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The Effect of Dry Matter Content and Silage Additives on the Fermentation of Bunker-Made Grass Silage on Commercial Farms in England 1984-91
J. agric. Engng Res. (1996) 64, 249 – 259
REVIEW PAPER
The Effect of Dry Matter Content and Silage Additives on the Fermentation of Bunker-Made Grass Silage on Commercial Farms in England 1984 – 91 P. M. Haigh ADAS, Pwllpeiran, Research Centre, Cwmystwyth, Aberystwyth, Dyfed SY23 4AB, UK (Receiy ed 3 July 1995; accepted in rey ised form 19 February 1996)
A total of 14 636 samples of silage made in bunkers on commercial farms between 1984 and 1991 were analysed to investigate the effect of dry matter (DM) content and silage additives on fermentation as measured by ammonia-N concentration and pH. Increasing DM content without additive use had a major beneficial influence on fermentation. When silage DM contents were greater than 220 g / kg about 66% of the silages were well fermented. Below this with diminishing DM concentration the proportion of well fermented silages declined such that with DM below 180 g / kg only 27% were well fermented. The benefit of silage additives, albeit at poorly defined and often inadequate rates, was extremely variable. Below DM concentrations of 220 g / kg, formic acid consistently improved the proportion of well fermented silages compared with non-additivetreated silages by about 20%. Similarly use of formic acid based, inorganic acid and acid with formalin additives increased the proportion of well fermented silages by about 15%. Acid mixtures, salts, inoculants and sugars provided little or no benefit compared with non-additive-treated silages, whilst use of enzymes increased the proportion of well fermented silages by about 8%. Above DM 220 g / kg, formic acid, acid with formalin and inoculant additives improved the proportion of well fermented silages, compared with non-additivetreated silages by about 15%. Similarly, formic acid based, inorganic acids and enzymes improved the proportion of well fermented silages by about 10%. Acid mixtures, salts and sugars produced less than 5% benefit. The minimum DM necessary to produce wellfermented silage without additive use was approximately 255 g / kg. Use of formic acid containing additives and inorganic acids reduced the target to about 240 g / kg. Similarly, the target DM for inoculant, sugar and enzyme treated silages was about 250, acid mixtures 260 and salts 270 g / kg. 0021-8634 / 96 / 080249 1 11 $18.00 / 0
It is concluded that on commercial farms, weather conditions during ensilage, i.e. amount of rainfall and sunshine have a considerable effect upon subsequent silage fermentation. However, when silage DM was below 220 g / kg, additives containing acid with or without formalin significantly increased the proportion of well fermented silages. ÷ 1996 Silsoe Research Institute
1. Introduction It is estimated1 that 22?5 Mt of bunker silage was made in England in 1994 of which about half2 was treated with one of the 138 proprietary silage additives available.3 The benefits of silage additives, both in terms of improving silage fermentation and subsequent animal performance, when the silage is fed have been well documented,4 and it has been shown that despite the absence of effects on fermentation, some additives improve animal performance relative to untreated material.5 Therefore, in the development of silage additives to date, although fermentation control is important, attention is also paid to methods of improving the nutritive value of the product and reducing dry matter (DM) losses.4 Routine chemical analysis, e.g. ammonia-N and pH, of commercial farm silos may be used to indicate silage fermentation quality. However, there may be no improvement in fermentation quality or digestibility of the resultant silage relative to those achieved in an untreated silage, but nevertheless improved animal performance may result when the silage is fed.6 With commercial farm silos, increasing DM of silages leads to improved silage fermentation.2,7,8 The benefits of silage additives, albeit at poorly defined and often inadequate rates has been shown to be small2,9 with additives being used on wetter silages. Information is lacking on the effectiveness of the newer biological additives on commercial farms. The
249
÷ 1996 Silsoe Research Institute
250
P. M. HAIGH
following investigation reports results of 14 636 samples of silage analysed by ADAS collected in England during 1984 – 1991.
2.4 . Silage fermentation 2.4 .1 . Ammonia -N An ammonia-N value of less than 100 g / kg N was used to indicate well fermented silage.2
2. Materials and methods
2.1. Sampling Only two methods of taking samples for analysis were used. Silage samples were taken mainly by coring to a depth of 1?3 m with a 30 mm diameter corer designed by Alexander.10 Occasionally grab samples, taken from the face of the silo, were used for analysis. Details of the nature of the additive used were collected from farmers at the time of sampling.
2.2. Chemical analysis Oven dry matter (DM), crude protein determined on the oven dried material (CP), pH, ammonia-N (NH3-N) and modified acid detergent fibre (MAD fibre) were determined according to Ministry of Agriculture, Fisheries and Food.11 During the period 1984 – 1987 metabolisable energy (ME) was calculated on a toluene dry matter basis (TDM) using the equation12 ME (MJ / kg TDM) 5 15?33 2 0?0152 MADF (g / kg TDM) From 1988 – 1991 ME was estimated from the prediction of in y iy o organic matter digestibility using near infra-red diffuse spectrum spectroscopy (NIR) based on the procedures described by Barber et al .13 This method gave ME values approximately 0?5 MJ / kg DM higher than that predicted from MADF.13
2.3. Additiy es applied The silage additives applied were divided into ten distinct categories according to their main active ingredients and mode of action,3 namely, no additive treatment, formic acid, formic acid based, acid mixtures, inorganic acids, acid with formalin, salts, inoculants, enzymes and sugars.
2.4 .2 . pH Many workers have used pH as the sole criterion for assessing silage fermentation. However, pH alone is an unreliable guide, because with increasing DM level, stable conditions may be achieved4 at much higher pH. For this survey, the desirable pH of silages, at different DM concentrations is given in Table 1. For each silage, if the observed pH value was below the predicted pH value, it was taken to be well fermented. Overall, a silage was assumed to be well fermented if both the ammonia-N and pH value were below the predicted values.
2.5 . Statistical analysis Analysis of variance was used to test the effects of additives and year upon silage composition.15 Linear regression was used to assess the relationship between DM and ammonia-N and pH. To differentiate the effect of additives upon the DM required for successful preservation, a generalized linear model assuming Poisson errors16 was used.
3. Results The incidence of additive use in relation to DM, CP and ME, is given in Tables 2 and 3 and the mean DM, CP and ME contents of silages in Table 4.
3.1. The relationship between additiy e use and DM concentration About 43% of the silages sampled had received additive (Table 2). Average DM concentration of the non-additive-treated silages was 270 g / kg compared with about 210 – 240 g / kg for treated silages. Above a DM concentration of 300 g / kg only 17% of the silages were treated with additive. Additive use increased with decreasing DM content, by about 7% for each 200 g / kg decrease in DM, from 29% in the DM range 280 – 300 g / kg to 39% in the DM range 240 – 260 g / kg. Below DM 220 g / kg additive was used on about 65% of the samples. Overall, formic acid and formic acid
251
FERMENTATION OF BUNKER-MADE GRASS SILAGES IN ENGLAND
Table 1 Maximum pH required to produce well fermented silage at different ranges of dry matter14 Dry matter range (g / kg) pH required
min max
180 200 4?1
,180 4?0
200 220 4?2
220 240 4?3
240 260 4?4
260 280 4?5
280 300 4?6
.300 4?8
3.2. The relationship between additiy e use and CP
based additives were both applied to about 5% of the silages. Below DM 220 g / kg, they were used on about 10% of the silages. Their use then declined with increasing DM content, so that for silages with DM greater than 300 g / kg only 2% of the silages were treated. Inorganic acids were applied to about 14% of silages with DM below 240 g / kg, above this DM there was a tendency for their use to decrease with increasing DM content, so that for silages with DM above 300 g / kg only 3% of silages were treated. Acid with formalin additives were applied to about 15% of silages with DM concentration below 220 g / kg, above this DM concentration their use tended to decline with increasing DM content, so that for silages with DM above 300 g / kg only 3% of silages were treated. Inoculants were applied to about 8% of the silages, but their use appeared to be independent of DM except for very dry silages, i.e. DM above 300 g / kg, when only 4% of the samples were treated. Enzymes and sugars were applied to about 2% of silages, whilst less than 1% of samples were treated with either acid mixtures or salts. Overall, the results indicated that, when possible, farmers attempted to increase the DM content of silage by wilting. When wilting was not possible they tended to use an acid based additive, whereas inoculant additives tended to be used on about 8% of samples irrespective of DM content.
The incidence of additive use increased with increasing CP (Table 3). The mean CP (Table 4) of non-additive-treated silages was 137 g / kg DM, which was significantly (P , 0?001) less than other treatments except salts. 3.3. The relationship between additiy e use and ME The incidence of additive use increased with increasing ME (Table 3). The mean ME (Table 4) of non-additive-treated silages was 10?0 MJ / kg DM, which was significantly (P , 0?001) less than other treatments except salts and enzymes.
3.4 . Silage fermentation 3.4 .1. Effect of silage DM in the absence of additiy e use The ammonia-N (Table 5) and pH values (Table 6) of silages at given DM ranges indicate that the fermentation quality (Table 7) of silages was enhanced by increased DM. The proportion of silages in each DM range which were well fermented, decreased by about 8% in each DM range from 84% for silages
Table 2 Incidence of additive use in relation to dry matter Additiy e Dry matter range (g / kg )
Formic None acid
Formic acid based
Acid mixtures
Acid Inorganic with acids formalin Salts
Inoculants
Enzymes
Sugars
Total
,180 180 – 200 200 – 220 220 – 240 240 – 260 260 – 280 280 – 300 .300
482 522 678 881 1257 1055 1271 2141
118 141 207 163 108 79 68 55
109 82 181 125 94 79 64 40
15 11 20 12 7 11 7 6
228 188 256 220 122 94 77 73
234 214 276 216 203 113 93 77
24 15 12 9 11 6 4 3
144 145 164 163 212 125 139 107
26 22 53 48 29 36 43 47
44 35 54 37 29 32 24 21
1421 1372 1898 1871 2070 1648 1788 2568
Total
8287
939
774
89
1258
1426
84
1199
304
276
14 636
252
P. M. HAIGH
Table 3 Incidence of additive use in relation to CP and ME of silages Formic None acid
Formic acid based
Acid mixtures
Acid Inorganic with acids formalin Salts Inoculants Enzymes
Sugars
Total
CP (g / kg DM) ,120 120 – 140 140 – 160 160 – 180 .180
1694 2395 1391 1291 1516
47 129 304 261 198
7 25 212 299 231
8 25 19 21 16
171 231 365 300 191
91 289 352 442 272
5 32 33 12 2
77 205 329 384 204
22 61 75 100 46
42 48 72 75 39
2164 3420 3152 3185 2715
ME (MJ / kg TDM) ,9?5 9?5 – 10?0 10?0 – 10?5 10?5 – 11?0 11?0 – 11?5 11?5 – 12?0 .12?0
925 2159 2249 1534 1015 273 132
7 136 221 241 219 94 21
15 102 191 188 173 85 20
5 7 35 11 17 9 5
83 301 345 285 201 35 8
69 152 267 377 295 207 59
12 19 23 16 9 4 1
69 135 231 268 302 110 84
22 29 95 50 45 34 29
7 37 58 71 65 23 15
1214 3077 3715 3041 2341 874 374
with DM above 300 g / kg to only 27% in the DM range less than 180 g / kg. The exceptions to this were in the DM ranges 180 – 200 g / kg, when 35% of the silages were well fermented rising to 53% in the DM range 200 – 220 g / kg. In the DM range 220 – 260 g / kg about 60 – 65% of the silages were well fermented.
3.4.2. Formic acid Formic acid was consistently the most effective silage additive. It reduced the ammonia-N content by about 20 g / kg N and pH values of silages by 0?50 units compared with non-additive-treated silages. It thereby improved the proportion of well fermented silages, particularly below DM concentrations of 280 g / kg, when the percentage of well fermented silages was increased by about 20% at each DM range compared with non-additive-treated silages. Above DM 280 g / kg
the improvement was less, so that 90% of the silages treated with formic acid were well fermented, compared with 80% of non-additive-treated silages. 3.4 .3. Formic acid based additiy es Formic acid based additives reduced the ammoniaN content by 10 g / kg N and pH values of silages by 0?41 units compared with non-additive-treated silages. They were particularly effective for silages with DM below 280 g / kg, when the proportion of well fermented silages was increased by 14% compared with non-additive-treated silages, but the effect was consistently about 6% less than formic acid treatment. Above DM 280 g / kg they provided a small but consistent improvement with 85% of the silages being well fermented compared with 80% of non-additivetreated silages.
Table 4 DM, ammonia-N, pH, CP and ME content of silages in relation to additive use
Samples DM (g / kg) NH3N (g / kg N) pH CP (g / kg DM) ME (MJ / kg TDM) Proportion well fermented
No additiy e
Formic acid
Formic acid based
Acid mixtures
Inorganic acids
Acid with formalin
Salts
Inoculants
Enzymes
Sugars
s.e.d.
8287 a 270 bc 104 4?42 a 137 a 10?0 0?67
939 bc 228 a 84 a 3?92 cd 153 cd 10?3 0?74
774 bc 228 ab 94 b 4?01 cd 154 d 10?4 0?68
89 bc 230 bc 103 dc 4?13 bc 147 bc 10?2 0?54
1258 ab 222 bc 103 cd 4?11 d 160 d 10?4 0?65
1426 ab 224 ab 92 bc 4?04 cd 154 bc 10?2 0?68
84 d 208 d 128 f 4?25 ab 138 a 10?0 0?45
1199 bc 228 bc 103 dc 4?14 cd 152 d 10?4 0?67
304 c 243 bc 104 bcd 114?07 cd 156 ab 10?1 0?72
276 bc 231 cd 113 ef 4?19 cd 153 bc 10?2 0?57
5?04 4?7 0?023 2?9 0?05
s.e.d. 5 standard error of difference between two means. Means on the same line, with the same or no superscript do not differ significantly (P , 0?001).
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FERMENTATION OF BUNKER-MADE GRASS SILAGES IN ENGLAND
Table 5 The ammonia-N values (g / kg N) of silages at each DM range in relation to additive use Formic Acid DM range No Formic acid Acid Inorganic with (g / kg ) additiy e acid based mixtures acids formalin Salts ,180 180 – 200 200 – 220 220 – 240 240 – 260 260 – 280 280 – 300 .300 s.e.d. LSD
176 155 122 109 100 94 88 84
121 90 86 78 71 66 70 67
4?5 14?8
6?1 20?1
129 104 94 92 82 70 83 78 5?4 17?8
212 189 121 127 106 97 81 89
132 112 103 102 86 74 81 79
10?1 33?2
130 108 88 87 73 74 70 63
12?2 40?2
189 156 115 92 64 75 76 71
7?5 24?7
15?9 52?3
Inocu Number of lants Enzymes Sugars samples s.e.d. LSD 204 165 101 89 66 70 67 66 7?8 25?7
175 166 115 90 88 85 81 83 11?5 37?8
162 155 114 98 89 85 79 80
1421 1372 1898 1871 2070 1648 1788 2568
27?4 15?1 9?5 6?1 6?9 6?5 6?1 5?1
90?2 49?7 31?3 20?1 22?7 21?4 20?1 16?8
15?9 52?3
s.e.d. 5 standard error of difference between two means. LSD 5 least significant differences at P , 0?001.
3.4.4. Acid mixtures Only 89 samples were treated with acid mixtures. Therefore, it was somewhat difficult to draw conclusions. Overall, their use had little effect upon ammonia-N content but decreased the pH value by 0?29 units compared with non-additive-treated silages. They were therefore generally ineffective in enhancing silage fermentation compared with non-additivetreated silages at any DM concentration.
pared with non-additive-treated silages. They reduced the ammonia-N content of silages with DM below 200 g / kg by about 45 g / kg N and they consistently improved the proportion of well fermented silages with DM below 280 g / kg by 14%. Above this DM content they provided only a small improvement (about 5%) compared with non-additive-treated silages.
3.4 .6 . Acid with formalin 3.4.5. Inorganic acids Inorganic acids had little effect upon ammonia-N content but decreased silage pH by 0?31 units com-
Overall, acid with formalin use ammonia-N content by 12 g / kg N and silages by 0?38 units compared with treated silages. They consistently
reduced the pH values of non-additivereduced the
Table 6 The pH values of silages at each DM range in relation to additive use DM range (g / kg )
Formic Acid Number No Formic acid Acid Inorganic with of additiy e acid based mixtures acids formalin Salts Inoculants Enzymes Sugars samples s.e.d. LSD
,180 180 – 200 200 – 220 220 – 240 240 – 260 260 – 280 280 – 300 .300
4?59 4?47 4?27 4?28 4?28 4?33 4?41 4?61
4?11 3?89 3?85 3?84 3?84 3?95 4?02 4?08
4?19 3?99 3?89 4?01 3?85 3?89 4?26 4?31
4?67 4?51 4?18 4?29 4?24 4?30 4?31 4?56
4?27 4?14 4?05 4?04 4?03 3?98 4?18 4?19
4?25 4?07 3?93 3?98 3?94 4?00 4?08 4?14
4?51 4?32 4?03 4?09 4?07 4?08 4?13 4?37
4?59 4?37 4?20 4?08 3?92 3?96 4?00 4?04
4?39 3?97 4?01 4?03 3?96 3?94 4?00 4?27
4?36 4?26 4?15 4?07 4?04 4?11 4?21 4?36
s.e.d. LSD
0?015 0?049
0?027 0?089
0?032 0?105
0?112 0?369
0?101 0?332
0?019 0?063
0?156 0?514
0?021 0?069
0?141 0?464
0?137 0?450
s.e.d. 5 standard error of difference between two means. LSD 5 least significant difference at P , 0?001.
1421 1372 1898 1871 2070 1648 1788 2568
0?191 0?129 0?028 0?028 0?031 0?024 0?029 0?031
0?629 0?425 0?092 0?092 0?102 0?079 0?095 0?102
254
P. M. HAIGH
Table 7 The proportion of well fermented silages at each DM range in relation to additive use
DM range (g / kg )
No additiy e
Formic acid
Formic acid based
Acid mixtures
,180 180 – 200 200 – 220 220 – 240 240 – 260 260 – 280 280 – 300 .300 Mean
0?27 0?35 0?53 0?64 0?61 0?71 0?76 0?84 0?67
0?44 0?60 0?75 0?79 0?83 0?90 0?89 0?89 0?74
0?39 0?52 0?68 0?70 0?75 0?88 0?82 0?87 0?68
0?20 0?30 0?58 0?58 0?61 0?72 0?83 0?84 0?54
Inorganic Acid with acids formalin Salts 0?42 0?51 0?66 0?70 0?75 0?90 0?83 0?86 0?65
ammonia-N content and pH of silages with DM below 220 g / kg by about 40 g / kg N and 0?3 – 0?4 units respectively. Irrespective of DM content they consistently improved the percentage of well fermented silages by about 15% compared with non-additive-treated silages. 3.4.7. Salts Only 84 silages were treated with salts. Therefore, it was difficult to draw firm conclusions from the results. Overall however, they increased the ammonia-N content by 24 g / kg N and reduced the pH values of silages by 0?17 units compared with non-additive-treated silages. The proportion of well fermented silages with DM concentrations below 240 g / kg was consistently less than that of non-additive-treated silages. Above this DM level the proportion of well fermented silages was similar to that of non-additive-treated silages. 3.4.8. Inoculants Overall, inoculant use had little effect upon ammonia-N but decreased silage pH by 0?28 units compared with non-additive-treated silages. Their effectiveness was particularly influenced by the DM content of the silages. Below DM 220 g / kg they provided little benefit in ammonia-N concentration or pH and the proportion of well fermented silages compared with non-additive-treated silages. Above this DM concentration they reduced the ammonia-N content by 10 g / kg N and pH values by 0?37 units compared with non-additive-treated silages. 3.4.9. Enzymes Overall, enzyme use had little effect upon the ammonia-N content, but reduced the pH value by 0?35 units compared with non-additive-treated silages,
0?39 0?51 0?72 0?74 0?81 0?85 0?88 0?91 0?68
0?15 0?28 0?49 0?62 0?77 0?78 0?75 0?84 0?45
Inoculants
Enzymes
Sugars
Mean
0?18 0?33 0?58 0?73 0?80 0?91 0?94 0?93 0?67
0?29 0?49 0?61 0?74 0?75 0?84 0?87 0?90 0?72
0?28 0?35 0?50 0?65 0?65 0?74 0?87 0?85 0?57
0?33 0?43 0?62 0?69 0?68 0?76 0?80 0?85 0?67
and thereby improved the proportion of well fermented silages by about 10% irrespective of silage DM content. 3.4 .10 . Sugars Sugars increased the ammonia-N content by 9 g / kg N and decreased the pH value by 0?23 units compared with non-additive-treated silages. Their use however, irrespective of silage DM, provided little benefit in terms of silage fermentation, compared with non-additive-treated silages.
3.5. The relationship between silage composition and the year in which it was made There was considerable year-to-year variation in silage quality. The contrast between 1985 (Table 8) and 1990 (Table 9) was most noticable. Between these years the proportion of well fermented non-additivetreated silages increased from 44% to 85%, despite the fact that the average DM content was about 280 g / kg in each year. Similarly the CP content of silages increased from 127 to 156 g / kg DM and ME value from 9?9 to 10?3 MJ / kg DM.
3.6 . Silage DM , additiy es and fermentation The linear relationships between silage DM using ammonia-N and pH as independent variables with additive use are given in Table 10. Using ammonia-N and pH as the criteria for effective fermentation the
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FERMENTATION OF BUNKER-MADE GRASS SILAGES IN ENGLAND
Table 8 Composition of silages in relation to additive use 1985
Samples DM (g / kg) NH3N (g / kg N) pH CP (g / kg DM) ME (MJ / kg TDM) Proportion well fermented
Formic No additiy e acid
Formic acid based
Acid mixtures
Inorganic acids
Acid with formalin
Salts
Inoculants
Sugars
203 232a 102ab 4?03a 154c 10?3c 0?67
67 223a 126ab 4?15b 148bc 10?3c 0?48
18 236a 133abd 4?22bc 140abc 10?3c 0?42
43 191 160bcd 4?38d 150bc 10?2bc 0?27
277 231a 127abc 4?21b 150bc 10?2bc 0?49
25 231a 186cd 4?35d 138ab 10?0ab 0?26
79 237a 120ab 4?33cd 138ab 10?1abc 0?47
35 244a 123ab 4?18bc 151c 10?3c 0?54
1110 277 133abc 4?57 127a 9?9a 0?44
s.e. between two means
6?7 10?1 0?034 4?6 0?07
From May to September 1985 was fairly wet with little sunshine.17 Means on the same line, with the same or no superscript do not differ significantly (P , 0?001).
calculated minimum DM necessary to produce wellfermented non-additive-treated silages needed to be about 255 g / kg. The use of formic-acid-containing additives and inorganic acids reduced the target to about 240 g / kg. Similarly the target DM for inoculant, sugar and enzyme treated silages was about 250, acid mixtures 260, and salts 270 g / kg. 4. Discussion 4.1. Silage DM content The survey demonstrated that over 60% of nonadditive-treated silages with DM concentrations above 220 g / kg were well fermented. Below this DM content, fermentation quality declined as silages became more moist. This conclusion suggests that the silage making techniques used in the present survey have improved compared with previous surveys2,7,8 which
showed that silages with DM concentrations above 250 g / kg were well fermented without additive use, whilst silages of lower DM content were not.
4.2 . Formic acid The survey results show that formic acid was far more effective in producing well fermented silages in the DM range less than 220 g / kg than shown in previous surveys2 and that it reduced pH.9 Nevertheless, its effectiveness declined with decreasing DM content and it did not, in practice, consistently produce well preserved silages when used with wet crops. Its effectiveness may have been reduced because of low and variable rates of application and the fact that it is highly volatile and may disappear during field applications on commercial farms,2 and because effluent production is greater when formic acid is applied.18
Table 9 Composition of silages in relation to additive use 1990
Samples DM (g / kg) NH3N (g / kg N) pH CP (g / kg DM) ME (MJ / kg TDM) Proportion well fermented
No additiy e
Formic acid
Formic acid based
Acid mixtures
Inorganic acids
Acid with formalin
Inoculants
Enzymes
Sugars
s.e. between two means
1148 275c 71ab 4?32 156c 10?3bc 0?85
36 239ab 58a 4?03bc 170e 10?5c 0?88
187 240ab 59a 3?95a 169de 10?5c 0?83
4 259bc 70ab 4?07c 126a 9?9a 0?73
139 227a 60a 3?94a 165cde 10?6c 0?90
123 229a 61a 3?95a 160cde 10?4bc 0?90
239 242ab 61a 3?97ab 162cde 10?6c 0?83
39 266b 70ab 4?02bc 159cd 10?4bc 0?77
13 229a 86b 4?08c 144b 10?1ab
6?9 4?9 0?021 3?3 0?11
From May to September 1990 was dry and sunny.17 Means on the same line, with the same or no superscript do not differ significantly (P , 0?001).
256
P. M. HAIGH
Table 10 Relationships between silage ammonia-N (g / kg N) , pH and DM (g / kg) with additive use Additiy e
Results
Relationship with DM
Min DM for presery ation
s .e.
r2
P
8287
No additive
292 2 0?379 NH3-N 174 1 18?8 pH
254 257
16?5 17?1
0?329 0?173
,0?001 NS
939
Formic acid
262 2 0?219 NH3-N 162 1 18?1 pH
240 239
19?4 21?3
0?399 0?172
,0?001 NS
774
Formic acid based
276 2 0?351 NH3-N 140 1 23?9 pH
241 242
21?7 22?1
0?415 0?123
,0?001 NS
Acid mixtures
288 2 0?291 NH3-N 359 2 22?8 pH
259 261
16?5 17?9
0?372 0?111
,0?001 NS
1258
Inorganic acids
261 2 0?191 NH3-N 315 2 17?1 pH
242 243
15?9 17?2
0?331 0?109
,0?001 NS
1426
Acid with formalin
261 2 0?187 NH3-N 154 1 20?3 pH
242 241
14?9 15?1
0?411 0?119
,0?001 NS
Salts
368 2 0?971 NH3-N 178 1 21?4 pH
271 268
17?1 18?3
0?292 0?171
,0?01 NS
Inoculants
276 2 0?273 NH3-N 315 2 15?1 pH
249 250
14?9 15?1
0?421 0?097
,0?001 NS
304
Enzymes
279 2 0?267 NH3-N 200 1 12?0 pH
252 252
16?9 16?5
0?302 0?006
,0?01 NS
276
Sugars
269 2 0?214 NH3-N 27?3 1 51?2 pH
248 247
15?9 16?5
0?297 0?011
,0?01 NS
89
84 1199
4.3. Formic acid based additiy es Irrespective of DM content, formic acid based additives were less effective than formic acid at producing well fermented silage. It is probable that the products available, contained less acid than formic acid.19
4.4. Acid mixtures The results of the survey confirm those of previous surveys,2,8 that organic acid mixtures appear to produce silage which is no better on average than that receiving no treatment at all.
higher than those for formic acid treated silages, a pattern noted in Ireland.9
4.6 . Acid with formalin Overall, acid with formalin use produced similar results to formic acid based additives. For silages with a DM content below 220 g / kg however, the pH values were higher, a pattern noted generally for formic acid with formalin treated silages, when compared with formic acid treatment.21 For silages with a DM content below 220 g / kg the results were far superior to those found for sulphuric acid plus formalin treated silages;2 probably because the present products contain a far higher level of acid.3,22
4.5. Inorganic acids Inorganic acids produced a similar benefit in terms of improvement in fermentation to formic acid treated silages for silages with a DM content below 180 g / kg. Thereafter, they were generally not as effective as formic acid probably because they have no specific anti-microbial properties and merely act as acidifying agents.20 The pH of inorganic-acid-treated silages was
4.7 . Salts Use of these additives produced silages which on average were no better fermented than non-additivetreated silage, a conclusion which agrees with Haigh.2 Generally, investigations on the use of salts (sodium nitrite plus calcium formate) have produced incon-
FERMENTATION OF BUNKER-MADE GRASS SILAGES IN ENGLAND
clusive results.4,20 Although previous surveys7,8 have shown them to reduce pH of silages compared with non-additive-treated silage. 4.8. Inoculants Inoculant treatment produced no benefit in terms of fermentation compared with non-additive-treated silages for silages with DM content below 220 g / kg. This conclusion agrees with Haigh et al.23 that inoculants failed to show any benefit when low DM grass is ensiled in farm-scale silos. The reason for this would appear to result from a lack of readily available carbohydrate and the fact that inoculants were added as powders, which gives a poorer distribution over the plant surface than a liquid.23 Their lack of succcess could be that they also provided less than the 106 organisms per gram of grass commonly recommended.3 As silage DM content increased so did the proportion of well fermented silages compared with non-additive-treated silages suggesting that inoculants work best with high sugar crops.4,20 4.9. Enzymes Treatment with enzymes for silages with DM below 220 g / kg tended to produce silages with pH values intermediate between those of formic acid treated and non-additive-treated silages, and ammonia-N values similar to those of non-additive-treated silages. Consequently, the proportion of well preserved silages was intermediate between that of non-additive-treated and formic acid treated silages. Other work24–26 has tended to show that enzyme treatment produced silages with a similar pH value but higher ammonia-N content than formic acid treated silages. Enzymes work as a means of increasing the content of fermentable sugars4 particularly with direct-cut rather than wilted silages.20 The poor results in the present survey suggest that comparisons are open to wide interpretation because enzyme sources and activities may differ widely;24 and perhaps not speed up the hydrolysis process to produce sugars for fermentation early in the ensiling process. 4.10. Sugars On average, use of sugars produced silages which were no better fermented than non-additive-treated silages. This pattern has been noted elsewhere, particularly for low DM silage.9,27 To obtain maximum benefit, it is probable that they should be used at high concentrations4 of about 40 – 50 kg / t, which farmers find difficult to apply.27
257
4.11 . Effect of silage -making year Previous reports on farm silages have shown that year to year variation in silage quality was a feature of the results.9,28,29 This report shows a similar trend; 1985 and 1990 were two contrasting years. Between these years, the percentage of well fermented silages dramatically increased. Probably because the water soluble carbohydrate content of the herbage ensiled was high30 and better inoculant additives were available.3 This pattern is consistent with the weather during silage making, which in 1990 was very dry and sunny, whereas in 1985 it was very wet and dull. These results support the conclusions of Haigh28 and Wilson and O’Keily9 that silage quality on commercial farms in terms of fermentation may be ascribed to climatic conditions during harvesting.
4.12 . Silage DM , additiy es and fermentation The results of the present survey support those of Haigh28 that the minimum DM necessary to produce well-fermented non-additive-treated silages needed to be about 255 g / kg, and that formic acid additives reduced the target to about 240 g / kg. The fact that other additives appear to perform less well on commercial farms than in present experiments31 may be inherent in their composition compared with present day additives.
5. Conclusions On commercial farms, weather conditions during ensilage, i.e. amount of rainfall and sunshine, have a considerable effect upon subsequent silage fermentation. Increasing DM content without additive use had a major beneficial influence on fermentation. When silage DM contents were above 220 g / kg about 66% of the silages were well fermented, with average ammonia-N concentrations of 93 g / kg N and pH 4?42. Below this, with diminishing DM concentration, the proportion of well fermented silages declined. In the DM range 200 – 220 g / kg, 53% of silages were well fermented with ammonia-N concentrations of 122 g / kg N and pH 4?27; in the DM range 180 – 200 g / kg, 35% were well fermented with ammonia-N 155 g / kg N and pH 4?47; with DM below 180 g / kg DM only 27% were well fermented with ammonia-N concentrations of 176 g / kg N and pH 4?59.
258
P. M. HAIGH
The benefit of silage additives, albeit at poorly defined and often inadequate rates, was extremely variable. At DM concentrations below 220 g / kg, formic acid consistently improved the proportion of well fermented silages compared with non-additive-treated silages by about 20%, ammonia-N by about 50 g / kg N and pH by about 0?5 units. Similarly, use of formic acid based, inorganic acid and acid with formalin increased the proportion of well fermented silages by about 15% by reducing the ammonia-N concentrations by about 40 g / kg N and pH by 0?3 – 0?4 units respectively. Acid mixtures, salts, inoculants and sugars provided little or no benefit compared with non-additive-treated silages, whilst use of enzymes increased the proportion of well fermented silages by about 8% and reduced the pH by 0?3 units. Above DM 220 g / kg, formic acid, acid with formalin and inoculant additives improved the proportion of well fermented silages, compared with non-additive-treated silages by about 15 percentage units, by reducing the ammonia-N by 20 g / kg N and pH by 0?4 units respectively. Similarly, formic acid based, inorganic acids and enzymes improved the proportion of well fermented silages by about 10% by decreasing the ammonia-N by about 10 g / kg N and pH by about 0?3 units respectively. Acid mixtures, salts and sugars produced less than 5% benefit although salts and sugars decreased the ammonia-N by about 15 g / kg N and pH by 0?2 units respectively. The minimum DM necessary to produce well-fermented silage without additive use was approximately 255 g / kg. Use of formic acid containing additives and inorganic acid reduced the target to about 240 g / kg. Similarly, the target DM for inoculant, sugar and enzyme treated silages was about 250, acid mixtures 260 and salts 270 g / kg. Acknowledgements
5
6
7
8
9
10
11
12
13
14
15
16
17
18
The author thanks ADAS Laboratory Services for technical assistance. 19 20
References 1
2
3
4
Ministry of Agriculture, Fisheries and Food Agricultural returns for England, December 1994 Haigh P M The effect of dry matter content and silage additives on the fermentation of grass silage on commercial farms. Grass and Forage Science 1987, 42: 1 – 8 Jacklin D; Haigh P M Silage additives-1993. ADAS pamphlet P3189, Oxford Spires; ADAS, 1993. McDonald P; Henderson A R; Heron S J E The Biochemistry of Silage. Marlow: Chalcombe Publications, 1991
21
22
23
Mayne C S; Steen R W J A review of animal production responses to formic acid and inoculant treatment of grass silage in trials at the Agricultural Research Institute of Northern Ireland. In: Silage Research 93—Proceedings of the Tenth International Conference on Silage Research (O’Kiely, P; O’Connell, M; Murphy, J. eds). Pp. 178 – 179. Dublin: Dublin City University, 1993 Steen R W J; Unsworth E F; Gracey H I; Kennedy S J; Anderson R; Kilpatrick D J Evaluation studies in the development of a commercial bacterial inoculant as an additive for grass silage. 3. Responses in growing cattle and interaction with protein supplementation. Grass and Forage Science 1989, 44: 381 – 390 Ibbotson C F Some observations on the effectiveness of silage additives on commercial farms, silage additive studies 1972 – 75. Fourth Silage Conference, Hurley Crawshaw R; Hughes J G A national survey of the effectiveness of additives in preventing a clostridial fermentation. Animal Production 1978, 26: 364 Wilson R K; O’Kiely P A note on the chemical composition of Irish farm silages 1985 – 1988. Irish Journal of Agricultural Research 1990, 29: 71 – 75 Alexander R H The sampling of silage pits by coring. Journal of Agricultural Engineering Research 1960, 5: 118 – 122 Ministry of Agriculture, Fisheries and Food The analysis of Agricultural Materials, RB427 Ministry of Agriculture Fisheries and Food. 3rd ed. London: HMSO, 1986 Agricultural Development and Advisory Service ADAS Nutrition Chemists’ Conference (unpublished), 1986 Barber G D; Givens D I; Kridis M S; Offer N W; Murray I Prediction of the organic matter digestibility of grass silage. Animal Feed Science and Technology 1990, 28: 115 – 128 Haigh P M Effectiveness of silage additives on commercial farms. M.Phil Thesis University of Nottingham, 1983 Lawes Agricultural Trust Genstat V Mark 4.01. Rothamsted Experimental Station, Harpenden 1977 Birch M W Maximum likelihood in 3-way contingency tables. Journal Royal Statistical Society 1963, 25: 220 – 233 MORECS Bulletin Meteorological Office weekly bulletins for May to September 1985 and 1990 Jones D I H; Jones R The effect of crop characteristics and ensiling methodology on grass silage effluent production. Journal of Agricultural Engineering Research 1995, 60: 73 – 81 Haigh P M Silage additives—1991. London: MAFF, 1991 Woolford M K The Silage Fermentation. New York: Marcel Dekker, 1984 Haigh P M; Parker J W G Effect of silage additives and wilting on silage fermentation, digestibility and intake, and on liveweight change of young cattle. Grass and Forage Science 1985, 40: 429 – 436 Agricultural Development and Advisory Service. Silage additives available in 1975. Technical Note Nutrition Chemistry Department, Leeds, 1975 Haigh P M; Appleton M; Clench S F Effect of commercial inoculant and formic acid Ú formalin silage additives on silage fermentation and intake and on liveweight change of young cattle. Grass and Forage Science 1987, 42: 405 – 410
FERMENTATION OF BUNKER-MADE GRASS SILAGES IN ENGLAND 24
25
26
27
Jacobs J L; McAllan A B Enzymes as silage additives. 1. Silage quality, digestion, digestibility and performance in growing cattle. Grass and Forage Science 1991, 46: 63 – 73 Jacobs J L; McAllan A B Protein supplementation of formic acid-and enzyme-treated silages. 1. Digestibilities, organic matter and fibre digestion. Grass and Forage Science 1992, 47: 103 – 113 Jacobs J L; Haines M J; McAllan A B The effects of different protein supplements on the utilisation of untreated, formic acid-treated or enzyme-treated silages by growing steers. Grass and Forage Science 1992, 47: 121 – 127 Haigh P M The effect of wilting and silage additives on the fermentation of autumn-made grass silage ensiled in bunkers on commercial farms in South
28
29
30
31
259
Wales 1983 – 85. Grass and Forage Science 1988, 43: 337 – 345 Haigh P M Effect of herbage water-soluble carbohydrate content and weather conditions at ensilage on the fermentation of grass silages made on commercial farms. Grass and Forage Science 1990, 45: 263 – 271 Wheeler B; Wilson R K; Flynn A V The chemical composition of Irish farm silage. Irish Journal of Agricultural Research 1983, 22: 149 – 160 Haigh P M The composition of first cut grass for ensilage in England and Wales 1988 – 91. Grass and Forage Science 1995, 50: 63 – 67 O’Kiely P; O’Connell M; Murphy J (1993) Silage Research 1993—Proceedings of the Tenth International Conference on Silage Research. Dublin: Dublin City University, 1993
REVIEW PAPER
The Effect of Dry Matter Content and Silage Additives on the Fermentation of Bunker-Made Grass Silage on Commercial Farms in England 1984 – 91 P. M. Haigh ADAS, Pwllpeiran, Research Centre, Cwmystwyth, Aberystwyth, Dyfed SY23 4AB, UK (Receiy ed 3 July 1995; accepted in rey ised form 19 February 1996)
A total of 14 636 samples of silage made in bunkers on commercial farms between 1984 and 1991 were analysed to investigate the effect of dry matter (DM) content and silage additives on fermentation as measured by ammonia-N concentration and pH. Increasing DM content without additive use had a major beneficial influence on fermentation. When silage DM contents were greater than 220 g / kg about 66% of the silages were well fermented. Below this with diminishing DM concentration the proportion of well fermented silages declined such that with DM below 180 g / kg only 27% were well fermented. The benefit of silage additives, albeit at poorly defined and often inadequate rates, was extremely variable. Below DM concentrations of 220 g / kg, formic acid consistently improved the proportion of well fermented silages compared with non-additivetreated silages by about 20%. Similarly use of formic acid based, inorganic acid and acid with formalin additives increased the proportion of well fermented silages by about 15%. Acid mixtures, salts, inoculants and sugars provided little or no benefit compared with non-additive-treated silages, whilst use of enzymes increased the proportion of well fermented silages by about 8%. Above DM 220 g / kg, formic acid, acid with formalin and inoculant additives improved the proportion of well fermented silages, compared with non-additivetreated silages by about 15%. Similarly, formic acid based, inorganic acids and enzymes improved the proportion of well fermented silages by about 10%. Acid mixtures, salts and sugars produced less than 5% benefit. The minimum DM necessary to produce wellfermented silage without additive use was approximately 255 g / kg. Use of formic acid containing additives and inorganic acids reduced the target to about 240 g / kg. Similarly, the target DM for inoculant, sugar and enzyme treated silages was about 250, acid mixtures 260 and salts 270 g / kg. 0021-8634 / 96 / 080249 1 11 $18.00 / 0
It is concluded that on commercial farms, weather conditions during ensilage, i.e. amount of rainfall and sunshine have a considerable effect upon subsequent silage fermentation. However, when silage DM was below 220 g / kg, additives containing acid with or without formalin significantly increased the proportion of well fermented silages. ÷ 1996 Silsoe Research Institute
1. Introduction It is estimated1 that 22?5 Mt of bunker silage was made in England in 1994 of which about half2 was treated with one of the 138 proprietary silage additives available.3 The benefits of silage additives, both in terms of improving silage fermentation and subsequent animal performance, when the silage is fed have been well documented,4 and it has been shown that despite the absence of effects on fermentation, some additives improve animal performance relative to untreated material.5 Therefore, in the development of silage additives to date, although fermentation control is important, attention is also paid to methods of improving the nutritive value of the product and reducing dry matter (DM) losses.4 Routine chemical analysis, e.g. ammonia-N and pH, of commercial farm silos may be used to indicate silage fermentation quality. However, there may be no improvement in fermentation quality or digestibility of the resultant silage relative to those achieved in an untreated silage, but nevertheless improved animal performance may result when the silage is fed.6 With commercial farm silos, increasing DM of silages leads to improved silage fermentation.2,7,8 The benefits of silage additives, albeit at poorly defined and often inadequate rates has been shown to be small2,9 with additives being used on wetter silages. Information is lacking on the effectiveness of the newer biological additives on commercial farms. The
249
÷ 1996 Silsoe Research Institute
250
P. M. HAIGH
following investigation reports results of 14 636 samples of silage analysed by ADAS collected in England during 1984 – 1991.
2.4 . Silage fermentation 2.4 .1 . Ammonia -N An ammonia-N value of less than 100 g / kg N was used to indicate well fermented silage.2
2. Materials and methods
2.1. Sampling Only two methods of taking samples for analysis were used. Silage samples were taken mainly by coring to a depth of 1?3 m with a 30 mm diameter corer designed by Alexander.10 Occasionally grab samples, taken from the face of the silo, were used for analysis. Details of the nature of the additive used were collected from farmers at the time of sampling.
2.2. Chemical analysis Oven dry matter (DM), crude protein determined on the oven dried material (CP), pH, ammonia-N (NH3-N) and modified acid detergent fibre (MAD fibre) were determined according to Ministry of Agriculture, Fisheries and Food.11 During the period 1984 – 1987 metabolisable energy (ME) was calculated on a toluene dry matter basis (TDM) using the equation12 ME (MJ / kg TDM) 5 15?33 2 0?0152 MADF (g / kg TDM) From 1988 – 1991 ME was estimated from the prediction of in y iy o organic matter digestibility using near infra-red diffuse spectrum spectroscopy (NIR) based on the procedures described by Barber et al .13 This method gave ME values approximately 0?5 MJ / kg DM higher than that predicted from MADF.13
2.3. Additiy es applied The silage additives applied were divided into ten distinct categories according to their main active ingredients and mode of action,3 namely, no additive treatment, formic acid, formic acid based, acid mixtures, inorganic acids, acid with formalin, salts, inoculants, enzymes and sugars.
2.4 .2 . pH Many workers have used pH as the sole criterion for assessing silage fermentation. However, pH alone is an unreliable guide, because with increasing DM level, stable conditions may be achieved4 at much higher pH. For this survey, the desirable pH of silages, at different DM concentrations is given in Table 1. For each silage, if the observed pH value was below the predicted pH value, it was taken to be well fermented. Overall, a silage was assumed to be well fermented if both the ammonia-N and pH value were below the predicted values.
2.5 . Statistical analysis Analysis of variance was used to test the effects of additives and year upon silage composition.15 Linear regression was used to assess the relationship between DM and ammonia-N and pH. To differentiate the effect of additives upon the DM required for successful preservation, a generalized linear model assuming Poisson errors16 was used.
3. Results The incidence of additive use in relation to DM, CP and ME, is given in Tables 2 and 3 and the mean DM, CP and ME contents of silages in Table 4.
3.1. The relationship between additiy e use and DM concentration About 43% of the silages sampled had received additive (Table 2). Average DM concentration of the non-additive-treated silages was 270 g / kg compared with about 210 – 240 g / kg for treated silages. Above a DM concentration of 300 g / kg only 17% of the silages were treated with additive. Additive use increased with decreasing DM content, by about 7% for each 200 g / kg decrease in DM, from 29% in the DM range 280 – 300 g / kg to 39% in the DM range 240 – 260 g / kg. Below DM 220 g / kg additive was used on about 65% of the samples. Overall, formic acid and formic acid
251
FERMENTATION OF BUNKER-MADE GRASS SILAGES IN ENGLAND
Table 1 Maximum pH required to produce well fermented silage at different ranges of dry matter14 Dry matter range (g / kg) pH required
min max
180 200 4?1
,180 4?0
200 220 4?2
220 240 4?3
240 260 4?4
260 280 4?5
280 300 4?6
.300 4?8
3.2. The relationship between additiy e use and CP
based additives were both applied to about 5% of the silages. Below DM 220 g / kg, they were used on about 10% of the silages. Their use then declined with increasing DM content, so that for silages with DM greater than 300 g / kg only 2% of the silages were treated. Inorganic acids were applied to about 14% of silages with DM below 240 g / kg, above this DM there was a tendency for their use to decrease with increasing DM content, so that for silages with DM above 300 g / kg only 3% of silages were treated. Acid with formalin additives were applied to about 15% of silages with DM concentration below 220 g / kg, above this DM concentration their use tended to decline with increasing DM content, so that for silages with DM above 300 g / kg only 3% of silages were treated. Inoculants were applied to about 8% of the silages, but their use appeared to be independent of DM except for very dry silages, i.e. DM above 300 g / kg, when only 4% of the samples were treated. Enzymes and sugars were applied to about 2% of silages, whilst less than 1% of samples were treated with either acid mixtures or salts. Overall, the results indicated that, when possible, farmers attempted to increase the DM content of silage by wilting. When wilting was not possible they tended to use an acid based additive, whereas inoculant additives tended to be used on about 8% of samples irrespective of DM content.
The incidence of additive use increased with increasing CP (Table 3). The mean CP (Table 4) of non-additive-treated silages was 137 g / kg DM, which was significantly (P , 0?001) less than other treatments except salts. 3.3. The relationship between additiy e use and ME The incidence of additive use increased with increasing ME (Table 3). The mean ME (Table 4) of non-additive-treated silages was 10?0 MJ / kg DM, which was significantly (P , 0?001) less than other treatments except salts and enzymes.
3.4 . Silage fermentation 3.4 .1. Effect of silage DM in the absence of additiy e use The ammonia-N (Table 5) and pH values (Table 6) of silages at given DM ranges indicate that the fermentation quality (Table 7) of silages was enhanced by increased DM. The proportion of silages in each DM range which were well fermented, decreased by about 8% in each DM range from 84% for silages
Table 2 Incidence of additive use in relation to dry matter Additiy e Dry matter range (g / kg )
Formic None acid
Formic acid based
Acid mixtures
Acid Inorganic with acids formalin Salts
Inoculants
Enzymes
Sugars
Total
,180 180 – 200 200 – 220 220 – 240 240 – 260 260 – 280 280 – 300 .300
482 522 678 881 1257 1055 1271 2141
118 141 207 163 108 79 68 55
109 82 181 125 94 79 64 40
15 11 20 12 7 11 7 6
228 188 256 220 122 94 77 73
234 214 276 216 203 113 93 77
24 15 12 9 11 6 4 3
144 145 164 163 212 125 139 107
26 22 53 48 29 36 43 47
44 35 54 37 29 32 24 21
1421 1372 1898 1871 2070 1648 1788 2568
Total
8287
939
774
89
1258
1426
84
1199
304
276
14 636
252
P. M. HAIGH
Table 3 Incidence of additive use in relation to CP and ME of silages Formic None acid
Formic acid based
Acid mixtures
Acid Inorganic with acids formalin Salts Inoculants Enzymes
Sugars
Total
CP (g / kg DM) ,120 120 – 140 140 – 160 160 – 180 .180
1694 2395 1391 1291 1516
47 129 304 261 198
7 25 212 299 231
8 25 19 21 16
171 231 365 300 191
91 289 352 442 272
5 32 33 12 2
77 205 329 384 204
22 61 75 100 46
42 48 72 75 39
2164 3420 3152 3185 2715
ME (MJ / kg TDM) ,9?5 9?5 – 10?0 10?0 – 10?5 10?5 – 11?0 11?0 – 11?5 11?5 – 12?0 .12?0
925 2159 2249 1534 1015 273 132
7 136 221 241 219 94 21
15 102 191 188 173 85 20
5 7 35 11 17 9 5
83 301 345 285 201 35 8
69 152 267 377 295 207 59
12 19 23 16 9 4 1
69 135 231 268 302 110 84
22 29 95 50 45 34 29
7 37 58 71 65 23 15
1214 3077 3715 3041 2341 874 374
with DM above 300 g / kg to only 27% in the DM range less than 180 g / kg. The exceptions to this were in the DM ranges 180 – 200 g / kg, when 35% of the silages were well fermented rising to 53% in the DM range 200 – 220 g / kg. In the DM range 220 – 260 g / kg about 60 – 65% of the silages were well fermented.
3.4.2. Formic acid Formic acid was consistently the most effective silage additive. It reduced the ammonia-N content by about 20 g / kg N and pH values of silages by 0?50 units compared with non-additive-treated silages. It thereby improved the proportion of well fermented silages, particularly below DM concentrations of 280 g / kg, when the percentage of well fermented silages was increased by about 20% at each DM range compared with non-additive-treated silages. Above DM 280 g / kg
the improvement was less, so that 90% of the silages treated with formic acid were well fermented, compared with 80% of non-additive-treated silages. 3.4 .3. Formic acid based additiy es Formic acid based additives reduced the ammoniaN content by 10 g / kg N and pH values of silages by 0?41 units compared with non-additive-treated silages. They were particularly effective for silages with DM below 280 g / kg, when the proportion of well fermented silages was increased by 14% compared with non-additive-treated silages, but the effect was consistently about 6% less than formic acid treatment. Above DM 280 g / kg they provided a small but consistent improvement with 85% of the silages being well fermented compared with 80% of non-additivetreated silages.
Table 4 DM, ammonia-N, pH, CP and ME content of silages in relation to additive use
Samples DM (g / kg) NH3N (g / kg N) pH CP (g / kg DM) ME (MJ / kg TDM) Proportion well fermented
No additiy e
Formic acid
Formic acid based
Acid mixtures
Inorganic acids
Acid with formalin
Salts
Inoculants
Enzymes
Sugars
s.e.d.
8287 a 270 bc 104 4?42 a 137 a 10?0 0?67
939 bc 228 a 84 a 3?92 cd 153 cd 10?3 0?74
774 bc 228 ab 94 b 4?01 cd 154 d 10?4 0?68
89 bc 230 bc 103 dc 4?13 bc 147 bc 10?2 0?54
1258 ab 222 bc 103 cd 4?11 d 160 d 10?4 0?65
1426 ab 224 ab 92 bc 4?04 cd 154 bc 10?2 0?68
84 d 208 d 128 f 4?25 ab 138 a 10?0 0?45
1199 bc 228 bc 103 dc 4?14 cd 152 d 10?4 0?67
304 c 243 bc 104 bcd 114?07 cd 156 ab 10?1 0?72
276 bc 231 cd 113 ef 4?19 cd 153 bc 10?2 0?57
5?04 4?7 0?023 2?9 0?05
s.e.d. 5 standard error of difference between two means. Means on the same line, with the same or no superscript do not differ significantly (P , 0?001).
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FERMENTATION OF BUNKER-MADE GRASS SILAGES IN ENGLAND
Table 5 The ammonia-N values (g / kg N) of silages at each DM range in relation to additive use Formic Acid DM range No Formic acid Acid Inorganic with (g / kg ) additiy e acid based mixtures acids formalin Salts ,180 180 – 200 200 – 220 220 – 240 240 – 260 260 – 280 280 – 300 .300 s.e.d. LSD
176 155 122 109 100 94 88 84
121 90 86 78 71 66 70 67
4?5 14?8
6?1 20?1
129 104 94 92 82 70 83 78 5?4 17?8
212 189 121 127 106 97 81 89
132 112 103 102 86 74 81 79
10?1 33?2
130 108 88 87 73 74 70 63
12?2 40?2
189 156 115 92 64 75 76 71
7?5 24?7
15?9 52?3
Inocu Number of lants Enzymes Sugars samples s.e.d. LSD 204 165 101 89 66 70 67 66 7?8 25?7
175 166 115 90 88 85 81 83 11?5 37?8
162 155 114 98 89 85 79 80
1421 1372 1898 1871 2070 1648 1788 2568
27?4 15?1 9?5 6?1 6?9 6?5 6?1 5?1
90?2 49?7 31?3 20?1 22?7 21?4 20?1 16?8
15?9 52?3
s.e.d. 5 standard error of difference between two means. LSD 5 least significant differences at P , 0?001.
3.4.4. Acid mixtures Only 89 samples were treated with acid mixtures. Therefore, it was somewhat difficult to draw conclusions. Overall, their use had little effect upon ammonia-N content but decreased the pH value by 0?29 units compared with non-additive-treated silages. They were therefore generally ineffective in enhancing silage fermentation compared with non-additivetreated silages at any DM concentration.
pared with non-additive-treated silages. They reduced the ammonia-N content of silages with DM below 200 g / kg by about 45 g / kg N and they consistently improved the proportion of well fermented silages with DM below 280 g / kg by 14%. Above this DM content they provided only a small improvement (about 5%) compared with non-additive-treated silages.
3.4 .6 . Acid with formalin 3.4.5. Inorganic acids Inorganic acids had little effect upon ammonia-N content but decreased silage pH by 0?31 units com-
Overall, acid with formalin use ammonia-N content by 12 g / kg N and silages by 0?38 units compared with treated silages. They consistently
reduced the pH values of non-additivereduced the
Table 6 The pH values of silages at each DM range in relation to additive use DM range (g / kg )
Formic Acid Number No Formic acid Acid Inorganic with of additiy e acid based mixtures acids formalin Salts Inoculants Enzymes Sugars samples s.e.d. LSD
,180 180 – 200 200 – 220 220 – 240 240 – 260 260 – 280 280 – 300 .300
4?59 4?47 4?27 4?28 4?28 4?33 4?41 4?61
4?11 3?89 3?85 3?84 3?84 3?95 4?02 4?08
4?19 3?99 3?89 4?01 3?85 3?89 4?26 4?31
4?67 4?51 4?18 4?29 4?24 4?30 4?31 4?56
4?27 4?14 4?05 4?04 4?03 3?98 4?18 4?19
4?25 4?07 3?93 3?98 3?94 4?00 4?08 4?14
4?51 4?32 4?03 4?09 4?07 4?08 4?13 4?37
4?59 4?37 4?20 4?08 3?92 3?96 4?00 4?04
4?39 3?97 4?01 4?03 3?96 3?94 4?00 4?27
4?36 4?26 4?15 4?07 4?04 4?11 4?21 4?36
s.e.d. LSD
0?015 0?049
0?027 0?089
0?032 0?105
0?112 0?369
0?101 0?332
0?019 0?063
0?156 0?514
0?021 0?069
0?141 0?464
0?137 0?450
s.e.d. 5 standard error of difference between two means. LSD 5 least significant difference at P , 0?001.
1421 1372 1898 1871 2070 1648 1788 2568
0?191 0?129 0?028 0?028 0?031 0?024 0?029 0?031
0?629 0?425 0?092 0?092 0?102 0?079 0?095 0?102
254
P. M. HAIGH
Table 7 The proportion of well fermented silages at each DM range in relation to additive use
DM range (g / kg )
No additiy e
Formic acid
Formic acid based
Acid mixtures
,180 180 – 200 200 – 220 220 – 240 240 – 260 260 – 280 280 – 300 .300 Mean
0?27 0?35 0?53 0?64 0?61 0?71 0?76 0?84 0?67
0?44 0?60 0?75 0?79 0?83 0?90 0?89 0?89 0?74
0?39 0?52 0?68 0?70 0?75 0?88 0?82 0?87 0?68
0?20 0?30 0?58 0?58 0?61 0?72 0?83 0?84 0?54
Inorganic Acid with acids formalin Salts 0?42 0?51 0?66 0?70 0?75 0?90 0?83 0?86 0?65
ammonia-N content and pH of silages with DM below 220 g / kg by about 40 g / kg N and 0?3 – 0?4 units respectively. Irrespective of DM content they consistently improved the percentage of well fermented silages by about 15% compared with non-additive-treated silages. 3.4.7. Salts Only 84 silages were treated with salts. Therefore, it was difficult to draw firm conclusions from the results. Overall however, they increased the ammonia-N content by 24 g / kg N and reduced the pH values of silages by 0?17 units compared with non-additive-treated silages. The proportion of well fermented silages with DM concentrations below 240 g / kg was consistently less than that of non-additive-treated silages. Above this DM level the proportion of well fermented silages was similar to that of non-additive-treated silages. 3.4.8. Inoculants Overall, inoculant use had little effect upon ammonia-N but decreased silage pH by 0?28 units compared with non-additive-treated silages. Their effectiveness was particularly influenced by the DM content of the silages. Below DM 220 g / kg they provided little benefit in ammonia-N concentration or pH and the proportion of well fermented silages compared with non-additive-treated silages. Above this DM concentration they reduced the ammonia-N content by 10 g / kg N and pH values by 0?37 units compared with non-additive-treated silages. 3.4.9. Enzymes Overall, enzyme use had little effect upon the ammonia-N content, but reduced the pH value by 0?35 units compared with non-additive-treated silages,
0?39 0?51 0?72 0?74 0?81 0?85 0?88 0?91 0?68
0?15 0?28 0?49 0?62 0?77 0?78 0?75 0?84 0?45
Inoculants
Enzymes
Sugars
Mean
0?18 0?33 0?58 0?73 0?80 0?91 0?94 0?93 0?67
0?29 0?49 0?61 0?74 0?75 0?84 0?87 0?90 0?72
0?28 0?35 0?50 0?65 0?65 0?74 0?87 0?85 0?57
0?33 0?43 0?62 0?69 0?68 0?76 0?80 0?85 0?67
and thereby improved the proportion of well fermented silages by about 10% irrespective of silage DM content. 3.4 .10 . Sugars Sugars increased the ammonia-N content by 9 g / kg N and decreased the pH value by 0?23 units compared with non-additive-treated silages. Their use however, irrespective of silage DM, provided little benefit in terms of silage fermentation, compared with non-additive-treated silages.
3.5. The relationship between silage composition and the year in which it was made There was considerable year-to-year variation in silage quality. The contrast between 1985 (Table 8) and 1990 (Table 9) was most noticable. Between these years the proportion of well fermented non-additivetreated silages increased from 44% to 85%, despite the fact that the average DM content was about 280 g / kg in each year. Similarly the CP content of silages increased from 127 to 156 g / kg DM and ME value from 9?9 to 10?3 MJ / kg DM.
3.6 . Silage DM , additiy es and fermentation The linear relationships between silage DM using ammonia-N and pH as independent variables with additive use are given in Table 10. Using ammonia-N and pH as the criteria for effective fermentation the
255
FERMENTATION OF BUNKER-MADE GRASS SILAGES IN ENGLAND
Table 8 Composition of silages in relation to additive use 1985
Samples DM (g / kg) NH3N (g / kg N) pH CP (g / kg DM) ME (MJ / kg TDM) Proportion well fermented
Formic No additiy e acid
Formic acid based
Acid mixtures
Inorganic acids
Acid with formalin
Salts
Inoculants
Sugars
203 232a 102ab 4?03a 154c 10?3c 0?67
67 223a 126ab 4?15b 148bc 10?3c 0?48
18 236a 133abd 4?22bc 140abc 10?3c 0?42
43 191 160bcd 4?38d 150bc 10?2bc 0?27
277 231a 127abc 4?21b 150bc 10?2bc 0?49
25 231a 186cd 4?35d 138ab 10?0ab 0?26
79 237a 120ab 4?33cd 138ab 10?1abc 0?47
35 244a 123ab 4?18bc 151c 10?3c 0?54
1110 277 133abc 4?57 127a 9?9a 0?44
s.e. between two means
6?7 10?1 0?034 4?6 0?07
From May to September 1985 was fairly wet with little sunshine.17 Means on the same line, with the same or no superscript do not differ significantly (P , 0?001).
calculated minimum DM necessary to produce wellfermented non-additive-treated silages needed to be about 255 g / kg. The use of formic-acid-containing additives and inorganic acids reduced the target to about 240 g / kg. Similarly the target DM for inoculant, sugar and enzyme treated silages was about 250, acid mixtures 260, and salts 270 g / kg. 4. Discussion 4.1. Silage DM content The survey demonstrated that over 60% of nonadditive-treated silages with DM concentrations above 220 g / kg were well fermented. Below this DM content, fermentation quality declined as silages became more moist. This conclusion suggests that the silage making techniques used in the present survey have improved compared with previous surveys2,7,8 which
showed that silages with DM concentrations above 250 g / kg were well fermented without additive use, whilst silages of lower DM content were not.
4.2 . Formic acid The survey results show that formic acid was far more effective in producing well fermented silages in the DM range less than 220 g / kg than shown in previous surveys2 and that it reduced pH.9 Nevertheless, its effectiveness declined with decreasing DM content and it did not, in practice, consistently produce well preserved silages when used with wet crops. Its effectiveness may have been reduced because of low and variable rates of application and the fact that it is highly volatile and may disappear during field applications on commercial farms,2 and because effluent production is greater when formic acid is applied.18
Table 9 Composition of silages in relation to additive use 1990
Samples DM (g / kg) NH3N (g / kg N) pH CP (g / kg DM) ME (MJ / kg TDM) Proportion well fermented
No additiy e
Formic acid
Formic acid based
Acid mixtures
Inorganic acids
Acid with formalin
Inoculants
Enzymes
Sugars
s.e. between two means
1148 275c 71ab 4?32 156c 10?3bc 0?85
36 239ab 58a 4?03bc 170e 10?5c 0?88
187 240ab 59a 3?95a 169de 10?5c 0?83
4 259bc 70ab 4?07c 126a 9?9a 0?73
139 227a 60a 3?94a 165cde 10?6c 0?90
123 229a 61a 3?95a 160cde 10?4bc 0?90
239 242ab 61a 3?97ab 162cde 10?6c 0?83
39 266b 70ab 4?02bc 159cd 10?4bc 0?77
13 229a 86b 4?08c 144b 10?1ab
6?9 4?9 0?021 3?3 0?11
From May to September 1990 was dry and sunny.17 Means on the same line, with the same or no superscript do not differ significantly (P , 0?001).
256
P. M. HAIGH
Table 10 Relationships between silage ammonia-N (g / kg N) , pH and DM (g / kg) with additive use Additiy e
Results
Relationship with DM
Min DM for presery ation
s .e.
r2
P
8287
No additive
292 2 0?379 NH3-N 174 1 18?8 pH
254 257
16?5 17?1
0?329 0?173
,0?001 NS
939
Formic acid
262 2 0?219 NH3-N 162 1 18?1 pH
240 239
19?4 21?3
0?399 0?172
,0?001 NS
774
Formic acid based
276 2 0?351 NH3-N 140 1 23?9 pH
241 242
21?7 22?1
0?415 0?123
,0?001 NS
Acid mixtures
288 2 0?291 NH3-N 359 2 22?8 pH
259 261
16?5 17?9
0?372 0?111
,0?001 NS
1258
Inorganic acids
261 2 0?191 NH3-N 315 2 17?1 pH
242 243
15?9 17?2
0?331 0?109
,0?001 NS
1426
Acid with formalin
261 2 0?187 NH3-N 154 1 20?3 pH
242 241
14?9 15?1
0?411 0?119
,0?001 NS
Salts
368 2 0?971 NH3-N 178 1 21?4 pH
271 268
17?1 18?3
0?292 0?171
,0?01 NS
Inoculants
276 2 0?273 NH3-N 315 2 15?1 pH
249 250
14?9 15?1
0?421 0?097
,0?001 NS
304
Enzymes
279 2 0?267 NH3-N 200 1 12?0 pH
252 252
16?9 16?5
0?302 0?006
,0?01 NS
276
Sugars
269 2 0?214 NH3-N 27?3 1 51?2 pH
248 247
15?9 16?5
0?297 0?011
,0?01 NS
89
84 1199
4.3. Formic acid based additiy es Irrespective of DM content, formic acid based additives were less effective than formic acid at producing well fermented silage. It is probable that the products available, contained less acid than formic acid.19
4.4. Acid mixtures The results of the survey confirm those of previous surveys,2,8 that organic acid mixtures appear to produce silage which is no better on average than that receiving no treatment at all.
higher than those for formic acid treated silages, a pattern noted in Ireland.9
4.6 . Acid with formalin Overall, acid with formalin use produced similar results to formic acid based additives. For silages with a DM content below 220 g / kg however, the pH values were higher, a pattern noted generally for formic acid with formalin treated silages, when compared with formic acid treatment.21 For silages with a DM content below 220 g / kg the results were far superior to those found for sulphuric acid plus formalin treated silages;2 probably because the present products contain a far higher level of acid.3,22
4.5. Inorganic acids Inorganic acids produced a similar benefit in terms of improvement in fermentation to formic acid treated silages for silages with a DM content below 180 g / kg. Thereafter, they were generally not as effective as formic acid probably because they have no specific anti-microbial properties and merely act as acidifying agents.20 The pH of inorganic-acid-treated silages was
4.7 . Salts Use of these additives produced silages which on average were no better fermented than non-additivetreated silage, a conclusion which agrees with Haigh.2 Generally, investigations on the use of salts (sodium nitrite plus calcium formate) have produced incon-
FERMENTATION OF BUNKER-MADE GRASS SILAGES IN ENGLAND
clusive results.4,20 Although previous surveys7,8 have shown them to reduce pH of silages compared with non-additive-treated silage. 4.8. Inoculants Inoculant treatment produced no benefit in terms of fermentation compared with non-additive-treated silages for silages with DM content below 220 g / kg. This conclusion agrees with Haigh et al.23 that inoculants failed to show any benefit when low DM grass is ensiled in farm-scale silos. The reason for this would appear to result from a lack of readily available carbohydrate and the fact that inoculants were added as powders, which gives a poorer distribution over the plant surface than a liquid.23 Their lack of succcess could be that they also provided less than the 106 organisms per gram of grass commonly recommended.3 As silage DM content increased so did the proportion of well fermented silages compared with non-additive-treated silages suggesting that inoculants work best with high sugar crops.4,20 4.9. Enzymes Treatment with enzymes for silages with DM below 220 g / kg tended to produce silages with pH values intermediate between those of formic acid treated and non-additive-treated silages, and ammonia-N values similar to those of non-additive-treated silages. Consequently, the proportion of well preserved silages was intermediate between that of non-additive-treated and formic acid treated silages. Other work24–26 has tended to show that enzyme treatment produced silages with a similar pH value but higher ammonia-N content than formic acid treated silages. Enzymes work as a means of increasing the content of fermentable sugars4 particularly with direct-cut rather than wilted silages.20 The poor results in the present survey suggest that comparisons are open to wide interpretation because enzyme sources and activities may differ widely;24 and perhaps not speed up the hydrolysis process to produce sugars for fermentation early in the ensiling process. 4.10. Sugars On average, use of sugars produced silages which were no better fermented than non-additive-treated silages. This pattern has been noted elsewhere, particularly for low DM silage.9,27 To obtain maximum benefit, it is probable that they should be used at high concentrations4 of about 40 – 50 kg / t, which farmers find difficult to apply.27
257
4.11 . Effect of silage -making year Previous reports on farm silages have shown that year to year variation in silage quality was a feature of the results.9,28,29 This report shows a similar trend; 1985 and 1990 were two contrasting years. Between these years, the percentage of well fermented silages dramatically increased. Probably because the water soluble carbohydrate content of the herbage ensiled was high30 and better inoculant additives were available.3 This pattern is consistent with the weather during silage making, which in 1990 was very dry and sunny, whereas in 1985 it was very wet and dull. These results support the conclusions of Haigh28 and Wilson and O’Keily9 that silage quality on commercial farms in terms of fermentation may be ascribed to climatic conditions during harvesting.
4.12 . Silage DM , additiy es and fermentation The results of the present survey support those of Haigh28 that the minimum DM necessary to produce well-fermented non-additive-treated silages needed to be about 255 g / kg, and that formic acid additives reduced the target to about 240 g / kg. The fact that other additives appear to perform less well on commercial farms than in present experiments31 may be inherent in their composition compared with present day additives.
5. Conclusions On commercial farms, weather conditions during ensilage, i.e. amount of rainfall and sunshine, have a considerable effect upon subsequent silage fermentation. Increasing DM content without additive use had a major beneficial influence on fermentation. When silage DM contents were above 220 g / kg about 66% of the silages were well fermented, with average ammonia-N concentrations of 93 g / kg N and pH 4?42. Below this, with diminishing DM concentration, the proportion of well fermented silages declined. In the DM range 200 – 220 g / kg, 53% of silages were well fermented with ammonia-N concentrations of 122 g / kg N and pH 4?27; in the DM range 180 – 200 g / kg, 35% were well fermented with ammonia-N 155 g / kg N and pH 4?47; with DM below 180 g / kg DM only 27% were well fermented with ammonia-N concentrations of 176 g / kg N and pH 4?59.
258
P. M. HAIGH
The benefit of silage additives, albeit at poorly defined and often inadequate rates, was extremely variable. At DM concentrations below 220 g / kg, formic acid consistently improved the proportion of well fermented silages compared with non-additive-treated silages by about 20%, ammonia-N by about 50 g / kg N and pH by about 0?5 units. Similarly, use of formic acid based, inorganic acid and acid with formalin increased the proportion of well fermented silages by about 15% by reducing the ammonia-N concentrations by about 40 g / kg N and pH by 0?3 – 0?4 units respectively. Acid mixtures, salts, inoculants and sugars provided little or no benefit compared with non-additive-treated silages, whilst use of enzymes increased the proportion of well fermented silages by about 8% and reduced the pH by 0?3 units. Above DM 220 g / kg, formic acid, acid with formalin and inoculant additives improved the proportion of well fermented silages, compared with non-additive-treated silages by about 15 percentage units, by reducing the ammonia-N by 20 g / kg N and pH by 0?4 units respectively. Similarly, formic acid based, inorganic acids and enzymes improved the proportion of well fermented silages by about 10% by decreasing the ammonia-N by about 10 g / kg N and pH by about 0?3 units respectively. Acid mixtures, salts and sugars produced less than 5% benefit although salts and sugars decreased the ammonia-N by about 15 g / kg N and pH by 0?2 units respectively. The minimum DM necessary to produce well-fermented silage without additive use was approximately 255 g / kg. Use of formic acid containing additives and inorganic acid reduced the target to about 240 g / kg. Similarly, the target DM for inoculant, sugar and enzyme treated silages was about 250, acid mixtures 260 and salts 270 g / kg. Acknowledgements
5
6
7
8
9
10
11
12
13
14
15
16
17
18
The author thanks ADAS Laboratory Services for technical assistance. 19 20
References 1
2
3
4
Ministry of Agriculture, Fisheries and Food Agricultural returns for England, December 1994 Haigh P M The effect of dry matter content and silage additives on the fermentation of grass silage on commercial farms. Grass and Forage Science 1987, 42: 1 – 8 Jacklin D; Haigh P M Silage additives-1993. ADAS pamphlet P3189, Oxford Spires; ADAS, 1993. McDonald P; Henderson A R; Heron S J E The Biochemistry of Silage. Marlow: Chalcombe Publications, 1991
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Mayne C S; Steen R W J A review of animal production responses to formic acid and inoculant treatment of grass silage in trials at the Agricultural Research Institute of Northern Ireland. In: Silage Research 93—Proceedings of the Tenth International Conference on Silage Research (O’Kiely, P; O’Connell, M; Murphy, J. eds). Pp. 178 – 179. Dublin: Dublin City University, 1993 Steen R W J; Unsworth E F; Gracey H I; Kennedy S J; Anderson R; Kilpatrick D J Evaluation studies in the development of a commercial bacterial inoculant as an additive for grass silage. 3. Responses in growing cattle and interaction with protein supplementation. Grass and Forage Science 1989, 44: 381 – 390 Ibbotson C F Some observations on the effectiveness of silage additives on commercial farms, silage additive studies 1972 – 75. Fourth Silage Conference, Hurley Crawshaw R; Hughes J G A national survey of the effectiveness of additives in preventing a clostridial fermentation. Animal Production 1978, 26: 364 Wilson R K; O’Kiely P A note on the chemical composition of Irish farm silages 1985 – 1988. Irish Journal of Agricultural Research 1990, 29: 71 – 75 Alexander R H The sampling of silage pits by coring. Journal of Agricultural Engineering Research 1960, 5: 118 – 122 Ministry of Agriculture, Fisheries and Food The analysis of Agricultural Materials, RB427 Ministry of Agriculture Fisheries and Food. 3rd ed. London: HMSO, 1986 Agricultural Development and Advisory Service ADAS Nutrition Chemists’ Conference (unpublished), 1986 Barber G D; Givens D I; Kridis M S; Offer N W; Murray I Prediction of the organic matter digestibility of grass silage. Animal Feed Science and Technology 1990, 28: 115 – 128 Haigh P M Effectiveness of silage additives on commercial farms. M.Phil Thesis University of Nottingham, 1983 Lawes Agricultural Trust Genstat V Mark 4.01. Rothamsted Experimental Station, Harpenden 1977 Birch M W Maximum likelihood in 3-way contingency tables. Journal Royal Statistical Society 1963, 25: 220 – 233 MORECS Bulletin Meteorological Office weekly bulletins for May to September 1985 and 1990 Jones D I H; Jones R The effect of crop characteristics and ensiling methodology on grass silage effluent production. Journal of Agricultural Engineering Research 1995, 60: 73 – 81 Haigh P M Silage additives—1991. London: MAFF, 1991 Woolford M K The Silage Fermentation. New York: Marcel Dekker, 1984 Haigh P M; Parker J W G Effect of silage additives and wilting on silage fermentation, digestibility and intake, and on liveweight change of young cattle. Grass and Forage Science 1985, 40: 429 – 436 Agricultural Development and Advisory Service. Silage additives available in 1975. Technical Note Nutrition Chemistry Department, Leeds, 1975 Haigh P M; Appleton M; Clench S F Effect of commercial inoculant and formic acid Ú formalin silage additives on silage fermentation and intake and on liveweight change of young cattle. Grass and Forage Science 1987, 42: 405 – 410
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Jacobs J L; McAllan A B Enzymes as silage additives. 1. Silage quality, digestion, digestibility and performance in growing cattle. Grass and Forage Science 1991, 46: 63 – 73 Jacobs J L; McAllan A B Protein supplementation of formic acid-and enzyme-treated silages. 1. Digestibilities, organic matter and fibre digestion. Grass and Forage Science 1992, 47: 103 – 113 Jacobs J L; Haines M J; McAllan A B The effects of different protein supplements on the utilisation of untreated, formic acid-treated or enzyme-treated silages by growing steers. Grass and Forage Science 1992, 47: 121 – 127 Haigh P M The effect of wilting and silage additives on the fermentation of autumn-made grass silage ensiled in bunkers on commercial farms in South
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