An approach to ensiling conditions for preservation of cassava foliage in Cambodia

Transcription

1 Livestock Research for Rural Development (13) An approach to ensiling conditions for preservation of cassava foliage in Cambodia Chhay Ty, J Ly and Lylian Rodríguez University of Tropical Agriculture Foundation, Royal University of Agriculture Chamcar Daung, PO Box 2423, Phnom Penh 3, Cambodia chhayty@uta.edu.kh Abstract An experiment was designed at laboratory scale to study the effect of time (0, 14, 28, 42 and 56 days), origin of the cultivar (Kampong Cham province and Chamcar Daung, Phnom Penh) and levels of added sugar palm syrup (2.5, 5 and 7.5% in fresh basis) for ensiling of cassava foliage. Average air temperature was 27 C, and crude protein content of both sources of cassava foliages was 18.1 and 22.2% in dry basis, respectively. There was no significant interactions between factors studied. The overall ph profile of the ensiled material showed a sharp drop at 14 days after ensiling ( from 6.10 to 3.73), with slight fluctuations thereafter. A significant effect (P<0.001 ) of sugar palm syrup concentration on ph values was found in favour of 5% addition of the source of carbohydrate. There was a significant correlation (R² = 0.31; P<0.001) between ph values and neutralizing capacity of the preserved material. The cyanide concentration of the silages exhibited a significant negative (P<0.001) linear dependence on time. In spite of the fact that the Kampong Cham variety had a higher initial HCN content (86 mg/kg fresh foliage) as compared to that from Chamcar Daung (73 mg/kg fresh leaves), there were no differences in HCN content after 56 days of ensiling (overall value, 20 mg/kg fresh foliage).

2 It is suggested the use of sugar palm syrup at the level of 5% in the preparation of cassava foliage silages in Cambodia. According to results from the present experiment, the HCN content is in the range of safe utilization for monogastric animals such as pigs, after 56 days of ensiling the material. Key words: cassava leaves, sugar palm syrup, ensiling, ph, cyanide, crude protein Introduction Managing cassava as a perennial forage has been claimed to be a very important component of integrated farming systems in tropical countries (Preston et al 1999). In this connection, some constraints to cassava utilization in pig feeding, such as the cyanogenic glucosides present in the plant (Gómez and Valdivieso 1985; Ravindran and Ravindran 1988) can be neutralized succesfully after ensiling (Ravindran 1992). On the other hand, cassava leaves silage has been used in metabolism studies (Du Thanh Hang et al 1997; Nguyen and Rodríguez 1998) and growth trials (Du Thanh Hang 1998) indicating a promising use in tropical pig production. The aim of this study was to evaluate different ensiling conditions for preservation of cassava foliage in Cambodian farms. Materials and methods 60 laboratory silos were made by adding 2.5, 5 and 7.5% in fresh basis of palm (Borassus flabellifer L.) syrup to freshly harvested cassava foliage. The cassava foliage was from periodical cuts of plantations at the University. About one metre of the top of the plants was cut and there was no separation of leaves, stems and

3 petioles. Two cultivars of unknown origin were utilized, from Kampong Cham (KCh) and Chamcar Daung (ChD) respectively, from which the only apparent difference was the color of leaf petioles: red in KCh and white in ChD. Some characteristics of the harvested cassava foliage are set out in Table 1. The ChD cultivar contained higher DM content than that from KCh. On the other hand, the ChD cultivar was better than the KCh in crude protein (Nx6.25) and HCN concentration. Table 1: Proximal analysis of the cassava foliage Kampong Cham Chamcar Daung Dry matter, % Water soluble DM, % Nx6.25, % in DM Organic matter, % in DM NDF, % in DM HCN. mg/kg fresh basis The laboratory silos consisted of cylindrical plastic cans of 350 cm 3 capacity where the leaves with petioles and green stems were pressed after chopping (particle size less than 1 cm) and mixed with palm syrup, then covered with a sheet of polyethylene before sealing with the cap. The contents of each silo weighed 200 g approximately. The palm syrup was obtained in the local market, and was mixed with water (2:1 by weight) to achieve a brix (soluble sugars) of near 40.. The silos were opened at random after 0, 14, 28, 42 and 56 days of storage at an average air temperature of 27 C. Samples of fresh materials or silages were analysed for DM by drying to constant weight by microwave radiation (Undersander et al 1993). The N and ash content in fresh leaves were determined according to AOAC (1990) recommendations, whereas the NDF fraction was estimated following Van Soest et al (1991). In the fresh silages the ph was recorded by a glass electrode and the

4 neutralizing capacity was determined in aqueous extracts (1:4 by weight) by titrating with 0.1 N KOH until ph = 6.5. The cyanide content was determined in another aliquote of the silage by steam distillation and thereafter titrating with AgN0 3 after boiling the sample in chloroform and reaction with KOH. The data were subjected to analysis of variance (Steel and Torrie 1980) following a general linear model procedure of the Minitab statistical package (version 10.2). In addition, an analysis of regression was conducted in the required cases. Results and discussion There was no significant interaction (P>0.05) concerning any of the factors studied. The profile of DM content in the silages is shown in Figure 1. Figure Error! Bookmark not defined.: Dry matter concentration changes after ensiling Both types of silages showed a slight decrease in DM concentration from 0 to 14 days, thereafter being practically invariable until 56 days of ensiling, when a certain decrease in DM content appeared

5 to be evident. On the other hand, silages made with the KCh cultivar had always significantly higher DM concentration (P<0.001) than the ChD cultivar. The DM concentration in the ensiled cassava foliage was lower than that reported by Du Thanh Hang (1998) which was as high as 35%. Cassava leaves were wilted during one day prior to ensiling with 5% sugar cane molasses in the experiment of Du Thanh Hang 1998). Figure 2 shows the rapid decrease in the overall ph value of cassava foliage between 0 and 14 days of ensiling (from 6.10 to 3.73). A similar sharp decrease in ph of the experimental silos was observed by Du Thanh Hang (1998) when sugar cane molasses or rice bran were used for ensiling cassava leaves. Between 42 and 56 days of ensiling a slight, not significant increase in ph values of the media was encountered. However, a significant effect (P<0.001) of sugar palm syrup concentration in silos on ph values was found in favour of 5% addition of the source of carbohydrate. Figure Error! Bookmark not defined.: ph value of cassava foliage after ensiling

6 The neutralizing capacity of the cassava foliage was only measured after 28 days of ensiling (Figure 3). No effect of the level of sugar palm syrup was observed in any case. However, a significant effect (P<0.001) of cultivar source was found in the samples examined. In this opportunity, the ChD cultivar showed a higher neutralizing capacity value. There was a significant correlation (R 2 = 0.31; P<0.001) between ph values and the neutralizing capacity of the preserved material, the equation being Y = X, where Y was ph and X the neutralizing capacity (meq NaOH/100 g material). In this case, the value of S yx was ± Figure Error! Bookmark not defined.: Neutralizing capacity of ensiled cassava foliage Figures 4 and 5 describes the change in the HCN content in the ensiled foliage. The cyanide concentration of silos exhibited a significant (P<0.001) linear dependence on time. In spite of the fact that the KCh foliage was higher in initial HCN content (86 mg/kg fresh material) as compared to that from ChD (73 mg/kg fresh material), there were no differences in HCN content after 56 days of ensiling (overall value, 20 mg/kg fresh foliage). Wilting of cassava

7 leaves during one day was shown by Du Thanh Hang (1998) to reduce considerably the HCN content, as compared to the data presented in this paper. It is known that the destruction of cell wall structures by different methods favours the intracellular reaction of linamarase with the cyanoglucosides present in cassava, thus contributing to a rapid HCN elimination from the material (Ravindran 1992). Even so, the ensiling process permited the steady elimination of these compounds to low levels of this antinutritional factor. Figure 4: Changes in HCN content during the ensiling period (fresh matter basis) Figure 5: Changes in HCN content during the ensili period (dry matter basis) Gómez (1991) has suggested that 100 mg HCN/kg feed [on dry matter basis] as indicated by the Council of the European Community, could be the permissible maximum level. However, there is no clear evidence concerning either toxic levels of HCN for pigs or the influence of this acid on production traits of economic importance in pigs fed cassava foliage. This could be so, perhaps because of the well known amino acid imbalance in cassava leaves (Eggum 1970) and the considerable proportion of cell wall

8 (González et al 1999) present in the aerial part of cassava could be major constraints to the utilization of considerable amounts of cassava foliage in the feed for pigs. In fact, neither in growingfattening pigs (Mahendranathan 1971; Hutagalung 1972; Sarwat et al 1988) nor in breeding sows (Tewe and Maner 1981) are there reports of death of animals caused by HCN intoxication. This has been recognized in several reviews concerning this subject (Oke 1978; Gómez 1991; Tewe 1992; Ravindran 1993; Ly 1999). On the other hand, the use of ensiled cassava leaves with a relatively high level of HCN (147 mg/kg DM) resulted in better digestive indices than sun-dried cassava leaves (22.5 mg/kg DM) in growing pigs, as was encountered by Bui Huy Nhu Phuc et al (1996). It seems that more research concerning the interaction between HCN and monogastric animals performance in the context of well balanced diets is necessary. This appears to be evident from the point of view of the methionine content of the diet, taking into account the participation of this amino acid in the detoxification process of cyanide. Conclusions It is suggested to use sugar palm syrup at the level of 5% in the preparation of cassava foliage silages in Cambodia. According to results from the present experiment, HCN content is probably in the range of safe utilization for monogastric animals such as pigs, after 56 days of ensiling the material. References

9 AOAC Official Methods of Analysis. Association of Official Analytical Chemists. 15th edition (K Helnick ed.) Arlington pp 1230 Bui Huy Nhu Phuc, Ogle R B, Lindberg J E and Preston T R The nutritive value of sun-dried and ensiled cassava leaves for growing pigs. Livestock Research for Rural Development, Volume 8, Number 3, September 1996 ( Du Thanh Hang 1998 Ensiled cassava leaves and duckweed as protein sources for fattening pigs on farms in Central Vietnam. Livestock Research for Rural Development Volume 10, Number 3, December 1998 ( Du Thanh Hang, Nguyen Van Lai, Rodríguez L and Ly J 1997 Nitrogen digestion and metabolism in Mong Cai pigs fed sugar cane juice and different foliages as sources of protein. Livestock Research for Rural Development. Volume 9, Number 2, May 1997 ( Eggum O L 1970 The protein quality of cassava leaves. British Journal of Nutrition 24: Gómez G G 1991 Use of cassava products in pigs feeding. Pigs News and Information 12: Gómez G and Valdivieso M Cassava foliage: chemical composition, cyanide content and effect of drying on cyanide elimination. Journal of the Science of Food and Agriculture 36: González D A, González C, Díaz I, Ly J and Vecchionacce H Determinación de la digestibilidad de nutrientes de dietas de follaje de yuca amarga (Manihot esculenta Crantz) y aceite de palma (Elaeis guineensis Jacq.) en cerdos. Revista Computadorizada de Producción Porcina 6(1): Hutagalung R I Nutritional value of leaf meal, tapioca root meal, normal maize and opaque-2 maize and pineapple bran for pigs and poultry. Proceedings of the 17th Annual Conference of the Malaya Veterinary Association. Kuala Lumpur p 1-10 Ly J Uso de raíces de yuca para cerdos: factores antinutricionales. Revista Computadorizada de Producción Porcina 5(3):1-37 Mahendranathan T The effect of feeding tapioca (Manihot utilissima Pohl) leaves to pigs. Malayan Agricultural Journal 48:60-68 Nguyen Van Lai, Rodríguez L and Preston T R Digestion and N metabolism in Mong Cai and Large White pigs having free access to sugar cane juice or ensiled cassava root supplemented with duckweed or ensiled cassava leaves.

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