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

Ensiled fish by-products as a protein supplement
for fattening pigs

 

Le Van Lien, Nguyen Thi Phung, and Le Viet Ly

National Institute of Animal Husbandry, Hanoi

 

Abstract

Experiments were conducted to evaluate methods of preserving fish by-products and to evaluate their use in pig diets. In Experiment 1 whole ground small fish were treated with different levels of formic acid or a mixture of formic acid and a 10% solution of sulphuric acid (1:1). The results showed that ground, whole fish can be preserved by ensiling with at least 2.0% formic acid on a wet weight basis. In Experiment 2 ground small fish was ensiled with  "C" molasses. The pH of the silage was approximately 6 at the time of manufacture. After 5 days of fermentation the pH dropped to under 4.5, and with proportions of 20% molasses or higher this value remained or was even lower after 60 days of storage. In Experiment 3 twenty four crossbred growing pigs (Landrace x Large White) were fed diets without or with fish silage replacing 50% or 100% of the crude protein from fish meal in the control diet (6% or 12% of dietary dry matter). Replacement of fish meal by fish silage resulted in reduced intakes and lower rates of daily gain.  It is concluded that further studies are needed to improve the palatability of the silage and determine the optimum level of replacement.

 

Key words: Pigs, silage, fish, by-products, molasses, growth performance

 

Introduction

Lack of suitable protein sources is one of the major constraints to developing monogastric livestock production in Vietnam. Offal from the fish industry and by-catch fish (fish which are caught incidentally and cannot be sold for human consumption) are one of the main protein sources for livestock. So far the processing method of these fish has been by drying only. However, in many small scale-processing plants there are no facilities for drying and fish waste is therefore discarded and causes pollution problems to the environment (Johnsen and Skrede 1981).

 

The process of making fish silage offers the potential of utilizing fish by-products in areas where the quantity of waste is insufficient to justify the production of fish meal. The process of ensiling fish may therefore become competitive with drying to fish meal due to a number of advantages, including a reduction in pollution problems (fly infestation) and lower energy requirements for processing. The method could also provide extra income both for fishermen and farmers ( Green et al 1983).

In this study processing methods for fish by-products were evaluated, and the nutritive value of the resulting silage for growing pigs under small-scale production conditions was investigated.

 

Materials and  methods

Experiment 1.  Preservation of  fish by-products with acid mixtures

Whole small fish were ground and mixed with different levels of formic acid or mixtures of formic acid and a 10% solution of sulphuric acid (1:1) and stored anaerobically. The concentrations of acid were 1.0, 1.5, 2.0, 2.5 and 3.0% of the wet weight of the fish. The pH values were measured for all treatments at 0, 1, 2, 3, 4, 8 and 12 weeks after ensiling.

 

Experiment 2.  Preservation of  fish by-products with “C” molasses

“C” molasses was added to whole, ground small fish at levels of 10, 15, 20, 25 and 30% of the wet weight of the fish. The mixtures of fish and molasses were fermented anaerobically in plastic containers. The pH values were measured for each treatment at 0, 3,  5,  7,  14,  21  30 and 60 days after ensiling.

 

Experiment 3. Evaluation of fish silage for growing pigs

Diets and feeding

The best fish by-products silage (preserved with 20% molasses [FS]  replaced 50 or 100% of the crude protein in a conventional concentrate to give the following diets:

 

·        Control (0% FSM)

·        FS50 (50% of the crude protein from fish meal in the control diet was replaced by FS)

·        FS100 (100% of the crude protein from fish meal in the control diet was replaced by FS)

 

When the mean pen live weights reached 30 and 60 kg the protein concentrations of the diets were reduced.

 

Animals and Management

Twenty four crossbred growing pigs (Landrace x Large White) with a mean initial live weight of around 15 kg were randomly divided into 3 groups (8 pigs per group, 4 males and 4 females) and individually fed restricted amounts of the experimental diets. Growth rates, feed intakes and feed conversion were measured until the pigs reached the slaughter weight of 90 kg. 

 

 

 

Results and discussion

Experiment 1.

 

Table 2.  Changes in pH of fish ensiled  with different levels of formic acid (FA) or mixtures of formic acid and sulphuric acid (MIX)
Time of storage of silage (weeks)	Proportion of acid  (% of fresh fish weight)
	1.0	-----1.5-----		-----2.0----		----2.5----		----3.0----
	FA	FA	MIX	FA	MIX	FA	MIX	FA	MIX
0	3.87	3.58	4.07	4.32	3.81	3.23	3.29	3.77	3.50
1	4.50	3.85	4.70	4.46	4.23	3.63	4.01	4.05	3.91
2	4.79	4.40	-	4.55	4.75	3.56	4.21	4.11	3.88
3	-	5.70	-	4.53	-	3.63	4.60	4.08	4.45
4		-		4.35		-	-	3.90	-
8				4.42				3.95
12				4.40				3.95

 

The data in Table 2 show that proportions of 1.0 and 1.5 % of formic acid, and up to 2.5% of the mixture of acids, were insufficient to preserve the silage, which started to deteriorate after 2 to 3 weeks of ensiling. With proportions of formic acid of 2.0% and above, and 3.0% of the mixture, the pH of the silage remained below 4.5 during the 3 months of storage.      

 

Experiment 2.

Changes in pH and visual observations were used to assess the quality of fish silage preserved with different proportions of molasses (Table 3).

 

 

At all levels of addition of molasses, the pH values fell within 5 days to acceptable levels, although after 30 days the 10% molasses mixture had started to deteriorate. With molasses concentrations of 20% and above pH values remained below 4.6 two months after ensiling, at which stage visual observations also confirmed that the silage was acceptable, as it had a yellowish colour and pleasant odour.

Experiment 3. 

Mean daily feed intakes for the three diets were similar for the first 35 days of the trial, but from 35 days to slaughter intakes were 30 – 40% higher on the control diet.  These results indicate that palatability of the diet was significantly reduced with the inclusion of the fish silage in the diet.

 

Mean daily weight gains decreased with increasing levels of inclusion of fish silage. Between 35 days and slaughter the mean daily weight gains of the FSM pigs were significantly lower than for the other two diets, probably as a result of lower intakes of the diets containing fish silage. Feed conversion ratios were poorer on the fish silage diets due to the significantly lower weight gains.

 

 

Conclusions

·        Fish can be stored for up to 3 months or longer by mixing with 2% (on a wet weight basis) of formic acid, or with 3% by weight of a mixture of formic and sulphuric acids. Under these conditions the pH remained at 4.3 - 4.4 for the  duration of storage.

·        Fresh, ground fish can be preserved with 10% by weight of “C” molasses for up to 30 days, and for at least 60 days with 20% or more of molasses.

·        Fish ensiled with molasses can replace fish meal in diets for growing pigs, but inclusion rates of 6% (DM basis) or more resulted in reduced intakes and growth rates.

·        Further studies are required to improve the palatability of the silage and determine the optimum rate of inclusion.

Acknowledgements

Thanks are due to SIDA-SAREC for funding support and to Dr. Brian Ogle, Dr. Thomas Preston, Dr. Luu Trong Hieu and others who helped with this study.

 

References

Green S, Wiseman J and Cole D J A  1983 Fish silage in pig diets. Pig News and Information  (4)  3

Johnsen F and Skrede A 1981 Evaluation of fish viscera silage as a feed resource. Chemical Caracteristics. Acta Agriculture Scandinavica 31

 

 

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