Livestock Research for Rural Development 14 (2) 2002

 A short-term study of growth and digestibility indices in Mong Cai pigs fed rubber seed meal

Nguyen Thi Thuy* and J Ly**

University of Tropical Agriculture Foundation
Chamcar Daung, PO Box 2423, Phnom Penh, Cambodia
*Present address: Animal Husbandry Department, Cantho University, Cantho City, Vietnam
** Visiting scientist at the UTA Foundation
Present address: Swine Research Institute, Punta Brava near Havana City, Cuba and



A 2x2 factorial arrangement was employed in a short-term study (28 days) of growth and digestibility indices in four Mong Cai and four Large White female pigs weighing on average 22.9 kg fed ad libitum diets containing rubber seed meal (0 or 27%) as replacement for rice bran.

There was no significant interaction for genotype x diet. Daily feed intake and live weight gain were lower  (P<0.01) in the Mong Cai as compared to the Large White gilts (1.36 and 2.09 kg DM/day;  273 and 533 g/day). The Mong Cai genotype also had a poorer (P<0.05) DM conversion.  Rubber seed tended to increase feed intake (2.01 and 1.45 kg DM/day respectively), but had  no effect on daily gain and feed conversion.

There were neither genotype nor diet effects on total tract digestibility of DM, organic matter, NDF and N.  Mong Cai appeared to digest N less efficiently than the Large White genotype and the reverse tended to be true for NDF digestibility. Rubber seeds in the diet appeared to negatively influence NDF digestibility. N digestibility was high in all cases.  There was no correlation between DM (or organic matter) digestibility and performance traits. Similarly there was no significant interaction between  feed conversion and any other  indicator.

Differences in performance traits between Mong Cai and Large White female pigs appear to be  more marked than differences in total tract digestibility indices. There appear to be no disadvantages if substantial amounts of rubber seeds (27% in diet DM) are used for feeding pigs. However, more performance data are necessary in order to assess the  long-term effects of rubber seeds as a feed resource for pig production.

Key words: pigs, genotype, rubber seed, digestibility, performance traits


Rubber seed is one of the by-products obtained from the rubber tree (Hevea brasiliensis) which is widely grown in South East Asia. The crude protein content of rubber seeds and its products can range from 12% in whole rubber seeds to 27% in commercial decorticated rubber seed oil meal (Narahari and Kothandaraman 1984). However, rubber seeds contain a toxic factor, the presence of which could involve certain problems in their use as animal feed. Even so, the toxic factor, which is recognized to be a cyanogenic glucoside, decomposes slowly during storage even with no further detoxifying treatment (see for example Ong and Yeong 1978; Narahari and Kothandaraman 1984).

From earlier studies of Siriwardene and Nugara (1972) and Fetuga et al (1977) to that of Agumbiade et al (1996), several experiments conducted with chickens and pigs have been reported with different types of rubber seed by-products. Nevertheless, very little is known of the feeding value of whole rubber seeds in pigs. In this connection, data from Ly et al (2001) suggest that Cambodian whole rubber seeds used in pig diets have high digestibility indices of organic matter and N. The use of whole rubber seeds in animal feeding is considered to be of interest, because in many countries of South East Asia, where rubber production is substantial, rubber tree plantations are mainly managed by smallholders (Horne et al 1994), thus the whole rubber seeds can be fed to their own animals in an integrated farming system.

The use of indirect methods to determine total tract digestibility of diets used in performance trials can be considered to have practical consequences, since the determination of the nutritive value of the diet can be done in animals fed either on-farm or on-station. In this connection the use of acid insoluble ash as an inert marker has been proven to be satisfactory both in ruminants (Van Keulen and Young 1977) and in  pigs (Ly and Samkol 2001).

The aim of the present communication is to report preliminary data on the feeding value of Cambodian whole rubber seeds for pigs, arising from a short-term growth study conducted with two pig genotypes fed whole rubber seed meal.

Materials and methods

Characteristics of the rubber seeds and diets

Rubber seeds from plantations in the Cambodian province of Kampong Cham were ground after an unknown period of storage, then mixed with the other components of the diets. The characteristics of the whole rubber seeds after grinding were DM 84.9% and organic matter (OM) 96.8, NDF 65.9, crude protein (Nx6.25) 13.5 and crude fat 27.3% in dry basis respectively. Cyanide content determined by AOAC (1990) procedures was 61.2 mg/kg DM.

Diets were formulated to contain 22% crude protein (Table 1) and rubber seeds were introduced in the diet as a partial substitute of rice bran. Fresh water dried fish and rice bran were of local origin and were purchased in Phnom Penh markets. The cassava bran was a by-product from cassava starch factories in Kampong Cham, and was incorporated into the diets after grinding.

Table 1. Main ingredients and chemical composition of the diets    (percentage  in dry basis)


Whole rubber seeds, %







Cassava bran



Rice bran



Dried fresh water fish



Whole rubber seed






Vitamins and minerals1






Dry matter



Organic matter






Crude protein



1 According to NRC (1998) requirements for vitamins and minerals

Animals and general management

Eight female pigs including four Mong Cai animals and four Large White, weighing on average 23 kg, were allocated at random to two treatments consisting of the two diets described in Table 1. Both diets were offered ad libitum. The animals were housed in individual pens in an open stable with cement floor. Water was available through drinking nipples. Feed refusal and live weight were recorded daily and weekly, respectively.

Two weeks after starting the feeding period, faecal samples were obtaining from every pig immediately after voiding, in the morning. Samples of feeds and faeces were thoroughly mixed and stored at -20 C for subsequent analysis.

Analytical procedures

Dry matter content in every sample was estimated by microwave radiation (Undersander et al 1993). Ash and N were determined following standard procedures (AOAC 1990) and NDF analyses were carried out according to the method of Van Soest et al (1991). The acid insoluble ash concentration in faeces was determined by treating the ash with a HCl 2N solution (Van Keulen and Young 1977). The same analytical techniques were applied to feeds. In addition, pH values were estimated in fresh aliquots of faeces with the aid of a glass electrode.

Biometrical evaluation

The experiment was designed as a 2 x 2 factorial arrangement where the first factor was the genotype and the second factor was the diet. Standard techniques of analysis of variance were performed according to Steel and Torrie (1980). The general linear model included in the Minitab statistical software (Ryan et al 1985) was used in all cases. The Pearson correlation matrix was used as a screening search for any interdependence amongst performance traits and digestibility indices. In the appropriate cases the regression analysis was conducted following Steel and Torrie (1980) methodology.

Results and discussion

During the experiment the animals were generally in good health and no negative symptom associated with the consumption of whole rubber seeds was observed. There were no significant interactions between genotype and diet.

As shown in Table 2, daily feed intake and gain were lower (P<0.01) in the Mong Cai as compared to the Large White gilts. In comparison with the Large White, the Mong Cai genotype showed a poorer  (P<0.05)  DM conversion. Very little is known about growth traits in Mong Cai pigs. However, the results of the present experiment are in agreement with other reports indicating a slower growth rate of Mong Cai animals (Molenat and Tran 1991; Nguyen et al 1996; Hoan and Nguyen 2000). Perhaps the lower growth rates could be associated with a decreased voluntary intake in Mong Cai pigs, as was observed in this study.

Incorporation of rubber seeds in the diet tended  to increase daily feed intake (P<0.10), but there was no diet effect on growth rate and feed conversion. Variability amongst animals was high when overall performance traits were considered.  The increase in voluntary feed intake could be related to the increase in cell wall content of the diet formulated with rubber seed. It has been argued that pigs tend to increase voluntary feed intake in direct relationship with the level of fibrous materials included in the feed (see Close 1993) in order to compensate the decrease in energy density of the diet. However, it is doubtful that this hypothesis could fully explain the results obtained in this experiment, due to the fact that whole rubber seeds are oily materials. An unexpected low bulkiness of the diet as defined by its water holding capacity (Kyriazakis and Emmans 1995; Tsaras 1998), could have contributed to enhance voluntary feed intake in pigs fed whole rubber seeds.

Table 2. Effect of genotype and diet on performance traits of Mong Cai and Large White pigs


DM intake,

Live weight gain, ,g/day

DM conversion





Mong Cai




Large White
















Rubber seed








+ P<0.10; * P<0.05; ** P<0.01

Results from the performance test obtained in this study do not support the previous data found by Rajaguru and Ravindran (1979) who used defatted rubber seed up to 30% in diets for growing pigs. Rajaguru and Ravindran (1979) considered that the amino acid inbalance was the primary cause of poor daily gains and feed conversion in their trial. Even with lower levels of rubber seed in the diet, Babatunde et al (1990) observed a trend for the performance of pigs to decline with increased levels of rubber seeds as replacement for soybean meal. In contrast, Stosic and Kaykay (1981) did not find any constraint in growing pig performance when a diet was formulated with 40% of non-defatted rubbed seed kernel, the other protein source being skim milk powder. It is probable that the animal protein (skim milk powder) used by Stosic and Kaykay (1981) and the dried fish used in the present study tended to balance the deficit in sulphur amino acids derived from the use of rubber seeds in the diets of the  pigs.

Overall DM and organic matter digestibility were rather low, probably due to the high cell wall content of the diets (see Table 1). On comparing both genotypes, no breed differences regarding the apparent digestibility coefficients of any of the measured chemical constituents of the diets were noted (Table 3). Even so, Mong Cai pigs appeared to digest N less efficiently than the Large White genotype, while the reverse tended to be true for NDF digestibility. Rubber seeds in the diet appeared to negatively influence NDF digestibility, probably due to the high cell wall content. On the other hand, it is well established that the increase in fibrous materials in the diet results in a reduction of energy density in the diet (Fernandez and Jorgensen 1986). Nevertheless, the negative influence of cell walls from rubber seeds on energy utilization could be greatly compensated by a high crude fat digestibility (Ly et al 2001b). N digestibility was high in all cases.

Table 3. Nutrient digestibility in Mong   Cai and Large White pigs fed ground whole rubber seeds


Faecal pH

Digestibility, %











Mong Cai






Large White
























Rubber seed












There was a significant positive correlation among N, DM and organic matter digestibility coefficients. Furthermore, DM and organic matter digestibility were highly correlated ( R2 0.99; P<0.001).  A similar relationship was found in other experiments conducted with growing pigs fed graded levels of rubber seed meal in the diet (Bun Tean et al 2002), thus suggesting that the determination of DM digestibility could be a practical approach to digestive evaluation of other nutrients in pig diets.

Daily gain was positively correlated (P<0.05) with feed intake and N digestibility. Furthermore, feed intake was significantly correlated with NDF fraction digestibility. These results suggest that pigs with a high voluntary feed intake and high cell wall utilization, at the time show a low total N digestion parameter. This was the case in the animals fed with rubber seed meal. There was no significant interaction between feed conversion and any other parameter.  

There was no correlation between digestibility indices for DM and organic matter and growth performance. It is possible that the lack of significant response in these parameters was due to a small population size. In this respect, Siers (1975) studied the Pearson correlation coefficients between performance traits and digestibility indices in a population size of 66 Yorkshire pigs, and found that fast growing pigs ate more feed, had a better  feed conversion but lower total digestibility of DM, N and fat.

Table 4. Pearson correlation coefficients for digestibility and performance parameters of Mong  Cai and Large White pigs fed diets with and without rubber seed meal


















































DMD, OMD, NDFD and ND are DM, organic matter, NDF and N digestibility respectively. INT, GAIN and CONV are daily DM intake, daily gain and DM feed conversion respectively
P<0.05 for r>0.64



The authors would like to thank Mr. Hean Pheap, from the Maharishi Vedic University (Prey Veng) for the care of the animals and his assistance in the laboratory, and Mr. Pok Samkol for his assistance in the laboratory. This experiment could be carried out thanks to funds supplied by the MEKARN Program for Research Cooperation for Livestock-based Sustainable Farming Systems in the Lower Mekong Basin.


Agumbiade J A, Wiseman J and Cole D J A 1996 Improving the nutritive value of Nigerian rubber kernel (Hevea brasiliensis) products through processing. II. Apparent nutrient and metabolizable energy values. Tropical Agriculture (Trinidad) 73:124-132


AOAC 1990 Official Methods of Analysis. Association of Official Analytical Chemists. 15th edition (K Helrick editor). Arlington pp 1230


Babatunde G M, Pond W G and Peo Jr E R 1990 Nutritive value of rubber seed (Hevea brasiliensis) meal: utilization by growing pigs of semipurified diets in which rubber seed meal partially replaced soybean meal. Journal of Animal Science 68:392-397


Bun Tean, Keo Sath, Pok Samkol and  Ly J  2002 Utilization by pigs of diets containing Cambodian rubber seed meal. Livestock Research for Rural Development 14 (1): 


Close W H 1993 Fibrous diets for pigs. In: Animal Production in Developing Countries (M Gill, E Owen, G E Pollot and T L J Lawrence, editors) British Society of Animal Production Occasional Publication No 16 p 107-116


Fernandez J A and Jorgensen J H 1986  Digestibility and absorption of nutrient as affected by fiber content in the diet of the pig. Quantitative aspects. Livestock Production Science. 15:53-59


Fetuga B C, Ayani T O, Olaniyan A, Balogun M A, Babatunde G M and Oyenuga V A 1977 Biological evaluation of para-rubber seed (Hevea brasiliensis). Nutrition Report International 15:497-510


Hoang N D and Nguyen K D 1996  Pig breeding in Central Vietnam and its improvement. In: Exploring Approach to Research in the Animal Science in Vietnam (W J Pryor, editor). Australian Centre of International Agricultural Research. Camberra p 123-126


Horne P M, Ismail T and Chong Dai Thai 1994  Agroforestry plantation systems: sustainable forage and animal production in rubber and oil palm plantation. In: Agroforestry and animal production for human welfare (J W Copland, A Djajanegra and M Sabrani, editors). Australian Centre for International Agricultural Research Proceedings No 55. Camberra p 89-98


Kyriazakis I and Emmans G C 1995 The voluntary food intake of pigs given feeds based on wheat bran, dried citrus pulp and grass meal, in relation to measurements of food bulk. British Journal of Nutrition 73:191-207


Ly J, Chhay Ty and Chiev Phiny 2001 Evaluation of nutrients of rubber seed meal in Mong Cai pigs. Livestock Research for Rural Development 13(2):


Ly J, Pok Samkol and T R Preston 2001 Nutritional evaluation of tropical leaves for pigs: Pepsin/pancreatin digestibility of thirteen plant species. Livestock Research for Rural Development 13(5):


Molenat M and Tran T T 1991 La production porcine au Vietnam et son amelioration. World Animal Review 68(3):26-36


Nguyen T, Phung T V, Pham H D, Nguyen N, Nguyen K Q and Vo T H 1996 Improvement of productivity and meat quality of pigs in the Red River Delta region by crossbreeding. In: Exploring Approach to Research in the Animal Sciences in Vietnam (W J Pryor, editor). Australian Centre of International Agricultural Research. Camberra p 86-89


Narahari D and Kothandaraman P 1984  Chemical composition and nutritional values of para-rubber seed and its products for chickens. Animal Feed Science and Technology 10:257-267


NRC 1998  Nutrient Requirements of Swine. National Academy of Science. 9th edition. National Academic Press. Washinton D C


Ong H K and Yeong S W 1978  Prospects of the use of rubber seed meal for feeding swine and poultry. In: Proceedings of the Symposium of Feeedingstuffs for Livestock in South East Asia (C Devendra and R I Hutagalung, editors). Malayasian Society of Animal Production. Kuala Lumpur p 337-344


Ragajuru A S B and Ravindran V 1979 Rubber seed meal as a protein supplement in growing swine rations. Journal of the National Science Council of Sri Lanka 7:101-104


Ryan B F, Joiner B L and Ryan Jr T A 1985 Minitab (2nd edition) Hilliday Lithograph


Siers D G 1975 Chromic oxide determined digestion coefficients and their relationship to rate of gain and feed efficiency in individually fed Yorkshire boars, barrows and gilts. Journal of Animal Science 41:1266-1269


Siriwardene J A  and Nugara D 1972  Metabolizable energy of rubber seed meal in poultry diets. Ceylon Veterinary Journal 20:61-63


Steel R G D and Torrie J A 1980 Principles and Procedures of Statistics: a Biometrical Approach. McGraw-Hill Book Company (second edition) Toronto pp 481


Stosic D D and Kaykay J M 1981 Rubber seeds as animal feed in Liberia. World Animal Review 39(3):29-39


Tsaras L N, Kyriazakis I and Emmans G C 1998 The voluntary food intake of pigs given feeds based on wheat bran, dried citrus pulp and grass meal, in relation to measurements of food bulk. British Journal of Nutrition 73:191-207


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


Van Keulen J and Young B A 1977 Evaluation of acid-insoluble ash as natural marker in ruminant digestibility. Journal of Animal Science. 44:282-286


Van Soest P J, Robertson J B and Lewis B A 1991 Methods for dietary fiber, neutral detergent fiber and non starch polysaccharides in relation to animal nutrition. Journal of Dairy Science 74:3583-3593


 Received 3 October 2001

Go to top