Apparent digestibility and N retention in growing pigs fed rice bran supplemented with different proportions of ensiled Taro foliage (Colocacia esculenta) and rice distillers’ by-product

Nouphone Manivanh, Le Duc Ngoan and T R Preston

Animal Science Department;
Souphanouvong University (SU),
Luang Prabang, Lao PDR
nouphone2007@yahoo.com

Abstract

The experiment was carried out in  the farm of the Faculty of Agriculture (Animal Science Department), situated about 7 Km from Luang prabang City, Luang prabang province, Laos PDR. Four crossbred castrated male pigs (Duroc x Large White), weighing on average 25 kg, were allotted at random to 4 diets within a 4*4 Latin square design, to study effects on digestibility and N retention of level of rice distillers’ by-product  (0, 10, 20, 30 % in DM) replacing  ensiled Taro foliage (leaves and stems)  in a basal diet of rice bran.

Feed intake and N retention were increased, but apparent digestibility of DM was reduced with no differences in crude protein digestibility, as the  rice distillers’ by-product  replaced ensiled Taro foliage.  Daily retention of N and N retained as percent of N digested increased linearly with replacement of Taro foliage silage by rice distiller's by-product and rice bran. It is suggested that the biological value of the protein in rice distillers'  by-product is superior to that of  ensiled Taro foliage.

Key words: Biological value, feed intake, protein

Introduction

As the human population grows, there will be a need for more food to meet the increasing demand. The production of meat from non-ruminants (pigs and poultry) is increasing faster than from the ruminants because of the quick turnover of the capital and the ease of access to the marke. Pigs are widely kept throughout the country of Lao PDR, with 64 percent of all households involved in pig production (ILRI 2002). The number of pigs kept by smallholders varies between an average of 1.4 and 3.7 animals per household, depending on the region (Kaufmann et al 2003). Almost all farmers use agricultural by - products such as rice bran for feeding their pigs but this cannot support full performance because of their poor nutritive value (ILRI 2002).

Taro (Colocasia esculenta) is known as a food crop which has a high yield of roots (or corms) and foliage.  Taro is known in Khmer as 'Trao' and is planted as food for both humans and animals. However the foliage (leaves plus stems) of Taro is now receiving much attention as as a feed for pigs (Preston 2006).

The leaves from Taro are a good source minerals and vitamins (http://en.wikipedia.org/wiki/Taro).  The major constraint to the use of Taro foliage is the presence of oxalate salts which form crystals on the surface of the leaves and stems and which cause irritation (itching) of the skin and especially the mouth when the fresh foliage is eaten. In a survey in Cambodia (Pheng Buntha et al 2008) it was found that farmers traditionally "boiled" the leaves before feeding them to pigs as in the fresh state the leaves were not readily consumed. Recently, ensiling of the Taro foliage has been developed (Rodriguez and Preston 2009) and has proved to be effective in reducing the oxalate content (Du Thanh Hang and Preston 2008). Initially sugar cane juice (Rodriguez and Preston 2008) and molasses (Malavanh et al 2008). was used in the ensiling of Taro leaves. However, the finding that the stem contained a high level of sugars led to the idea of ensiling the leaves and stem together (Rodríguez and Preston 2009), obviating the need for additional sources of sugars.

“Khilao” or rice distillers’ by-product is another potential source of high quality protein in rural areas of Lao PDR. "Khilao" is the residue after distilling the alcohol derived by yeast fermentation of sticky rice (Taysayavong Lotchana and Preston 2010) The farmers traditionally use it as a mixture with other feeds such as rice bran and broken rice in diets for fattening pigs (Oosterwijk et al 2003). The farmers in Vietnam also use rice distillers’ by-product (known as “hem”) as a traditional feed for pigs (Luu Huu Manh 2000). The protein content of "hem" ranged from 17 to 33% (mean of 23%) in dry matter with a well-balanced array of amino acids (Luu Huu Manh et al 2003). These authors reported that this product could replace completely the fish meal in growing and fattening pig diets with no loss of performance.

 The aim of this study therefore was to determine the effects of inclusion of rice distillers’ by-product into diets containing different proportions of ensiled Taro foliage and rice bran.

Material and methods

Location and duration

The experiment was carried out from 3^rd April 2011 to 12^th May 2011, in Souphanouvong University, located in Donmai village, Luang Prabang district, Luang Prabang province about 17 Km from the City,

Experimental design

Four treatments were compared in a 4*4 Latin Square arrangement with 4 pigs and 4 periods (Table 1). The treatments were:  

RD0: Taro silage (TS) 59% with rice bran (RB) 40% and minerals 1%.

RD10: Rice distillers’ by-product (RD) 10% mixed with TS 39% , RB 50 % and minerals 1%.

RD20: RD 20% mixed with TS 24%,  RB 55% and minerals 1%

RD30: RD 30% mixed with TS 10%, RB 59% and minerals 1%

The duration of the experiment was 40 days with 4 periods each of 10 days, the first 5 days for adaptation then 5 days for collection (feces and urine). The composition of the diets is in Table 2.

Animals and housing

The pigs (castrated male; Duroc x Large White), weighing on average 25 kg, were individually housed in cages made of wood, designed to separate feces and urine (Photo 1). The floor area was 60*70 cm. 

Feeds and feeding

The Taro (leaves and stems) were collected in the vicinity of Souphanouvong  University where it was growing wild (Photo 2). The rice bran was bought from a rice mill in Luang Prabang city and rice distillers’ by-product was bought from farmers in Donmai village. 

The leaves and stems were chopped into small pieces (2-3 cm length) (Photo 3) and exposed to sunlight for 6 hours to reduce the moisture to about 75%, prior to packing tightly into 50 litre plastic bags where it was stored for 14 days (Photo 4) before being fed to the pigs. All ingredients were mixed and fed together two times per day at 6:30 AM and 5:30 PM, the amount being based on an offer level of 40-50 g DM/kg live weight. Water was supplied ad libitum through nipple drinkers.

Measurements and data collection

The pigs were weighed in the morning before starting each period. Feed offered was recorded and refusals collected daily. The refusals were stored in a refrigerator (4 °C) until the end of each collection period when they were mixed and sub-samples taken for analysis of DM, ash and N. Feces and urine were collected daily. Each day 20 ml of 15 % H₂SO₄ were added to the urine container to maintain the pH of the urine below 4.0.  All the feces were stored in the refrigerator until the end of the collection period when they were mixed and a sub-sample taken for analysis of DM, ash and N. A sub-sample of urine was taken daily and stored in the refrigerator until the end of the collection period when the samples were mixed and a sub-sample taken for analysis for N.

Chemical analysis

Samples of feeds offered and refused and faeces were analysed for DM, ash and N using the procedures of AOAC (1990). Urine was analysed for N (AOAC 1990).  

Statistical analysis

The data were analyzed using the general linear model (GLM) option of the ANOVA program in the MINITAB software (Minitab 2000). Sources of variation were pigs, periods, treatments and error.

Results and discussion

Chemical composition of feed

The content of crude protein in the rice bran was very low indicating that the quality of the bran was low with probably a high percentage of husks (Table 3).  The crude protein in the rice distillers’ by-product was in the range reported by Luu Huu Manh et al (2009).

Feed intake

The mixed diets were consumed completely. The daily DM intake (Table 4) showed a curvilinear relationship (Figure 1; R² =  0.98) with the  maximum at 23% of the diet DM as rice distillers’ by-product. The trends for OM intake were similar. On all treatments the intake levels were high (40 to 46 g DM/kg LW).

Figure 1: DM intake of pigs fed ensiled Taro foliage and rice bran, or mixtures of the two, with rice distillers’ by-product	Figure 2: Proportions of dietary ingredients (as DM) in pigs fed ensiled Taro foliage and rice bran, or mixtures of the two, with rice distillers’ by-product

Apparent digestibility coefficients

The apparent digestibility of DM decreased when rice distillers' by-product replaced ensiled Taro foliage (Table 5; Figure 3) with no differences among the levels of the rice distillers' by-product.  Apparent digestibility of OM was lower with 33% of the diet DM as rice distillers’ by-product compared with the control diet with no rice distillers’ by-product. Intermediate levels of rice distillers’ by-product did not from the zero and maximum levels of rice distillers’ by-product.  As the increase in rice distillers’ by-product was associated with an increase in per cent of rice bran in the diet (Table 2), the resultant increase in fibre (higher in rice bran than in Taro silage) could explain the decrease in apparent digestibility of DM and OM (Kass et al 1980).

Nitrogen balance

N intake and N retention increased with increasing level of rice distillers' by-product replacing ensiled Taro foliage (Table 6; Figures 4 and 5). Part of the increase in N retention was apparently due to the increased N intake, in turn the result of increased DM intake caused by replacement of Taro silage with rice distillers’ by-product. However, ccorrecting the N retention data for differences in N intake (Figure 6)  did not affect the linear response in N retention as the level of rice distillers’ by-product was increased. There was a similar trend in N retained as per cent of N digested, as rice distillers' by-product replaced ensiled Taro foliage (Figure 7).  The improvement in N retention with increasing levels of rice distillers’ by-product replacing taro silage contrasts with the lack of difference in apparent N digestibility. The implication from these results is that the higher N retention for diets containing rice distiller’s by-product, compared with ensiled taro leaves and stems, is due to the higher  biological value of the protein and not its digestibility. The other possibility is that the rice distillers'  by-products contain other useful nutrients such as  B-vitamins. 

Figure 4.  N intake in pigs fed increasing levels of rice distillers’ by-product replacing ensiled Taro foliage	Figure 5.  N retention intake in pigs fed increasing levels of rice distillers’ by-product replacing ensiled Taro foliage

Figure 6. N retention corrected for  differences in N intake, in pigs fed increasing levels of rice distillers’ by-product replacing ensiled Taro foliage	Figure 7. N retained as per cent of N digested in pigs fed increasing levels of rice distillers’ by-product replacing ensiled Taro foliage

Conclusions

• Feed intake  was increased, apparent digestibility of DM and crude protein tended to decrease, but N retention was increased when rice distillers' by-product replaced ensiled Taro foliage in a basal diet of rice bran fed to growing pigs.

Acknowledgements

We would like to thank the MEKARN program, supported by Sida, for the financial support for this research. W also wish to thank the students from the Faculty of Agriculture of Souphanouvong University for their assistance with the feeding of the animals. This research formed part of the requirements of the senior author for the MSc degree in Animal Production "Specialized in Response to Climate Change and Depletion of Non-renewable Resources" of Cantho University, Vietnam.

References

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Received 5 March 2012; Accepted 21 March 2012; Published 2 April 2012

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