Livestock Research for Rural Development 5 (1) 1993

Citation of this paper

Growing and ensiling soybean forage between rice crops as a protein supplement for pigs in north Vietnam

Bui Van Chinh, Nguyen Huu Tao and Do Viet Minh

Animal Husbandry Research Institute, Hanoi, Vietnam


In North Vietnam a farming system of two rice crops and one winter crop system is common but only in the land where the summer rice crop is harvested early. The chance for a winter crop to mature is minor in the land where the summer crop is harvested late.

Trials were therefore made to evaluate the use of the land for a forage crop, specifically soybean which was harvested at the flowering stage (60-70 days). The yield was 8,100 kg of green foliage from one ha, which contained 360 kg of crude protein equal to the amount of crude protein normally produced from one ha of soybean harvested as grain. The harvested soybean foliage was chopped and supplemented with rice bran (5 kg rice bran: 100 kg of chopped material) prior to ensiling in a pit. The silage was fed after 60 - 70 days. Crossbred pigs ( Local x Large White) were used as experimental animals. The silage was used to substitute 25-37% of the crude protein in the ration for growing pigs and 20-30% in that for fattening pigs. The silage was palatable.

The control diet consisted of (%): rice bran 30.5; maize 50; fish meal 7.5; groundnut cake 7.5; soybean meal 3; mineral premix 1; vitamin premix 0.5. This was partially substituted in the two treatment groups by soybean silage which provided 25.3% or 37.5% of the total protein. Weight gains from 20 to 50 kg were (g/d): 435"33.3, 406"29.0 and 395"27.6. Results during the fattening phase (0, 19, 31% substitution of the protein with soybean foliage) were weight gain (g/d): 610"12, 600"46.7 and 601"12.6. Feed cost for 1 kg of liveweight gain decreased by 24% in the group substituted with 30% protein from ensiled soybean foliage.

KEY WORDS: Pigs, soybean foliage, silage, growth-fattening, protein



Per capita food production in Vietnam is low, at around 300 kg/year. Therefore food and, in particular, protein-rich feeds for animal production are very limited. In recent years, in several regions in the North of Vietnam, a system of two rice crops and one winter crop has been practiced, but only on land where the summer rice crop matures early. The possibility of growing a winter crop is small in areas where the summer rice crop is harveted late, and where the interval between the two rice crops is only from 60 - 70 days.

As a result, studies on the utilization of land unused for winter crops have been carried out, growing soybean for leaf production, the leaves being preserved as silage for use as a protein-rich livestock feed.

In North Vietnam it is comparatively cold in winter, causing problems for crop production, and the interval between the two rice crops is short (60 - 70 days), which makes it difficult to grow maize and soybeans. Therefore, growing soybeans for leaf production is more suited to the climatic conditions as well as to current farming practices in North Vietnam.

An experiment on soybean silage making has been conducted, with satisfactory results. As is the case with other legume silages, soybean leaf silage requires chemicals, such as formic acid, phosphoric acid, hydrochloric acid etc. to prevent the growth of harmful microorganisms and to promote fermentation by beneficial microorganisms. Since these chemicals are largely unavailable and in any case very expensive in Vietnam, a study on the supplementation of 5% rice bran to soybean leaf for silage has been carried out.


Material and methods

A soybean variety (V74) with a high yield of green material in Vietnam was used. A total of 40 kg of urea, 43 kg P2O5 and 3,500 kg of green manure were applied per ha. The whole plant (leaves included) was harvested at 50-55 days, at the flowering stage. This was then chopped and rice bran added with a ratio of 5 kg rice bran per 100 kg of chopped material before being placed in a silage pit, with the following measurements: 2.5 m x 2.5 m x 1.2 m. The silage was fed after 60 - 70 days to growing crossbred pigs ( Local x Large White). The silage replaced 25 - 37% of the crude protein in the rations of weaning pigs and 20 - 30% in those for fattening pigs. The experiment was conducted at the Phung Thuong Cooperative pig farm, Hanoi.


Results and discussion

Soybean plants harvested at the flowering stage yielded 8,100 kg green material/ha (ie: one ha produced 360 kg crude protein), while growing soybeans for grain production in Vietnam yields on average around 800 kg/ha, equal to 314 kg crude protein. The silage was yellowish in colour, and readily accepted by the pigs. Its nutritional value is presented in Table 1.

The silage had relatively high contents of short chain fatty acids, which are good sources of energy for the pig, which means that the silage provided energy as well as protein, vitamins and minerals.


Table 1:Nutritional composition of the soybean foliage silage
Parameter Fresh basis (%)
pH 4.5
Lactic acid 0.93
Acetic acid 0.45
Butyric acid 0.04
Dry matter 37.5
Crude protein 5.6
Ca 1.67
P 0.44
Crude fibre 7.47



Experiment 1: Utilization of soybean foliage silage for weaner pigs

Weaner pigs at 60 days of age were given the basal ration for a 30 day-preparatory period before the soybean foliage silage was substituted for 25 - 37% of the N x 6.25 in the ration (Table 2). The results for pig performance shown in Table 3.

Table 2: Ration for experimental pigs
  Soybean silage Control
  38 25  
Concentrate feed (kg/d) 1.22 1.39 1.73
Soybean silage (kg/d) 1.87 1.17 0
Crude protein (g/d)      
Total 272.0 259.0 241.0
From silage 102.0 65.5 0


The concentrate feed used in the experiment consisted of: rice bran 30.5% ; maize 50%; fish meal 7.5%; groundnut cake 7.5%; soybean meal 3%; mineral premix 10%; vitamin premix 0.5%. The analyzed nutrient content was: 13.9% crude protein and 5.6% crude fibre. The ration for the experimental pigs is presented in in Table 3.

The fibre content of the soybean foliage silage was rather high, and consequently that in the ration of the experimental groups is also high (9.9 - 11.5% in dry matter). This had a negative effect on the growth rates of the animals, although the difference was not significant (P= 0.05). Feed costs per kg of live weight gain in the silage fed groups were lower than in the control group.


Experiment 2: Utilization of soybean silage for fattening pigs

The average body weight of the experimental pigs at the start of the trial was 40 - 50 kg.

Table 3: Effects of soyabean silage on the performance of weaner pigs

SB silage

  Control 38 25
N x 6.25 (g/d) 272.0 259.0 241.0
N x 6.25 from      
silage (%) 37.5 25.3 0
Liveweight (kg)      
Initial 20.1 20.1 20.2
Final 55.6 56.6 59.4
Daily gain (g) 39527 40629 43533
Feed costs/kg gain,      
% of control 89.8 93.6 100



The concentrate feeds were compounded according to 3 different formulas, with a protein (N x 6.25) content in dry matter in the treatments of soybean silage of 10.5% and 12% versus 13% for the control, respectively. The nutrient composition of the diets for the fattening pigs is presented in Table 4.

Table 4. Composition of diets for the fattening pigs

SB silage

  38 25  
Feed intake (kg/d)      
Concentrate 2.18 2.33 2.60
Soybean silage 1.81 1.20 0
Total N x 6.25 0.329 0.345 0.338
N x 6.25 from      
silage (%) 30.8 19.4 0


The results for pig performance are shown in Table 5.

The data in Table 5 show that the growth rates of the experimental animals were satisfactory (600 - 610 g/day), which is above average for Vietnamese conditions. There were no differences between treatments. Feed costs per kg weight gain of the pigs fed with soybean silage were only 76 - 85% of those of the control animals.

From these two experiments it is clear that soybean silage is more suitable for fattening pigs than for weaners. Using soybean silage in growing pig rations decreases the amounts of protein-rich supplements and concentrates required, significantly reducing feed costs per kg weight gain. The technique of silage making is well accepted by farmers, with the advantages of being able to make it on the farm, and improving the fertility of their land.

Table 5. Effect of soybean silage on the performance of fattening pigs

SB silage

  38 25  
Crude protein (g/d) 329 345 338
Protein from      
silage (%) 30.8 19.4 0
Liveweight (kg)      
Initial 48.5 48.5 48.7
Final 84.7 84.5 85.3
Weight gain (g/d) 60113 60047 61012
Feed costs      
(% control) 76 85 100




Growing a winter soybean crop for leaf production is an effective and profitable way of utilizing otherwise unused land, and producing a protein-rich feed resource. Green material yield reached up to 8,000 kg/ha, equivalent to 360 kg crude protein/ha, which equals the protein yield from one ha of soybeans grown for grain production. Ensiling permits the preservation of protein-rich soybean silage, which can be fed to pigs for up to 6 months after ensiling. The technique is simple, cheap and suited to current Vietnamese conditions.

Soybean silage can substitute for 20 - 37% of the protein in the rations for weaning and fattening pigs with no reduction in performance.

Soybean silage is more efficiently utilized by fattening pigs than by weaners; feed costs for fatteners were reduced by around 24% when 30% of the protein of a conventional concentrate was replaced by the silage.

(Received 1 February 1993)