Sci. 68, 427–439. Allen, S., 1989. Chemical Analysis of Ecological Materials. Blackwell Scientific Publications. Bonnett, G.D., Incoll, L.D., 1992. The potential pre-anthesis and post-anthesis contributions of stem internodes to grain yield in crops of winter barley. Ann. Bot. 69, 219–225. Bonnet, G.D., Incoll, L.D., 1993. Effects on the stem of winter barley of manipulating the source and sink during grain filling, II. Changes in the composition of water-soluble carbohydrates of internodes. J. Exp. Bot. 44, 83–91. Bruno-Soares, A.M., Murray, I., Paterson, R.M., Abreu, J.M.F., 1998. Use of near infrared reflectance spectroscopy (NIRS) for the prediction of the chemical composition and nutritional attributes of green crop cereals. Anim. Feed Sci. Technol. 75, 15–25. Cherney, J.H., Marten, G.C., 1982. Small grain crop forage potential: II. Interrelationships among biological, chemical, morphological and anatomical determinants of quality. Crop Sci. 22, 240–245. Corrall, A.J., Heard, A.J., Fenlon, J.S., Terry, C.P., Lewis, G.C., 1977. Whole-crop forages. In: Relationship Between Stage of Growth, Yield and Forage Quality in Small Grain Cereal and Maize. Grassland Research Institute, Hurley, U.K, Technical Report N◦ 22. De Ruiter, J.M., Hanson, R., 2004. Whole-crop cereal silage. In: Production and Use in Dairy, Beef, Sheep and Deer Farming. New Zealand Institute for Crop and Food Research Limited, Christchurch, NZ, p.33. Dowman, M.G., Collins, F.C., 1982. The use of enzymes to predict the digestibility of animal feeds. J. Sci. Fd. Agric. 33, 689–696. Edwards, R.A., Donaldson, E., MacGregor, A.W., 1968. Ensilage of whole-crop barley, I. Effects of variety and stage of growth. J. Sci. Fd. Agric. 19, 656–660. Fisher, L.J., Lessard, J.R., Lodge, G.A., 1972. Whole-crop barley as conserved forage for lactating cows. Can. J. Anim. Sci. 52, 497–504. Fussell, R.J., McCalley, D.V., 1987. Determination of volatile fatty acids (C2 –C5 ) and lactic acid in silage by gas chromatography. Analyst 112, 1213–1216. Harvey, J.J., 1992. Assessing whole-crop cereal maturity in the field. In: Stark, B.A., Wilkinson, J.M. (Eds.), Whole-crop Cereals. Chalcombe Publications, Canterbury, UK, pp.39–50. Hill, J., Leaver, J.D., 1999. Effect of stage of growth at harvest and level of urea application on chemical changes during storage of whole-crop wheat. Anim. Feed Sci. Technol. 77, 281–301. Hill, J., Leaver, J.D., 2002. Changes in chemical composition and nutritive value of urea treated whole-crop wheat during exposure to air. Anim Feed Sci. Technol. 102, 181–195. Juskiw, E., Patricia, Jame, Y.W., Kryzanowski, L., 2001. Phenological development of spring barley in a short-season growing area. Agron. J. 93, 370–379. Keppler, D., Decker, K., 1984. In: Bergmeyer, H.U. (Ed.), Methoden der enzymetischen Analyse, 2. Verlag, Weinheim, Germany, pp. 1171–1176.
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