Livestock Research for Rural Development 14 (6) 2002

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Digestibility studies in growing pigs fed diets based on full-fat rubber seeds or soya beans supplemented with water spinach

Pok Samkol, Pech Sovanno*, T R Preston and J Ly

University of Tropical Agriculture Foundation,
Royal University of Agriculture, Chamcar Daung, Phnom Penh, Cambodia
poksamkol@uta.edu.kh
* General Department of Rubber Plantation, Chup Rubber Plantation,
Ministry of Agriculture, Phnom Penh, Cambodia

Abstract

A digestibility trial was conducted to evaluate the nutritive value of diets composed of either Cambodian full-fat rubber (Hevea brasiliensis) seeds or soya beans using 16 Mong Cai*Large White pigs. Rubber seeds of unknown falling day and storing period, and extruded soy beans were used in this study. Water spinach (Ipomoea aquatica) was given ad libitum as a complementary protein-rich foliage supplement. The design was a 2*2*2 factorial arrangement to compare the effect of protein source (full-fat rubber seeds or soya beans), DL-methionine supplementation (0 or 0.3%) and animal live weight (40 or 60 kg).

Average crude protein content of the diets was 13.1 ± 1.05% in dry basis and voluntary intake of water spinach was 22.3 ± 2.6 and 16.2 ± 1.4% of the consumed dry matter, for animals of 40 and 60 kg live weight, respectively. There was no significant interaction (P>0.05) amongst any of the studied factors. There was no significant influence of animal live weight on digestibility coefficients. Full-fat rubber seeds were associated with a highly significant decrease in DM and organic matter digestibility, compared with soya beans, but there was no effect on N digestibility, which was always low.

Digestibility indices appeared to be higher in diets supplemented with DL-methionine, and this effect tended to be significant for organic matter digestibility. The high crude fibre content in the diets had a highly significant, negative influence on digestibility of DM and organic matter (R² 0.73 and 0.75, respectively). There was no influence of dietary crude fibre level on N digestibility.

A slight decrease in dry matter digestibility in the rubber seed diet does not necessarily imply a decrease in energy availability to the animals due to the high crude fat content of this diet (on average 12.5 ± 0.74 % in dry basis). It could be suggested that little, if any, N is linked to the cell walls in the rubber seed since in this experiment full-fat rubber seeds accounted for approximately 34 % of the diets.

Key words: pigs, full-fat rubber seed, water spinach, digestibility, nitrogen

Introduction

Rubber plantations in Cambodia are not so great as compared to other countries of South East Asia (see for example FAO 1999). However, in the northeastern Cambodian provinces there are some 39,700 ha of rubber trees (MAFF 2001), from which could be obtained a substantial amount of rubber seed meal, since the annual yield of seeds has been estimated to be 800 to 1200 kg per ha (Siriwardene and Nugara 1972). Until now, Cambodian farmers never used rubber seed as a feeding stuff for pigs, even if Cambodia has a long history of rubber plantations (Pech Sovanno 2002).

Several studies have been devoted to study the potential value as feed of rubber seed meal and water spinach as protein sources in monogastric animals. From the point of view of the nutritive value of the whole rubber seeds for pigs, very little information is available (Siriwanathanukul 1982; Babatunde et al 1990; Nutdechanun 1991; Agumbiade et al 1996). Nevertheless, recently published papers suggest that the nutritive value of Cambodian full-fat rubber seeds is quite high and not greatly impaired by the presence of the highly fibrous husk in the whole seed (Ly et al 2001; Nguyen Thi Tuy and Ly 2002).

On the other hand, it is well known that rubber seed protein is relatively low in DL-methionine (Orok and Bowland 1974; Bressani et al 1983; Narahari and Kothandaraman 1984; Nwokolo 1987). At the same time, rubber seeds contain cyanide precursors, which in turn can be detoxified by the use of methyl groups provided by donor compounds such as DL-methionine (see for example, Bressani et al 1983).

Water spinach has been studied as a source of foliage for pigs in recent years (see for example, Le Thi Men 1999) and, in Cambodia, the use of water spinach for feeding pigs is very common. Nevertheless, little is known concerning its nutritive value as a source of protein in Cambodian rations.

The main objectives of this study were to evaluate, on the one hand, the nutritive value of full-fat rubber seeds and full-fat soya bean as sources of protein in growing pigs fed water spinach ad libitum and, on the other hand, the effect of animal live weight on digestibility indices. The acid insoluble ash technique (Van Keulen and Young 1977) was used to estimatge digestibility indices.

Materials and Methods

The experiment was carried out at the site of the University of Tropical Agriculture Foundation, located at Chamcar Daung near Phnom Penh. The animals were individually housed in an open stable with a concrete floor. During the conduct of this study (November 2001 too March 2002) air temperature, as measured daily at 12:00, was 31.8 ± 1.7^oC.

Four different diets, divided into two types containing either full-fat rubber seeds or full-fat, extruded soya beans were used. The rubber seeds were from the Chup Rubber Plantation, Kampong Cham province. The soya beans were of commercial origin, and were extruded. Both types of seeds were ground before mixing with the other dry components of the feeds. Both diets were supplemented or not with 0.3% DL-methionine.

The dry ingredients of the feeds were prepared every 15 days in a meal form. The composition of the dry fraction of the rations is shown in Table 1. The water spinach was obtained daily from local markets around the University, and thereafter chopped in the fresh state (DM 9.45 %) by a cutting machine. The water spinach was offered ad libitum. The voluntary intake of water spinach was 22.3 ± 2.6 and 16.2 ± 1.4% of the daily fed ration in dry matter basis when the animals were 40 and 60 kg live weight, respectively.

Table 1. Composition of the dry fraction of the feeds given to the pigs (per cent in dry basis)
	Full-fat rubber seeds		Full-fat soy beans
	No DL-methionine	Plus DL-methionine	No DL-methionine	Plus DL-methionine
Full-fat rubber seeds	41.9	41.7	-	-
Full-fat soy beans	-	-	17.1	17.1
Dried fresh water fish	16.2	16.2	8.6	8.5
Cassava root meal	41.9	41.7	74.3	73.9
DL-methionine	-	0.5	-	0.5

The chemical composition of the entire rations is shown in Table 2. Full-fat rubber seeds used in the current study had organic matter 98.0, crude fibre 49.5, NDF 59.7, acid ether extract 22.6 and crude protein (Nx6.25) 9.53 % in dry basis. The diets were formulated to contain 12% crude protein (Nx6.25) in dry basis. However, in practice, the crude protein of the diets was slightly higher than planned and variable, due to the variability in fresh water spinach intake. Taking into account the daily feed ration, the actual level of DL-methionine introduced in the diets decreased from 0.5% to 0.3%. One characteristic of these feeds were its high level of cell walls, accounting on average for 44% and 38% of the rations formulated either with full-fat rubber seeds or soy beans respectively.

Table 2. Chemical characteristics of the rations
	Composition, % in dry basis
	Gross energy¹	Organic matter	Crude fibre	NDF	Crude fat	N x 6.25
40 kg live weight
Full-fat rubber seeds
Without DL-methionine	20.2	92.4	24..9	43.6	12.1	13.5
With DL-methionine	19.9	92.0	25.0	43.5	11.6	13.6
Full-fat soy beans
Without DL-methionine	18.1	92.9	13.3	36.3	4.52	13.6
With DL-methionine	18.1	93.1	11.7	38.8	4.76	12.9
60 kg live weight
Full-fat rubber seeds
Without DL-methionine	20.7	93.1	24.6	43.6	13.3	12.7
With DL-methionine	20.1	92.6	24.6	43.5	12.9	13.6
Full-fat soy beans
Without DL-methionine	19.7	93.5	11.9	39.1	4.73	12.9
With DL-methionine	18.3	93.2	12.3	39.2	4.92	14.2
¹ In kJoule/g DM, calculated according Nehring and Haenlein (1973)

A total of sixteen Mong Cai x Large White pigs, castrated males and females (1:1) were available as part of a growth trial (Pech Sovanno 2002) arranged as a 2x2 factorial of sources of protein (rubber seed or soya bean) and addition or not of DL-methionine. The acid insoluble ash content of feeds and faeces was estimated according to Van Keulen and Young (1977) when the animals were on average 40 and 60 kg, respectively. Faeces were obtained directly from the rectum by grab sampling during the morning, before distribution of the feed.

The DM content of feeds and faeces was determined by drying to constant weight by microwave radiation (Undersander et al 1993). The ash, crude fibre, acid ether extract and N content of the samples were assayed using AOAC (1990) procedures. The cell wall (NDF) of the feeds was estimated following the method of Van Soest et al (1991). The organic matter of feeds and faeces was calculated as 100 minus % ash.

The digestibility indices were calculated by standard procedures following the method of indirect digestibility (Crampton and Harris 1969), using the acid insoluble ash as inert marker or reference substance.

A 2x2x2 factorial arrangement (full-fat rubber seeds or soybean meal), DL-methionine supplementation (0 or 0.3%) and animal live weight (40 or 60 kg) was used in the statistical analysis of the data, using analysis of variance following the general linear model as outlined in the Minitab 12 software (Ryan et al 1985). Regression analysis (Steel and Torrie 1980) was used to relate digestibility indices with dietary components.

Results

During the conduct of the experiment, there were no symptoms of cyanide intoxication in any of the pigs. All the animals were healthy and pig growth did not appear to be impaired by any circumstance due to any anti-nutritional factor. There was no significant influence of animal live weight on any of the digestibility coefficients (Table 3).

Table 3. Digestibility indices in pigs offered diets based on oil seeds and water spinach
	Faecal DM, %	Digestibility, %
	Faecal DM, %	Dry matter	Organic matter	N
Animal live weight, kg
40	34.50	70.9	73.7	66.0
60	35.93	67.7	71.7	62.6
SE ±	3.75	4.01⁺	4.04	2.75
Protein source
Full-fat rubber seeds	43.81	59.8	63.1	63.7
Full-fat soy beans	26.62	78.8	82.8	65.3
SE ±	2.07***	2.10***	2.05***	2.81
DL-methionine supplementation
None	32,83	68.0	71.1	63.2
0.3%	37.61	70.5	74.3	65.3
SE±	3.66***	4.03	4.01⁺	2.79
⁺ P<0.10; *** P<0.001

Faecal DM levels were significantly higher in pigs fed full-fat rubber seeds compared with soya bean seed, and in those receiving DL-methionine. Digestibility coefficients for DM and organic matter were lower (P<0.001) for diets with full-fat rubber seeds compared with diets containing soya beans, but there was no effect on N digestibility, which was always relatively low. Digestibility indices tended to be higher in diets supplemented with DL-methionine. The high crude fibre content in the diets was negatively related with digestibility of DM and organic matter (R² 0.73 and 0.75, respectively) but not with N digestibility (Table 4).

Table 4. Influence of crude fibre content of the diets (x) on digestibility indices (y)
	a	b	S_yx	R²	Sig
Dry matter digestibility	97.50	- 1.52	± 5. 94	0.73	P<0.001
Organic matter digestibility	101.21	- 1.54	± 5.74	0.75	P<0.001
N digestibility	65.19	- 0.05	± 7.97	0.20	P<0.83

Discussion

Two of the most important characteristics of full-fat rubber seeds are the high content of cell walls and fat (Ly et al 2001). In this connection, since the negative influence of high fibre fractions contained in the feed on digestibility indices in pigs is well known (Just 1982; Jorgensen et al 1996), a negative influence of rubber seeds on digestibility indices must be expected. Furthermore, the crude fibre level was very high in the diets examined in the current study, due to the contribution of water spinach to the total feed consumption of the pigs.

In fact it has been shown that if full-fat rubber seeds are included in diets where the other ingredients are very low or devoid of cell walls, such as sugar palm syrup, nutrient digestibility is not seriously impaired, as can be deduced from data shown in Table 5.

Table 5. Fibre fraction level and nutrient digestibility in full-fat rubber seed diets for pigs
Level, %		Rubber seeds, %	Digestibility, %			Reference
Crude fibre	NDF	Rubber seeds, %	DM	OM	N	Reference
Control diets
-	-¹	0	89.7	91.8	88.4	Ly et al (2001)
11.9	39.2	0	81.5	84.9	64.0	Current study
12.3	39.2	0	76.1	79.7	65.7	Current study
-	50.4	0	70.7	70.6	79.1	Nguyen Thi Thuy and Ly (2002)
Rubber seed containing diets
-	10.1¹	18.7	87.7	90.9	86.3	Ly et al (2001)
-	43.7	27.3	73.2	73.3	73.6	Nguyen Thi Thuy and Ly (2002)
24.9	43.6	33.4	59.6	63.7	66.7	Current study
25.0	43.5	34.2	60.0	62.5	60.8	Current study
-	21.8¹	40.5	86.7	87.7	88.6	Ly et al (2001)
¹ Sugar palm syrup was the main energy source of the diet

A high digestibility of the crude fat fraction in whole rubber seeds (Ly et al 2001), could balance to some extent the undesirable influence of cell walls on the digestibility of the feeds as examined in the current study. Therefore, a slight decrease in dry matter digestibility should not necessarily imply a decrease in energy availability to the animals due to the high crude fat content of these same rations: on average 12.5 ± 0.74 % in dry basis (see Table 2).

Taking into account that there was no difference in N digestibility between diets containing rubber seeds or soya bean seeds, it could be inferred that little if any of the N in the rubber seeds is linked to cell walls, especially as in this experiment the full-fat rubber seeds accounted for approximately 34% of the rations. Moreover, in other experiments it has been found that N retention was not impaired due to the inclusion of full-fat rubber seeds in the diet (Ly et al 2001).

From the point of view of the use of water spinach as a complementary protein source in the diet, it was observed in the present experiment that its contribution to the diet, when offered ad libitum in the chopped fresh state, was not affected by the main dietary treatments (source of oilseeds and supplementation with methionione). Iin the present experiment, the contribution of water spinach to overall daily protein consumption was 33.8 and 27.0% at the time when the digestibility indices were determined. These levels imply an appreciable contribution to animal needs of the protein from the water spinach, and support the idea that water spinach can be an important factor to consider in improving the protein nutrition of pigs fed locally available feeds in Cambodia.

We cannot explain the tendency towards higher digestibility indices in diets containing added DL-methionine, but in any event these effects were slight (reaching P<0.10 only for organic matter digestibility). The effect of a synthetic amino acid introduced in the feed on total tract digestibility indices in pigs is difficult to assess, amongst other reasons, due to microbial activity in the hind gut (Jorgensen and Jensen 1994).

Conclusions

Digestibility indices for dry matter and organic matter, but not nitrogen, were reduced when full-fat rubber seeds, rather than full-fat soya bean seeds, were major components of diets for growing diets. Live weight (40 or 60 kg) had no effect on these parameters.

The deleterious effect of the high fibre content of the rubber seeds on organic matter digestibility is nevertheless likely to be compensated in part by the high oil content in this feed.

It is suggested that little, if any, of the N in whole rubber seeds is linked to the cell walls in the husk portion.

Acknowledgments

The authors wish to express their gratitude to the Chup Rubber Plantation (CRP) for providing financial support for this study, and the staff of the University of Tropical Agriculture, for allowing the use of the research farm and laboratory facilities. Thanks are also given to Mr. Keo Saeth for helping during the conduct of this experiment.

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