Digestibility and nitrogen retention in Mong Cai pigs fed sugar palm (Borassus flabiller) juice and fresh water 
fish ensiled with rice bran and sugar palm syrup

Chiev Phiny and Lylian Rodríguez

University of  Tropical Agriculture, Royal University of Agriculture,  
Chamcar Daung, PO Box 2423, Phnom Penh 3, Cambodia
phiny@uta.edu.kh

Abstract

The present study aimed at testing different combinations of sugar palm syrup and cassava root as additives for ensiling fresh water fish and to determine the nutritive value for pigs of the fish silage.  Small fish  were mixed with rice bran (65% fresh fish, 30% rice bran) and six combinations of sugar palm syrup and chopped fresh cassava root (4.5 and 0.00; 3.6 and 1.1; 2.7 and 2.1; 1.8 and 3.1; 0.9 and 4.2; 0.00 and 5.2%, respectively. The mixtures were placed in plastic bottles, which were sealed hermetically after pressing the contents to remove air.  There were 4 replicates for each sampling time at 5, 10, 15, 20, 25 and 30 days after ensiling. Larger quantities (about 9 kg) of the same mixtures were ensiled for 14 days and fed as a supplement to diluted (40 Brix) sugar palm syrup. Four Mong Cai male pigs  were allocated to the six diets.  The sugar palm syrup and the fish silages were mixed in the ratio of 64: 36 (fresh basis) and fed ad libitum.

The pH of the mixtures was in the range of 6.3 to 6.5 before ensiling and had fallen to 4.5 to 5.0 after ensiling for five days, remaining stable until 30 days. The average pH measured at 5-day intervals between 5 and 30 days was 4.51 for the silage with the highest proportion of palm syrup (4.5%) and was lower than for all the other silages (range of 4.96 to5.06).  All the silages were well preserved as indicated by the smell and absence of spoilage. There was no apparent effect of the different proportions of the additives (palm syrup and chopped fresh cassava root) on the apparent digestibility of dry matter and of nitrogen, or on nitrogen retention. The high values for apparent digestibility of nitrogen (range 80 to 88%) and nitrogen retention (range of 36 to 54% of nitrogen intake) indicate that the method of conservation had retained the nutritive value of the original material. 

It is concluded that ensiling small freshwater fish with rice bran (50% of the fresh weight of the fish) and either sugar palm syrup syrup (7% of the weight of the fish) or freshly chopped cassava root (8% of the weight of fish), or combinations of the two additives, is a satisfactory method of preservation which retains the nutritive value of the fish protein.

 Key words: Fish silage, sugar palm juice, pigs, digestibility, nitrogen retention

Introduction

Sugar palm trees (Borassus flabiller), fresh water fish and rice bran are abundant in Cambodia. The Tonle Sap lake is thought to supply about 70% of the protein consumed by the 10 million inhabitants. The lake was reported in 1990 to occupy an area of 460,000 ha . It is one of the richest inland fishing lakes in the world and is considered to be nearly 10 times as productive as the best fishing grounds in the North Atlantic, with fish yields of at least 65kg/ha, calculated on the basis of the dry season area of the lake. Fishing activities start when the water flows out from the lake into the Tonle Sap river at the beginning of the dry season (December). There are two occasions, in January  and February, when especially large quantities of fish are harvested along the Tonle Sap river. It is traditional practice to sun-dry the small fish that are harvested at this time and to  sell the product to farmers as a protein supplement for pigs and chicken.

Ensiling is an alternative method of preserving fish and a number of methods have been developed for this purpose (Green et al 1983).  Addition of mineral or organic acids, or in situ fermentation of molasses,  are the most common methods, of which the latter appears to be one of the most relevant in tropical countries (Perez 1997), where sugar-rich crops such as sugar cane and sugar palm are commonly grown.

The present study had two objectives:

• To test different combinations of sugar palm syrup and cassava root as additives for ensiling the fresh water fish
• To determine the nutritive value for pigs of the fish silage

Materials and methods   

Location

The experiments were done in the Ecological Farm of the University of Tropical Agriculture (UTA),  situated on the campus of the Royal University of Agriculture, Chamkar Daung village, some 12 km from Phnom Penh. The mean air temperature is in the range of  26 to 29 °C.

Experiment 1: Ensiling fresh water fish 

Procedure

Small fish (less than 5 cm in length) taken at one of the peak harvest periods from Tonle Sap river were purchased in the local market and were partially eviscerated before mixing with rice bran, palm syrup and chopped fresh cassava roots in six different proportions (Table 1), based on previous experiences with ensiling of freshwater fish and palm syrup (Khieu Borin et al 2000). The mixtures were immediately placed in plastic bottles (500 ml capacity), which were sealed hermetically after pressing the contents to remove air.  There were 4 replicates with separate bottles for each sampling time at 5, 10, 15, 20, 25 and 30 days after ensiling. 

Measurements 

Samples were taken of the fresh mixtures prior to ensiling and at 5, 10, 15, 20, 25 and 30 days after ensiling to determine the  pH, which was measured using a digital pH meter. 

Experiment 2:  Digestibility and nitrogen retention in pigs

Experimental design

 The six experimental diets were composed of sugar palm juice as a protein-free energy source supplemented with one of the six silages of the same composition (Table 1) as those used in Experiment 1.  Sugar palm juice (see Khieu Borin and Preston 1995 for background information and composition) was used as the energy source as it is essentially free of protein (1.5% in dry matter) and being composed of soluble sugars can be considered to be 100% digestible. 

Four Mong Cai male pigs ( 8-12 kg liveweight) were allocated the diets according to an unbalanced Latin Square design (4*3) so that each diet was evaluated by two of the four pigs (Table 2). Each experimental period was of 7 days: four days for adaptation and 3 days for collection of faeces and urine. 

The metabolism cages were made from rattan fixed to a wooden frame in a composite unit (1.6m length and 0.7m wide) for 2 animals (Photo 1). The floors were composed of lengths of rattan poles of 1.5cm diameter with 1cm spacing to facilitate passing of the faeces .  Area per pig was 0.56m² (0.7m*0.8m). The cage divisions of half rattan sections were 0.5m high.  The faeces collector, suspended 10cm below the floor, was a rigid sheet of plastic net used traditionally for sealing windows against entrance of insects. Urine fell through the net and was collected over a sheet of polyethylene  suspended in the form of a shallow “V” with the lowest point emptying into a filter placed in a funnel suspended over a plastic bucket. The cages were equipped with automatic water drinkers. 

Photo 1: View of the metabolism cages

Diets and feeding system 

The fish silages were prepared at the beginning of the trial in amounts of 9 kg and with the same composition as shown in Table 1. The mixtures were put in polyethylene bags (20 litres capacity) which were then placed in plastic buckets to facilitate compression of the mixtures to eliminate the air.  The ensiling period was for 14 days.  The sugar palm syrup (Brix = 80 [total sugars 80%]) was purchased in the local market and diluted with water on a 1:1 basis before feeding. 

The silages and the sugar palm syrup were mixed in the ratio 36: 64 (fresh basis) and fed ad libitum.  During the experimental period, the  intakes of palm syrup and fish silage were measured daily by weighing amounts offered and refused.  Samples of the mixtures of sugar palm juice and fish silage, offered and refused, were collected daily for dry matter and nitrogen determination. Dry matter was determined by weighing to constant weight after drying in a micro-wave oven (Undersander  et al 1993). Nitrogen was measured by the Kjeldahl procedure using the Foss-Tecator apparatus for digestion and distillation. Urine was collected and weighed daily, using a few drops of N  H₂SO₄ to keep the pH below 4 in order to preserve the ammonia. The total daily quantities from each pig were stored in a large bucket until the end of the collection period,  when the contents were mixed and a representative sample taken to analyze for nitrogen.  Faeces were collected and weighed daily. The total amount of the faeces for each pig was stored in a freezer (-18ºC) and at the end of the period was mixed, ground and a representative sample taken for analysis of nitrogen (on the fresh faeces) and for dry matter. 

Statistical analyses  

The data for pH of the silages, for  feed intakes, and apparent coefficients of digestibility of nitrogen and dry matter were analysed by ANOVA using the GLM (General Linear Model) option of the Minitab statistical software (Release 12.2). Variables were: silages, sampling dates and error for the silages; and diets and error for the digestibility and intake data of the pigs.

Results and discussion 

Experiment 1: Fish silage 

The pH of the mixtures was in the range of 6.3 to 6.5 before ensiling and had fallen to 4.5 to 5.0 after ensiling for ten days, remaining stable at around these values until 30 days (Table 3; Figure 1).  The average pH measured at 5-day intervals between 10 and 30 days was 4.51 for the silage with the highest proportion of palm syrup (4.5%) and was lower (P=0.001) than for all the other silages (range of 4.96 to5.06).  All the silages were well preserved as indicated by the smell and absence of spoilage.  These pH values are similar to those reported by Le Van Lien et al (2000) who used 2% formic acid or levels of from 10% to 30% “C” molasses as sole additives for ensiling small fresh fish.  They reported that the 10% molasses level was adequate only up to 30 days after which spoilage occurred.  With 20% molasses the silages were well preserved for up to 60 days. Their results and ours are not strictly comparable as in our experiment rice bran  accounted for almost 50% of the silage on a dry matter basis.

Figure1: Changes in pH in fish ensiled with different proportions of palm syrup
(Percentages are shown of the palm syrup) replaced by fresh cassava root 

 Experiment 2: Digestibility and nitrogen retention 

There was no apparent effect of the additives used to ensile the fish (different proportions of palm syrup and chopped fresh cassava root) on feed intake, on apparent digestibility of dry matter and of nitrogen, or on nitrogen retention (Table 4).  The high values for apparent digestibility of nitrogen and daily nitrogen retention reflect the use of whole fish as the protein source and indicate that the method of conservation had retained the nutritive value of the original material. Similar high values for dry matter digestibility were reported for Mong Cai pigs fed sugar cane juice and either duckweed (Rodríguez and Preston 1996) or soya bean meal (Rodríguez et al 1997). The values for nitrogen digestibility are similar to those reported for sugar cane juice and soya bean meal (Rodríguez et al 1997) and higher than for diets of sugar cane juice and either duckweed (Rodríguez and Preston 1996) or ensiled cassava leaves (Du Thanh Hang et al 1997).

The average weight gain of the pigs over the 21 day period of the trial was 99±5.5 g/day, which is lower than the values reported by  Nguyen Van Lai (1998) for Mong Cai pigs of comparable body weight, fed ensiled cassava root waste, rice bran and duckweed, and also much lower than those reported by Khieu Borin et al (2000).  On the assumption that most of the tissue growth of pigs in the 10-14 kg weight range is muscle, then this rate of growth of gain can would be expected to contain of the order of 3 g of nitrogen which is in accordance with the data in Table 4.

Conclusions

Ensiling small freshwater fish with rice bran (50% of the fresh weight of the fish) and either sugar palm syrup (7% of the weight of the fish) or freshly chopped cassava root (8% of the weight of fish), or combinations of the two additives is a satisfactory method of preservation which retains the nutritive value of the fish protein.

Acknowledgements

This research formed part of the thesis of the Senior Author as partial fulfillment of the requirements for the Bachelor of Science degree of  the Royal University of Agriculture.

References

Du Thanh Hang, Nguyen Van Lai, Ly J and Rodriguez D 1997 Nitrogen digestion and metabolism in Mong Cai pigs fed sugar cane juice and different foliages as sources of protein. Livestock Research for Rural Development (9) 2: http://www.cipav.org.co/lrrd/lrrd9/2/hang92 

Green S, Wiseman J and Cole D J A 1983  Fish silage in pig diets. Pig News and Information 4(3): 269-273

Khieu Borin and Preston T R 1995  Conserving biodiversity and the environment and improving the well-being of poor farmers in Cambodia by promoting pig feeding systems using the juice of the sugar palm tree (Borassus flabellifer). Livestock Research  for Rural Development  (7) 2: http://www.cipav.org.co/lrrd/lrrd7/2/5.htm  

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http://www.fao.org/WAICENT/FAOINFO/AGRICULT/AGA/AGAP/FRG/APH132/Contents.htm

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Rodriguez Lylian, Preston T R,  Ly J and Nguyen Van Lai 1997 Parameters of digestion and N metabolism in Mong Cai piglets having free access to sugar cane juice and soya bean meal.  Livestock Research for Rural Development.  (9) 5: http://www.cipav.org.co/lrrd/lrrd9/5/lyli951

Undersander D, Mertens D R and Thiex N 1993 Forage analysis procedures. National Forage Testing Association. Omaha pp 154

Received 18 February 2001

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