Back to contents

Workshop-seminar "Making better  use of local feed resources" SAREC-UAF,  January , 2000.

 

Ensiling techniques and evaluation of cassava leaf silage for Mong Cai sows in Central Vietnam

 

Nguyen Thi Loc, Nguyen Thi Hoa Ly, Vo Thi Kim Thanh

and Hoang Nghia Duyet
                                               

Hue University of Agriculture and Forestry

 

Abstract

 

Cassava is the main food crop in central Vietnam for both livestock and human consumption. Traditionally the leaves are used as green manure, but are a potential protein source for animals if they can be preserved at harvesting for later use. These studies therefore focused on the effect of using different additives for ensiling the leaves, such as rice bran, molasses and cassava root meal mixed with fresh leaves at levels of 5% and 10% of dry matter on proximate composition, pH and HCN contents of the resulting silage. Replacing 10% of dietary dry matter of traditional growth and gestation diets for Mong Cai gilts diets by ensiled cassava leaves (ECL) had no significant effects on growth rate or reproductive parameters, but a level of  20% ECL  inclusion significantly delayed age at 3^rd oestrus  and reduced piglet live weight at birth.  Inclusion of 15% ECL in gestation and lactation diets for mature Mong Cai sows had no effects on litter size, but piglet weaning weights were significantly higher.

 

Key words: Cassava leaf silage, additives, reproduction, Mong Cai sows

 

Introduction

 

Cassava and its by-products, and other crop by-products such as rice bran, are the main energy sources for pigs in Central Vietnam. These feeds have low protein contents, which must be supplied from other, protein-rich feeds. Potential protein supplements in the region are fermented fish and groundnut cake, which are relatively expensive, and quantities are also limited. There is therefore a need to identify and study processing methods of other locally available protein sources, particularly those that can be produced at small-scale farmer level. There are around 700,000 tons of cassava roots and 70,000 tons of cassava leaves produced annually in Central Vietnam by small farmers. Buitrago (1990) stated that the greatest limitation to the use of cassava as animal feed is its content of cyanogenic glucosides. The most common procedures for reducing the concentrations of these substances are sun-drying and artificial dehydration, which are technically difficult to carry out, and  ensiling.

 

The objectives of the experiments therefore were to study the effects of different levels of various additives on the quality of cassava leaf silages and to evaluate the effects of including ensiled cassava leaves in traditional diets for Mong Cai gilts and sows on reproductive performance. 

Material and methods

 

On-station evaluation of the effect of different additives on the quality of cassava leaf silage

Fresh cassava leaves were collected when the roots were harvested. The leaves were then mixed with 0.5% salt and 0, 5 or 10 % (of fresh cassava leaf weight) of molasses, rice bran or cassava root meal and sealed in plastic bags. The treatments were:

 

Control (Ctrl): Cassava leaves + 0.5% salt

M5: Cassava leaves + 0.5% salt + 5% “A” molasses

M10: Cassava leaves + 0.5% salt + 10% “A” molasses

CRM5: Cassava leaves + 0.5% salt + 5% cassava root meal

CRM10: Cassava leaves + 0.5% salt + 10% cassava root meal

RB5: Cassava leaves + 0.5% salt + 5% rice bran

RB10: Cassava leaves + 0.5% salt + 10% rice bran

 

Samples of silage were taken after 0, 7, 14, 21, 28 and 56 days of ensiling and analysed for proximate components, pH, and HCN (AOAC 1980).

 

On-station feeding trial with Mong Cai gilts

The experiment was carried out at the research farm of the Hue University of Agriculture and Forestry, from February 1998 to January 1999.

 

Animals and experimental design

Twelve Mong Cai gilts with an average initial live weight of 9 to 10 kg were purchased after weaning. After vaccination and 3 weeks for adaptation to their new environment they were randomly allocated to three treatments with four replicates (individually housed and fed) per treatment. The gilts were inseminated at third oestrus by AI using semen from a Large White boar. The diets shown  below were fed up to farrowing.

 

Diets and feeding

Ctrl : control diet consisting of:  rice bran (61.5%), cassava root meal (23.1%), fishmeal (11.5%) and sweet potato leaves (3.9%). CP, 11.9%; ME, 10.38 MJ/kg.

ECL10: 10% of the control diet  (DM) was replaced by ensiled cassava leaves. 

ECL20: 20% of the control diet  (DM) was replaced by ensiled cassava leaves.

 

The ECL10 and ECL20 diets had similar contents of CP and ME as the control diet.

 

On-farm feeding trial with pregnant and lactating Mong Cai sows

The experiment was carried out in sixteen households in Huong Van village near Hue from October 1997 to August 1998.

 

Animals and experimental design

Sixteen third litter Mong Cai sows were randomly allocated after mating to the sixteen households and then to one of the two treatments: control (Ctrl) and experimental (ECL15) diets. The gestation control diet was made up (DM basis) of rice bran (53.8%), cassava root meal (20.8%), fermented fish (10.0%), sweet potato leaves (15.4%) and bone meal, and contained (DM basis) 13.1% CP and 14.0 MJ/kg ME. The lactation control diet included (DM basis) rice bran (27.5%), cassava root meal (27.5%), broken rice (17.0%), fermented fish (11.0%), sweet potato leaves (12.8%) and bone meal (4.2%), and contained 13.2% CP and 13.5 MJ/kg ME.

 

ECL15: 15% (DM) of the control gestation and lactation diets was replaced by ensiled cassava leaves.

 

Results and discussion

On-station evaluation of different additives on the quality of cassava leaf silage

The effects of the additives on chemical changes in the silages are presented in Figure 1 and Tables 1 to 3.   For all treatments observations of colour and odour indicated that the silages were well preserved.  As is clearly shown in Figure 1 and Table 1 the concentration of HCN decreased rapidly for all treatments from initial values of around 300 mg/kg fresh silage, and stabilised after 56 days at around 150 mg/kg for the control  treatment (5% salt) and at a mean of around 100 mg/kg silage for the other treatments.  The traditional method of ensiling with salt was therefore shown to be fairly effective, but the major disadvantage of such a high concentration of salt is that the low palatability of the silage limits its level of inclusion in feeds.

 

 

 

 

 

 

Changes in pH with time confirmed the visual observations that all treatments resulted in silage of acceptable quality, as pH values fell within 7 days to between 3.7 to 4.3, and either remained at these levels (control, 5% salt) or fell further, to 3.6-3.8, for the other treatments (Table 2).

 

 

Concentrations of crude protein in the silages fell for all treatments by between 2 – 5 percentage units (Table 3), probably as a result of bacterial degradation. 

 

On-station trial with growing gilts given ensiled cassava leaves

There were no effects (P>0.05) on growth rate or reproductive parameters (Table 4) when 10% of the dry matter of the control diet was replaced by ensiled cassava leaves (ECL10), but age at insemination (3^rd oestrus) of the gilts given the diet with 20% ensiled cassava leaves (ECL20) was higher (P<0.05) than for the control group (197and 169 days, respectively), and as a result live weight at insemination was also higher (P<0.01).

This suggests that anti-nutritional factors in the cassava leaf silage could have negatively influenced the attainment of puberty. There was also a trend towards an increase in the duration of pregnancy with increasing levels of ECL, but the difference was not significant (P=0.14).  Although mean litter size at birth and weaning were not affected by treatment, mean piglet liveweight at birth was lower (P<0.05) for the ECL20 treatment compared with the control and ECL10 diets, although the difference had disappeared at weaning. These results can be compared with a similar study carried out in Vietnam (Lam Quang Nga et al 2000), in which 30% of the dry matter of conventional diets for pregnant and lactating primiparous Mong Cai sows was replaced by cassava leaf meal.  Litter size and mean piglet live weights at birth and weaning were not affected by dietary treatment, although weaning to oestrus interval was significantly longer for the sows receiving cassava leaves, which again suggests possible negative effects on attainment of oestrus.

 

 

On-farm trial with mature sows given ensiled cassava leaves

The effects of replacing 15% of the DM of a traditional (control) diet with ensiled cassava leaves are shown in Table 5.  There were no significant between treatment differences in duration of pregnancy, nor in litter size at birth, 21 days or weaning. However, mean piglet live weight for the ECL15 sows was higher at 21 days (P <0.05) and at weaning (P<0.001), which could have been a result of the lower mean litter size compared to the control sows.

 

Conclusions

 

Ensiling is a convenient way of preserving the nutritional value and reducing the toxicity of fresh cassava leaves. Good quality silage was obtained by ensiling the leaves with as little as 5% of cassava root meal,  rice bran or “A” molasses, and HCN concentrations were reduced by about 60%.Replacing 10% of the dry matter in traditional gestation and lactation diets for Mong Cai gilts by ensiled cassava leaves did not affect reproductive performance, although a level of 20% delayed the onset of puberty and reduced piglet liveweight at birth.  A replacement level of 15% of traditional diets for mature Mong Cai sows did not influence reproduction, except for higher piglet live weights at weaning.

 

References

 

AOAC 1980 Official Methods of Analysis (12^th Ed). Association of Official Analytical Chemists. Washington DC

 

Buitrago J A 1990 La yuca en la alimentacion animal. Publication del Centro Internacional de Agricultura Tropical (CIAT). No 85, Cali, Colombia

 

Lam Quang Nga,  Magnusson U  and Ogle B  2000  Comparison of the reproductive performance of indigenous Vietnamese (Mong Cai) gilts and Large White x Mong Cai  crosses given conventional or high-forage diets. In:  Proceedings of SAREC national seminar “Sustainable Livestock Production on Local Feed Resources”  (Editors: T R Preston and R B Ogle). Ho Chi Minh City, January 18– 21, 2000