Use of Lactobacillus plantarum inoculate to
improve the fermentation process of shrimp by-products silage and
evaluation of the silage as a protein source for
ducks
Le Van Lien, Pham Thi Thoa, Nguyen Viet Thai and Nguyen Huu Tao
NIAH, Hanoi, Vietnam
Lienvlv40@yahoo.com
Abstract
Ensiling of shrimp by-product using a lactic acid bacteria inoculum created a rapid fall in pH to around 4.5 after 3 days and increased the lactic acid concentration to a level which is favorable for the storage and preservation of the by-product. Two hundred growing ducks were fed a diet without or with shrimp by-product silage (SS), with 25, 35 or 55% replacing a commercial feed.
Daily weight gains were not affected by inclusion levels of the SS at up to 35% of the diet, but gains were lower at the 55% replacement level. Replacing 55% of the commercial concentrate by SS improved the feed conversion rate and the cost of feed per kg gain by 33.3 %.
The
results show that shrimp by-product silage can be successfully used
in diets for growing Bau ducks at levels up to 35% of the diet
fresh weight, without affecting growth performance. At higher
levels of inclusion, up to 55%, growth rates were reduced, but the
economic efficiency was improved.
Keywords: Ducks, feed conversion, growth, Lactic acid
bacteria, molasses, silage
Introduction
In Vietnam, shrimp by-products account for about 50% of the total raw shrimp weight, and over 80,000 million tonnes were produced in 2000 (General Statistical Office 2001). Shrimp by-products have a high protein content and can be a good substrate for biological ensiling, especially in the tropics, where the warm and humid climate makes ensiling an attractive preservation method (Levin 1994). In Vietnam, ensiling without starter culture (lactic acid bacteria) but with sugar cane molasses, cassava root meal or rice bran has been used. The silage was successfully fed to growing pigs and chickens (Lien et al 1994; Ngoan et al 2000; Le Duc Ngoan 2002). While the silage used in previous studies was of good quality, it sometimes takes too long for the pH to be reduced, due to low numbers of lactic acid bacteria in shrimp by-products. In traditional methods of natural fermentation this can occasionally result in unstable end-products.
Therefore the present study was
carried out to evaluate a method for the more rapid preservation of
shrimp by-products by adding a starter culture (lactic acid
bacteria) to the mixture of shrimp by-products and molasses, and on
the use of the resulting shrimp by-products silage for growing
local ducks.
Materials and methods
Ensiling process
Shrimp by-products were collected from Hai Binh - Tinh Gia -
Thanh Hoa province, and molasses from the sugar factory in Thanh
Hoa province. The starter culture (Lactobacillus plantarum)
was provided by the Institute of Biotechnology in Hanoi. Different
amounts of inoculate (0, 5 and 10%) were added to the mixture of
ground shrimp by-products and molasses at the ratio of 4 : 1 on a
wet weight basic. The mixtures were placed in plastic bags and
sealed to prevent air contamination. The bags were put in buckets
and stored at room temperature (20-300C). pH and
organic acid concentrations (acetic, butyric and lactic acid) were
measured for each treatment at 0, 3, 5, 7, and 10 days after
ensiling.
Feeding trial
The feeding trial was conducted at the poultry breeding station in Thanh Hoa province. Two hundred local (Bau) growing ducks were divided into 4 groups of 50, according to a completely randomized block design. There were 4 diets with increasing levels of shrimp by-products silage (Table 1).
|
Table 1. Composition of diets, fresh basis (%) |
||||
|
|
SS0 |
SS25 |
SS35 |
SS55 |
|
Shrimp by-product silage |
0 |
25.0 |
35.0 |
55.0 |
|
Commercial feed (Guyo 2) |
100 |
75.0 |
65.0 |
45.0 |
|
Crude protein (%) |
18.0 |
16.1 |
15.0 |
13.3 |
|
Dry matter (%) |
78.0 |
70.0 |
67.0 |
56.0 |
|
ME (Kcal/kg DM) |
2800 |
2644 |
2581 |
2457 |
|
NaCl (%) |
0.2 |
0.3 |
0.3 |
0.3 |
|
Calcium (%) |
1.3 |
1.5 |
1.6 |
1.9 |
|
Phosphorus (%) |
0.6 |
0.5 |
0.5 |
0.5 |
Feed offered and refusals were weighed and recorded
daily. Live
weight of the ducks was measured weekly.
Results and discussion
Effect of lactic acid bacteria on fermentation
process for ensiling shrimp by-products with
molasses
Effects of the starter culture in pH change of
the silage
The starter culture was prepared by mixing the bacterial strain with cereal containing some fermentable sugar. A 5-10% starter culture was used, which in solution contained about 1.05 x 109 CFU lactic acid bacteria. This preparation was mixed with the silage material, consisting of shrimp by-products and molasses in a ratio of 80 : 20. This resulted in a rapid decrease in the pH values of the silage, as shown in Table 2 and Figure 1).
|
Table 2. Effects of concentration of starter culture and incubation time on the pH of shrimp silage |
|||||
|
Concentration of starter culture (%) |
Incubation time (days) |
||||
|
|
0 |
3 |
5 |
7 |
10 |
|
0 |
7.07 |
5.87 |
5.17 |
4.94 |
4.22 |
|
5 |
7.02 |
4.52 |
4.29 |
4.15 |
4.11 |
|
10 |
7.00 |
4.05 |
3.95 |
4.28 |
4.20 |
Figure 1: Effect of starter culture concentration (%) and
incubation timeon the pH of ensiled shrimp wate
Concentrations of starter culture
of 5-10% reduced the pH to 4.52 - 4.05 after 3 days at room
temperature (20-300C). Meanwhile in the control
treatment without starter culture, it took 10 days to reach these
pH values. This rapid fall in pH is important in preserving silage
because it decreases concentrations of undesirable bacteria (Le
Thanh Binh and Pham Ngoc Lan 1997).
Effects of starter culture on organic acid production
during the fermentation of shrimp by-product silage
The dynamics of lactic acid, acetic acid and butyric acid production in the silage were studied with respect to the time of incubation and level of starter culture added (Table 3).
|
Table 3. Concentration of lactic, acetic and butyric acids in shrimp by-product silage (%) |
||||
|
Days of incubation |
Starter culture |
Lactic acid |
Acetic acid |
Butyric acid |
|
Three |
0 |
3.11 |
0.53 |
0.18 |
|
5 |
3.53 |
0.97 |
0.10 |
|
|
10 |
3.70 |
0.91 |
0.09 |
|
|
Ten |
0 |
3.10 |
1.04 |
0.08 |
|
5 |
3.96 |
1.04 |
0.00 |
|
|
10 |
4.01 |
1.18 |
0.00 |
|
At all ensiling
times and at every level of starter culture, lactic acid production
was very high, with concentrations reaching 3 to 4%. The concentration
of acetic acid was much lower and there was essentially no butyric acid, which
is the main product of anaerobic bacteria and which results in poor feed
quality. In the silage with 10% of the starter culture the amount
of lactic acid at 10 days of incubation was higher than in silage without
the culture (4.0 and
3.1%, respectively).
Effects of level of shrimp by-product silage on
daily live weight gains and feed conversion of growing ducks
The growth rate on the 55% silage level (SS55) was lower than for the other treatments (Table 4) but there were no differences between the control diet and silage levels of 35 and 25%.
|
Table 4. Growth rate of Bau ducks fed silage of shrimp by-products and molasses as replacement for a commercial feed |
||||
|
|
SS0 |
SS25 |
SS35 |
SS55 |
|
N0 of experimental ducks |
50 |
50 |
50 |
50 |
|
Initial body weight (g) |
403 |
383 |
402 |
424 |
|
Final body weight (g) |
1750 |
1700 |
1630 |
1600 |
|
Live weight gain (g/day) |
29.9 b |
29.2 b |
27.2b |
26.1a |
|
Dry matter intake (g/head/day) |
71.1 b |
60.0 b |
53.3 b |
44.4a |
|
Dry matter conversion (kg/kg) |
2.3 b |
2.0 b |
1.9 b |
1.7 a |
|
Feed cost/kg of LWG (VND/kg) |
11,140 |
9,320 |
9,205 |
7,425 |
|
Feed cost/kg of LWG (% of SS0) |
100.0 |
83.6 |
82.6 |
66.6 |
|
a,b Means with different letters within rows are different at P < 0.05 |
||||
Despite the lower growth on the high silage level, feed conversion and economic benefits were best on this diet. This indicates that the problem was probably the lower palatability (Figure 2), perhaps due to too high a concentration of lactic acid, but that the nutrients in the silage were used efficiently in direct proportion to the level of silage (Figure 3).
 |
 |
|
|
Figure 2: Effect of level of shrimp silage on DM intake in growing ducks |
Figure 3: Effect of level of shrimp silage on DM feed conversion in growing ducks |
Conclusions
-
Addition of 5 to10% of a Lactobacillus plantarum starter culture to the shrimp by-product silage fermentation material resulted in a more rapid fall in pH to between 4.52 and 4.05 after 3 days of fermentation. Without a starter culture it took 10 days for the material to reach these pH values.
-
Lactic acid concentration in the shrimp by-products silage with a starter culture was higher than in silage without the starter culture
-
Feed conversion rate and economic benefits in growing ducks were in direct proportion to the level of shrimp silage in the diet, replacing a commercial concentrate.
References
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Uppsala.
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