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Investigations of the treatment of sawdust for rabbit feeding. 1. Effect of sodium hydroxide treatment
Animal Feed Science and Technology, 6 (1981) 43--50
43
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
INVESTIGATIONS OF THE TREATMENT OF SAWDUST FOR RABBIT FEEDING. 1. EFFECT OF SODIUM HYDROXIDE TREATMENT
T.A. OMOLE and O.C. ONWUDIKE
Department o f Animal Science University o f Ire, Ile-Ife (Nigeria) (Received
ABSTRACT Omole, T.A. and Onwudike, O.C., 1981. Investigations of the treatment of sawdust for rabbit feeding. 1. Effect of sodium hydroxide treatment. Anim. Feed Sci. Technol., 6: 43--50. A total of one hundred and eighty-four New Zealand White rabbits were used in three separate experiments: to establish the concentration of sodium hydroxide solution needed to improve the nutritive quality of sawdust for rabbit feeding; to investigate whether there is any difference between the nutritive quality of hardwood- or softwoodsawdust when treated with o p t i m u m sodium hydroxide solution; and to study the extent to which NaOH-treated sawdust can be substituted for the conventional feeds in rabbit diets. F o o d consumption was significantly (P< 0.05) greater in rabbits given diets containing sawdust treated with 6% solutions o f NaOH, than with sawdust treated with 0--3% solutions. Rabbits given sawdust treated with 4 or 5% NaOH showed significantly (P < 0.05) better rate of gain and efficiency of feed utilization than those given sawdust treated with 0 or 1% sodium hydroxide solutions, and also grew slightly, but non-significantly, faster than those fed on sawdust treated with 3 and 6% NaOH. Alkali treatment o f sawdust increased carcass yield. Hardwood-responded better than softwood-sawdust to alkali treatment, and a higher concentration of alkali may be required for the latter. Rabbits may tolerate and efficiently utilize up to 15% of treated sawdust without any reduction in performance. Beyond this level, there was a significant (P<0.05) decrease in the rate of gain, feed/gain ratio and carcass yield.
INTRODUCTION
The continuing increase in the cost of conventional feeds for animal production has stimulated interest in low-cost feed substitutes, such as sawdust. A large amount of this product accumulates in the yards of saw-milling plants, constituting both disposal and environmental problems. The degree of utilization of sawdust by livestock is affected by its pre-treatment. Millett et al. (1970) used gamma irradiation, ammonia swelling, vibratory-ball milling and dilute sodium hydroxide solutions to increase digestibility in vitro, with varying degrees of success. Of these methods, alkali treatment ap-
0377-8401/81/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company
44
peared most economically feasible and increased the digestibility of all the hardwoods tried (MeUenberger et al., 1971). The effect of alkali treatment depends b o t h on whether the sawdust is from s o f t w o o d or h a r d w o o d and on the alkali concentration. S o f t w o o d does n o t respond much to alkali treatm e n t (Baker et al. 1975). Baker et al. (1975) also reported that 5--6 g of NaOH per 100 g of w o o d were necessary for maximum effect on digestibility in vitro, whilst Rexen et al. (1976) reported that the best results were obtained b y treating sawdust or straw with up to 7% NaOH. The following experiments were c o n d u c t e d to identify the concentration of NaOH required to improve the nutritive quality of sawdust, and to observe growth and carcass performance of fryer rabbits given graded levels of treated sawdust in partial replacement for conventional feeds. MATERIALS AND METHODS
Experiment I Fifty-six six-week-old New Zealand White rabbits (average weight 605 g) were randomly allotted to seven treatment-groups of eight rabbits each. The rabbits were fed on the same basal diet (Table I) containing 10% softwoodTABLE I Composition of basal diets for Experiments I and II (%; air-dry basis)
Ingredients Yellow maize (8.5% protein) G r o u n d n u t cake (48.0% protein) Fish meal Sawdust Palm oil Dicalciura phosphate Oyster shell Salt Vitamin-raineral premix 1 Ofurason=
63.0 15.0 6.0 10.0 2.0 2.0 1.0 0.5 0.25 0.25
Chemical composition (by analysis of dry-matter) Crude protein Crude fibre
17.25 8.36
~To provide the following per 100 kg of the diet: 440 mg, riboflavin; 720 mg, calcium pantothenate; 2 g, niacin; 2.2 g, choline chloride; 15 rag, folic acid; 1 rag, vitamin B 12 ; 15 rag, retinol; 165 ,g, vitamin D2; 1000 rng, D L-~-tocopherol acetate; 1700 rng, copper; 200 rag, iodine; 3000 rag, manganese; 5000 rng, zinc; 10 000 rag, iron. 2A commercial coccidiostat with nitrofurazone base.
sawdust. Since Baker et al. (1975) have shown that there is a better response to alkali treatment b y h a r d w o o d than b y softwood, it was decided to use s o f t w o o d in establishing the alkali concentration b e y o n d which there would
45 be no more improvement in animal performance. Such o p t i m u m NaOH concentration could then be applied to both softwood and hardwood sawdust. The sawdust incorporated into the diets was treated with 0--6% levels of sodium hydroxide solutions (weight/volume), giving a total of 7 treatmentgroups. The sodium hydroxide solutions were made up with tap water. The treatment of sawdust involved soaking it in 200-1 drums of the appropriate concentration of sodium hydroxide solutions for a period of 24 h. The quantity of solution added was just enough to cover the a m o u n t of sawdust put in the drum. The sawdust was thereafter sun-dried before being incorporated into rabbit diets. The animals were housed in groups of 4 and maintained in cages with wire-screen floors 90 cm from the concrete floor. Row cages of size 76 X 62 X 42 cm were used. The wire-screen floor permitted faeces to fall out of reach of the rabbits. Animals were weighed at weekly intervals and feed consumption was recorded daily. Feed and water were available ad libitum during all trials. Two rabbits from each cage, representing four rabbits per treatment, were selected for post-mortem studies eight weeks after the comm e n c e m e n t of the experiment. Each rabbit was killed by dislocating its neck, the skin, head, stomach, kidney, kidney fat, intestine, liver, lungs and heart were removed before weighing the warm carcass. The carcass value was calculated from the sum of the warm carcass and skin weights expressed as a proportion of the final live-weight. Water or blood t h a t might adhere to the liver and kidney were removed with filter paper. The kidney fat (being a reasonable estimate of overall fatness; Rico and Menchaca, 1973) was also weighed. Results were statistically evaluated by analysis of variance (Steel and Torrie, 1960), and the Duncan Multiple Range test was used to detect differences among means.
Experiment H From the results of Experiment I, it was observed that the diets in which sawdust was treated with 4 or 5% NaOH gave the best overall performance. Therefore, a second experiment was performed to determine the effect of 4--5% alkali treatment on sawdust from either hardwood or softwood. A total of forty-eight eight-week-old New Zealand white rabbits (average weight 886 g) were randomly allotted to 6 treatment-groups of eight rabbits each. The rabbits were fed on the same basal diet as in Experiment I, but with the sawdust supplied from either hardwood or softwood. The treatments involved alkali treatment of softwood or hardwood sawdust with 0, 4 or 5% solutions of NaOH, giving a total of 6 treatment-groups. The experimental details were as in Experiment I.
Experiment III As Experiments I and II showed t h a t rabbits fed on sawdust from either hardwood or softwood responded best when such sawdust was treated with 4 or 5% NaOH, this experiment was conducted to test the feasibility of sub-
46 stituting 4% N a O H - - t r e a t e d s a w d u s t f o r as m u c h as 30% o f t h e c o n v e n t i o n a l feeds in r a b b i t diets. A t o t a l o f e i g h t y - f o u r six-week-old N e w Zealand w h i t e rabbits (average w e i g h t 584 g) were r a n d o m l y a l l o t t e d t o seven t r e a t m e n t - g r o u p s o f 18 rabbits each. T h e rabbits were fed o n t h e e x p e r i m e n t a l diets (Table II) conraining 0, 5, 10, 15, 20, 25 or 30% o f h a r d w o o d s a w d u s t t r e a t e d w i t h 4% N a O H . T h e e x p e r i m e n t a l details were as in E x p e r i m e n t I. TABLE
II
Composition of diets for Experiment III (%; air-dry basis) Sawdust (%)
0
5
10
15
20
25
30
Ingredients Yellow maize Groundnut cake Fish meal Sawdust Palm oil Dicalcium phosphate Oyster shell Salt Vitamin-mineral premix I Ofurason~
73.0 68.0 62.0 56.0 50.0 44.0 39.0 15.0 15.0 16.0 17.0 18.0 19.0 19.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 -5.0 10.0 15.0 20.0 25.0 30.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25
Chemical composition (by analysis of dry matter) Crude protein Crude fibre
17.83 17.57 18.03 17.80 17.92 18.30 18.10 3.71 5.90 8.17 10.45 12.63 14.84 16.94
1To provide the following per 100 kg of the diet: 440 rag, riboflavin; 720 mg, calcium pantothenate; 2 g, niacin; 2.2 g, choline chloride; 15 rag, folic acid; 1 mg, vitamin B~2; 15 mg retinol; 165 ug, vitamin D2; 1000 rag, DL-a-tocopherol acetate; 1700 rag, copper; 200 mg iodine; 3000 mg manganese; 5000 mg zinc; 10 000 mg iron. 2A commercial coccidiostat with nitrofurazone base.
RESULTS
Experiment I E f f e c t o f N a O H c o n c e n t r a t i o n - - T h e s a w d u s t t r e a t e d w i t h 4 or 5% N a O H gave significantly ( P < 0 . 0 5 ) b e t t e r results t h a n t h a t t r e a t e d with 0, 1 o r 2% levels o f N a O H , in t e r m s o f daily gain. T h e h i g h e r g r o w t h rates o f t h e animals fed o n the 4 a n d 5% N a O H - t r e a t e d s a w d u s t were n o t significantly d i f f e r e n t f r o m t h o s e fed on t h e 3 and 6% N a O H t r e a t e d sawdust. F e e d intake with s a w d u s t t r e a t e d with 4, 5 or 6% N a O H was also significantly ( P < 0 . 0 5 ) higher t h a n t h a t with s a w d u s t t r e a t e d w i t h N a O H b e l o w 3% con-
47 TABLE nI E f f e c t o f t r e a t m e n t o f s a w d u s t w i t h d i f f e r e n t c o n c e n t r a t i o n s o f N a O H o n live, carcass and o r g a n m e a s u r e m e n t s o f g r o w i n g rabbits ( E x p e ~ m e n t I) C o n c e n t x a t i o n o f s o d i u m h y d r o x i d e s o l u t i o n (%)
Initial w e i g h t (g) Final w e i g h t (g) Daily f e e d i n t a k e (g) Daily gain (g) Feed/galn ratio L i v e r (% b o d y w e i g h t ) K i d n e y s (% b o d y weight) K i d n e y fat (% b o d y weight) Carcass v a l u e (%) Daily gain a d j u s t e d for carcass v a l u e (g)
0
1
604 1483 62.3 a 15.7 a 3.97 c 3.45
605 1607 6 5 . 3 ab 1 7 . 7 ab 3 . 6 5 bc 3.11
0.63
2
3
4
5
6
+- S.E.M.
609 1628 63.0 a 1 8 . 2 abc 3 . 4 6 ab 3.28
604 1752 64.6 ab 2 0 . 5 cd 3.15 a 3.36
598 282~ 70.3 ° c 21.9 d 3.21 a 3.22
603 1813 6 8 . 5 abc 21.6 d 3.17 a 3.18
611 1720 73.7 c 19.8 bcd 3 . 7 2 bc 3.16
--3.43 1.26 0.15 0.18
0.57
0.55
0.62
0.56
0.57
0.61
0.05
0.43 59.8
0.41 61.5
0.39 65.2
0.40 62.8
0.36 65.2
0.38 64.9
0.37 62.4
0.09 3.07
9.39
10.89
11.87
12.87
14.28
14.02
12.36
--
a , b , c , d = V a l u e s in e a c h r o w w i t h a c o m m o n l e t t e r o r w i t h n o l e t t e r are n o t significantly d i f f e r e n t at (P
centration. The untreated sawdust gave the lowest values for daily feed intake, daily gain, and feed/gain ratio. The treatment of sawdust did n o t significantly affect the carcass yield, liver, kidney and kidney fat yield. The NaOH treatment of sawdust, however, generally gave slightly, but nonsignificantly, higher values for carcass yield than did the untreated sawdust. Daffy gain adjusted for carcass value showed a pattern similar to the absolute body-gains. In general, alkali treatment improved feed consumption, growth rate and efficiency of feed conversion. The regression equations were Y1 = 61.46 + 0.60x (r = 0.71, $1 = 3.43, $2 = 0.27) Y: = 15.68 + 0.41x (r = 0.88, $1 = 1.26, $2 = 0.10) Y3= 2 . 7 8 + 0 . 0 3 x ( r = 0 . 1 ,$1 = 0 . 1 5 , $ 2 = 0 . 1 0 ) , where Y1 = Y3 = $2 = x =
feed intake, Y2 = daily gain, feed efficiency, $1 = standard error of estimate, standard error of regression coefficient, NaOH added (%), and r = correlation coefficient.
Experiment H E f f e c t o f alkali treatment on hardwood and s o f t w o o d sawdust -- The results of this study are presented in Table IV. Feed intake was lowest with the untreated hardwood sawdust and highest (P<0.05) with the hardwood sawdust treated with 5% NaOH. Rate of gain was significantly lower for the untreated hardwood or softwood sawdust and highest with the 4% NaOH-treated hardwood. In each of the treatments, hardwood sawdust promoted better gains and efficiency than the corresponding softwood, but the improvements were non-significant. In intake, gain and feed conversion efficiency, it appears that treatment with higher concentration of alkali is required for the softwood
48 TABLE IV E f f e c t o f t r e a t m e n t o f s o f t w o o d a n d h a r d w o o d s a w d u s t o n live, carcass a n d o r g a n m e a s u x e m e n t s o f g r o w i n g r a b b i t s ( E x p e r i m e n t If) C o n c e n t r a t i o n o f s o d i u m h y d r o x i d e s o l u t i o n (%) 0
Initial w e i g h t (g) Final w e i g h t (g) Daffy f e e d i n t a k e (g) Daffy gain (g) Feed/gain ratio L i v e r (% b o d y w e i g h t ) K i d n e y s (% b o d y w e i g h t ) Carcass v a l u e (%) Daffy gain a d j u s t e d f o r carcass v a l u e (g)
4
+ S.E.M.
5
Hard
Soft
Hard
Soft
Hard
Soft
883 1841 63.8 a 17.1 ab 3.73 ab 3.52 0.62 60.2
891 1798 65.6 ab 16.2 a 4.05 b 3.57 0.59 59.5
885 2134 69.1 ab 22.3 c 3.10 a 3.40 0.57 62.6
882 1996 64.9 ab 19.9 a b c 3.26 a 3.68 0.61 61.3
883 2104k 70.2" 21.3 c 3.22 a 3.30 0.61 63.6
889 2015 6 6 . 7 ab 20.1 b c 3.32 a 3.46 0.57 62.8
10.29
9.64
13.96
12.20
13.86
12.62
--
-2.79 1.84 0.31 0.29 0.04 2.16 --
a,b,c = V a l u e s in e a c h r o w w i t h a c o m m o n l e t t e r o r w i t h n o l e t t e r are n o t significantly d i f f e r e n t a t (P<0.05).
t h a n f o r t h e h a r d w o o d . T h e use o f h a r d w o o d or s o f t w o o d s a w d u s t did n o t
affect any of the organ or carcass values.
Experiment Ill Effect o f increasing level o f sawdust -- The results of growth and carcass performance of rabbits given graded levels of sawdust appear in Table V. Feed intake was not influenced by the level of dietary sawdust. Rabbits given 5, 10 or 15% sawdust grew at about the same rate as those given the conventional diet without sawdust. Rate of growth was significantly (P<0.05) lower with 20% sawdust than with none. There was a steady decline in daily gain as TABLE V E f f e c t s o f d i f f e r e n t levels o f t r e a t e d s a w d u s t o n live, carcass a n d o r g a n m e a s u r e m e n t s of g r o w i n g rabbits (Experiment III) S a w d u s t (%)
Initial w e i g h t (g) Final w e i g h t (g) Daily f o o d i n t a k e (g) Daily gain (g) Feed/gain ratio L i v e r (% b o d y w e i g h t ) K i d n e y s (% b o d y weight) K i d n e y f a t (% b o d y weight) Carcass v a l u e (%) Daily gain a d j u s t e d f o r c a r c a s s v a l u e (g)
+ S.E.M.
0
5
10
15
20
25
30
587 1953 ~]~3 24.4 d 3.01 a 3.48
778 1905 72.5 23.7 cd 3.06 a 3.55
872 1915 72.4 2 3 . 8 cd 3.04 a 3.43
584 1934 75.0 24.1 c d 3.11 a 3.50
579 1682 75.6 19.7 bc 3 . 8 4 ab 3.54
592 1572 74.4 1 7 . 5 ab 4.25 b 3.72
584 1413 73.0 14.8 a 4.93 b 3.77
--3.16 2.17 0.55 0.18
0.58
0.55
0.57
0.55
0.54
0.61
0.59
0.04
0.37 a 63.7 bc
0.35 a 62.3 hc
0.36 a 65.2 c
0.39 ab 62.9 bc
0 42 ab 6 i .4 a b c
0.47 b 87.4 ab
0.47 b 57.6 a
0.04 3.02
15.54
14.81
15.52
15.16
12.10
10.22
8.23
--
a , b , c , d = V a l u e s in e a c h r o w w i t h a c o m m o n l e t t e r o r w i t h n o l e t t e r are n o t s i g n i f i c a n t l y d i f f e r e n t (P<0.05).
49
the sawdust level increased from 20 to 30%. The efficiency of feed utilization followed a pattern similar to that of growth rate. Although the feed conversion ratio for 20% sawdust was poorer than that for the control, the differences was not statistically significant. Giving 25 or 30% sawdust led to substantially poorer (P<0.05) feed utilization. Kidney fat was increased (P<0.05), whilst the carcass yield was reduced (P<0.05), b y diets containing more than 20% sawdust. Both gain and carcass value declined sharply at 25 and 30% dietary sawdust-levels. Growth adjusted for carcass value showed that increase due to meat was substantially reduced at these levels. In general, rate of gain and efficiency of feed utilization slightly declined as the level of treated sawdust increased in the diet. The regression equations were Y2 = 26.69 - 0.27x (r = - 0 . 7 9 , $1 = 2.17, $2 = 0.09) Y3 = 2.58 + 0.05x (r = 0.79, $1 = 0.55, $2 = 0.02}, where x = proportion of sawdust in the diet (%). DISCUSSION
The increased performance of animals given alkali-treated sawdust in all the experiments suggests that the treatment increases the extent to which sawdust can be utilized by rabbits. The cellulose in sawdust is largely unavailable because o f the crystalline nature of its molecule and the existence of a lignin--carbohydrate complex. The main consequence of alkali treatment appears to be the breaking (by saponification) of intermolecular ester bonds (Tarkow and Feist, 1968, 1969; Feist et al., 1970; Baker et al., 1975}. The saponification of ester bonds permits more than the usual amount of swelling in the w o o d and increased accessibility of the sawdust to hydrolytic attack b y enzymes and some micro-organisms. A number of workers have also reported that alkali treatment of sawdust leads to a higher digestibility in vitro and b y some ruminants (Wilson and Pigden, 1964; Tarkow and Feist, 1968; Mellenberger et al., 1971; Rexen et al., 1976). It would, therefore, appear that the treatment of sawdust with sodium hydroxide increased its digestibility and utilization by the rabbits. Another important observation, from the results of Experiment I, is the higher feed-intake of animals given treated sawdust. Alkali treatment, by breaking ester bonds, m a y render the sawdust less coarse and, therefore, more acceptable to the animals. The better response to alkali treatment of h a r d w o o d sawdust than of softw o o d sawdust as observed in this study has been reported b y Baker et al. (1975). It would, therefore, appear to be better to use h a r d w o o d sawdust for the feeding of rabbits. In this study, it appears that the o p t i m u m level of incorporation o f treated sawdust in rabbit diets is 15%. It m a y be that the overall digestibility of the diet declined as the level of sawdust increased bey o n d this point. Such a view has been expressed by Tarkow and Feist (1969) and Mellenberger et al. (1971). Another factor which might have affected the performance of the rabbits as the dietary level of sawdust increased bey o n d 15% is the a m o u n t of unreacted NaOH left in the sawdust. After alkali
50
treatment, the sawdust was neither washed with water to remove excess NaOH nor neutralized with acid. Washing causes a loss of soluble nutrients which may approach 10--25% (Saarinen et al., 1958). It is not known to what extent the rabbits in this study were affected by unreacted NaOH. Rexen et al. (1976) have, however, reported that with cattle, neutralisation of straw after alkali-treatment improved performance, feed intake and palatability. Increasing the level of sawdust beyond the 15% limit might also have adversely affected the nutrient balance of the diets so that the animals were not obtaining enough nutrients for optimum performance. It is also possible that the amount of crude fibre in the diet when the 15% level of sawdust was exceeded could not be easily handled by the rabbits. A minimum fibre level of 6% in the diet of rabbits has been suggested by Davidson and Spreadbury (1975); the rabbits in this study tolereated up to 10% fibre beyond which there was growth depression. Further work is needed to identify more precisely the specific fibre levels needed in rabbit diets.
REFERENCES Baker, A.J., MiUett, M.A. and Satter, L.D., 1975. Wood and wood-based residues in animal feeds. In: A.F. Turbak (Editor) Cellulose Technology Research. American Chemical Society, Washington, D.C. Davidson, J. and Spreadbury, D., 1975. Nutrition of the New Zealand White rabbit. Proc. Nutr. Soe., 34: 75--83. Feist, W.C., Baker, A.J. and Tarkow, H., 1970. Alkali requirements for improving Digestibility and nutritive value of poplar bark. J. Anita. Sci., 30: 832--835. Mellenberger, R.W., Satter, L.D., Millett, M.A. and Baker, A.J., 1971. Digestion of aspen, alkali-treated aspen, and aspen bark by goats. J. Anita. Sci., 32: 756--763. Millett, M.A., Baker, A.J., Feist, W.C., Mellenberger, R.W. and Satter, L.D., 1970. Modifying wood to increase its in vitro digestibility. J. Anita. Sci., 31: 781--788. Rexen, F., Stigsen, P. and Kristensen, V.F., 1976. The effect of a new alkali technique on the nutritive value of straws. In: H. Swan and D. Lewis (Editors), Feed Energy Sources for Livestock, pp. 65--82. Rico, C. and Menchaca, M., 1973. Studies on genotype---environment interaction and optimum protein level in rabbit diets. Cuban J. Agric. Sci., 7: 9--15. Saarinen, P., Jensen, W.J. and Alhojarvi, J., 1958. Investigations on cellulose fodder. (Cited by Mellenberger et al., 1971 J. Anim. Sci., 32: 756--763). Steel, R.G.D. and Torrie, J.H., 1960. Principles and Procedures of Statistics. McGraw-Hill, New York. Tarkow, H. and Feist, W.C., 1968. The super-swollen state of wood. Tappi, 51 : 80--83. Tarkow, H. and Feist, W.C., 1969. Cellulases and their Applications. Adv. Chem. Series, 95: 197--217. Wilson, R.K. and Pigden, W.J., 1964. Effect of a sodium hydroxide treatment on the utilization of wheat straw and poplar wood by tureen micro-organisms. Can. J. Anita. Sci., 44: 112--122.
43
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
INVESTIGATIONS OF THE TREATMENT OF SAWDUST FOR RABBIT FEEDING. 1. EFFECT OF SODIUM HYDROXIDE TREATMENT
T.A. OMOLE and O.C. ONWUDIKE
Department o f Animal Science University o f Ire, Ile-Ife (Nigeria) (Received
ABSTRACT Omole, T.A. and Onwudike, O.C., 1981. Investigations of the treatment of sawdust for rabbit feeding. 1. Effect of sodium hydroxide treatment. Anim. Feed Sci. Technol., 6: 43--50. A total of one hundred and eighty-four New Zealand White rabbits were used in three separate experiments: to establish the concentration of sodium hydroxide solution needed to improve the nutritive quality of sawdust for rabbit feeding; to investigate whether there is any difference between the nutritive quality of hardwood- or softwoodsawdust when treated with o p t i m u m sodium hydroxide solution; and to study the extent to which NaOH-treated sawdust can be substituted for the conventional feeds in rabbit diets. F o o d consumption was significantly (P< 0.05) greater in rabbits given diets containing sawdust treated with 6% solutions o f NaOH, than with sawdust treated with 0--3% solutions. Rabbits given sawdust treated with 4 or 5% NaOH showed significantly (P < 0.05) better rate of gain and efficiency of feed utilization than those given sawdust treated with 0 or 1% sodium hydroxide solutions, and also grew slightly, but non-significantly, faster than those fed on sawdust treated with 3 and 6% NaOH. Alkali treatment o f sawdust increased carcass yield. Hardwood-responded better than softwood-sawdust to alkali treatment, and a higher concentration of alkali may be required for the latter. Rabbits may tolerate and efficiently utilize up to 15% of treated sawdust without any reduction in performance. Beyond this level, there was a significant (P<0.05) decrease in the rate of gain, feed/gain ratio and carcass yield.
INTRODUCTION
The continuing increase in the cost of conventional feeds for animal production has stimulated interest in low-cost feed substitutes, such as sawdust. A large amount of this product accumulates in the yards of saw-milling plants, constituting both disposal and environmental problems. The degree of utilization of sawdust by livestock is affected by its pre-treatment. Millett et al. (1970) used gamma irradiation, ammonia swelling, vibratory-ball milling and dilute sodium hydroxide solutions to increase digestibility in vitro, with varying degrees of success. Of these methods, alkali treatment ap-
0377-8401/81/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company
44
peared most economically feasible and increased the digestibility of all the hardwoods tried (MeUenberger et al., 1971). The effect of alkali treatment depends b o t h on whether the sawdust is from s o f t w o o d or h a r d w o o d and on the alkali concentration. S o f t w o o d does n o t respond much to alkali treatm e n t (Baker et al. 1975). Baker et al. (1975) also reported that 5--6 g of NaOH per 100 g of w o o d were necessary for maximum effect on digestibility in vitro, whilst Rexen et al. (1976) reported that the best results were obtained b y treating sawdust or straw with up to 7% NaOH. The following experiments were c o n d u c t e d to identify the concentration of NaOH required to improve the nutritive quality of sawdust, and to observe growth and carcass performance of fryer rabbits given graded levels of treated sawdust in partial replacement for conventional feeds. MATERIALS AND METHODS
Experiment I Fifty-six six-week-old New Zealand White rabbits (average weight 605 g) were randomly allotted to seven treatment-groups of eight rabbits each. The rabbits were fed on the same basal diet (Table I) containing 10% softwoodTABLE I Composition of basal diets for Experiments I and II (%; air-dry basis)
Ingredients Yellow maize (8.5% protein) G r o u n d n u t cake (48.0% protein) Fish meal Sawdust Palm oil Dicalciura phosphate Oyster shell Salt Vitamin-raineral premix 1 Ofurason=
63.0 15.0 6.0 10.0 2.0 2.0 1.0 0.5 0.25 0.25
Chemical composition (by analysis of dry-matter) Crude protein Crude fibre
17.25 8.36
~To provide the following per 100 kg of the diet: 440 mg, riboflavin; 720 mg, calcium pantothenate; 2 g, niacin; 2.2 g, choline chloride; 15 rag, folic acid; 1 rag, vitamin B 12 ; 15 rag, retinol; 165 ,g, vitamin D2; 1000 rng, D L-~-tocopherol acetate; 1700 rng, copper; 200 rag, iodine; 3000 rag, manganese; 5000 rng, zinc; 10 000 rag, iron. 2A commercial coccidiostat with nitrofurazone base.
sawdust. Since Baker et al. (1975) have shown that there is a better response to alkali treatment b y h a r d w o o d than b y softwood, it was decided to use s o f t w o o d in establishing the alkali concentration b e y o n d which there would
45 be no more improvement in animal performance. Such o p t i m u m NaOH concentration could then be applied to both softwood and hardwood sawdust. The sawdust incorporated into the diets was treated with 0--6% levels of sodium hydroxide solutions (weight/volume), giving a total of 7 treatmentgroups. The sodium hydroxide solutions were made up with tap water. The treatment of sawdust involved soaking it in 200-1 drums of the appropriate concentration of sodium hydroxide solutions for a period of 24 h. The quantity of solution added was just enough to cover the a m o u n t of sawdust put in the drum. The sawdust was thereafter sun-dried before being incorporated into rabbit diets. The animals were housed in groups of 4 and maintained in cages with wire-screen floors 90 cm from the concrete floor. Row cages of size 76 X 62 X 42 cm were used. The wire-screen floor permitted faeces to fall out of reach of the rabbits. Animals were weighed at weekly intervals and feed consumption was recorded daily. Feed and water were available ad libitum during all trials. Two rabbits from each cage, representing four rabbits per treatment, were selected for post-mortem studies eight weeks after the comm e n c e m e n t of the experiment. Each rabbit was killed by dislocating its neck, the skin, head, stomach, kidney, kidney fat, intestine, liver, lungs and heart were removed before weighing the warm carcass. The carcass value was calculated from the sum of the warm carcass and skin weights expressed as a proportion of the final live-weight. Water or blood t h a t might adhere to the liver and kidney were removed with filter paper. The kidney fat (being a reasonable estimate of overall fatness; Rico and Menchaca, 1973) was also weighed. Results were statistically evaluated by analysis of variance (Steel and Torrie, 1960), and the Duncan Multiple Range test was used to detect differences among means.
Experiment H From the results of Experiment I, it was observed that the diets in which sawdust was treated with 4 or 5% NaOH gave the best overall performance. Therefore, a second experiment was performed to determine the effect of 4--5% alkali treatment on sawdust from either hardwood or softwood. A total of forty-eight eight-week-old New Zealand white rabbits (average weight 886 g) were randomly allotted to 6 treatment-groups of eight rabbits each. The rabbits were fed on the same basal diet as in Experiment I, but with the sawdust supplied from either hardwood or softwood. The treatments involved alkali treatment of softwood or hardwood sawdust with 0, 4 or 5% solutions of NaOH, giving a total of 6 treatment-groups. The experimental details were as in Experiment I.
Experiment III As Experiments I and II showed t h a t rabbits fed on sawdust from either hardwood or softwood responded best when such sawdust was treated with 4 or 5% NaOH, this experiment was conducted to test the feasibility of sub-
46 stituting 4% N a O H - - t r e a t e d s a w d u s t f o r as m u c h as 30% o f t h e c o n v e n t i o n a l feeds in r a b b i t diets. A t o t a l o f e i g h t y - f o u r six-week-old N e w Zealand w h i t e rabbits (average w e i g h t 584 g) were r a n d o m l y a l l o t t e d t o seven t r e a t m e n t - g r o u p s o f 18 rabbits each. T h e rabbits were fed o n t h e e x p e r i m e n t a l diets (Table II) conraining 0, 5, 10, 15, 20, 25 or 30% o f h a r d w o o d s a w d u s t t r e a t e d w i t h 4% N a O H . T h e e x p e r i m e n t a l details were as in E x p e r i m e n t I. TABLE
II
Composition of diets for Experiment III (%; air-dry basis) Sawdust (%)
0
5
10
15
20
25
30
Ingredients Yellow maize Groundnut cake Fish meal Sawdust Palm oil Dicalcium phosphate Oyster shell Salt Vitamin-mineral premix I Ofurason~
73.0 68.0 62.0 56.0 50.0 44.0 39.0 15.0 15.0 16.0 17.0 18.0 19.0 19.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 -5.0 10.0 15.0 20.0 25.0 30.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25
Chemical composition (by analysis of dry matter) Crude protein Crude fibre
17.83 17.57 18.03 17.80 17.92 18.30 18.10 3.71 5.90 8.17 10.45 12.63 14.84 16.94
1To provide the following per 100 kg of the diet: 440 rag, riboflavin; 720 mg, calcium pantothenate; 2 g, niacin; 2.2 g, choline chloride; 15 rag, folic acid; 1 mg, vitamin B~2; 15 mg retinol; 165 ug, vitamin D2; 1000 rag, DL-a-tocopherol acetate; 1700 rag, copper; 200 mg iodine; 3000 mg manganese; 5000 mg zinc; 10 000 mg iron. 2A commercial coccidiostat with nitrofurazone base.
RESULTS
Experiment I E f f e c t o f N a O H c o n c e n t r a t i o n - - T h e s a w d u s t t r e a t e d w i t h 4 or 5% N a O H gave significantly ( P < 0 . 0 5 ) b e t t e r results t h a n t h a t t r e a t e d with 0, 1 o r 2% levels o f N a O H , in t e r m s o f daily gain. T h e h i g h e r g r o w t h rates o f t h e animals fed o n the 4 a n d 5% N a O H - t r e a t e d s a w d u s t were n o t significantly d i f f e r e n t f r o m t h o s e fed on t h e 3 and 6% N a O H t r e a t e d sawdust. F e e d intake with s a w d u s t t r e a t e d with 4, 5 or 6% N a O H was also significantly ( P < 0 . 0 5 ) higher t h a n t h a t with s a w d u s t t r e a t e d w i t h N a O H b e l o w 3% con-
47 TABLE nI E f f e c t o f t r e a t m e n t o f s a w d u s t w i t h d i f f e r e n t c o n c e n t r a t i o n s o f N a O H o n live, carcass and o r g a n m e a s u r e m e n t s o f g r o w i n g rabbits ( E x p e ~ m e n t I) C o n c e n t x a t i o n o f s o d i u m h y d r o x i d e s o l u t i o n (%)
Initial w e i g h t (g) Final w e i g h t (g) Daily f e e d i n t a k e (g) Daily gain (g) Feed/galn ratio L i v e r (% b o d y w e i g h t ) K i d n e y s (% b o d y weight) K i d n e y fat (% b o d y weight) Carcass v a l u e (%) Daily gain a d j u s t e d for carcass v a l u e (g)
0
1
604 1483 62.3 a 15.7 a 3.97 c 3.45
605 1607 6 5 . 3 ab 1 7 . 7 ab 3 . 6 5 bc 3.11
0.63
2
3
4
5
6
+- S.E.M.
609 1628 63.0 a 1 8 . 2 abc 3 . 4 6 ab 3.28
604 1752 64.6 ab 2 0 . 5 cd 3.15 a 3.36
598 282~ 70.3 ° c 21.9 d 3.21 a 3.22
603 1813 6 8 . 5 abc 21.6 d 3.17 a 3.18
611 1720 73.7 c 19.8 bcd 3 . 7 2 bc 3.16
--3.43 1.26 0.15 0.18
0.57
0.55
0.62
0.56
0.57
0.61
0.05
0.43 59.8
0.41 61.5
0.39 65.2
0.40 62.8
0.36 65.2
0.38 64.9
0.37 62.4
0.09 3.07
9.39
10.89
11.87
12.87
14.28
14.02
12.36
--
a , b , c , d = V a l u e s in e a c h r o w w i t h a c o m m o n l e t t e r o r w i t h n o l e t t e r are n o t significantly d i f f e r e n t at (P
centration. The untreated sawdust gave the lowest values for daily feed intake, daily gain, and feed/gain ratio. The treatment of sawdust did n o t significantly affect the carcass yield, liver, kidney and kidney fat yield. The NaOH treatment of sawdust, however, generally gave slightly, but nonsignificantly, higher values for carcass yield than did the untreated sawdust. Daffy gain adjusted for carcass value showed a pattern similar to the absolute body-gains. In general, alkali treatment improved feed consumption, growth rate and efficiency of feed conversion. The regression equations were Y1 = 61.46 + 0.60x (r = 0.71, $1 = 3.43, $2 = 0.27) Y: = 15.68 + 0.41x (r = 0.88, $1 = 1.26, $2 = 0.10) Y3= 2 . 7 8 + 0 . 0 3 x ( r = 0 . 1 ,$1 = 0 . 1 5 , $ 2 = 0 . 1 0 ) , where Y1 = Y3 = $2 = x =
feed intake, Y2 = daily gain, feed efficiency, $1 = standard error of estimate, standard error of regression coefficient, NaOH added (%), and r = correlation coefficient.
Experiment H E f f e c t o f alkali treatment on hardwood and s o f t w o o d sawdust -- The results of this study are presented in Table IV. Feed intake was lowest with the untreated hardwood sawdust and highest (P<0.05) with the hardwood sawdust treated with 5% NaOH. Rate of gain was significantly lower for the untreated hardwood or softwood sawdust and highest with the 4% NaOH-treated hardwood. In each of the treatments, hardwood sawdust promoted better gains and efficiency than the corresponding softwood, but the improvements were non-significant. In intake, gain and feed conversion efficiency, it appears that treatment with higher concentration of alkali is required for the softwood
48 TABLE IV E f f e c t o f t r e a t m e n t o f s o f t w o o d a n d h a r d w o o d s a w d u s t o n live, carcass a n d o r g a n m e a s u x e m e n t s o f g r o w i n g r a b b i t s ( E x p e r i m e n t If) C o n c e n t r a t i o n o f s o d i u m h y d r o x i d e s o l u t i o n (%) 0
Initial w e i g h t (g) Final w e i g h t (g) Daffy f e e d i n t a k e (g) Daffy gain (g) Feed/gain ratio L i v e r (% b o d y w e i g h t ) K i d n e y s (% b o d y w e i g h t ) Carcass v a l u e (%) Daffy gain a d j u s t e d f o r carcass v a l u e (g)
4
+ S.E.M.
5
Hard
Soft
Hard
Soft
Hard
Soft
883 1841 63.8 a 17.1 ab 3.73 ab 3.52 0.62 60.2
891 1798 65.6 ab 16.2 a 4.05 b 3.57 0.59 59.5
885 2134 69.1 ab 22.3 c 3.10 a 3.40 0.57 62.6
882 1996 64.9 ab 19.9 a b c 3.26 a 3.68 0.61 61.3
883 2104k 70.2" 21.3 c 3.22 a 3.30 0.61 63.6
889 2015 6 6 . 7 ab 20.1 b c 3.32 a 3.46 0.57 62.8
10.29
9.64
13.96
12.20
13.86
12.62
--
-2.79 1.84 0.31 0.29 0.04 2.16 --
a,b,c = V a l u e s in e a c h r o w w i t h a c o m m o n l e t t e r o r w i t h n o l e t t e r are n o t significantly d i f f e r e n t a t (P<0.05).
t h a n f o r t h e h a r d w o o d . T h e use o f h a r d w o o d or s o f t w o o d s a w d u s t did n o t
affect any of the organ or carcass values.
Experiment Ill Effect o f increasing level o f sawdust -- The results of growth and carcass performance of rabbits given graded levels of sawdust appear in Table V. Feed intake was not influenced by the level of dietary sawdust. Rabbits given 5, 10 or 15% sawdust grew at about the same rate as those given the conventional diet without sawdust. Rate of growth was significantly (P<0.05) lower with 20% sawdust than with none. There was a steady decline in daily gain as TABLE V E f f e c t s o f d i f f e r e n t levels o f t r e a t e d s a w d u s t o n live, carcass a n d o r g a n m e a s u r e m e n t s of g r o w i n g rabbits (Experiment III) S a w d u s t (%)
Initial w e i g h t (g) Final w e i g h t (g) Daily f o o d i n t a k e (g) Daily gain (g) Feed/gain ratio L i v e r (% b o d y w e i g h t ) K i d n e y s (% b o d y weight) K i d n e y f a t (% b o d y weight) Carcass v a l u e (%) Daily gain a d j u s t e d f o r c a r c a s s v a l u e (g)
+ S.E.M.
0
5
10
15
20
25
30
587 1953 ~]~3 24.4 d 3.01 a 3.48
778 1905 72.5 23.7 cd 3.06 a 3.55
872 1915 72.4 2 3 . 8 cd 3.04 a 3.43
584 1934 75.0 24.1 c d 3.11 a 3.50
579 1682 75.6 19.7 bc 3 . 8 4 ab 3.54
592 1572 74.4 1 7 . 5 ab 4.25 b 3.72
584 1413 73.0 14.8 a 4.93 b 3.77
--3.16 2.17 0.55 0.18
0.58
0.55
0.57
0.55
0.54
0.61
0.59
0.04
0.37 a 63.7 bc
0.35 a 62.3 hc
0.36 a 65.2 c
0.39 ab 62.9 bc
0 42 ab 6 i .4 a b c
0.47 b 87.4 ab
0.47 b 57.6 a
0.04 3.02
15.54
14.81
15.52
15.16
12.10
10.22
8.23
--
a , b , c , d = V a l u e s in e a c h r o w w i t h a c o m m o n l e t t e r o r w i t h n o l e t t e r are n o t s i g n i f i c a n t l y d i f f e r e n t (P<0.05).
49
the sawdust level increased from 20 to 30%. The efficiency of feed utilization followed a pattern similar to that of growth rate. Although the feed conversion ratio for 20% sawdust was poorer than that for the control, the differences was not statistically significant. Giving 25 or 30% sawdust led to substantially poorer (P<0.05) feed utilization. Kidney fat was increased (P<0.05), whilst the carcass yield was reduced (P<0.05), b y diets containing more than 20% sawdust. Both gain and carcass value declined sharply at 25 and 30% dietary sawdust-levels. Growth adjusted for carcass value showed that increase due to meat was substantially reduced at these levels. In general, rate of gain and efficiency of feed utilization slightly declined as the level of treated sawdust increased in the diet. The regression equations were Y2 = 26.69 - 0.27x (r = - 0 . 7 9 , $1 = 2.17, $2 = 0.09) Y3 = 2.58 + 0.05x (r = 0.79, $1 = 0.55, $2 = 0.02}, where x = proportion of sawdust in the diet (%). DISCUSSION
The increased performance of animals given alkali-treated sawdust in all the experiments suggests that the treatment increases the extent to which sawdust can be utilized by rabbits. The cellulose in sawdust is largely unavailable because o f the crystalline nature of its molecule and the existence of a lignin--carbohydrate complex. The main consequence of alkali treatment appears to be the breaking (by saponification) of intermolecular ester bonds (Tarkow and Feist, 1968, 1969; Feist et al., 1970; Baker et al., 1975}. The saponification of ester bonds permits more than the usual amount of swelling in the w o o d and increased accessibility of the sawdust to hydrolytic attack b y enzymes and some micro-organisms. A number of workers have also reported that alkali treatment of sawdust leads to a higher digestibility in vitro and b y some ruminants (Wilson and Pigden, 1964; Tarkow and Feist, 1968; Mellenberger et al., 1971; Rexen et al., 1976). It would, therefore, appear that the treatment of sawdust with sodium hydroxide increased its digestibility and utilization by the rabbits. Another important observation, from the results of Experiment I, is the higher feed-intake of animals given treated sawdust. Alkali treatment, by breaking ester bonds, m a y render the sawdust less coarse and, therefore, more acceptable to the animals. The better response to alkali treatment of h a r d w o o d sawdust than of softw o o d sawdust as observed in this study has been reported b y Baker et al. (1975). It would, therefore, appear to be better to use h a r d w o o d sawdust for the feeding of rabbits. In this study, it appears that the o p t i m u m level of incorporation o f treated sawdust in rabbit diets is 15%. It m a y be that the overall digestibility of the diet declined as the level of sawdust increased bey o n d this point. Such a view has been expressed by Tarkow and Feist (1969) and Mellenberger et al. (1971). Another factor which might have affected the performance of the rabbits as the dietary level of sawdust increased bey o n d 15% is the a m o u n t of unreacted NaOH left in the sawdust. After alkali
50
treatment, the sawdust was neither washed with water to remove excess NaOH nor neutralized with acid. Washing causes a loss of soluble nutrients which may approach 10--25% (Saarinen et al., 1958). It is not known to what extent the rabbits in this study were affected by unreacted NaOH. Rexen et al. (1976) have, however, reported that with cattle, neutralisation of straw after alkali-treatment improved performance, feed intake and palatability. Increasing the level of sawdust beyond the 15% limit might also have adversely affected the nutrient balance of the diets so that the animals were not obtaining enough nutrients for optimum performance. It is also possible that the amount of crude fibre in the diet when the 15% level of sawdust was exceeded could not be easily handled by the rabbits. A minimum fibre level of 6% in the diet of rabbits has been suggested by Davidson and Spreadbury (1975); the rabbits in this study tolereated up to 10% fibre beyond which there was growth depression. Further work is needed to identify more precisely the specific fibre levels needed in rabbit diets.
REFERENCES Baker, A.J., MiUett, M.A. and Satter, L.D., 1975. Wood and wood-based residues in animal feeds. In: A.F. Turbak (Editor) Cellulose Technology Research. American Chemical Society, Washington, D.C. Davidson, J. and Spreadbury, D., 1975. Nutrition of the New Zealand White rabbit. Proc. Nutr. Soe., 34: 75--83. Feist, W.C., Baker, A.J. and Tarkow, H., 1970. Alkali requirements for improving Digestibility and nutritive value of poplar bark. J. Anita. Sci., 30: 832--835. Mellenberger, R.W., Satter, L.D., Millett, M.A. and Baker, A.J., 1971. Digestion of aspen, alkali-treated aspen, and aspen bark by goats. J. Anita. Sci., 32: 756--763. Millett, M.A., Baker, A.J., Feist, W.C., Mellenberger, R.W. and Satter, L.D., 1970. Modifying wood to increase its in vitro digestibility. J. Anita. Sci., 31: 781--788. Rexen, F., Stigsen, P. and Kristensen, V.F., 1976. The effect of a new alkali technique on the nutritive value of straws. In: H. Swan and D. Lewis (Editors), Feed Energy Sources for Livestock, pp. 65--82. Rico, C. and Menchaca, M., 1973. Studies on genotype---environment interaction and optimum protein level in rabbit diets. Cuban J. Agric. Sci., 7: 9--15. Saarinen, P., Jensen, W.J. and Alhojarvi, J., 1958. Investigations on cellulose fodder. (Cited by Mellenberger et al., 1971 J. Anim. Sci., 32: 756--763). Steel, R.G.D. and Torrie, J.H., 1960. Principles and Procedures of Statistics. McGraw-Hill, New York. Tarkow, H. and Feist, W.C., 1968. The super-swollen state of wood. Tappi, 51 : 80--83. Tarkow, H. and Feist, W.C., 1969. Cellulases and their Applications. Adv. Chem. Series, 95: 197--217. Wilson, R.K. and Pigden, W.J., 1964. Effect of a sodium hydroxide treatment on the utilization of wheat straw and poplar wood by tureen micro-organisms. Can. J. Anita. Sci., 44: 112--122.