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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 crops harvested at increasing maturity and dry matter content
Animal Feed Science and Technology, 18 (1987) 257-269
257
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Treatment of Whole-crop Cereals with Alkali. 1. The Influence of Sodium H y d r o x i d e and Ensiling on the Chemical Composition and In Vitro Digestibility of Rye, Barley and Wheat Crops Harvested at Increasing Maturity and Dry Matter Content R.M. TETLOW and V.C. MASON
The AFRC Institute for Grassland and Animal Production, Hurley, Maidenhead, Berks. SL6 5LR (Gt. Britain) (Received 22 July 1986; accepted for publication 8 April 1987 )
ABSTRACT Tetlow, R.M. and 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 crops harvested at increasing maturity and dry matter content. Animal Feed Sci. Technol., 18: 257-269. Whole crops of rye, barley and wheat were each cut at three stages of maturity and dry matter (DM) content, and were ensiled in polythene bag silos directly or after wilting to ~ 600 g DM kg- ~,with ( 50 g kg - ~DM ) or without the addition of "pearl" sodium hydroxide ( NaOH ). Fourth cuts of barley and wheat were ensiled directly, with or without NaOH, when their DM content reached ~ 600 g kg- 1. With advancing maturity, the DM contents of crops increased. For rye, the contents of watersoluble carbohydrate (WSC) and starch also increased, although the level of starch was low. In contrast, the WSC in the more mature barley and wheat crops decreased as starch increased. There was a general trend for nitrogen content to fall, most markedly for rye. For all crops, WSC was lost and organic matter digestibility fell during wilting. In silages made from young crops ( < 400 g DM kg- ~), WSC and pH were low and products of fermentation high. In high DM silages, there were reduced contents of lactic acid, ethanol and ammonia. Treatment of the crop with NaOH raised the pH and the proportion of hot-water-insoluble nitrogen in all silages and tended to enhance the effect of DM on organic acid production. Organic matter digestibility of the crops was always higher than in the corresponding untreated silage. The response to NaOH improved as the crops matured, resulting in increases of up to 6 percentage units for Cut 1 and of between 15 and 20 units for the later cuts. With the relatively low DM rye silages, wilting improved the effect of NaOH by up to 9 units. It is concluded that whole-crop cereals, directly harvested at ~ 600 g DM kg- 1, can be effectively preserved and upgraded by ensilage with 50 g NaOH kg- 1 DM. At this maturity, crop yields are close to maximum and the potential nutritive value of the upgraded material is high.
0377-8401/87/$03.50
© 1987 Elsevier Science Publishers B.V.
258 INTRODUCTION Following ear emergence, immature ( ~ 350 g DM k g - 1) crops of small grain cereals can be successfully ensiled without additive (Edwards et al., 1968; MacGregor and Edwards, 1968; Demarquilly, 1970; Wilson and Wilkins, 1972a; Bolsen et al., 1983 ) and subsequently used as the principal forage component in rations for dairy cows (Horne, 1969; Fisher et al., 1972) and growing cattle (Oltjen and Bolsen, 1978). However, at this stage of growth the yield of dry matter (DM) has not reached its potential. Furthermore, fermentation in the silo can be rapid and extensive, resulting in low pH material which would predispose animals to acidosis. At more mature stages of plant development, yields of DM from cereals may equal or surpass those obtained from 3-4 cuts of grass (Corrall et al., 1977). However, lignification of the straw is more extensive (Hartley, 1981 ) and unless the pericarp is disrupted, the resistance of whole grain to digestion is also high (Orskov, 1979 ). Together these factors depress digestibility. In addition, silages made from high DM crops are often unstable when exposed to air (Woolford et al., 1982 ). The feasibility of treating cereals with alkali to disrupt the pericarp of the grain and render the ligno-cellulosic component of the straw more digestible has been demonstrated on several occasions ( Greenhalgh and Pirie, 1979; Bolsen et al., 1983; Davis and Greenhalgh, 1983; Orskov et al., 1983). At this Institute, we have shown that ensiling barley or wheat with sodium hydroxide (NaOH) can increase in vitro digestibility, the effect improving as the crop matures (Bolsen et al., 1983). The purpose of the present work was to investigate the significance of moisture content, stage of maturity and chemical composition in these responses, as a preliminary to larger scale investigations of nutritive value involving sheep (Tetlow et al., 1987; Deschard et al., 1987a) and cattle ( Deschard et al., 1987b ). MATERIALSAND METHODS Whole crops of winter rye (cv. Rheidol) (Experiment 1 ), or of spring barley (cv. Athos) and winter wheat (cv. Sicco) (Experiment 2) were each cut at three stages of development during the summers of 1978 and 1979, respectively, at DM contents below ~ 600 g k g - 1. Half of each was harvested directly and the remainder after field-wilting to ~ 600 g k g - 1. An additional cut of more mature barley and wheat was harvested without wilting and ensiled at ~ 600 g DM k g - 1 (Table I). All materials were chopped with a New Holland 717 metered-chop forage harvester and blown into farm trailers. Six sub-samples of 1.3 kg DM for rye and four sub-samples of 2.0 kg DM for barley and wheat were taken of both unwilted or wilted material. DM and chemical composition were determined
259 TABLE I Harvest dates for unwilted and wilted crops of rye, barley and wheat Cut No. 1 1 2 2 3 3 4
Wilt -/+ + + + -
Experiment 1 (1978)
Experiment 2 (1979)
Rye
Barley
Wheat
30 May 6 June 12 June 15 June 27 June 4 July --
11 July 14 July 16 July 20 July 7 Aug. 10 Aug. 15 Aug.
16 July 18 July 6 Aug. 10 Aug. 20 Aug. 22 Aug. 29 Aug.
on each sub-sample. H a l f the sub-samples were ensiled directly in polythenebag silos by the method of Wilson and Wilkins (1972b); the remainder were spread thinly and individually hand-sprinkled with N a O H at an application rate of ~ 50 g k g - 1 DM, prior to ensilage by the same technique. The 36 minisilos of rye and the 28 mini-silos of both barley and wheat were stored at ambient temperature for up to 32 weeks. Each was then weighed and opened and samples taken for analysis o f p H , D M content and chemical composition. D M content of fresh crops and silages was determined by drying samples overnight in a forced draught oven at 100°C. A glass electrode was used to determine p H values of cold water extracts of fresh silages. Lactic acid, volatile acids and ammonia were determined on acid extracts of fresh silage by the methods of Wilson and Wilkins (1978). Ethanol was measured by gas chromatography of acid extracts at the same time as the volatile fatty acids. Freeze-dried samples were used for all the other analyses. Total nitrogen ( N ) was estimated by the methods of the Association of Official Agricultural Chemists (1965). Hot-water-insoluble nitrogen ( I N S N ) was determined after extraction with boiling water (four boilings each of 10 min). Watersoluble carbohydrate ( W S C ) was extracted with cold water, hydrolysed with 0.2 N HeSO4 and determined by the alkaline ferricyanide method of Smith et al. (1964). Starch ( S T C H ) was extracted with boiling water, incubated with amyloglucosidase at p H 4.8, filtered and the filtrate hydrolysed and measured as for WSC. Neutral detergent fibre ( N D F ) was determined after pre-digestion with amyloglucosidase (Terry and Outen, 1973) by the method of Van Soest and Wine (1967). Digestibility of the organic matter ( O M D ) was determined by the two-stage method of Tilley and Terry (1963), with the addition of 10 mg of nitrogen as a m m o n i u m sulphate at the start of the first stage. The data from each cereal were subjected to analysis of variance in two ways. Firstly, an overall analysis of variance was undertaken in which all data were
260 included. This allowed comparisons of any of the means within or between cuts within each crop type. Secondly, analysis was restricted to data from each cutting date for each of the three crops. In both types of analysis, differences between means were tested by t-test using the most appropriate standard error (SED). After omitting data from the final cut for barley and wheat, the data from all crop types were pooled and a multiple regression analysis was conducted in which the OMD of the treated silage was tested against the various parameters of the untreated crops before ensiling. Because of the marked differences between rye on the one hand and barley and wheat on the other, regressions were also done on the crops separately. RESULTS
Chemical composition of crops and silages The effects of maturity, wilting, ensiling and treatment with NaOH on the DM contents and composition of crops and silages are shown in Tables II-VI. Addition of NaOH resulted in increases in Na content from 0.6, 0.6 and 0.1 to 27.9, 27.4 and 25.0 g kg- 1 DM for rye, barley and wheat silages, respectively.
Dry matter and structural carbohydrate In all cases, the DM content of the crops increased significantly with maturity and wilting (Table II), but the oven DM contents of the silages were generally lower than before ensiling. Changes in the NDF content during ensiling were small, but NaOH treatment generally resulted in lower levels in treated than in untreated silages. This effect was significant in many cases (P<0.05).
Water-soluble carbohydrates and starch For rye, the WSC content increased as the crop matured (Table III). In contrast, that of barley and wheat decreased. Wilting tended to reduce the WSC content of crops, particularly those with a high level at cutting. For all crops, WSC content in the silages was lower than in the corresponding crops, particularly in the less mature and unwilted silages with low DM content. In all crops, starch content increased as crops matured, although rye contained less starch than barley or wheat. Starch content of the silages was equal to or lower than that in the crops, although this effect was only significant in a few cases and, with the exception of wilted wheat in Cut 3, was largely confined to unwilted silage. Starch content of the silages was unaffected by treatment with NaOH.
261
T A B L E II
Influence of plant maturity, wilting and NaOH treatment on the dry matter ( D M ) and neutral detergent fibre ( N D F ) contents of cereal crops and silages Cut no.
Wilt
NaOH D M ( g k g -1)
-/+
-/+
Rye Crop 1 1 1 1
--+ +
+ +
225 243 605 619
SED ~ 2 2 2 2
+ +
+ +
313 353 593 618
+ +
+ +
372 391 573 590
SED 2
193 196 , 572 592
300 320 586 583
.
. +
. --
285 317 553 590
408 432 600 662
470 482 654 666
Rye
369 387 552 620
431 467 618 636
617 661
622 642
294 305 570 544
628 529 639 599
11 420 433 704 722
Barley
372 404 662 694
498 520 718 742
475 509 692 730
493 576 571 569
18
638 635 11
520 463 543 463
Wheat
630 596 626 577
592 564 622 595
612 562 641 573
438 405 515 383
----
607 534 633 545
419 397 522 385
530 388 418 332
462 324 433 372
508 467 552 446
425 432 13
543 481 536 460 24
588 435 457 375
43 556 493
698 576 546 571 20
25
12 ---
526 583 620 477 37
22
4.5 641 634
523 554 511 483 33
5.5
12
--
' d f = 16 for rye; 8 for barley and Mf = 4 for barley and wheat.
328 342 612 575
13
332 341 545 576
--
262 279 562 528 16
4.4 . -
Wheat
Silage Crop Silage Crop Silage Crop Silage Crop Silage Crop Silage
14
SED' 4 4
Barley
2.7
SED 1 3 3 3 3
NDF (gkg -1DM)
609 536 467 357 50
589 454
562 420 23
wheat.
Total and hot-water-insoluble nitrogen There was an overall tendency for N content to increase during ensiling, but in only a few cases was this effect significant ( Table IV). In almost all comparisons, INSN in untreated silage was lower than in the original crops, particularly for unwilted and early cuts of barley and wheat. Wilting sometimes reduced the significance of this effect, but rarely removed or reversed it. On the other hand, NaOH treatment did so, particularly in barley and wheat when these crops were wilted. At the same level of wilting, the INSN content of treated silage was always higher than that of untreated silage.
Extent and pattern of fermentation Products of fermentation are shown in Table V. When the DM content of silages was low, residual WSC and pH were low and the products of fermentation were high. In unwilted silages, there was a tendency for the fermentation
262 T A B L E III
Influence of plant maturity, wilting and Na0H treatment on the water-soluble carbohydrate ( W S C ) and starch contents of cereal crops and silages Cut no.
WSC (gkg-IDM)
Wilt NaOH
-/+
Barley
Rye Crop 1 1 1 1
+ +
+ +
70 61 80 61
SED l 2 2 2 2
+ +
+ +
131 135 112 111
+ +
SED 1 4 4 SED 2
Silage
Crop
Silage
0 0 19 42
196 168 164 132
15 16 72 102
11 12 44 52
28 26 22 19
13 9 14 17
49 47 54 62
.
. +
. --
---
150 115 103 82
4.2 96 75 55 44
5.3 45 20 34 27
75 60 39 31
2.8 34 27 25 22
7.7 . -
Barley
Silage C r o p
13 30 65 78
183 162 112 86
Rye
Crop
9.7 + +
Wheat
Silage
1.7
SED 1 3 3 3 3
Starch (gkg-~DM)
-/+
29 23 19 15
2,6
16 10 20 10
18 16
11 15 4.5
14 21 19 23
60 59 58 52
38 24 63 67
239 160 178 201
----
30 39 32 38
216 195 164 218
197 193 361 280
215 262 244 304
219 175 228 222
315 330 27
160 181 213 211 20
229 278 338 318
44 277 252
18 20 15 21 6.8
36
6.3 ---
19 17 52 64 6.2
4.3
2.3 21 17
1.7
22 19 18 19
Silage C r o p Silage
61 36 50 61
2.4
14 11 15 21 12
23 22
36 16 27 13
Crop
Wheat
186 239 216 216 35
175 308
188 64 51
l d f = 16 for rye; 8 for barley and wheat. 2df=4 for barley and wheat.
to produce predominantly lactic acid, rather less acetic acid, some ethanol and relatively high amounts of ammonia-N. Wilting reduced the contents of lactic acid, ethanol and ammonia-N, but had less effect on acetic acid. Addition of NaOH increased the pH of all silages, particularly when the DM content was high. Its effect on the extent and pattern of fermentation was also modified by DM content. When DM content was <400 g kg -1, NaOH increased the content of fermentation acids. In most cases, this increase was in lactic, but in two cases (both < 300 g kg -1 ) one was acetic and one butyric. At DM contents > 400 g kg- 1, addition of NaOH reduced the contents of fermentation acids, largely at the expense of lactic acid. In the majority of cases, NaOH reduced the content of ammonia-N.
Organic matter digestibility The effects of ensiling and alkali treatment on the in vitro digestibility of organic matter (OMD) in the various crops and silages are illustrated in Table
263 T A B L E IV
Influence of plant maturity, wilting and NaOH treatment on the nitrogen content and the proportion of hotwater insoluble nitrogen ( I N S N ) in cereal crops and silages Cut
Wilt
NaOH N i t m g e n ( g k g - ~ D M )
No.
-/+
-/+ Rye
Barley
INSN (gkg
Wheat
Rye
1DM)
Barley
Wheat
Crop Silage Crop Silage Crop Silage Crop Silage Crop Silage Crop Silage 1 1 1 1
÷ ÷
÷ ÷
16 14 14 13
SED 1 2 2 2 2
+ ÷
÷ ÷
12 11 11 11
SED 2
13 12 13 11
+ +
÷ +
11 10 11 10
12 11 12 10
16 14 16 14
.
. ÷
. --
--
14 12 17 15
16 15 17 15
15 14 15 15
15 13
17 15 0.63
14 12 14 12
596 606 499 509
0.28 12 11 12 11
13 12 13 11
10 11 13 11
12 11 12 10
544 535 602 558
10 8 0.93
650 680 600 550
293 492 317 570
458 461 440 587
279 409 292 532
731 648 705 654
----
797 719 725 676
596 767 642 743
766 644 860 755
507 753 674 833
660 544 664 579
736 809 32
407 710 644 784 30
736 533 704 681
51 785 632
392 666 539 718 46
24
31 ---
480 680 460 620 27
44
0.77 10 10
408 443 379 491 22
0.41
0.87
--
~df= 16 for rye; 8 for barley and 2dr= 4 for barley and wheat.
11 11 12 12
0.44
0.27 . -
18 18 18 15 0.92
0.49
SED ~ 4 4
17 15 16 16
0.36
SED l 3 3 3 3
16 13 14 13
427 710 675 712 55
688 574
692 773 64
wheat.
VI. In untreated silages, OMD was always lower than in the corresponding crop, whether or not it was wilted. Treatment with NaOH, followed by ensiling, restored OMD in the silage to a value similar to or very much greater than that of the original untreated crop. Wilting improved the effect of N a O H treatment at all D M contents, but was most effective for the lower D M rye materials. The best upgrading was achieved with the mature barley and wheat crops harvested at ~ 600 g D M k g - 1 without wilting. The multiple regression analysis was conducted in an attempt to discover the factors affecting the response to treatment with NaOH. D M content was the only parameter highly correlated with O M D c o m m o n to all crops. In addition, for barley and wheat there was a general relationship between OMD and the indices of crop maturity such as WSC and STCH. This analysis confirmed that wilting immature crops also increased the response.
. -
.
÷
.
0.06
9.0
24 82 6 2
3.7
62 87 4 1
5.0
72 41 17 8
.
--
--
1.0
34 23 19 20
3.1
36 25 18 23
2.3
32 96 20 24
' d f = 16 for rye; 8 for barley and wheat. 2df= 4 for barley and wheat.
SED 2
4 4
SED'
3.9 4.8 4.3 8.6
+ ÷
0.15
÷ ÷
SED 1
3 3 3 3
4.2 5.6 4.6 8.2
+ +
4.8 7.5 4.6 8.1
0.08
÷ ÷
+ +
2 2 2 2
÷ ÷
1 1 1 1
gkg 'N
. --
--
1.6
8 9 0 0
3.2
16 6 12 0
2.8
10 43 2 0
--
--
16
107 110 94 123
3.4
144 73 64 29
13
182 316 76 63
Lactic Acetic E t h a n o l A m m o n i a acid acid
NaOH Rye silages -/+ pH gkg-lDM
SED 1
Wilt -/+
Cut No.
0.15
4.7 9.8
0.05
4.2 8.9 4.4 9.5
0.19
4.2 5.6 4.4 8.8
0.02
4.1 5.3 5.3 8.7
pH
0.50
18 0
3.7
56 13 27 0
5.6
14 81 9 5
6.3
79 107 14 0
Lactic acid
gkg-lN
0.70
17 13
5.2
34 17 19 14
2.1
19 27 19 14
5.0
25 18 12 34
--
0 0
0.11
3 0 0 0
0.24
8 2 0 0
6.6
43 13 22 0
3.2
74 32
7.1
113 18 98 20
5.1
100 43 97 29
15
114 78 62 49
Acetic E t h a n o l A m m o n i a acid
gkg-lDM
Barley silages
0.03
4.5 9.2
0.12
3.9 8.9 4.5 9.6
0.10
4.0 5.2 4.4 9.0
0.11
3.9 4.8 4.4 7.5
pH
0.08
16 2
0.72
33 10 18 1
43
102 70 24 2
3.2
77 158 24 8
Lactic acid
gkg-lN
4.5
12 21
2.2
14 27 14 13
1.1
14 29 16 17
1.3
19 32 24 30
--
0 0
0.26
8 0 0 0
1.9
44 3 0 0
3.2
47 10 5 0
11
110 20
11
132 46 95 30
3.7
146 50 100 26
2.4
76 65 77 42
Acetic E t h a n o l Ammonia acid
gkg-lDM
W h e a t silages
Influence of plant maturity, wilting and N a O H t r e a t m e n t on the p H and products of fermentation in cereal silages
TABLE V
b~
265 TABLE VI Influence of plant maturity, wilting and NaOH treatment on the in vitro organic matter digestibility of cereal crops and silages Cut No.
Wilt -/+
NaOH -/+
Organic matter digestibility (g kg- 10M ) Rye
1 1 1 1
+ +
+ +
Silage
Crop
Silage
Crop
Silage
597 701 575 667
511 599 532 692
731 761 685 744
646 726 602 772
602 700 564 678
476 648 460 669
10 + +
-+ +
518 659 520 647
+ +
+ +
553 654 482 653
SED' 3 3 3 3
SED
18 494 630 508 700
741 746 668 771
516 637 474 719
654 786 739 843
11
SED 1 4 4
.
. +
2
---
664 772 627 790
620 704 596 714
620 808 626 822
572 733 637 798
692 786
530 720 524 742 16
30
. --
6
19
11 . -
Wheat
Crop
SED 1 2 2 2 2
Barley
490 762 518 764 27
652 846 24
556 799
478 752 32
ldf= 16 for rye; 8 for barley and wheat. Mf= 4 for barley and wheat. DISCUSSION T h e rye crop of E x p e r i m e n t 1 was h a r v e s t e d relatively early in the y e a r to fit i n t o a d o u b l e - c r o p p i n g p r o g r a m m e w i t h c r o p s o f m a i z e , s u n f l o w e r a n d r y e g r a s s f o l l o w i n g C u t s 1, 2 a n d 3, r e s p e c t i v e l y ( T a b l e I ). F o r t h i s r e a s o n , c u t t i n g w a s s t a r t e d w h e n t h e r y e w a s a t a less m a t u r e s t a g e o f g r o w t h t h a n t h e b a r l e y a n d w h e a t o f E x p e r i m e n t 2.
Changes in crop composition during maturation and wilting Differences in the pattern of changes in non-structural carbohydrate cont e n t w i t h a d v a n c i n g m a t u r i t y i n rye, c o m p a r e d t o t h o s e i n b a r l e y a n d w h e a t , r e f l e c t t h e f a c t t h a t t h e f o r m e r c r o p w a s less m a t u r e a n d w a s a c t i v e l y p r o d u c i n g
266
sugars by photosynthesis throughout the period of growth. Starch was low and increased only marginally by Cut 3. In contrast, the barley and wheat crops had probably completed the most active phase of photosynthesis and any further production of WSC was overshadowed by the conversion of WSC to starch stored in the grain. Wilting may have caused small reductions in WSC through respiration, but it cannot account for large increases in starch concentrations and OMD, such as those found in Cut 3 for wilted barley and wheat. Nor can it explain the changes in the content of the relatively inert NDF fraction. Whenever starch and digestibility were abnormally high, nitrogen was also high and NDF low. It is possible that these effects reflected unrepresentative straw/grain ratios in the sub:samples as a result of separation of grain and straw in the high DM crops during harvesting, tipping and handling. Consequently, the validity of some comparisons between cuts and between wilting treatments within cuts is questionable, as are many of the statistically significant effects and interactions found by analysis of variance. Thorough mixing of the 1-2-kg sub-samples before and after ensiling was feasible, so at this level the sampling was much more reliable. For these reasons, statistical comparisons were largely confined to changes in chemical composition during ensiling and the impact of these on fermentation pattern and digestibility.
Changes in composition during ensiling In accord with earlier findings for grass silages ( McDonald, 1976; Woolford et al., 1979 ) and for barley and wheat silages (Bolsen et al., 1983 ), the results of the present studies confirm that the moisture content of the crop at ensiling is of great importance in determining the extent and pattern of fermentation in the silo. The similarity of the fermentation of all silages with a DM content of ~ 600 g kg-1, regardless of source and crop composition, suggests that it may be possible to produce consistently silages with a limited fermentation, either by wilting or by delaying cutting date. Such silages tended to retain a higher proportion of their original WSC than unwilted wetter ones, with generally lower levels of organic acids and, except for rye in Cut 3, much reduced proteolysis, as indicated by the low production of ammonia-N. Addition of NaOH enhanced these changes, in direct contrast to its effect in the wetter silages, in which the fermentation was extended, producing in one case butyric acid. The relatively high content of INSN in the NaOH-treated barley and wheat silages confirms the findings of Flipot et al. (1976) and Bolsen et al. (1983) for lucerne and maize silages and whole-crop wheat and barley silages, respectively. However, levels of INSN in NaOH-treated silages did not differ markedly from those in the untreated crop at harvest, which may indicate little
267
change in the nature of the protein during ensiling with alkali. On the other hand, alkali is known to affect proteins by modifying linkages within and between amino acids, resulting in a decrease in their nutritive value, particularly for rats {de Groot and Slump, 1969; Feron et al., 1977; Struthers et al., 1979). Alternatively, reduced N solubility may occur as a result of heat production during treatment, resulting in denaturation of protein, the production of Maillard products or the binding of nitrogen to fibre. The apparent decreases in the in vitro OMD of untreated silages compared with the crop material may have been slightly over-estimated, since the analyses were made on freeze-dried samples which could have incurred the partial loss of volatile highly digestible compounds such as acetic acid, ethanol and ammonia. Nevertheless, the OMD values illustrate several points of interest. Alkali treatment restored the OMD of the silage to a level similar to or greater than that of the original crop. The upgrading response improved with advancing crop maturity and for the moister crops was greatest when the material was wilted. The former was expected since it is recognised that the magnitude of the response in straws is related to the degree of lignification (Hartley, 1981 ) and the OMD before treatment (Givens et al., in press). Although neither lignin, NDF nor OMD were measured on the straw fraction of these materials, the range of maturity covered would have ensured large differences not apparent from the analyses of the whole crop in which changes in the straw are masked by increases in the grain fraction. Low acidity, together with a readily available energy source and high overall digestibility are all attractive features of high DM cereal silages for animal feeding, but more evidence is required on the stability of such silages when exposed to air during the feed-out period. An important feature of this work was the demonstration that whole-crop cereals directly harvested at a DM content of ~ 600 g k g - 1 (hard dough stage) can be effectively preserved and upgraded by ensilage with NaOH. At this stage of growth, crop yields of DM are close to maximum and the potential nutritive value when upgraded with NaOH in high. Thus, full advantage can be taken of this high quality feed, at the same time avoiding the problems of poor or extensive fermentation associated with low DM crops. ACKNOWLEDGEMENTS
The authors would like to express their thanks to R.F. Wilson and R.J. Barnes and their staff for chemical analyses, to R.W. Walmsley and N.P. Gardner for their technical assistance and to Dr. J.M. Cobby and his staff for statistical analyses. The support and helpful advice of Drs. R.J. Wilkins and J.M. Wilkinson are gratefully acknowledged. The Institute for Grassland and Animal Production is financed through the Agricultural and Food Research Council.
268 REFERENCES Association of Official Agricultural Chemists, 1965. Official Methods of Analysis of the Association of Official Agricultural Chemists, 10th edn. AOAC, Washington, DC, 957 pp. Bolsen, K.K., Tetlow, R.M. and Wilson, R.F., 1983. The effect of calcium and sodium hydroxides and of sodium acrylate on the fermentation and digestibility in vitro of ensiled whole-crop wheat and barley harvested at different stages of maturity. Anim. Feed Sci. Technol., 9: 37-47. Corrall, A.J., Heard, A.J., Fenlon, J.S., Terry, Cora P. and Lewis, G.C., 1977. Whole-crop forage. Grassland Research Institute, Hurley, Tech. Rep. No. 22, 35 pp. Davis, M. and Greenhalgh, J.F.D., 1983. Effects of urea, aqueous NH3, anhydrous NH3 and NaOH treatment on the intake and digestibility of mature whole-crop barley. British Society of Animal Production Winter Meeting, Scarborough, Paper No. 39. Anita. Prod. 36, p. 511. De Groot, A.P. and Slump, P., 1969. Effects of severe alkali treatment of proteins on amino acid composition and nutritive value. J. Nutr., 98: 45-56. Demarquilly, C., 1970. Evolution de la digestibilitd et de la quantitd ingerde des plantes entibres d'avoine, de bl~ et d'orge entre la floraison et la maturation du grain. Ann. Zootech., 19: 413-422. Deschard, G., Tetlow, R.M. and Mason, V.C., 1987a. Treatment of whole-crop cereals with alkali. 3. Voluntary intake and digestibility studies in sheep given wheat ensiled with sodium hydroxide, urea or ammonia. Anim. Feed Sci. Technol., 18: 283-293. Deschard, G., Mason, V.C. and Tetlow, R.M., 1987b. Treatment of whole-crop cereals with alkali. 4. Voluntary intake and growth in steers given wheat ensiled with sodium hydroxide, urea or ammonia. Anita. Feed Sci. Technol., in press. Edwards, R.A., Donaldson, E. and MacGregor, A.W., 1968. Ensilage of whole-crop barley. 1. Effects of variety and stage of growth. J. Sci. Food Agric., 19: 656-660. Feron, V.J., van Beek, L., Slump, P. and Beerns, R.B., 1977. Toxicological aspects of alkali treatment of food proteins. In: J. Alder-Nissen, B.O. Eggum, L. Munck and H.S. Olsen (Editors), Biochemical aspects of new protein food. l l t h Meeting, Fed. Eur. Biochem. Soc. (Copenhagen), Pergamon Press, 44: 139-147. Fisher, L.J., Lessard, J.R. and Lodge, G.A., 1972. Whole-crop barley as conserved forage for lactating cows. Can. J. Anim. Sci., 52: 497-504. Flipot, P., Mowat, D.N., Parkins, J.J. and Buchanan-Smith, J.G., 1976. Ensiling characteristics of silages treated with sodium hydroxide. Can. J. Plant Sci., 56: 935-940. Givens, D.I., Adamson, A.H. and Cobby, J.M., 1987. The effect of ammoniation on the nutritive value of wheat barley and oat straws. II. In vivo digestibility and energy value measurements, and their prediction from laboratory measurements. Anim. Feed Sci. Technol., in press. Greenhalgh, J.F.D. and Pirie, R., 1979. Alkali treatment of barley straw, hay, dried grass, bean straw and whole-crop oats. Anim. Prod., 28:431 (abstract). Hartley, R.D., 1981. Chemical constitution, properties and processing of ligno-cellulose wastes in relation to nutritional quality for animals. Agric. Environ., 6: 91-113. Home, B., 1969. Barley silage for dairy cows. Bridgets Experimental Husbandry Farm, Ministry of Agriculture, Fisheries and Food, Annu. Rep. No. 10: 9-12. MacGregor, A.W. and Edwards, R.A., 1968. Ensilage of whole-crop barley. 2. Composition of barley and barley silage at different stages of growth. J. Sci. Food Agric., 19: 661-666. McDonald, P., 1976. Trends in silage making. Microbiology in Agriculture, Fisheries and Food, Society for Applied Bacteriology, No. 4. Academic Press, London, 274 pp. Oltjen, J.W. and Bolsen, K.K., 1978. Wheat, barley and oat silages for beef cattle. Bulletin 613, Agricultural Experimental Station, Kansas State University, Manhattan 66506, KS, U.S.A., 12 pp. Orskov, E.R., 1979. Recent information on processing of grain for ruminants. Livest. Prod. Sci., 6: 335-347. Orskov, E.R., Reid, G.W., Holland, S.M., Tait, C.A.G. and Lee, N.H., 1983. The feeding value for
269
ruminants of straw and whole-crop barley and oats treated with anhydrous or aqueous ammonia or urea. Anim. Feed Sci. Technol., 8: 247-257. Smith, D., Paulsen, G.M. and Raguse, C.A., 1964. Extraction of total available carbohydrates from grass and legume tissue. Plant Physiol., 39: 960-962. Struthers, B.J., Dahlgren, R.R., Hopkins, D.T. and Raymond, M.L., 1979. Lysinoalanine: Biological effects and significance. In: H.L. Wilcke, D.T. Hopkins and D.H. Waggle (Editors), Soy Protein and Human Nutrition. Academic Press, New York, pp. 235-260. Terry, R.A. and Outen, G.E., 1973. The determination of cell-wall constituents in barley and maize. Chem. Ind., 23: 1116-1117. Tetlow, R.M., Mason, V.C. and Deschard, G., 1987. Alkali treatment of whole-crop cereals. 2. Voluntary intake and digestibility studies in sheep fed cereals ensiled with sodium hydroxide. Anita. Feed. Sci. Technol., 18: 271-281. Tilley, J.M.A. and Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc., 18: 104-111. Van Soest, P.J. and Wine, R.H., 1967. Use of detergents in the analysis of fibrous feeds. IV. Determination of plant cell-wall constituents. J. Assoc. Off. Anal. Chem., 50: 50-55. Wilson, R.F. and Wilkins, R.J., 1972a. The ensiling of autumn-sown rye. J. Br. Grassl. Soc., 27: 35-41. Wilson, R.F. and Wilkins, R.J., 1972b. An evaluation of laboratory ensiling techniques. J. Sci. Food Agric., 23: 377-385. Wilson, R.F. and Wilkins, R.J., 1978. Paraformaldehyde as a silage additive. J. Agric. Sci., 91: 23-29. Woolford, M.K., Honig, H. and Fenlon, J.S., 1979. (Studies on the aerobic deterioration of silage using a small-scale technique. 3. The microbiological, physical and chemical changes during the aerobic deterioration of direct-cut and wilted grass silage made in the absence and in the presence of air.) Wirtschaftseigene Futter, 25:158-177 (in German). Woolford, M.K., Bolsen, K.K. and Peart, L.A., 1982. Studies on the aerobic deterioration of wholecrop cereal silages. J. Agric. Sci., 98: 529-535.
257
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Treatment of Whole-crop Cereals with Alkali. 1. The Influence of Sodium H y d r o x i d e and Ensiling on the Chemical Composition and In Vitro Digestibility of Rye, Barley and Wheat Crops Harvested at Increasing Maturity and Dry Matter Content R.M. TETLOW and V.C. MASON
The AFRC Institute for Grassland and Animal Production, Hurley, Maidenhead, Berks. SL6 5LR (Gt. Britain) (Received 22 July 1986; accepted for publication 8 April 1987 )
ABSTRACT Tetlow, R.M. and 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 crops harvested at increasing maturity and dry matter content. Animal Feed Sci. Technol., 18: 257-269. Whole crops of rye, barley and wheat were each cut at three stages of maturity and dry matter (DM) content, and were ensiled in polythene bag silos directly or after wilting to ~ 600 g DM kg- ~,with ( 50 g kg - ~DM ) or without the addition of "pearl" sodium hydroxide ( NaOH ). Fourth cuts of barley and wheat were ensiled directly, with or without NaOH, when their DM content reached ~ 600 g kg- 1. With advancing maturity, the DM contents of crops increased. For rye, the contents of watersoluble carbohydrate (WSC) and starch also increased, although the level of starch was low. In contrast, the WSC in the more mature barley and wheat crops decreased as starch increased. There was a general trend for nitrogen content to fall, most markedly for rye. For all crops, WSC was lost and organic matter digestibility fell during wilting. In silages made from young crops ( < 400 g DM kg- ~), WSC and pH were low and products of fermentation high. In high DM silages, there were reduced contents of lactic acid, ethanol and ammonia. Treatment of the crop with NaOH raised the pH and the proportion of hot-water-insoluble nitrogen in all silages and tended to enhance the effect of DM on organic acid production. Organic matter digestibility of the crops was always higher than in the corresponding untreated silage. The response to NaOH improved as the crops matured, resulting in increases of up to 6 percentage units for Cut 1 and of between 15 and 20 units for the later cuts. With the relatively low DM rye silages, wilting improved the effect of NaOH by up to 9 units. It is concluded that whole-crop cereals, directly harvested at ~ 600 g DM kg- 1, can be effectively preserved and upgraded by ensilage with 50 g NaOH kg- 1 DM. At this maturity, crop yields are close to maximum and the potential nutritive value of the upgraded material is high.
0377-8401/87/$03.50
© 1987 Elsevier Science Publishers B.V.
258 INTRODUCTION Following ear emergence, immature ( ~ 350 g DM k g - 1) crops of small grain cereals can be successfully ensiled without additive (Edwards et al., 1968; MacGregor and Edwards, 1968; Demarquilly, 1970; Wilson and Wilkins, 1972a; Bolsen et al., 1983 ) and subsequently used as the principal forage component in rations for dairy cows (Horne, 1969; Fisher et al., 1972) and growing cattle (Oltjen and Bolsen, 1978). However, at this stage of growth the yield of dry matter (DM) has not reached its potential. Furthermore, fermentation in the silo can be rapid and extensive, resulting in low pH material which would predispose animals to acidosis. At more mature stages of plant development, yields of DM from cereals may equal or surpass those obtained from 3-4 cuts of grass (Corrall et al., 1977). However, lignification of the straw is more extensive (Hartley, 1981 ) and unless the pericarp is disrupted, the resistance of whole grain to digestion is also high (Orskov, 1979 ). Together these factors depress digestibility. In addition, silages made from high DM crops are often unstable when exposed to air (Woolford et al., 1982 ). The feasibility of treating cereals with alkali to disrupt the pericarp of the grain and render the ligno-cellulosic component of the straw more digestible has been demonstrated on several occasions ( Greenhalgh and Pirie, 1979; Bolsen et al., 1983; Davis and Greenhalgh, 1983; Orskov et al., 1983). At this Institute, we have shown that ensiling barley or wheat with sodium hydroxide (NaOH) can increase in vitro digestibility, the effect improving as the crop matures (Bolsen et al., 1983). The purpose of the present work was to investigate the significance of moisture content, stage of maturity and chemical composition in these responses, as a preliminary to larger scale investigations of nutritive value involving sheep (Tetlow et al., 1987; Deschard et al., 1987a) and cattle ( Deschard et al., 1987b ). MATERIALSAND METHODS Whole crops of winter rye (cv. Rheidol) (Experiment 1 ), or of spring barley (cv. Athos) and winter wheat (cv. Sicco) (Experiment 2) were each cut at three stages of development during the summers of 1978 and 1979, respectively, at DM contents below ~ 600 g k g - 1. Half of each was harvested directly and the remainder after field-wilting to ~ 600 g k g - 1. An additional cut of more mature barley and wheat was harvested without wilting and ensiled at ~ 600 g DM k g - 1 (Table I). All materials were chopped with a New Holland 717 metered-chop forage harvester and blown into farm trailers. Six sub-samples of 1.3 kg DM for rye and four sub-samples of 2.0 kg DM for barley and wheat were taken of both unwilted or wilted material. DM and chemical composition were determined
259 TABLE I Harvest dates for unwilted and wilted crops of rye, barley and wheat Cut No. 1 1 2 2 3 3 4
Wilt -/+ + + + -
Experiment 1 (1978)
Experiment 2 (1979)
Rye
Barley
Wheat
30 May 6 June 12 June 15 June 27 June 4 July --
11 July 14 July 16 July 20 July 7 Aug. 10 Aug. 15 Aug.
16 July 18 July 6 Aug. 10 Aug. 20 Aug. 22 Aug. 29 Aug.
on each sub-sample. H a l f the sub-samples were ensiled directly in polythenebag silos by the method of Wilson and Wilkins (1972b); the remainder were spread thinly and individually hand-sprinkled with N a O H at an application rate of ~ 50 g k g - 1 DM, prior to ensilage by the same technique. The 36 minisilos of rye and the 28 mini-silos of both barley and wheat were stored at ambient temperature for up to 32 weeks. Each was then weighed and opened and samples taken for analysis o f p H , D M content and chemical composition. D M content of fresh crops and silages was determined by drying samples overnight in a forced draught oven at 100°C. A glass electrode was used to determine p H values of cold water extracts of fresh silages. Lactic acid, volatile acids and ammonia were determined on acid extracts of fresh silage by the methods of Wilson and Wilkins (1978). Ethanol was measured by gas chromatography of acid extracts at the same time as the volatile fatty acids. Freeze-dried samples were used for all the other analyses. Total nitrogen ( N ) was estimated by the methods of the Association of Official Agricultural Chemists (1965). Hot-water-insoluble nitrogen ( I N S N ) was determined after extraction with boiling water (four boilings each of 10 min). Watersoluble carbohydrate ( W S C ) was extracted with cold water, hydrolysed with 0.2 N HeSO4 and determined by the alkaline ferricyanide method of Smith et al. (1964). Starch ( S T C H ) was extracted with boiling water, incubated with amyloglucosidase at p H 4.8, filtered and the filtrate hydrolysed and measured as for WSC. Neutral detergent fibre ( N D F ) was determined after pre-digestion with amyloglucosidase (Terry and Outen, 1973) by the method of Van Soest and Wine (1967). Digestibility of the organic matter ( O M D ) was determined by the two-stage method of Tilley and Terry (1963), with the addition of 10 mg of nitrogen as a m m o n i u m sulphate at the start of the first stage. The data from each cereal were subjected to analysis of variance in two ways. Firstly, an overall analysis of variance was undertaken in which all data were
260 included. This allowed comparisons of any of the means within or between cuts within each crop type. Secondly, analysis was restricted to data from each cutting date for each of the three crops. In both types of analysis, differences between means were tested by t-test using the most appropriate standard error (SED). After omitting data from the final cut for barley and wheat, the data from all crop types were pooled and a multiple regression analysis was conducted in which the OMD of the treated silage was tested against the various parameters of the untreated crops before ensiling. Because of the marked differences between rye on the one hand and barley and wheat on the other, regressions were also done on the crops separately. RESULTS
Chemical composition of crops and silages The effects of maturity, wilting, ensiling and treatment with NaOH on the DM contents and composition of crops and silages are shown in Tables II-VI. Addition of NaOH resulted in increases in Na content from 0.6, 0.6 and 0.1 to 27.9, 27.4 and 25.0 g kg- 1 DM for rye, barley and wheat silages, respectively.
Dry matter and structural carbohydrate In all cases, the DM content of the crops increased significantly with maturity and wilting (Table II), but the oven DM contents of the silages were generally lower than before ensiling. Changes in the NDF content during ensiling were small, but NaOH treatment generally resulted in lower levels in treated than in untreated silages. This effect was significant in many cases (P<0.05).
Water-soluble carbohydrates and starch For rye, the WSC content increased as the crop matured (Table III). In contrast, that of barley and wheat decreased. Wilting tended to reduce the WSC content of crops, particularly those with a high level at cutting. For all crops, WSC content in the silages was lower than in the corresponding crops, particularly in the less mature and unwilted silages with low DM content. In all crops, starch content increased as crops matured, although rye contained less starch than barley or wheat. Starch content of the silages was equal to or lower than that in the crops, although this effect was only significant in a few cases and, with the exception of wilted wheat in Cut 3, was largely confined to unwilted silage. Starch content of the silages was unaffected by treatment with NaOH.
261
T A B L E II
Influence of plant maturity, wilting and NaOH treatment on the dry matter ( D M ) and neutral detergent fibre ( N D F ) contents of cereal crops and silages Cut no.
Wilt
NaOH D M ( g k g -1)
-/+
-/+
Rye Crop 1 1 1 1
--+ +
+ +
225 243 605 619
SED ~ 2 2 2 2
+ +
+ +
313 353 593 618
+ +
+ +
372 391 573 590
SED 2
193 196 , 572 592
300 320 586 583
.
. +
. --
285 317 553 590
408 432 600 662
470 482 654 666
Rye
369 387 552 620
431 467 618 636
617 661
622 642
294 305 570 544
628 529 639 599
11 420 433 704 722
Barley
372 404 662 694
498 520 718 742
475 509 692 730
493 576 571 569
18
638 635 11
520 463 543 463
Wheat
630 596 626 577
592 564 622 595
612 562 641 573
438 405 515 383
----
607 534 633 545
419 397 522 385
530 388 418 332
462 324 433 372
508 467 552 446
425 432 13
543 481 536 460 24
588 435 457 375
43 556 493
698 576 546 571 20
25
12 ---
526 583 620 477 37
22
4.5 641 634
523 554 511 483 33
5.5
12
--
' d f = 16 for rye; 8 for barley and Mf = 4 for barley and wheat.
328 342 612 575
13
332 341 545 576
--
262 279 562 528 16
4.4 . -
Wheat
Silage Crop Silage Crop Silage Crop Silage Crop Silage Crop Silage
14
SED' 4 4
Barley
2.7
SED 1 3 3 3 3
NDF (gkg -1DM)
609 536 467 357 50
589 454
562 420 23
wheat.
Total and hot-water-insoluble nitrogen There was an overall tendency for N content to increase during ensiling, but in only a few cases was this effect significant ( Table IV). In almost all comparisons, INSN in untreated silage was lower than in the original crops, particularly for unwilted and early cuts of barley and wheat. Wilting sometimes reduced the significance of this effect, but rarely removed or reversed it. On the other hand, NaOH treatment did so, particularly in barley and wheat when these crops were wilted. At the same level of wilting, the INSN content of treated silage was always higher than that of untreated silage.
Extent and pattern of fermentation Products of fermentation are shown in Table V. When the DM content of silages was low, residual WSC and pH were low and the products of fermentation were high. In unwilted silages, there was a tendency for the fermentation
262 T A B L E III
Influence of plant maturity, wilting and Na0H treatment on the water-soluble carbohydrate ( W S C ) and starch contents of cereal crops and silages Cut no.
WSC (gkg-IDM)
Wilt NaOH
-/+
Barley
Rye Crop 1 1 1 1
+ +
+ +
70 61 80 61
SED l 2 2 2 2
+ +
+ +
131 135 112 111
+ +
SED 1 4 4 SED 2
Silage
Crop
Silage
0 0 19 42
196 168 164 132
15 16 72 102
11 12 44 52
28 26 22 19
13 9 14 17
49 47 54 62
.
. +
. --
---
150 115 103 82
4.2 96 75 55 44
5.3 45 20 34 27
75 60 39 31
2.8 34 27 25 22
7.7 . -
Barley
Silage C r o p
13 30 65 78
183 162 112 86
Rye
Crop
9.7 + +
Wheat
Silage
1.7
SED 1 3 3 3 3
Starch (gkg-~DM)
-/+
29 23 19 15
2,6
16 10 20 10
18 16
11 15 4.5
14 21 19 23
60 59 58 52
38 24 63 67
239 160 178 201
----
30 39 32 38
216 195 164 218
197 193 361 280
215 262 244 304
219 175 228 222
315 330 27
160 181 213 211 20
229 278 338 318
44 277 252
18 20 15 21 6.8
36
6.3 ---
19 17 52 64 6.2
4.3
2.3 21 17
1.7
22 19 18 19
Silage C r o p Silage
61 36 50 61
2.4
14 11 15 21 12
23 22
36 16 27 13
Crop
Wheat
186 239 216 216 35
175 308
188 64 51
l d f = 16 for rye; 8 for barley and wheat. 2df=4 for barley and wheat.
to produce predominantly lactic acid, rather less acetic acid, some ethanol and relatively high amounts of ammonia-N. Wilting reduced the contents of lactic acid, ethanol and ammonia-N, but had less effect on acetic acid. Addition of NaOH increased the pH of all silages, particularly when the DM content was high. Its effect on the extent and pattern of fermentation was also modified by DM content. When DM content was <400 g kg -1, NaOH increased the content of fermentation acids. In most cases, this increase was in lactic, but in two cases (both < 300 g kg -1 ) one was acetic and one butyric. At DM contents > 400 g kg- 1, addition of NaOH reduced the contents of fermentation acids, largely at the expense of lactic acid. In the majority of cases, NaOH reduced the content of ammonia-N.
Organic matter digestibility The effects of ensiling and alkali treatment on the in vitro digestibility of organic matter (OMD) in the various crops and silages are illustrated in Table
263 T A B L E IV
Influence of plant maturity, wilting and NaOH treatment on the nitrogen content and the proportion of hotwater insoluble nitrogen ( I N S N ) in cereal crops and silages Cut
Wilt
NaOH N i t m g e n ( g k g - ~ D M )
No.
-/+
-/+ Rye
Barley
INSN (gkg
Wheat
Rye
1DM)
Barley
Wheat
Crop Silage Crop Silage Crop Silage Crop Silage Crop Silage Crop Silage 1 1 1 1
÷ ÷
÷ ÷
16 14 14 13
SED 1 2 2 2 2
+ ÷
÷ ÷
12 11 11 11
SED 2
13 12 13 11
+ +
÷ +
11 10 11 10
12 11 12 10
16 14 16 14
.
. ÷
. --
--
14 12 17 15
16 15 17 15
15 14 15 15
15 13
17 15 0.63
14 12 14 12
596 606 499 509
0.28 12 11 12 11
13 12 13 11
10 11 13 11
12 11 12 10
544 535 602 558
10 8 0.93
650 680 600 550
293 492 317 570
458 461 440 587
279 409 292 532
731 648 705 654
----
797 719 725 676
596 767 642 743
766 644 860 755
507 753 674 833
660 544 664 579
736 809 32
407 710 644 784 30
736 533 704 681
51 785 632
392 666 539 718 46
24
31 ---
480 680 460 620 27
44
0.77 10 10
408 443 379 491 22
0.41
0.87
--
~df= 16 for rye; 8 for barley and 2dr= 4 for barley and wheat.
11 11 12 12
0.44
0.27 . -
18 18 18 15 0.92
0.49
SED ~ 4 4
17 15 16 16
0.36
SED l 3 3 3 3
16 13 14 13
427 710 675 712 55
688 574
692 773 64
wheat.
VI. In untreated silages, OMD was always lower than in the corresponding crop, whether or not it was wilted. Treatment with NaOH, followed by ensiling, restored OMD in the silage to a value similar to or very much greater than that of the original untreated crop. Wilting improved the effect of N a O H treatment at all D M contents, but was most effective for the lower D M rye materials. The best upgrading was achieved with the mature barley and wheat crops harvested at ~ 600 g D M k g - 1 without wilting. The multiple regression analysis was conducted in an attempt to discover the factors affecting the response to treatment with NaOH. D M content was the only parameter highly correlated with O M D c o m m o n to all crops. In addition, for barley and wheat there was a general relationship between OMD and the indices of crop maturity such as WSC and STCH. This analysis confirmed that wilting immature crops also increased the response.
. -
.
÷
.
0.06
9.0
24 82 6 2
3.7
62 87 4 1
5.0
72 41 17 8
.
--
--
1.0
34 23 19 20
3.1
36 25 18 23
2.3
32 96 20 24
' d f = 16 for rye; 8 for barley and wheat. 2df= 4 for barley and wheat.
SED 2
4 4
SED'
3.9 4.8 4.3 8.6
+ ÷
0.15
÷ ÷
SED 1
3 3 3 3
4.2 5.6 4.6 8.2
+ +
4.8 7.5 4.6 8.1
0.08
÷ ÷
+ +
2 2 2 2
÷ ÷
1 1 1 1
gkg 'N
. --
--
1.6
8 9 0 0
3.2
16 6 12 0
2.8
10 43 2 0
--
--
16
107 110 94 123
3.4
144 73 64 29
13
182 316 76 63
Lactic Acetic E t h a n o l A m m o n i a acid acid
NaOH Rye silages -/+ pH gkg-lDM
SED 1
Wilt -/+
Cut No.
0.15
4.7 9.8
0.05
4.2 8.9 4.4 9.5
0.19
4.2 5.6 4.4 8.8
0.02
4.1 5.3 5.3 8.7
pH
0.50
18 0
3.7
56 13 27 0
5.6
14 81 9 5
6.3
79 107 14 0
Lactic acid
gkg-lN
0.70
17 13
5.2
34 17 19 14
2.1
19 27 19 14
5.0
25 18 12 34
--
0 0
0.11
3 0 0 0
0.24
8 2 0 0
6.6
43 13 22 0
3.2
74 32
7.1
113 18 98 20
5.1
100 43 97 29
15
114 78 62 49
Acetic E t h a n o l A m m o n i a acid
gkg-lDM
Barley silages
0.03
4.5 9.2
0.12
3.9 8.9 4.5 9.6
0.10
4.0 5.2 4.4 9.0
0.11
3.9 4.8 4.4 7.5
pH
0.08
16 2
0.72
33 10 18 1
43
102 70 24 2
3.2
77 158 24 8
Lactic acid
gkg-lN
4.5
12 21
2.2
14 27 14 13
1.1
14 29 16 17
1.3
19 32 24 30
--
0 0
0.26
8 0 0 0
1.9
44 3 0 0
3.2
47 10 5 0
11
110 20
11
132 46 95 30
3.7
146 50 100 26
2.4
76 65 77 42
Acetic E t h a n o l Ammonia acid
gkg-lDM
W h e a t silages
Influence of plant maturity, wilting and N a O H t r e a t m e n t on the p H and products of fermentation in cereal silages
TABLE V
b~
265 TABLE VI Influence of plant maturity, wilting and NaOH treatment on the in vitro organic matter digestibility of cereal crops and silages Cut No.
Wilt -/+
NaOH -/+
Organic matter digestibility (g kg- 10M ) Rye
1 1 1 1
+ +
+ +
Silage
Crop
Silage
Crop
Silage
597 701 575 667
511 599 532 692
731 761 685 744
646 726 602 772
602 700 564 678
476 648 460 669
10 + +
-+ +
518 659 520 647
+ +
+ +
553 654 482 653
SED' 3 3 3 3
SED
18 494 630 508 700
741 746 668 771
516 637 474 719
654 786 739 843
11
SED 1 4 4
.
. +
2
---
664 772 627 790
620 704 596 714
620 808 626 822
572 733 637 798
692 786
530 720 524 742 16
30
. --
6
19
11 . -
Wheat
Crop
SED 1 2 2 2 2
Barley
490 762 518 764 27
652 846 24
556 799
478 752 32
ldf= 16 for rye; 8 for barley and wheat. Mf= 4 for barley and wheat. DISCUSSION T h e rye crop of E x p e r i m e n t 1 was h a r v e s t e d relatively early in the y e a r to fit i n t o a d o u b l e - c r o p p i n g p r o g r a m m e w i t h c r o p s o f m a i z e , s u n f l o w e r a n d r y e g r a s s f o l l o w i n g C u t s 1, 2 a n d 3, r e s p e c t i v e l y ( T a b l e I ). F o r t h i s r e a s o n , c u t t i n g w a s s t a r t e d w h e n t h e r y e w a s a t a less m a t u r e s t a g e o f g r o w t h t h a n t h e b a r l e y a n d w h e a t o f E x p e r i m e n t 2.
Changes in crop composition during maturation and wilting Differences in the pattern of changes in non-structural carbohydrate cont e n t w i t h a d v a n c i n g m a t u r i t y i n rye, c o m p a r e d t o t h o s e i n b a r l e y a n d w h e a t , r e f l e c t t h e f a c t t h a t t h e f o r m e r c r o p w a s less m a t u r e a n d w a s a c t i v e l y p r o d u c i n g
266
sugars by photosynthesis throughout the period of growth. Starch was low and increased only marginally by Cut 3. In contrast, the barley and wheat crops had probably completed the most active phase of photosynthesis and any further production of WSC was overshadowed by the conversion of WSC to starch stored in the grain. Wilting may have caused small reductions in WSC through respiration, but it cannot account for large increases in starch concentrations and OMD, such as those found in Cut 3 for wilted barley and wheat. Nor can it explain the changes in the content of the relatively inert NDF fraction. Whenever starch and digestibility were abnormally high, nitrogen was also high and NDF low. It is possible that these effects reflected unrepresentative straw/grain ratios in the sub:samples as a result of separation of grain and straw in the high DM crops during harvesting, tipping and handling. Consequently, the validity of some comparisons between cuts and between wilting treatments within cuts is questionable, as are many of the statistically significant effects and interactions found by analysis of variance. Thorough mixing of the 1-2-kg sub-samples before and after ensiling was feasible, so at this level the sampling was much more reliable. For these reasons, statistical comparisons were largely confined to changes in chemical composition during ensiling and the impact of these on fermentation pattern and digestibility.
Changes in composition during ensiling In accord with earlier findings for grass silages ( McDonald, 1976; Woolford et al., 1979 ) and for barley and wheat silages (Bolsen et al., 1983 ), the results of the present studies confirm that the moisture content of the crop at ensiling is of great importance in determining the extent and pattern of fermentation in the silo. The similarity of the fermentation of all silages with a DM content of ~ 600 g kg-1, regardless of source and crop composition, suggests that it may be possible to produce consistently silages with a limited fermentation, either by wilting or by delaying cutting date. Such silages tended to retain a higher proportion of their original WSC than unwilted wetter ones, with generally lower levels of organic acids and, except for rye in Cut 3, much reduced proteolysis, as indicated by the low production of ammonia-N. Addition of NaOH enhanced these changes, in direct contrast to its effect in the wetter silages, in which the fermentation was extended, producing in one case butyric acid. The relatively high content of INSN in the NaOH-treated barley and wheat silages confirms the findings of Flipot et al. (1976) and Bolsen et al. (1983) for lucerne and maize silages and whole-crop wheat and barley silages, respectively. However, levels of INSN in NaOH-treated silages did not differ markedly from those in the untreated crop at harvest, which may indicate little
267
change in the nature of the protein during ensiling with alkali. On the other hand, alkali is known to affect proteins by modifying linkages within and between amino acids, resulting in a decrease in their nutritive value, particularly for rats {de Groot and Slump, 1969; Feron et al., 1977; Struthers et al., 1979). Alternatively, reduced N solubility may occur as a result of heat production during treatment, resulting in denaturation of protein, the production of Maillard products or the binding of nitrogen to fibre. The apparent decreases in the in vitro OMD of untreated silages compared with the crop material may have been slightly over-estimated, since the analyses were made on freeze-dried samples which could have incurred the partial loss of volatile highly digestible compounds such as acetic acid, ethanol and ammonia. Nevertheless, the OMD values illustrate several points of interest. Alkali treatment restored the OMD of the silage to a level similar to or greater than that of the original crop. The upgrading response improved with advancing crop maturity and for the moister crops was greatest when the material was wilted. The former was expected since it is recognised that the magnitude of the response in straws is related to the degree of lignification (Hartley, 1981 ) and the OMD before treatment (Givens et al., in press). Although neither lignin, NDF nor OMD were measured on the straw fraction of these materials, the range of maturity covered would have ensured large differences not apparent from the analyses of the whole crop in which changes in the straw are masked by increases in the grain fraction. Low acidity, together with a readily available energy source and high overall digestibility are all attractive features of high DM cereal silages for animal feeding, but more evidence is required on the stability of such silages when exposed to air during the feed-out period. An important feature of this work was the demonstration that whole-crop cereals directly harvested at a DM content of ~ 600 g k g - 1 (hard dough stage) can be effectively preserved and upgraded by ensilage with NaOH. At this stage of growth, crop yields of DM are close to maximum and the potential nutritive value when upgraded with NaOH in high. Thus, full advantage can be taken of this high quality feed, at the same time avoiding the problems of poor or extensive fermentation associated with low DM crops. ACKNOWLEDGEMENTS
The authors would like to express their thanks to R.F. Wilson and R.J. Barnes and their staff for chemical analyses, to R.W. Walmsley and N.P. Gardner for their technical assistance and to Dr. J.M. Cobby and his staff for statistical analyses. The support and helpful advice of Drs. R.J. Wilkins and J.M. Wilkinson are gratefully acknowledged. The Institute for Grassland and Animal Production is financed through the Agricultural and Food Research Council.
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