Digestibility of diets containing increasing levels of NaOH-treated or untreated wheat straw

Animal Feed Science and Technology, 7 (1982) 331--340 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

331

DIGESTIBILITY OF DIETS CONTAINING INCREASING LEVELS OF NaOH-TREATED OR UNTREATED WHEAT STRAW*

N. WIGNJOSOESASTRO** and A.W. YOUNG*** Meat and Animal Science, 1675 Observatory Drive, Madison, WI 53706 (U.S.A.) (Received 18 July 1980; accepted for publication 1 December 1981)

ABSTRACT Wignjosoesastro, N. and Young, A.W., 1982. Digestibility of diets containing increasing levels of NaOH-treated or untreated wheat straw. Anita. Feed Sci. Technol., 7 : 331--340. Sodium hydroxide-treated or untreated wheat straw was included in a basal alfalfamaize diet at 0, 10, 20 and 40%. As the level of straw increased, the apparent digestibility of dry matter (DM) and organic m~tter (OM) by sheep, decreased linearly (P < 0.01), with a faster decrease (P < 0.05) for diets containing untreated straw. The digestibility of DM decreased by 0.22 and 0.41% and OM by 0.24 and 0.42% for treated and untreated straw diets, respectively, with each 1% increase of straw in the diets. Addition of treated straw increased (P < 0.05) digestibility of cell wall constituents (CWC), acid detergent fibre (ADF) and hemicellulose (HC). However, when untreated straw was added, the digestibility of HC was reduced, whereas the digestibility of CWC and ADF was dependent on the level of straw added. Increasing levels of NaOH-treated straw in the diets produced linear increases (P < 0.05) in digestibility of CWC, ADF and HC. However, significant (P > 0.05) linear or quadratic responses were not noted in the digestibility of CWC, ADF and HC with increasing levels of untreated straw in the diet. Apparent digestibility of crude protein was not affected by addition of either NaOHtreated or untreated straw to the diet. In general, although changes in nutrient digestibility of the basal component were small, large changes in the digestibility of nutrients in the straw component were apparent and accounted for the major differences in digestibility of the diets. The absence of curvilinearity in the regression equations suggested that there were no associative effects.

* Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison (project WISO2310) and the MUCIA-Indonesia Higher Agricultural Education Project. This is Meat and Animal Science Department manuscript No. 761. ** Present address: FKHP University Syiah Kuala, Darussalam-Banda Aceh, Indonesia. *** Present address: Animal Industries Department, Southern Illinois University, Carbondale, 62901, U.S.A.

0377-8401/82/0000--0000/$02.75 © 1982 Elsevier Scientific Publishing Company

332 INTRODUCTION

The potential for increasing world red meat production from low-quality roughages as crop residues is tremendous. According to most estimates, at least 50% of the plant dry matter remains as residue following grain harvest. For the United States alone this amounts to ca. 150 000 000 t of maize residues and 40 000 000 t of wheat residues annually (USDA, 1974). In many tropical countries, low-quality roughages constitute the major portion of the diet for ruminants during feed shortages in the dry season. The digestibility of these types of material is generally 50% or less. The low digestibility and the resultant poor nutritive value of crop residues are related to the extent of lignification of the cell-wall component. Processes which delignify the fibrous fraction or otherwise solubilize cellulose and hemicellulose should improve digestibility of residues. Several chemicals have been used for this purpose; however, as recently reviewed by Klopfenstein {1978), sodium hydroxide has been used in greatest quantity. Incorporation of straw into diets can be expected to reduce DM and OM digestibility, b u t the decreases are less when NaOH-treated straw is used (Mellenberger et al., 1971; Kohler et al., 1979). The purpose of this study is (1) to determine the effect of incorporating NaOH-treated or untreated straw at various levels on nutrient digestibility in sheep and (2) to calculate nutrient digestibility for the straw and basal components of the diet as the proportion of straw in the diet is changed. MATERIALS AND METHODS

Diet formulation Wheat straw (Triticum spp.) was shredded to 1--2 cm lengths in a hammermill. A solution of sodium hydroxide (26.7 g l-l) to provide 40 g NaOH/kg straw DM and a final moisture content of ca. 60% was sprayed on the straw in a horizontal mixer for 30 min. The straw was then sealed in a plastic-lined drum and stored at room temperature. Untreated straw was mixed with the same a m o u n t of water and stored in a similar manner. After a 10-day storage period, the straw was air
333 TABLE I C o m p o s i t i o n o f diets c o n t a i n i n g N a O H - t r e a t e d a n d u n t r e a t e d s t r a w ( p e r c e n t a g e o f d i e t a r y dry m a t t e r ) Ingredient

Alfalfa h a y , g r o u n d Ground maize Dry molasses Straw Urea (45% N)

International ref. no.

1-00-063 4-02-935 4-04-695 1-05-175

Diet a A

B/E

C/F

D/G

32.14 57.86 10.00 ---

28.93 52.07 9.00 9.69 0.31

25.71 46.29 8.00 19.38 0.62

19.28 34.72 6.00 38.76 1.24

aDiets B, C a n d D c o n t a i n e d N a O H - t r e a t e d straw, while diets E, F a n d G c o n t a i n e d unt r e a t e d ( w a t e r ) straw.

Chemical composition and dry matter digestibility in vitro Samples of straw and the experimental diets were analyzed for CWC and ADF by the methods of Goering and Van Soest (1970). Hemicellulose was calculated as the difference between CWC and ADF. Crude protein and DM contents were also determined (Association of Official Agricultural Chemists, 1960). Dry matter digestibility in vitro of treated and untreated straw and the diets containing these straws was determined in three separate incubations. Rumen liquor was obtained from a Holstein cow fed on a diet of approximately 70% forage and 30% concentrate, and anaerobic conditions were maintained by bubbling CO2 through the liquor during processing. Incubations were as described by Tilley and Terry (1963), except that a 0.25-g sample was weighed into a 50-ml polycarbonate tube and 20 ml of artificial saliva and 5 ml of rumen fluid added. Also, after incubation, 0.5 ml of a saturated mercuric chloride solution was added to stop microbial activity. After the supernatant had been discarded, the residue from the rumen liquor digestion was incubated with 25 ml of a 0.2% pepsin solution in a water bath for another 48 h. After incubation, the residue was filtered with a coarse sintered glass crucible and washed with 50 ml of hot water. The residue in the crucible was oven-dried at 105°C overnight.

Digestibility in vivo Seven wethers weighing ca. 35 kg were assigned to a 7 X 7 Latin square design with one extra period to estimate carry-over effects (Lucas, 1957). Animals were kept in metabolism crates for an initial adjustment period of 10 days, a preliminary period of seven days, and a seven-day collection period. The experimental diets were given at 90% of maximal intake, deter-

334 mined during the last five days of the initial adjustment period. The rations were given twice daily in equal portions at 0700 h and 1900 h. All lambs had access to trace-mineralized salt and water. Faeces were collected daily, were thoroughly mixed and a 50% sample was kept. Samples were stored at 4°C during the collection period, composited and frozen {-20°C) until analyzed. All analyses were as previously described. Digestibility of DM and other nutrients for the straw and basal components of the diets was determined by a series of simultaneous equations (Kromann, 1967). Regression equations were developed to estimate digestibility coefficients of the diets as the level of straw increased. Statistical analysis of variance was as described by Steel and Torrie {1960). Differences between means were tested using Duncan's New Multiple Range Test (Duncan, 1955), except for the regression analysis. RESULTS AND DISCUSSION

Chemical composition and digestibility in vitro Chemical composition of the NaOH-treated and untreated straw and of the experimental diets is presented in Table II. The NaOH-reduced CWC, ADF and HC contents without affecting DM and OM. Crude protein content was lowered slightly by NaOH treatment. Similar compositional changes have been reported in response to NaOH treatment of low-quality roughages (Ololade and Mowat, 1969; Ololade et al., 1970; Klopfenstein et al., 1972; Rexen and Thomsen, 1976). Dry matter digestibility in vitro of the straw {Table II) was increased by 18.4% by the alkali treatment (P < 0.05). As the level of straw increased, digestibility in vitro decreased, the decrease being more obvious for untreated than for treated straw. Digestibility in vitro was 15--20% higher than digestibility in vivo {see below).

Digestibility o f diets in vivo The animals remained healthy and in good condition for the duration of the experiment. On average 1.2 kg of diet was consumed daily, and there were no feed refusals. Apparent digestibility of DM and OM decreased (P < 0.01) when either treated or untreated straw was added to the basal diets (Table III). As shown in the regression equations in Table IV, digestibility of these two fractions decreased linearly {P ~ 0.01) as the levels of straw were raised, the rate of decrease (P ~ 0.05) being faster with increasing levels of untreated straw than with treated straw. Digestibility of DM decreased by 0.22 and 0.41% for each 1% increase in treated and untreated straw in the diets, respectively. Similar decreases in OM digestibility of 0.23 and 0.42% were observed for the treated and untreated straw, respectively. For both fractions rates of de-

73.1 73.1 74.2 74.2 73.6 73.8 74.0

Diet A. Basal diet (BD) B. 90% BD + 10% C. 80% BD + 20% D. 60% BD + 40% E. 90% BD + 10% F. 80% BD + 20% G. 60% BD + 40% 68.6 68.3 68.8 69.2 69.0 68.8 69.1

68.3 68.5

Organic matter

12.2 12.4 12.5 13.2 12.3 12.8 12.8

5.5 5.2

Crude protein

33.6 36.8 39.6 44.9 37.4 41.1 48.6

70.5 62.9

Cell wall constituents

14.5 17.8 20.9 27.4 18.4 21.7 28.8

50.5 46.0

Acid d e t e r g e n t fibre

19.0 19.1 18.7 18.6 19.1 19.4 19.7

20.0 16.9

Hemicellulose

81.0 ef 77.7 f 70.4 c

8 1 . 8 ef

87.5 d 84.6 de 83.4 de

48.5 b 66.9 c

Digestibility o f dry m a t t e r in vitro

aAll values r e p r e s e n t t h e m e a n o f 6 analyses. Diets w e r e s a m p l e d initially, in t h e m i d d l e o f and at the e n d o f t h e in vivo s t u d y . Analyses were c o n d u c t e d in d u p l i c a t e o n e a c h o f t h e s e samples. b,c,d,e,fValues in t h e same c o l u m n w i t h d i f f e r e n t s u p e r s c r i p t s are d i f f e r e n t (P < 0.05).

TS TS TS UTS UTS UTS

73.6 73.0

Dry matter

Components

U n t r e a t e d straw (UTS) T r e a t e d straw (TS)

Item

Chemical analyses a n d digestibility in vitro o f diets c o n t a i n i n g N a O H - t r e a t e d a n d u n t r e a t e d s t r a w a (%)

T A B L E II

e..O e~

336 T A B L E III Nutrient digestibility by sheep fed on diets a n d u n t r e a t e d s t r a w (%)

containing v a r i o u s

Diet

Dry matter

Organic matter

Crude protein

CWC

ADF

HC

A. B. C. D. E. F. G.

69.8 a 6 8 . 4 a5 66.2 b 61.09c 66.2 b 62.1 c 53.6 d +-1.05

71.7 a 6 9 . 5 a5 67.2 b 62.4 c 67.35 62.6 c 54.8 d +-1.15

67.4 68.0 67.4 70.0 67.4 69.1 70.2 +1.65

6 2 . 4 ad 6 4 . 5 ab 6 4 . 5 ab 66.1 b 56.4 c 58.1 c 5 9 . 0 cd +-1.03

43.2 a 4 6 . 9 bc 48.9 b 53.6 d 38.9 e 4 4 . 8 ac 4 7 . 7 bc +-1.17

77.7 a 81.6 b 82.6 b 88.4 c 73.9 d 72.9 d 75.0 d -+0.94

Basal diet + 10% TS + 20% TS + 40% TS + 10% UTS + 20% UTS + 40% UTS SE of mean

levels o f N a O H - t r e a t e d

a,b,c~d M e a n s in t h e s a m e c o l u m n b e a r i n g d i f f e r e n t s u p e r s c r i p t s a r e d i f f e r e n t (P < 0 . 0 5 ) .

crease were a b o u t doubled when untreated straw was included in the diets. Reports of decreases in DM digestibility for ruminants given increasing levels of wheat straw (Halevi et al., 1973; O'Donovan and Ghadaki, 1973), rice straw {White et al., 1974} or other roughages {Elliot and Loosli, 1959; Putnam and Loosli, 1959, Stone and Fontenot, 1965) are numerous in the literature. However, there is a scarcity of data concerning additions of various levels of alkali-treated roughage to diets. From somewhat comparable results to ours, Mellenberger et al. (1971) indicated that the rate of decline in digestibility of treated aspen diets was less than for untreated diets. Digestion coefficients for DM and OM of the basal and straw components of the diets are presented in Table V. There were only slight differences between diets in the DM digestibility of the basal component, but the digestibility of straw appeared to decrease as its concentration in the diet increased. These differences were n o t treated statistically because only the average digestibility values shown in Table III were used in the calculations. However, digestion coefficients of 20--22% higher were consistently in favour of the NaOH-treated straw component. The digestibility of CWC, ADF and HC for the diets is presented in Table III and the appropriate regression equations are in Table IV. Increasing the level of NaOH-treated straw in the diets produced a linear increase (P < 0.05} in digestibility of these nutrients. However, no significant response was noted for CWC, ADF and HC digestibility with increasing levels of untreated straw in the diet. It is generally accepted that the higher the proportion of fibrous food in the diet, the greater the digestibility of crude fibre {Forbes et al., 1969; Raven et al., 1969; Halevi et al., 1973; White et al., 1974}. In the present experiment, increasing the level of NaOH-treated straw increased the digestibility of CWC, ADF and HC. McGregor et al. {1976} found that increasing the amount of CWC and ADF in the diet also resulted in increased digesti-

Y=70.29 Y=71.87 Y=62.90 Y=43.71 Y=78.08

+ + +

0.224 0.234 0.083 0.253 0.256

X X X X X

0.98 0.98 0.88 0.98 0.97

<0.01 <0.01 <0.05 <0.05 <0.05

Y=70.10 Y=71.45 Y=59.78 Y=40.89 Y=75.77

+ -

0.410 0.424 0.047 0.158 0.051

X X X X X

Regression equation b

Probability

Regression equation b

r2

Untreated straw

NaOH-treated straw

a W h e r e Y = % d i g e s t i b i l i t y o f i t e m a n d X = % s t r a w in t h e diet. b O n l y l i n e a r r e s p o n s e s are p r e d i c t e d . Q u a d r a t i c r e s p o n s e s w e r e n o n s i g n i f i c a n t f o r all n u t r i e n t s (P > 0 . 0 5 ) . c R e g r e s s i o n c o e f f i c i e n t s are d i f f e r e n t f o r t r e a t e d a n d u n t r e a t e d s t r a w (P < 0 . 0 5 ) .

Dry matter c Organic m a t t e r c Cell wall c o n s t i t u e n t s c Acid d e t e r g e n t f i b r e c Hemicellulose c

Item

0.98 0.98 0.10 0.50 0.41

r2

R e s u l t s o f r e g r e s s i o n a n a l y s e s o f t h e e f f e c t s o f level o f N a O H - t r e a t e d a n d u n t r e a t e d s t r a w o n n u t r i e n t d i g e s t i b i l i t y a

TABLE IV

<0.01 <0.01 >0.05 (NS) >0.05 (NS) >0.05 (NS)

Probability

00 --.1

338 TABLE V Influence of level of NaOH-treated and untreated straw on nutrient digestibility (%) in the basal and straw components of the diet a Nutrients

Dry matter Basal diet Straw Organic matter Basal diet Straw Crude protein Basal diet Straw Cell wall constituent Basal diet Straw Acid detergent fibre Basal diet Straw Hemicellulose Basal diet Straw

NaOH-treated straw (%)

Untreated straw (%)

10

20

40

10

20

40

69.8 55.0

70.5 49.4

71.4 45.4

69.8 33.7

70.4 29.0

70.6 27.9

71.7 50.1

71.9 48.2

71.9 47.9

71.7 27.8

72.0 24.0

70.4 26.3

67.1 86.3

68.7 56.3

66.1 79.2

67.1 73.7

65.7 98.5

68.3 77.0

62.4 74.6

64.4 64.7

62.0 69.3

62.4 30.6

54.7 63.6

59.2 61.0

43.2 57.3

43.9 55.3

40.3 59.9

43.2 27.9

34.3 50.8

38.8 51.5

77.7 117.4

80.7 89.9

76.7 106.0

77.7 40.4

75.0 64.5

70.8 81.2

aCalculated from the average digestibility values in Table III by use of simultaneous equations (Kromann, 1967). bility o f t h e s e t w o c o m p o n e n t s . M a e n g e t al. ( 1 9 7 1 ) also r e p o r t e d increased CWC a n d A D F digestibility w h e n t h e level o f N a O H - t r e a t e d s t r a w was raised in t h e diet. Digestibility o f CWC, A D F and H C o f t h e basal a n d s t r a w c o m p o n e n t s o f t h e diets as c a l c u l a t e d f r o m s i m u l t a n e o u s e q u a t i o n s ( K r o m a n n , 1 9 6 7 ) is s h o w n in T a b l e V. A l t h o u g h t h e changes in n u t r i e n t digestibility o f t h e basal c o m p o n e n t w e r e small, large c h a n g e s in t h e s t r a w c o m p o n e n t w e r e a p p a r e n t a n d a c c o u n t e d f o r t h e m a j o r d i f f e r e n c e s in n u t r i e n t digestibility p r e v i o u s l y discussed. H e m i c e l l u l o s e digestibility is q u i t e variable even w i t h i n t h e s a m e p l a n t . Lignin m a y be p a r t i a l l y r e s p o n s i b l e f o r v a r i a t i o n s in H C digestibility since n o n h y d r o l y t i c o x i d a t i v e d e l i g n i f i c a t i o n results in large a m o u n t s o f t h e H C b e c o m i n g w a t e r - s o l u b l e a n d digestible (Sullivan, 1966}. V a n S o e s t (1973} c o n c l u d e d t h a t all celluloses, w h e n f r e e d o f lignin a n d o t h e r interfering m a t t e r , w e r e m o r e or less c o m p l e t e l y digestible b y r u m e n m i c r o o r ganisms. T h u s , it m a y b e possible t o c a l c u l a t e HC digestibility values in excess o f 100% f o r t h e N a O H - t r e a t e d s t r a w c o m p o n e n t ( T a b l e V), p a r t i c u l a r l y if t h e digestibility o f H C in t h e basal d i e t was u n d e r e s t i m a t e d . A p p a r e n t digestibility o f c r u d e p r o t e i n was n o t a f f e c t e d b y a d d i t i o n o f e i t h e r N a O H - t r e a t e d o r u n t r e a t e d s t r a w t o t h e diets ( T a b l e I I I ) . Results in

339

the present experiment and those of others (Halevi et al., 1973; O'Donovan and Ghadaki, 1973; White et al., 1974, McGregor et al., 1976} suggest no change in apparent crude protein digestibility as the level of roughage in the diet increases when nitrogen contents of the diets are maintained equal. In other studies {Raven et al., 1969; Kay et al., 1970; Maeng et al., 1971) where isonitrogenous intakes were n o t maintained, decreases in apparent crude protein digestibility were observed with the increasing level of straw in the diet. Thus, it appears that the depressing effect of increased dietary fibre level on crude protein digestibility is more significant when protein contents are not maintained, provided DM intakes are similar {Stone and Fontenot, 1965}. As the level of straw was increased in our study, urea, which would be 100% digestible, was also increased. Brouwer {1935) reported that urine pH may be considered a sensitive measure of the alkalinity of the feed. Fresh urine samples were obtained on the morning preceding each faeces collection period and pH was determined immediately. Urine pH ranged from 8.4--8.6 {SEM +0.11) and no significant dietary effect was observed. Rexen and T h o m s e n {1976} gave rations consisting mainly of NaOH-treated straw, which was given as an alkaline feed or neutralized with HCI prior to feeding. Neutralisation had no significant effect on the pH of sheep urine or on the pH of rumen contents.

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