Key words: Coconut oil meal, , nutrient digestibility, pigs, rubber seed meal

Introduction 

The coconut tree (Coconut nucifera) and the rubber tree (Hevea brasilensis) are two important tree crops in the tropics. Although coconut oil is facing increasing competition from other oils on the world market, especially from palm oil and soybean oil, today the area of coconut trees in Vietnam is 163,200 ha, with total production of around 968 thousand tons (Statistical Yearbook 2002). One by-product of the extraction of the oil from the nut is known as coconut oil meal (CCM), coconut cake or coconut copra meal, which represents approximately 34 to 42 % of the weight of the nut (Hutagalung 1981). It contains from 18 to 25% crude protein (CP), and is the principal feed produced from coconuts.

Latex is the main product of the rubber tree, and Asian plantations account for about 80% of the world latex production and are increasing year by year (Hertrampf  2002). The area in Vietnam under rubber was 407,000 ha in 1999 and  is estimated to reach 700,000 ha in 2005 (Statistical Yearbook 2000). Besides latex, estimated annual yield of the seeds is around 800 seeds per tree (1.3 kg), or around 0.2to 0.3 tonnes/ha (Hue 1997). The kernels are rich in oil, up to 41.2% of the total weight (Joachim 2002). Crushing them to extract the oil leaves rubber seed meal (RSM), which contains 21to 28 % CP (Joachim,2002) and can be fed to  livestock (Babatunde and Pond 1988). Limited research has been done on RSM for pigs (Ong and Yeong, 1977; Devendra, 1989; Ravindran, 1983; Fuller, 1988). However, the use of the ground whole rubber seed in pig diets is receiving increasing attention in Cambodia ( Ly et al  2001; Bun Tean et al 2002; Nguyen Thi Thuy and Ly  2002).

Supplying energy as well as protein to the diet, CCM and RSM can be partial replacements for higher protein sources. Some studies showed that CCM and RSM can be good protein sources for pigs. However their high crude fiber (CF) content can affect their digestibility. To use them more effectively, the aim of the present study is to determine the ileal and total tract digestibility of coconut meal (CCM) and rubber seed oil meal (RSM) produced by expeller and artisan methods in Vietnam.

Materials and methods

Animals, feeding and management

Three crossbred (Landrace x Yorkshire) castrated male pigs, with initial weight of 30 kg (SD ±1.5) kg were used. The pigs were surgically fitted with a simple post-valve T-caecum cannula (Van Leeuwen et al 1991), and were allowed a recovery period of two weeks before the experimental diets were introduced. Feed was given twice daily at 07.30 h and 19.30 h, in equal amounts as a wet mash in the proportion 1:1 (w: w). Daily feed intake was adjusted for individual animals at the start of each experimental period to correspond approximately  to 2.5 times the maintenance energy requirement. Water was available at all times through low-pressure nipples. Food refusals and spillage were recorded, and were used to correct the feed intake data. The pigs were housed individually in 2.5 m² concrete pens, and were restricted to a small area within the pens during digesta collection.

Oil meal products and diets

The oil meal products were produced in Ho Chi Minh City, Vietnam. The coconut meal (CCM)  and rubber seed meal (RSM) were collected at the oil pressing factories. The mechanical expeller process was used for CCM and the artisan expeller process for RSM. The oil meals were milled in a hammer mill through a 1-mm screen before mixing with the other diet ingredients.

The control diet was based on cassava root meal (CRM), while in the other diets the oil meal products replaced 300 g/kg of the CRM (DM basis). The CP content of the experimental diets followed the differences in the CP content of the oil meal (Table 2). Mineral and vitamin supplements were included in all diets. Chromium oxide was included as indigestible marker in all diets.  

Experimental design

The experiment was conducted as a 3x3 Latin-Square, with experimental periods of 12 days, comprising 7 days of adaptation to each diet followed by one day of collection of ileal digesta, one day of rest and a second day of collection of ileal digesta. For total tract digestibility, the collection of faeces started on day 8 of the experimental period and lasted for 5 days (until the end of the period).  

Digesta and faeces collection

For the determination of the ileal digestibility of nutrients, for each experimental period a total of 12 digesta samples from each pig were collected during the two days of collection. On each day of collection, samples were taken every second hour during the 12-h period between the morning and afternoon feedings, making 6 samples per day of collection. On each sampling occasion digesta were quantitatively collected for 1 h in a container through soft plastic tubing attached to the ileal cannula. The digesta were frequently removed from the tubing and container, and transferred to a larger container placed on crushed ice. These samples were homogenized and frozen at –18 ºC. Faeces were collected 4 times per day, and frozen at –18  ºC. Finally, ileal digesta and faecal samples were pooled within pigs and periods. Individual samples were thawed, mixed and dried. Ileal digesta flow and faecal excretion were estimated assuming complete recovery of chromium oxide at the two sites of sampling. The digestibility  of the oil meals was calculated by the difference method using the average digestibility values obtained for the control diet and the individual values for the experimental diets.  

Chemical analysis

Feed, digesta and faecal samples were dried at 60 ºC for 24 h and milled (1 mm screen) before analysis. All analyses were performed on dried samples, except for N of ileal digesta and faeces, which was determined in fresh samples. Dry matter (DM), ash, CP (N x 6.25), crude fat (EE) and crude fibre (CF) were determined in dry samples according to AOAC (1980). Neutral detergent fiber (NDF) was analysed according to Robertson and Van Soest (1977). Chromium was determined by atomic absorption spectrometry after digesting the sample in a mixture containing perchloric and nitric acids, according to Fenton and Fenton (1979). All analyses were performed in duplicate and are presented on a DM basis.  

Statistical analysis

Analysis of variance was performed according to a 3x3 Latin-Square design using the General Linear Models of  Minitab Statistical Software Version 12 (1998). The Tukey pair-wise comparisons procedure was used to determine differences between treatment means at  P<0.05.   

Results and discussion

Chemical composition and nutrient intake.

The chemical composition of the ingredients and the experimental diets are shown in Tables 1 and . The CP content of  CCM is in agreement with the results of Creswell and Brooks (1971) and  Hutagalung (1981). The  values for RSM are within the range reported by Joachim (2002) and Thieu (2002). These earlier studies showed that the CP content of RSM varied from 21 to 28% depending on how the seeds were processed. The results also show that the CP content of RSM was higher than that of coconut oil meal (24.4 vs 19.5 %) in this study. The low CP content of the oil meals compared to other protein sources can be a constraint in meeting animal requirements when they  are used as the sole protein sources in the diets. This problem can be seen with respect to the chemical composition of the experimental diets (Table 2). Both oil meal products contain more than 10% of CF (11.3 and 18.6%), with the highest levels found in the RSM. This value was higher than that reported by Thieu (2001), due to the fact that oil pressing can sometimes include corticated seeds, which have not had their hulls removed.

The artisan and expeller oil pressing methods lead to the high EE contents found in both CCM and RSM (12.4 and 15.8%, respectively),  that can cause problems in storage. However, the main constraint to using RSM is the presence of hydrocyanic acid in the seeds, on average about 11 mg/100 g DM in this study, which can be reduced by heat or storage (Devendra 1989).  The HCN content  of RSM was reported as 25 mg/100g  in the seeds, which was reduced to 9 mg/kg in the RSM (Narahari and Kothandaraman 1983). The rate of reduction in HCN level thus was  rapid during storage, leading to a  product that is safe for feeding to animals. The control cassava root meal based diet had low CP and EE content compared to requirements.

The daily food allowances were consumed by the pigs and the average daily DM intake was 1.55 kg and was not significantly different among diets (P>0.05). Thus, pigs fed the oil meal containing diets consumed more nutrients than when fed the control diet (P<0.001).

Ileal and total tract apparent digestbility and hind-gut disappearance 

The nutrient digestibilities of the experimental diets are  shown in Table 3. There were significant differences in nutrient digestibilities of the experimental diets due to the differences in nutrient content in the diets. The present study shows that the inclusion of oil meal products in a cassava root meal based diet for growing pigs resulted in a decrease in ileal and total tract digestibility of OM, CF, NDF and NFE (P<0.05). The control cassava root based diet had the highest OM digestibility, followed by the CCM and then RSM diets. The reduction of OM digestibility of the oil meal diets was probably due to the  increasing CF content in these diets. The CF digestibility of CRM was highest  (P<0.05), which  means that CF of CRM is more digestible than in CCM and RSM,   and the hard hull of RSM is more difficult to digest than that of CCM (P<005).

The lower apparent digestibility of CP and EE of the control diet may be partly explained by the effect of the endogenous materials on the low protein and EE content, as the control diet consisted mainly  of cassava root meal. However, there were  no significant differences in digestibility of CP and NFE between the CCM and RSM diets (P>0.05). 

The total tract apparent digestibility of nutrients was affected in a similar way to the ileal apparent digestibilities. By including CCM and RSM in the diet, the digestibility of OM, CF, and NDF decreased (P<0.05). However, there was an increase in the  digestibility of CP and EE. There was  no significant difference in the digestibility of NFE between CCM and RSM diets (P>0.05). It was calculated that 72.4 % of  the OM and 66.8 % of the CF of the CCM diet entering the hindgut disappeared (P<0.05),  while the corresponding values for RSM were lower (54.5 and 28.4 %, respectively) (Table 4). So, it is clear that the extent of fermentation in the hindgut of CCM was high.

The calculated ileal and total tract digestibility of nutrients of the oil meal products (Table 5) was higher for OM, CF and NDF at both sites of sampling for CCM compared to RSM (P<0.05). However, there were  no differences in the digestibility of CP, EE and NFE between CCM and RSM (P>0.05). It should be noted that the pigs digested only a small proportion (9.4%) of the CF of RSM at the ileum  and only 30.0% of the NDF. The estimated nutrient digestibilities of CCM and RSM  show the same tendency as in  the experimental diets. The presence of the hard hull, that is less digestible in RSM, leads to a lower digestibility of OM compared to CCM (64.5 vs 52.8 %, respectively).

The results show that around 66 % of  the CP of the oil meal products was  digested at the ileum level and around 77-78% was digested at the total tract level. Butterworth and Fox (1963) referred to the poor digestibility of coconut oil meal for pigs. Later, Hutagalung (1981) reported  a  value  of 74% for the digestibility of the protein in coconut oil meal. Recent Brazilian data reported levels as low as 67% for the digestibility of the nitrogen in expeller-pressed coconut oil meal (CNPSA 1991). The results of the present  study  are thus within the range of the values reported by these  authors.

It is concluded that CCM and RSM  are suitable for including in diets for growing pigs. However, they cannot be used as the sole protein source in the diets, and the decorticated product should be selected for feeding pigs.

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