Livestock Research for Rural Development 9 (1) 1997

Citation of this paper

Duckweed (Lemna spp) as protein supplement in an ensiled cassava root diet for fattening pigs

Bui Hong Van, Le thi Men, Vo van Son and T R Preston*

Department of Animal Husbandry, Faculty of Agriculture,
Cantho University, Vietnam
*University of Tropical Agriculture, Thu Duc, Ho Chi Minh City, Vietnam


An experiment was carried out during 120 days in 1995 at the experimental farm of Cantho University using 24 pigs (Yorkshire X Landrace-Baxuyen) allotted in a completely randomized design with two treatments and three replications. The pigs had an average initial liveweight of 25.8 kg and were fed (ECR) ensiled cassava root and duckweed (Lemna spp) with a protein supplement or (control) a concentrate diet based on rice by-products.

 There were no significant differences in daily weight gain or feed conversion between treatments. The pigs fed ensiled cassava root and duckweed had thinner back-fat as compared with control pigs (P= 0.002).

 It is concluded that a diet based on ensiled cassava root and with duckweed (Lemma spp) replacing part of the protein supplement can replace the rice by-products traditionally used to fatten pigs in Vietnam.

 Key words: Pigs, ensiled cassava root, duckweed, fattening



The Mecong delta, with a large acid-sulphate soil area, is the major rice-producing region in Vietnam. It also has good potential for growing sugar cane and cassava and the extensive water surfaces create opportunities for cultivation of water plants, especially water spinach (Ipomoea aquatica) and duckweed (Lemna spp).

 Previous research in Vietnam, on making better use of local feed resources was with by-products of sugar cane, showed that AA@ molasses and crude sugar could replace completely cereal grain products in the diets of fattening and breeding pigs (Bui Hong Van and Le Thi Men 1990; Bui Hong Van and Le Thi Men 1992; Bui Huy Nhu Phuc and Luu Trong Hieu 1993; Bui Huy Nhu Phuc 1995).

The aims of the present study were:

Materials and methods

The trial was conducted at the experimental farm of Cantho university from April to July 1995 and lasted for 120 days. The experimental animals were 24 crossbred pigs (Yorkshire X Landrace-Baxuyen) aged 3 months and with a mean live weight of 25.8 kg. The experimental design was a randomized block consisting of 2 treatments and 3 replications.

 The composition of the experimental diets is shown in Table 1. The concentrate used in the control diet contained broken rice 60, rice bran 33, Soya bean meal 2 and fishmeal 5. The ensiling of the cassava roots was done using the procedure described earlier (Le Thi Men et al 1997). Whole cassava roots were washed, chopped to thin chips and raw sugar added at the rate of 5%. The time of ensiling was 3 weeks. The duckweed was grown in earth-lined ponds fertilized with biodigester effluent as described by Bui Xuan Men et al (1996).


Table 1: Composition of experimental diets for fattening pigs (ECR = ensiled cassava root)



Dry matter basis












As % of DM



Intake, g/day




Results and discussion

Mean values for growth, feed intake and conversion are in Table 2. There were indications (P=0.08) that the pigs fed the diet based on rice by-products had slightly (5%) higher growth rates than those fed the ensiled cassava root diet. Conversion rates were similar for both treatments. The pigs fed ensiled cassava root and duckweed had thinner back-fat as compared with control pigs (P= 0.002).


Table 2: Mean values for weight gain, feed intake and conversion, for pigs fed a diet of rice by-products as compared with ensiled cassava root and protein supplement plus fresh duckweed (12 pigs per treatment)




Live weight (kg)






Daily gain




Feed intake (kg/d)












Total DM







Back fat depth (cm)





Little work appears to have been done on the feeding of duckweed to fattening pigs perhaps because emphasis in earlier studies was on producing a dry meal rather than developing a system to use the freshly harvested duckweed. Also the use of fertilizer or biodigester effluent to raise the protein and decrease the fibre level was perhaps not understood. Thus, in an experiment with a low protein/high fibre duckweed meal (23% N*6.25 and 7.5% fibre in DM) pig growth was reduced by 30% over 40 days when there was 10% of duckweed meal in the diet (Haustein et al 1992). In contrast, in a parallel study to the present one, the replacement of 50% of a conventional protein source (fish meal and soya bean meal) with fresh duckweed in the diet of breeding sows led to bigger litter size, improved rates of survival and heavier litter weights (Le thi Men et al 1996)

 Rodriguez and Preston (1996) reported that when fresh duckweed was fed as the only supplement to sugar cane juice, the digestibility of the total diet dry matter was 83% with duckweed supplying 45% of the diet dry matter. Protein (N*6.25) digestibility at this level of duckweed was 73%. In both these latter studies the protein content of the duckweed was over 30% in the dry matter.


Conclusions and Recommendations

It is concluded that a diet of ensiled cassava root with 25% of the protein provided by fresh duckweed can totally replace rice by-products and protein meals in diets for fattening pigs with no reduction in growth rate or conversion and with leaner carcasses.


This research was supported by the International Foundation of Science through a grant (B/2232-1) to Ms Le Thi Men.


Bui Huy Nhu Phuc and Luu Trong Hieu 1993 A molasses in diets for growing pigs. Livestock Research for Rural Development (5) 2:11-15

Bui Hong Van and Le Thi Men 1992 Feeding of sugar cane juce and "a" molasses to fattening pigs. Livestock Research for Rural Development (4) 3:1-5

Bui Hong Van and Le Thi Men 1990 A molasses in diets for growing pigs. Livestock Research for Rural Development (2) 3:76-79

Bui Huy Nhu Phuc 1993 The use of sugar cane juice and molasses in the diet of growing pigs. Livestock Research for Rural Development (5) 2:7-10

Haustein A T, Gonzalez A E, Gillman R H, Campos K, Caldas M, Armas F, Madrid C and Castro M 1992 Uso de Lemnaceae en la alimentacion del ganado porcino. Asociación Benéfica PRISMA Facultad de Medicina Veterinaria, Universidad Nacional Mayor de San Marcos

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Le thi Men, Bui Hong Van, Mai Thi Chinh and Preston T R 1997 Effect of dietary protein level and duckweed (Lemna spp) on reproductive performance of pigs fed a diet of ensiled cassava root or cassava root meal. Livestock Research for Rural Development. Volume 9, Number 1

Rodríguez L and Preston T R 1996 Comparative parameters of digestion and N metabolism in Mong Cai and Mong Cai Large White cross piglets having free access to sugar cane juice and duck weed. Livestock Research for Rural Development (8) 1:72-81

Received 15 November 1996