Use of Cassava as Animal Feed

http://mekarn.org/procKK/ly.htm

Studies on the nutritive value of ensiled cassava leaves for pigs in Cambodia

  
Julio Ly* and Lylian Rodríguez

 University of Tropical Agriculture Foundation
Royal University of Agriculture
Chamcar Daung, Dangkor District
PO Box 2423, Phnom Penh, Cambodia
* Visiting Researcher, Swine Research Institute, 
PO Box 1, La Habana, Cuba
jlca@yahoo.com; lylianr@utafoundation.org 

Abstract

Evidence has been accumulating suggesting that ensiling cassava leaves for pigs is not well understood.  In fact, most of the experiments to date have been conducted to study the ensiling process as a method to detoxify cassava leaves from the point of view of the cyanogenic glucosides. It is noteworthy that even with variable amounts of cyanide content in the silage, according to the level of ensiled leaves in the diet, there have been no reports of either deaths or symptoms of cyanide intoxication in the pigs. 

Conflicting results have been obtained from several balance experiments conducted with pigs fed ensiling cassava leaves, suggesting that a notable difference exists in the N retention, depending on the nature of the foliage used for ensiling. According to the recent experimental evidence obtained in the UTA ecological farm, cassava leaves from plantations managed to produce only forage, which are harvested periodically, have advantages, from the point of view of dietary utilization of N, over cassava leaves obtained as a by-product at the time of harvesting the roots. A hypothesis is advanced that the explanation for those differences could reside in the age of the leaves, and therefore, the nature of their chemical characteristics. A second explanation is that the improved N retention in pigs fed high levels of ensiled cassava leaves has been accompanied by inclusion of a protein supplement rich in sulphur amino acids, namely dried fresh water fish. 

A new approach to the feeding of ensiled cassava leaves to pigs could be the study of the acceptability of high levels of ensiled cassava leaves and of the performance traits in growing-finishing pigs fed high levels of cassava leaf silage derived from cassava managed as a semi-perennial forage and with supplementation of a protein source rich in sulphur amino acids. This approach would be facilitated by  the development of improved screening methods aimed at the rapid and easy evaluation of the nutritive value of the leaves, either old (crop residues) or young (repeated harvest of perennial forage), and ensiled with different conditions of wilting, in order to determine the most effective method for feeding pigs with this valuable foliage. 

Keywords: Ensiled cassava leaves, pigs, nutritive value

Introduction

During the last ten years, several reports have been published concerning the use of cassava leaves for pigs in Vietnam (Bui Van Chinh et al 1990; Bui Huy Nhu Phuc et al 1996; Du Thanh Hang  et al 1997; Nguyen Van Lai and Rodriguez 1998; Du Thanh Hang  2000) and Cambodia (Chhay Ty et al 2001). The attention of researchers has been drawn to the use of ensiled cassava leaves because this is an easy method of preservation of high amounts of foliage, obtained either during harvesting of the root, or after periodically harvesting of the aerial part. Results concerning the nutritive value of the ensiled cassava leaves have not been consistent, and several aspects remains to be studied, perhaps because the main interest of the above mentioned studies has been concentrated in the detoxifying process of cassava leaves. 

In the following text, it is intended to report a short review of the status of knowledge about ensiled cassava leaves and its use in pig nutrition. 

The detoxification effect of ensiling cassava leaves

From the early work of Bui Van Chinh et al (1992) to one of the most recent studies (Chhaty et al 2001), there is unequivocal evidence of the positive effect of ensiling on the hydrolysis of linamarin and posterior reduction of cyanide in the leaves. However, it is well known that the ensiling process by itself does not eliminate all the cyanogenic glucoside components present in the material. On the other hand, a preliminary wilting process, either in the shade or by sun drying, is a condition sine qua non to greatly improve the detoxification process, because linamarase is able to act on the cyanide precursors with a high efficiency.

It is noteworthy to point out that neither animal deaths nor symptoms of intoxication have been reported in any of the Vietnamese experiments  (Bui Van Chinh et al 1992; Bui Huy Nhu Phuc et al  1996; Du Thanh Hang et al  1997; Nguyen Van Lai and Rodriguez 1998; Du Thanh Hang 2000). The implication from this is that if some cyanide remains in the feed it may be of no significance in relation  to animal health and nutrition, perhaps because the rodhanase mainly present in the liver is quite effective in eliminating cyanide through the thiocyanate pathway.  In turn, there appear to be no consequences of the possible accumulation of thiocyanate in the animal body (for review, see Tewe 1992). 

The chemical characteristics of ensiled cassava leaves

Changes in certain chemical characteristics during the ensiling of cassava leaves have been reported by (Nguyen Van Lai and Rodriguez 1998; Du Thanh Hang 2000; Chhay Ty et al  2001). It can be concluded that ensiled cassava leaves used in pig experiments are characterized by a relatively low pH and a relatively high crude protein content (Nx6.25). However, the DM content of the ensiled product appears to be rather variable, and appears to be mainly a reflection of the degree of wilting of the leaves prior to ensiling (Table 1). 

Table 1. Characteristics of ensiled cassava leaves used in pig experiments
Days#	Component	pH	CN, mg/kg DM	DM  %	N %	References
-	Leaves	-	147	-	4.4	Bui H N P et al (1996)
-	-	-	-	30.0	4.4	Du T H et al  (1997)
56	Leaves	4.7	52	46.0	4.1	Nguyen V L & Rodriguez (1998)
21	Leaves##	-	61	34.5	4.1	Du T H  (2000)
84	Aerial part	3.6	133	19.0	4.3	Ly et al  (2001)###
56	Leaves####	4.4	120	41.3	3.9
28	Leaves####	4.6	108	46.1	5.3
#Days after ensiling; ## Without petioles; ### Unpublished data; #### With petioles

 
Ensiled cassava leaves and feed intake in pigs

Besides the bulky characteristics of the ensiled cassava leaves, which must determine to some extent the voluntary feed intake in the pig, it could be that the pig refuses to eat ensiled cassava leaves, especially when the rest of the diet is highly palatable, which is the case when sugar palm (Borassus flabellifer) syrup is the other constituent.  In the experiment reported in Table 2, anaerobiosis was not strictly established, and therefore, some heat would have been evolved during the storage of the material. This could negatively influence palatability through the synthesis of undesirable compounds (Wilkinson 1983a,b).

 

Some aspects of the nutritive value of ensiled cassava leaves for pigs

There is a considerable accumulation of results concerning N balance in pigs fed on diets contained graded levels of ensiled cassava leaves. However, there are few results describing the nutritive value of the ensiled product, either in vivo or in vitro. A summary of some of the data related to N balance under these conditions is presented in Table 3.

One of the most striking characteristics of the results from the N balance studies conducted with pigs fed graded levels of ensiled cassava leaves, is a general trend to a reduction in N retention with increased levels of the silage in the diet (Bui Huy Nhu Phuc et al (1996), Nguyen Van Lai and Rodriguez (1998) and Du Thanh Hang (2000), whereas the reverse has been observed in some recent studies in Cambodia (Ly et al 2001, unpublished data). The explanation for such disagreement is not apparent, but one difference is that the ensiled cassava leaves studied in the trials in Vietnam were obtained as a by-product after harvesting the roots, whereas Cambodia this same type of silage was made from foliage obtained from periodical harvests of the foliage in cassava plantations. It could be suggested that some differences exist between the two types of foliages from the point of view of the age of the leaf.. When leaves are the by-product  after harvesting the roots, they are much older than the leaves from foliage harvested periodically every 50 to 70 days. These differences could affect the relative nutritive value of the leaves from the two sources, from the point of view of lignification and availability of N.

More detailed information related to N balance studies in pigs fed on diets low in protein appears in Table 4. 

The data in Table 4 show a high value for digestibility of organic matter in pigs fed sugar palm syrup as the major source of energy, and an overall improvement in N digestibility and N retention in pigs fed increasing levels of ensiled cassava leaves in low protein diets, probably as a consequence of a dilution of the faecal excretion of endogenous protein in the undigested N residues from the diet.

Table 5 provides information concerning N balance studies in pigs fed diets high in protein. In accordance with previous results, the same trend was observed for N retention, in spite of a high intake of ensiled cassava leaves. 

Table 5. N balance in pigs fed ensiled cassava leaves. Diets high in protein.
	Ensiled cassava leaves, % of diet SM
	#	50.0##
Digestibility, %
Organic matter	90.0	85.1
N	81.5	78.4
N retention
As percentage of N intake	47.2	52.2
As percentage of N digested	56.8	67.7
# Dried fresh water fish was the only source of protein; ## The complementary source of N was dried fresh water fish (at 47% of total N) Source: Ly et al (2001; unpublished data)

Since the early report from Eggum (1970) it is well known that cassava leaves contain a relatively high proportion of lysine in the protein, but the contrary is true from the point of view of methionine. This evidence must be taken into account when high levels of cassava leaves are used in diet formulation for pigs, since methionine is involved in the detoxification process of cyanide in the animals. Results from a preliminary trial related to the effect of methionine on N balance of pigs fed high levels of ensiled cassava leaves suggest that this subject merits further research (Table 6).

Screening methods for rapid assessment of the nutritive value of ensiled cassava leaves

It has been shown that in vitro pepsin/pancreatin digestibility of N in pigs is closely related to the content of water soluble N contained in tropical foliages, cassava leaves included (Ly and Preston 2001). In turn, it is also known that there is a close relationship between in vivo, ileal digestibility in pigs, and in vitro pepsin/pancreatin digestibility (see for example, Boisen and Fernández 1995). Therefore, investigations applied to the nutritive value of silage made from cassava leaves could be greatly accelerated if some ready and easily applied methods were available. In this connection, results derived from preliminary studies carried out by UTA first in Thu Duc, in Vietnam and subsequently in Chamcar Daung, Cambodia, strongly suggest that the water soluble N method is appropriate for this purpose. Some data concerning an “on farm” approach to the study of the nutritive value of ensiled cassava leaves is shown in Table 7.  These data indicate that ensiled cassava leaves appear to be one of the most promising tropical foliages for feeding of pigs (Figure 1).  

Table 7. Dry matter and N solubility of cassava leaves (%)
	Dry matter			N
	Water solubility#		In vitro digestibility##	In cell walls###	Water solubility	In vitro digestibility
Cassava materials
Ensiled leaves	43.4	43.6		35.8	58.2	63.1
Foliage	48.3	54.1		14.8	41.0	68.0
Sun-dried foliage	49.6	52.7		23.6	40.7	51.7
Trees and shrub foliage
Hibiscus rosasinensis	52.0	48.7		23.7	59.6	74.2
Morus alba	43.7	45.0		10.2	39.3	47.9
Desmanthus virgatus	39.4	27.1		22.2	25.2	32.2
# Determined in a washing machine; ## Pepsin/pancreatin procedure; ### NDF-N Source: Ly et al (2001; unpublished data)

 Figure 1. Relationship between water soluble fractions (N and DM) and pepsin/pancreatin 
digestibility of leaves  from  cassava and some trees and shrubs

 Some implications

 A new approach in feeding ensiled cassava leaves to pigs could be the study of acceptability of high levels of ensiled cassava leaves and the determination of performance traits in growing-finishing pigs fed high levels of the silage. A  related need is to promote the use of improved screening methods to facilitate rapid and easy evaluation of the nutritive value of the leaves, both from old plants (residues after root harvest) and young plants (repeated harvest of cassava managed as perennial forage), and ensiled with different conditions of wilting, in order to determine the most effective method for pig feeding of this valuable foliage.
 

References

Boisen S and Fernandez J A 1995  Prediction of the apparent ileal digestibility of protein and amino acids in feedstuffs and feed mixtures for pigs by in vitro analyses. Animal Feed Science and Technology 51:29-43

Bui Huy Nhu Phuc, Preston T R, Ogle B and Lindberg J E 1996  The nutritive value of sun-dried and ensiled cassava leaves for growing pigs. Livestock Research for Rural Development  8: (3) http://cipav.org.co/lrrd/lrrd8/3/bui.htm

Bui Van Chinh,  Le Viet Ly, Nguyen H T and Do V M 1992  Using “C” molasses and ensiled cassava leaves for feeding pigs. Results of research 1985-1990. Agricultural Publishing House. Hanoi pp 46 

Chhay Ty, Ly J and Rodriguez L 2001  An approach to ensiling conditions for preservation of cassava foliage in Cambodia. Livestock Research for Rural Development 13(3): http://cipav.org.co/lrrd/lrrd13/3/chhayty.htm

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 10(3): http://cipav.org.co/lrrd/lrrd10/3hang103.htm

Du Thang Hang, Nguyen Van Lai, Rodriguez Lylian and Ly J 1997  Nitrogen digestion and metabolism in Mong Cai pigs fed sugar cane juice and different foliages as source of protein. Livestock Research for Rural Development 9(2): http://cipav.org.co/lrrd/lrrd9/2/Hang92.htm

Eggum O L 1970  The protein quality of cassava leaves. British Journal of Nutrition 24:761-769

Ly J and Preston T R 2001   In vitro estimates of nitrogen digestibility for pigs and water-soluble nitrogen are correlated in tropical forage feeds. Livestock Research for Rural Development 13(1): http://cipav.org.co.lrrd/lrrd13/1/ly131.htm

Nguyen Van Lai and Rodriguez Lylian 1998  Digestion and metabolism in Mong Cai and Large White pigs having free access to sugar cane juice or ensiled cassava root supplement with duckweed or ensiled cassava leaves. Livestock Research for Rural Development 10(2): http://cipav.org.co/lrrd/lrrd10/2.lai.htm

Tewe O O  1992  Detoxification of cassava products and effects of residual toxins on consuming animals. In: Roots, tubers, plantains and bananas in animal feeding (D. Machin and S. Nyvold, editors) FAO Animal Production and Health Paper 95. Rome p 81-98

Wilkinson J M 1983a  Silages made from tropical and temperate crops. I. The ensiling process and its influence on feed value. World Animal Review 45:36-42

Wilkinson J M 1983b  Silages made from tropical and temperate crops. II. Techniques for improving the nutritive value of silage. World Animal Review 46:35-40

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