A.K. Tuah ¹ and E.R. Orskov ²
¹ Department of Animal Science, Fac. of Agric. U.S.T., Kumasi, Ghana
² Rowett Research Institute, Bucksburn, Aberdeen, Scotland, U.K.
Abstract
Introduction
Materials and methods
Results
Discussion
Conclusion
Acknowledgements
References
The dry-matter disappearance (DMD) values of untreated, 3.5% ammonia-treated and water-soaked maize cobs and cocoa pod husks were determined in the rumen of cannulated steers using the nylon bag technique. Although cocoa pod husks contained a higher level of lignin (26.38%) than the maize cobs (9.60%), the DMD values of the untreated cocoa pod husks were greater than those of untreated corn cobs for all the incubation periods (of 44% and 34% at 48 h). Ammonia treatment of maize cobs increased the DMD values but soaking it in water for 24 h before incubation had no significant effect. Cocoa pod husks were not improved by ammonia treatment.
The maize cobs and cocoa pod husks were treated with different levels of sodium hydroxide, 0,6,8,10 and 12 g/100 g of product and incubated in the rumen of four sheep for 48 h. Sodium hydroxide treatment significantly (P<0.01) increased the DMD values of the products. Washing the products after sodium hydroxide treatment did not significantly (P<0.05) affect the DMD values of the maize cob. With cocoa pod husks, washing after sodium hydroxide treatment caused a significant (P<0.01) reduction in the DMD values because of losses of soluble fractions during washing.
In many tropical areas there is a problem of inadequate feed supply during the dry season. Agricultural wastes and byproducts could be fed to ruminants during this season to offset the detrimental effects of inadequate nutrition on reproduction and growth.
In Ghana, there are large quantities of cocoa pod husks and maize cobs which could be fed to ruminants but are allowed to waste. Ghana produced 639,000 metric tonnes of dry cocoa pod husks in 1982 (Tuah et al, 1985) and about 95,000 metric tonnes of maize cobs in 1984 (FAO, 1984). Collection of maize cobs is easier than that of maize stalk which is left in the field where the maize is harvested while the cobs are gathered before dehusking and shelling.
Very little work has been done in Ghana to evaluate these byproducts as ingredients in ruminant diets (Otchere et al, 1983; Tuah et al, 1985; Adomako and Tuah, 1987). This study was therefore undertaken to determine in in situ degradation characteristics of the two by-products.
The effects of soaking, ammonia and sodium hydroxide treatments on the degradation of the by-products in the rumen were also studied.
Cocoa pod husks and maize cobs
The cocoa pod husks was prepared from fresh ripe pods as described by Tuah et al (1985). The maize cobs were obtained from the Ghana Seed Company, Kumasi and they were from an assortment of Ghanaian varieties both materials were sun-dried prior to handling.
The cocoa pod husks and the maize cobs were ground through a laboratory hammermill with a screen size of 2.5 mm. About 0.5 kg each of these products was treated with anhydrous ammonia as described by Orskov et al (1983) using 3.5 g NH3/100 g of product. Samples of the products (100 g each) were treated with different quantities of sodium hydroxide dissolved in 100 ml of water. The levels of sodium hydroxide applied were 0,6,8,10 and 12 g NaOH per 100 g of air-dry weight of the material. The treated samples were kept in polythene bags in a laboratory (about 20°C) for 48 h. After this period each sample was divided into two halves: one half was dried in an oven for 48 h at 60 C. The other half was put into nylon bags and washed in a washing machine for about 15 minutes. They were then dried at 60°C for 48 h.
Animal feeding and management
Three rumen-cannulated steers (average weight 474 kg) and four rumen-cannulated sheep (average weight 63 kg) were used. The type of cannual and the procedures for cannulation are as described by Ganev et al (1979). The management and feeding of the animals were as described by Tuah et al (1986).
Procedures of incubation for the determination of dry-matter disappearance (DMD)
Samples (2 g each) of untreated, ammonia-treated and water soaked maize cobs and cocoa pod husks were incubated in the same manner as described by Tuah et al (1986). The equation of Orskov and McDonald (1979) was used to describe the course of digestion of each sample. The a,b,c, and asymptote values for each sample were determined. For the NaOH treated samples, they were incubated for 48 h in the rumens of sheep.
Chemical analysis
The untreated cocoa pod husks and maize cobs were analysed for nitrogen (N) by the automated Kjeldahl method of Davidson et al (1970) and dry matter (DM) by the AOAC (1975) method. They were also analysed for acid-detergent fibre (ADF), neutral detergent fibre (NDF) and lignin using the methods of Van Soest (1963) and Van Soest and Wine (1967). The hemicellulose content was estimated as the difference between NDF and ADF (NDF-ADF). The cellulose content was estimated as the difference between ADF and lignin (ADF-lignin). Cell content was estimated as 100-NDF.
Statistical analysis
The data were subjected to statistical analysis using the two way analysis of variance for the steer experiments end split plot analysis of variance for the sheep experiment (Snedecor and Cochran, 1976).
Chemical composition of the products
Table 1 contains the chemical composition of the untreated maize cobs and cocoa pod husks (Table 1 near hear). When these products were treated with ammonia, the nitrogen contents increased from 0.50 to 1.29% for maize cobs and from 1.12 to 3.53% for cocoa pod husks.
Degradation characteristics of the untreated and treated products
The degradation characteristics of untreated, ammonia-treated and water-soaked maize cobs and cocoa pod husks are shown in Table 2. (Table 2). Soaking the samples in water for 24 h increased the moisture content of the maize cobs to 76.7% and that of cocoa pod husks to 93.0%. Ammonia treatment of the maize cobs increased its DMD values. The increases were significant at 72 h (P<0.05) and 96 h (P<0.01) (Table 2).
Ammonia treatment of the cocoa pod husks significantly (P<0.05) increased the DMD value only at the 12 h incubation period. The DMD values of the ammonia-treated samples were less than those of the untreated samples at 48, 72 and 96 h incubation periods, the difference being significant (P<0.05) at 72 h.
Soaking the maize cob samples for 24 h before incubating in the rumen did not markedly increase the DMD values compared to the untreated samples. The DMD values of water-soaked cocoa pod husks were very low after correcting for soaking losses and therefore were not included in the statistical analysis of the cocoa pod husks data.
Table 1. Chemical composition of untreated maize cob and cocoa pod husk.
|
|
Chemical constituent (g/100 g DM) |
||||||||
|
DM(%) |
Ash |
ADF |
NDF |
Lignin |
Cellulose |
Hemicellulose |
Nitrogen |
Cell content |
|
|
Maize cob |
93.27 |
1.96 |
47.61 |
93.96 |
9.60 |
38.01 |
46.35 |
0.50 |
6.04 |
|
Cocoa cob Husk |
89.50 |
10.02 |
50.62 |
59.34 |
26.38 |
24.24 |
8.72 |
1.12 |
40.64 |
DM = dry matter.
ADF = acid-detergent fibre.
NDF = neutral-detergent fibre.
Table 2. Degradation characteristics of untreated, ammonia-treated and water-soaked maize cob and cocoa pod (fitted values in parentheses).
|
|
DMD values at the various incubation periods (g/100 g DM incubated) |
Asymptote (g/100 g DM incubated) |
a |
b |
c |
RSD |
|||||
|
Untreated maize cob |
12 |
18 |
24 |
48 |
72 |
96 |
62.6 |
-1.74 |
64.3 |
0.0182 |
3.12 |
|
Ammonia-treated maize cob |
18.6 |
26.0 |
37.4 |
42.5 |
55.8 |
63.1 |
73.4 |
8.3 |
65.1 |
0.0182 |
4.40 |
|
Water-soaked maize cob |
11.5 |
15.1 |
26.7 |
39.4 |
45.6 |
4.8.8 |
50.6 |
-11.0 |
61.6 |
0.0356 |
2.31 |
|
SED |
1.57NS |
2.59NS |
2.7NS |
2.06NS |
1.69** |
0.11** |
|
|
|
|
|
|
Untreated cocoa pod husk |
27.0 |
27.3 |
33.7 |
43.7 |
51.0 |
52.2 |
57.6 |
15.1 |
42.5 |
0.0234 |
1.90 |
|
Ammonia-treated cocoa pod husk |
31.0 |
32.5 |
36.9 |
40.8 |
41.2 |
44.4 |
43.9 |
23.0 |
20.9 |
0.0389 |
1.35 |
|
SED |
0.65* |
142NS |
1,45NS |
3.49NS |
1.10* |
1.88NS |
|
|
|
|
|
|
Water-soaked cocoa pod husk |
2.7 |
3.9 |
12.3 |
24.8 |
28.0 |
28.5 |
30.5 |
-16.9 |
47.4 |
0.0389 |
2.36 |
|
RSD = residual standard deviation. |
NS = not significant. |
|
DMD = dry-matter disappearance. |
* = P<0.05. |
|
SED = standard error of difference. |
** = P<0.01. |
The effects of different levels of ammonia and sodium hydroxide treatments of maize cobs and cocoa pod husks on 48 h DMD values are shown in Table 3. The DMD values were significantly (P<0.01) affected by the level of sodium hydroxide treatment. For the maize cobs, washing the samples after sodium hydroxide treatment had no significant (P<0.05) decreasing effects on the DMD value (means: 72.6% for unwashed and 63.3% for washed, SED 6.48). For the cocoa pod husk, washing the samples after sodium hydroxide treatment significantly (P<0.01) reduced the DMD values (means 35.7% for the washed and 43.9 for the unwashed, SED 2.58).
Table 3. The effect of different levels of sodium hydroxide treatment and ammonia treatment on the 48 h DMD values of maize cob and cocoa pod husk.
|
|
48h DMD values (g/100 g DM incubated) |
|
|||||
|
Level of sodium hydroxide (%) |
|||||||
|
0 |
6 |
8 |
10 |
12 |
Ammonia-treated |
SED |
|
|
Maize cob (not washed) |
35.6 |
68.9 |
81.0 |
85.3 |
90.6 |
45.3 |
3.36** |
|
Maize cob (washed) |
32.0 |
60.0 |
79.0 |
82.4 |
84.2 |
ND |
2.21 |
|
Cocoa pod husk (not washed) |
40.6 |
41.6 |
43.5 |
47.5 |
59.2 |
39.4 |
1.49 |
|
Cocoa pod husk (washed) |
26.5 |
28.8 |
36.2 |
39.7 |
47.5 |
ND |
1.28 |
DMD = dry-matter disappearance.
SED = standard error of the difference.
ND = not determined.
** = p<0.01
Degradation characteristics of untreated and water-soaked maize cobs and cocoa pod husks
At all the incubation periods the untreated cocoa pod husk had higher DMD values than the untreated maize cobs although the lignin content of cocoa pod husks was about three times higher than that of maize cobs. This to some extent disagrees with the theory of physical encrustation and entrapment of nutrients within lignified cell walls which Van Soest (1982) also disagrees with. With the maize cobs, most of the material was cell wall while the cocoa pod husk had a cell content of about 40.6% compared to 6.04% for the maize cobs. The hemicellulose content of the maize cobs was very high (46.4%) compared to that of cocoa pod husk (8.7%). Hemicellulose is more closely associated with lignin than any other polysaccharide fraction and is believed to be bonded to phenolic constituents (Van Soest, 1982). The cellulose and the hemicellulose of the maize cobs may therefore not be made readily available for microbial degradation, thus de creasing its DMD value. The cocoa pod husk on the other hand had high cell contents which were readily soluble. The dry-matter losses after 24 h soaking were 25.6% for cocoa pod husk and 3.0% for maize cob.
The cell wall of cocoa pod husk is relatively rich in pectin (about 11% of whole product on DM basis), which is totally digestible in the digestive tract of the sheep (Adomako and Tuah, 1987) and low in hemicellulose. Adomako (19 75) reported that cocoa pod husk has very short fibres. It is therefore interesting to note that it has a high lignin content. It is possibly not totally lignin but also same amounts of condensed tannins. Further work to characterise this "lignin" will be pursued.
Bateman and Fresnilo (1967) reported that in vivo dry matter digestibility of cocoa pod husks ranged from 32.3 to 39.7% which were close to the 24 h and 48 h DMD values observed in the present trial.
Kevelenge et al (1983) reported that the organic matter digestibilities of maize cob incubated in rumen fluid for 24, 48, 72 and 96 h followed by 48 h acid-pepsin digestion were about 8, 15, 26 and 50% respectively. Except for the 96 h period these values of Kevelenge et al (1983) were lower than those obtained in the present trial although the lignin content of their maize cobs was lower than that used in the present trial (5.8% vs 9.60%).
In the present trial soaking in water for 24 h did not increase the DMD values of the maize cobs at the various incubation periods as postulated by Kevelenge et al (1983).
With cocoa pod husk, soaking in water for 24 h caused reduction in the DMD values at the various incubation periods when soaking losses were corrected for because great quantities of cell contents were dissolved in the water. There seems to be no advantage in soaking any of the products, especially cocoa pod husks.
Degradation characteristics of ammonia-treated maize cob and cocoa pod husk
The DMD values of the ammonia-treated maize cobs were significantly improved only at 72 h (P<0.05) and 96 h (P<0.01) incubation periods compared to the untreated or water-soaked samples. It seems that anhydrous ammonia was not very effective in improving the DMD values of the maize cobs used in this trial.
Nelson et al (1984) using maize cobs containing 40% moisture reported the 48 h DMD values of 2, 3 and 4% ammonia treated samples to be 61.30, 61.69 and 65.94% respectively. These values were higher than the 48 h DMD values for ammonia treated maize cobs obtained in this trial. In the present trial, the moisture content of the maize cob was 6.4%. Kiangi and Kategile (1981) reported that moisture content of straws (20 or 40%) had less effect on the rate of ammonia treatment in improving their nutritive values. Borhami and Sundstol (1982), however, reported that if moisture content of straw was not above 2.5% then it adversely affected the improvement in its nutritive value with ammonia treatment. It is most likely that with maize cobs, the least moisture content for ammonia treatment to be effective would be higher than that of cereal straw. The optimum level of moisture content of maize cobs for ammonia treatment will be studied.
Cocoa pod husk was not responsive to ammonia treatment except at the 12 h incubation period although it caused an increase in the N content of the product (1.12% to 3.53%). Van Soest (1982) reported that grass lignin linkages are more susceptible to mild alkali treatment than those of wood or non grass forages due to the higher content of ester and a lower content of methoxyl groups compared to that of non-grass lignin. The ester linkages between lignin and carbohydrates are more easily cleaved by alkali than the other linkages. Cocoa is a dicotyledonous plant which possibly explains the unresponsiveness of its lignin to ammonia treatment.
Effect of level of sodium hydroxide treatment of maize cob and cocoa pod husk on their 48 h DMD values
The level of sodium hydroxide treatment significantly (P<0.01) improved the 48 h DMD values of maize cobs. The highest level of treatment resulted in the highest DMD value. When the sodium hydroxide-treated samples were washed after treatment to reduce the sodium content the DMD values were not significantly (P<0.05) reduced compared to the unwashed samples. The slight reduction in the DMD values of the samples after washing could be due to losses of water-soluble fractions and solubilised phenolic compounds.
Kategile and Frederiksen (1979) reported in vivo organic-matter digestibility of 10% sodium hydroxide-treated maize cobs to be 32.4%. Nagole et al (1983) reported that treatment of maize cobs with 4.5% sodium hydroxide increased in vivo dry-matter digestibility from 44.7 ± 1.6 to 54.2 ± 2.0%.
The sodium hydroxide-treatment significantly (P<0.01) increased the DMD values of the cocoa pod husks. Washing the treated samples reduced significantly (P<0.01) the DMD values compared to unwashed samples. This is because during the washing process some of the soluble digestible portions were lost.
The DMD value of maize cobs could be increased with sodium hydroxide treatment and excess sodium could be washed from the sample without affecting its nutritive value. Anhydrous ammonia treatment was not very effective in increasing the DMD value possibly due to the low moisture content. Cocoa pod husks did not respond to anhydrous ammonia treatment but was responsive to sodium hydroxide treatment. The lignin content per se of a product is not directly related to the DMD values as shown by cocoa pod husks and maize cobs in the present trial.
The financial assistance given to one of the authors (A. K. Tuah) by the Association of Commonwealth Universities is acknowledged. Mr. R.I. Smart of the Rowett Research Institute is thanked for the chemical analysis of the materials.
Adomako, D. 19 75 . A review of researches into the commercial utilisation of cocoa by-products with particular references to the prospects in Ghana. Research Review CMB Newsletter No. 61 pp. 12-20.
Adomako, D. and Tuah, A.K. 1987. Digestibility of cocoa pod husk pectic polysaccharides by sheep fed rations containing cocoa pod husk. 10th International Cocoa Research Conference, 17-23/5/87, held in Santo Domingo, Dominican Republic.
AOAC (Association of Official Analytical Chemists). 1975. Official methods of analysis. 12th ed. AOAC, Washington, D.C. U.S.A.
Bateman, J.V. and Fresnilo, O. 1967. Digestibility of Theobroma cacao pods when fed to cattle. J. Agric. Sci., Camb 58: 23-25.
Borhami, B.E.A. and Sundstol, F. 1982. Studies on ammonia-treated straw. 1. The effects of type and level of ammonia, moisture content and treatment time on the digestibility in vitro and enzyme soluble organic matter of oat straw. Animal Feed Sci. Tech 7: 45-51.
Davidson, J.; Mathieson, J. and Boyne, A.W. 1970. The use of automation in determining nitrogen by the Kjeldahl method with final calculations by computer. Analyst. London 95: 181 - 193.
F.A.O. (Food and Agriculture Organization). 1984. Monthly bulletin of statistics. Vol. 7, No. 12. FAO, Rome, Italy. p. 13.
Ganev, G.; Orskov, E.R. and Smart, R. 1979. The effect of roughage or concentrate feeding and rumen retention time on total degradation of protein in the rumen. J. Agric. Sci., Camb. 93: 651-656.
Kategile, J.A. and Frederiksen, J.H. 1979. Effect of level of sodium hydroxide treatment and volume of solution on the nutritive value of maize cobs. Anim. Feed. Sci. Tech. 4: 1-15.
Kevelengo, J.E.E.; Said, A.N. and Kiflewahid, B. 1983. The nutritive value of four arable farm byproducts commonly fed to dairy cattle by small-scale farmers in Kenya. I. Organic structural components and in vitro digestibility. Trop. Anim. Prod. 8: 162-170.
Kiangi, E.M.I. and Kategile, J.A. 1981. Different sources of ammonia for improving the nutritive value of low quality roughages. Anim. Feed Sci. Tech. 6: 377-386.
Nangole, F.N.; Kayongo-Male, H. and Said, A.N. 1985. Chemical composition, digestibility and feeding value of maize cobs. Anim. Feed. Sci. Tech. 9: 121-130.
Nelson, M.L.; Klopfenstein, T.J. and Britton, R.A. 1984. Protein supplementation of ammoniated roughages. Corn cobs supplemented with a blood meal-maize gluten meal mixture-lamb studies. J. Anim. Sci. 59: 1601-1609.
Orskov, E.R. and McDonald, I. 1979. The estimation of protein degradability in the rumen from incubation measurements weighted according to rate of passage. J. Agric. Sci., Camb. 92: 4990 503.
Orskov, E.R.; Roid, G.W.; Holland, S.M.; Tait, C.A.G. and Lee, NH 1983. The feeding value for ruminants of straw and whole-crop barley and oats treated with anhydrous or aqueous ammonia or urea. Anim. Feed Sci. Tech. 8: 247-257.
Otchere, EGO.; Musah, I.A. and Bafi-Yeboah, M. 1983. The digestibility of cocoa husk-based diets fed to sheep. Trop. Anim. Prod. 8: 3338.
Snedecor, G.W. and Cochran, W.G. 1976. Statistical methods. 6th ed. Iowa State University Press, Ames, Iowa.
Tuah, A.K.; Adomako, D. and Dzoagbe, S. 1985. Evaluation of cocoa pod husk as feed ingredient for sheep in Ghana. Proc. 9th Intl. Cocoa Res. Conf. held at Lome, Togo. pp. 505-509.
Tuah, A.K.; Lufadeju, E.; Orskov, E.R. and Blackett, G. 1986. Rumen degradation of straw. I. Untreated and ammonia treated barley, oat and wheat straw varieties and triticale straw. Animal. Prod. 43: 261-269.
Van Soest, P.J. 1963. Use of detergents in the analysis of fibrous feeds. II. A rapid method for the determination of fibre and lignin. J. Ass. Off. Anal. Chem. 46: 829-835
Van Soest, P.J. 1982. Nutritional ecology of the ruminant. O and B Books Inc., Corvallis, Oregon. pp. 112, 126 and 127.
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. Asso. Off. Anal. Chem. 56: 50-55.
