The effect of DL-methionine supplementation on digestibility and performance traits of growing pigs fed broken rice and water spinach (Ipomoea aquatica)

J Ly, Hean Pheap, Keo Saeth and Pok Samkol

University of Tropical Agriculture Foundation

Chamcar Daung, Phnom Penh, Cambodia

julioly@utafoundation.org and samkol@uta.edu.kh

Abstract

Sixteen Large White castrate male and female pigs (1:1) of 27 kg mean initial live weight were allotted at random to four treatments (none or  0.25, 0.50 and 0.75 % of  DL-methionine in diet DM) for the study of  digestive indices and performance traits on a diet of broken rice (30 g DM/kg body weight) and fresh water spinach given ad libitum.

Total feed DM intake was relatively low but tended to increase with increasing level of supplementation with  DL-methionine, due to increases in the water spinach component. Live weight gain and DM feed conversion were positively related with the level of added DL-methionine. Organic matter digestibility tended to decrease as the level of DL-methionine increased but this was probably due to the increasing proportion of water spinach in the diet.

It is concluded that simple diets  for growing pigs, formulated with broken rice and water spinach, can greatly be improved with the addition of 0.5% DL-methionine.  

Key words: pigs, performance traits, digestibility, DL-methionine, broken rice, water spinach

Introduction 

Pig production in Cambodia is currently characterized by a  scheme of production whereby animals are left to scavenge around houses or villages. To a certain extent, human food residues, rice products and water spinach (Ipomoea aquatica) and other foliages are major components of the daily ration (Delvert 1961; Khieu Borin 1994; Cameron and Twyford-Jones 1995; Altshul et al 1997; Solieng Mak 1998).      

Recent findings in our laboratory have highlighted the enormous potential of water spinach to produce protein-rich biomass, especially when heavily fertilized with biodigester effluent (Kean Sophea and Preston 2001). Another advantage of water spinach  is that it can be cultivated either in dry or flooded soils, as well as in shallow ponds and lagoons.  Rice bran is one of the main by-products used in pig raising (Rozemuller 1998). However, the rice-bran produced by traditional mills in Cambodia is of low energy density, which limits it potential as an energy source to complement fibrous sources of protein such as water spinach. Broken rice is another by-product of rice milling but with the advantage of a high energy density as it is almost free of fibre.

There is considerable information concerning the use of rice and rice by-products in pig production (see for example, the review of Farrell and Hutton 1990). In fact, rice and rice by-products have been used as non-conventional ingredients in pig diets of high energy density. The nutritional and feeding value of broken rice and water spinach have been studied in Vietnam (Bui Hong Van 1994; Le Thi Men 1999). However, the use of a combination of broken rice and water spinach in pig production has not received attention. As most proteins of vegetative origin tend to be deficient in sulphur-containing amino acids, it is hypothesised that  the use of water spinach as the main protein in source may imply an inefficient use of protein due to an imbalance in the  amino acids in this aquatic plant (Le Thi Men 1999: Buy Huy Nhu Phuc 2000). This aspect is very important if diets for pigs are designed to contain a rather low protein value (Bui Hong Van 1994).  

The aim of the present paper is to report a feeding trial conducted with growing pigs given diets based on broken rice and water spinach supplemented with DL-methionine.

Materials and Methods

Sixteen Large White castrate male and female pigs in the proportion of 1:1 and with an average initial live weight of 27 kg were allotted at random into four treatments consisting of four levels of DL- methionine added to diets of broken rice and water spinach. The animals were treated against parasites prior to the commencement of the trial. The chemical composition of the broken rice and water spinach is listed in Table 1. 

The animals were housed in individual pens in an open stable with concrete floor. Every pen had a feed trough and a nipple drinker. The animals were weighed and adapted to the experimental diets during seven days. Thereafter the pigs were weighed every two weeks. The broken rice was offered at 7:00am  mixed with a supplement of vitamins, minerals and DL-methionine. This compound feed was calculated to contain none, 0.3, 0.6 and 0.9% DL-methionine in dry basis, respectively. The mineral and vitamin premix (formulated according to NRC 1998) and NaCl were both added to the diets at concentration of 0.5% in dry basis. Two hours later the fresh, chopped water spinach was given.  A single batch of broken rice, purchased in the local market,  was used for the entire experimental period. Water spinach was bought every day from local suppliers who regularly harvest this vegetable from a lagoon fertilized naturally with sewage from Phnom Penh city.

The amount of broken rice to be given to the pigs was adjusted every two weeks to provide 30 g DM/kg body weight; the water spinach was offered ad libitum. Feed refusals were recorded every day before the distribution of the daily ration. Drinking water was always available.

Six weeks after the beginning of the trial, faecal samples were obtained directly from the rectum of each pig, to establish total tract digestibility indices by the indirect "acid insoluble ash" method. The samples of faeces were immediately analyzed for DM content  by micro-wave radiation (Undersander et al 1993). The AOAC (1995) procedures were followed for N, crude fibre and ash estimation in representative samples of feeds and faeces. NDF and acid insoluble ash in both types of samples were determined according to Van Soest et al (1990) and Van Keulen and Young (1977), respectively.

The water holding capacity (WHC) of water spinach was determined as outlined by Tsaras et al (1998) with slight modifications, consisting of filtering the suspension of the finely ground sample in water through a buchner funnel, and applying a gentle vacuum to the system during one minute. The vacuum was provided by a commercial dust aspirator, which was connected to the vacuum flask. A sample of filter paper, assuming to be pure cellulose, was used as standard. All samples were assayed in quadruplicate.

Means were contrasted through the analysis of variance technique according to a one-way classification. When a significant effect of treatment was detected, the means were separated by the Duncan’s multiple range and multiple F test (Steel and Torrie 1980). In addition, analysis of regression was applied to relate growth rate with methionine supplementation. The Minitab software package (version 12.0)  was employed for these analyses (Ryan et al 1985).

Results and Discussion

General

The chemical composition of broken rice and water spinach used in this experiment was very similar to that reported by Le Thi Men et al (2000). In this connection, Farrell and Hutton (1990) have reported that the sum of fat, crude fibre and ash in white rice could be as low as 1.5% in dry basis. It is assumed that physical form is the only major difference between broken and entire rice. The water holding capacity  (g water/g dry material) of the water spinach samples was 11.27 ± 1.04 compared with 2.64 ± 0.03 for the filter paper. This value for water spinach is considered to be very high as compared to other voluminous feeds (3.86 to 8.48 g water/g dry material) reported by Tsaras et al (1998).    

Performance traits

The DL-methionine content of the daily ration decreased to final values of 0, 0.25, 0.50 and 0.75% in dry basis, when the intake of water spinach was taken into account (Table 2). There was no treatment effect on daily DM feed intake, which was rather low. It appeared that a low voluntary intake of water spinach was responsible of an overall depression of daily DM intake. In fact, approximately 99.8% of the offered broken rice (30 g/kg body weight) was consumed by the animals. On the other hand, voluntary consumption of water spinach increased (P<0.01) from 13% of total dry feed intake in the diet with no amino acid supplementation, to an average of 21%, in treatments with DL-methionine supplementation.

The contribution of water spinach to total feed intake was  lower than that reported by Le Thi Men et al (2000) in breeding sows having free access to water spinach (on average 36.4 %). The maximum intake of fresh water spinach was found to be 15.2 g (DM)/kg body weight when given as the sole feed to 30 kg pigs (Bun Tean et al 2002). Pech Sovanno (2002) reported that water spinach given ad libitum as a supplement to a diet of wheat bran and whole rubber seed meal represented 18.7% of total daily DM intake in growing pigs in the range of 24 to 60 kg live weight. It is possible that adult pigs have a the higher capability for digestion of the cell wall, as compared to growing pigs (see for example Shi and Noblet 1993).  The high  water holding capacity of the water spinach in this study strongly suggests that the bulky characteristic of this feed could be a major constraint to intake in young pigs,  since the consumption of fibrous materials, of low energy density, is inversely proportional to the water holding capacity (Kyriaziakis and Emmans 1995; Tsaras et al 1998).

Broken rice contains only 6% protein in the dry matter thus the low intake of water spinach, which was the only additional source of protein (25% protein in DM),  led to a relatively low protein intake of 115 g/day. DL-methionine supplementation tended to increase the contribution of water spinach protein to total protein intake from 30.5 to 41.2%, but this effect was not significant (P>0.05). 

The pigs given diets containing 0.50 and 0.75% DL-methionine had a higher final weight (P<0.05), and as a consequence, average daily gain was higher (P<0.05) than in those pigs fed with none or the lowest level of DL-methionine in the feed (Table 3; Figure 1). Feed conversion rate, expressed either in DM or crude protein, did not appear to differ among diets (P=0.20). However the analysis of regression revealed a tendency for a linear effect of DL-methionine level on DM conversion (R² = 0.25; P<0.05) and protein conversion (R² = 0.19; P<0.09).  These results imply that methionine may be a limiting amino acid in water spinach as claimed by Le Thi Men (1999) and Bui Huy Nhu Phuc (2000). Broken rice is also considered to be deficient in methionine content according to Creswell (1988).  

Figure 1: Relationship between growth rate and level of added DL-methionine

Digestibility indices

Faecal concentration of DM appeared (P=0.10) to be depressed and faecal fresh material and water output increased by increasing levels of DL-methionine in the ration (Table 4), however, this was more logically due to the concomitant increase in intake of water spinach (Table 2). Regression analyses revealed a significant (P<0.05) linear effect of water spinach on  daily output of faecal fresh material (r = 0.53) and water (r = 0.52).

The average values for DM and organic matter digestibility were high (84.7 and 86.6%, respectively) reflecting the high level of broken rice in the feed, which is known to be highly digestible (Farrell and Warren 1982). On the other hand N digestibility (on average 73.8%) was rather low, probably influenced by the inclusion of water spinach in the feed (Le Thi Men 1999).

DM and N digestibility did not vary according to the studied treatments. However, a trend was observed (P=0.10) for organic matter to decrease with the increase of DL-methionine added to the diet, probably reflecting the higher proportion of water spinach in the diet when DL-methionine was added. This is supported by the linear relationships between water spinach proportion and DM and organic matter digestibility (r = - 0.49; P<0.05 and - 0.60; P<0.01, respectively).  Interestingly, neither DL-methionine supplementation nor the water spinach content in the feed influenced N digestibility.  

Conclusions

According to the results of this study, very simple diets, formulated to contain broken rice as energy source and water spinach as source of protein for growing pigs, can greatly be improved with the addition of no more than 0.5% DL-methionine to the total daily feed intake.

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Received 4 June 2002

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