Replacing rice bran by an ensiled mixture of taro (Colocasia esculenta) foliage and banana stem increases feed intake, diet digestibility and N retention in growing pigs

Chhay Ty, Aing Kimseang, Khieu Borin and T R Preston*

Center for Livestock and Agriculture Development. Pras Teat village, Rolous commune, Kandal Stung district, Kandal province.
P O Box 2423 Phnom Penh 3, Cambodia
chhayty@celagrid.org
* Center for Research and Technology Transfer, Nong Lam University
Thu Duc District, Ho Chi Minh City, Vietnam

Abstract

The experiment was conducted in the Center for Livestock and Agriculture Development (CelAgrid). Four crossbred (Large White x Local) castrate male pigs weighing on average 30.1±0.97kg were allotted at random to four diets. The level of rice bran was 10, 20, 30 and 40% in the diet (DM basis) and the remainder was taro foliage ensiled with banana stem. The proportion of taro foliage (leaves and stems) and banana stem silage was 50:50 in DM basis without adding any other ingredient. The design was a 4*4 Latin square.

The ensiled mixture of taro (Colocasia esculenta) foliage and banana stem was more palatable than rice bran. All measures of dietary nutritional value (DM intake, apparent digestibility of DM, CP and N retention) were increased when the ensiled mixture of taro and banana stem replaced rice bran.

Key words: fiber, forages, palatability, silage

Introduction

Small-scale pig production is important as a source of extra family income for poor rural farmers. However, small-scale pig producers mainly use poor quality rice by-products especially rice bran from village rice mills which has a high content of fiber and is low in protein (Chhay Ty et al 2014). For these reasons the pigs grow slowly and take a long time to reach slaughter weight. High quality rice bran and broken rice are expensive so that poor farmers cannot afford to buy them. The situation is similar for sources of good quality protein such as fish meal and soybean meal. This problem of protein supply has stimulated researchers to investigate the potential of tropical forages as alternative sources of protein (Preston 2006) as these can be grown by the farmer. Early work was with foliage from cassava (Bui Huy Nhu Phu et al 1996) and from mulberry (Phiny et al 2003). More recently, attention has been directed to the use of foliage from plants of the Araceae family (eg: Colocacia esculenta, Alocasia macrorrhiza, Xanthosoma sagittifolium) because of their high yield of biomass and ease of preservation by ensiling (Rodriguez and Preston 2009). Fresh leaves and ensiled leaves and stems of these species have been successfully fed to ducks (Chhay Ty et al 2011, Nguyen Tuyet Giang et al 2010,  2011) and pigs (Pham Sy Tiep et al 2006, Malavanh Chittavong et al 2008, Buntha et al 2008, Rodríguez et al 2009a,b; Du Thanh Hang and Preston 2008, 2010).

Banana stems are traditionally used as feed for pigs and cattle in Cambodia, usually by chopping them into small pieces and mixing them with rice bran. In Vietnam, it was found that although the banana stems are high in fiber they also contain soluble sugars and could be ensiled either directly or after mixing with stems and leaves of Taro (Tien et al 2013). Duyet and Preston (2013) fed Mong Cai sows with different ratios of rice bran and ensiled mixtures of banana stem and taro foliage. They found that the sows had satisfactory reproductive performance when fed only on ensiled banana stem and taro foliage; however, the feed conversion (feed DM per kg weaned piglet) was better when rice bran provided from 25 to 50% of the diet.

Objective

The aim of the present experiment was to study the nutritive value of combinations of rice bran and an ensiled mixture of banana stem and taro (Colocasia esculenta) foliage fed to growing crossbred pigs.

Materials and Methods

Location

The experiment was carried out at the Center for Livestock and Agriculture Development (CelAgrid) located in Prah Theat village, Sangkat Rolous, Khan Dangkor, approximately 25 km from Phnom Penh city.

Treatments and design

The experiment was conducted as a 4*4 Latin Square arrangement (Table 1) of the following treatments:

• RB10: Rice bran 10% and banana stem-taro silage 89%
• RB20: Rice bran 20% and silage 79%
• RB30: Rice bran 30% and silage 69%
• RB40: Rice bran 40% and silage 59%

The remaining 1% of the diet was for salt and sodium carbonate.. The ratios were on a DM basis.

Experimental feeds and feeding

Taro foliage was harvested from natural stands in ponds close to the CelAgrid center. Banana stem was purchased from local farmers and rice bran from a rice mill located near the CelAgrid center. The taro foliage (leaves and stems) and banana stem were chopped by hand in small pieces (about 2-3cm) and wilted one day under sunlight in order to reduce the moisture conten before being ensiled together with the proportion of 50:50 (DM basis).  Experience elsewhere (Tien et al 2013; Duyet and Preston 2013) indicated such a mixture could be ensiled satisfactorily without the need for any additive.  The silage was stored for one month before starting the experiment.

The pigs were fed thrice daily at 8:00 am, 12:00 am and 5:00 pm. The daily feed (Table 2) was offered at 4% (as DM) of live weight. The rice bran, salt and sodium carbonate were mixed together and fed first, followed by the silage from taro foliage and banana stem. Water was permanently supplied through low pressure nipples. The animals were weighed at the beginning of the trial and every 12 days.

Pigs and cages

Four crossbred (Large White x Local) castrate male pigs weighing on average 30.1±0.97 kg were housed in metabolism cages designed to allow the quantitative collection of feces and urine. Each experimental period consisted of 12 days; comprising 7 days adaptation to each diet followed by 5 days for collection of samples (feces, urine and feed refusals).

Data collection

During  the collection period, samples of feeds offered, refusals, urine and feces were collected every day and 5% of the amount was stored at -4ºC until the end of each collection period of 5 days. A representative sample was obtained from every treatment, mixed thoroughly by hand and then homogenized in a coffee grinder for analysis of DM, OM, CP and CF. Urine was collected in a plastic bucket to which sulphuric acid was added to maintain the pH below 4.0 (20ml of concentrated H₂SO₄). The volume of urine was measured every day and 5% of the volume stored at -4ºC until the end of each period, when a sample was taken for analysis of N.

Chemical analyses

The dry matter (DM) content was determined by drying at 60ºC for 48h. Ash, organic matter (OM) (100-ash), crude fiber (CF) and crude protein (CP) (N*6.25) were determined according to the methods of AOAC (1990). All analyses were performed in duplicate.

Statistical analyses

Analysis of variance was performed according to a 4*4 Latin-square design using the general linear model of Minitab software (Minitab 2010). Sources of variation were pigs, periods, treatments and error. When the F-test was significant at P<0.05, pair wise comparisons were performed using Turkey’s procedure (Minitab 2010). The model used was:

Y_ijk = μ + T_i + P_j +a_k + e_ijk where

Y_ijk = Dependent variable

μ = overall mean

T_i = treatment effect (1-4)

P_j = period effect (1-4)

A_k = animal effect (1-4)

e_ijk = random error

Results

Chemical composition of feed ingredients

The crude fiber level in the rice bran was 50% higher than that in the ensiled banana stem-taro foliage (Table 3).  The low pH of the silage confirmed that the combination of banana stem and taro can be preserved satisfactorily without the need for any fermentation additive.

Feed intake

The intakes of rice bran ranged from 80 to 85% of the planned levels (Table 4) which inplies that the pigs considered the banana stem-taro silage to be more palatable than the rice bran Because of the higher crude fiber level  in the rice bran (Table 3), the effect of increasing the offer level of the rice bran was to raise the overall crude fiber percent in the diet by 14% (Figure 2). The crude protein in the rice bran was similar to that  in the mixed banana stem-taro silage thus the dietary crude protein level in the final diet decreased only slightly with increased offer level of the rice bran. There was a linear decrease in DM intake as the offer level of rice bran was increased, the overall reduction reaching 7% at the highest offer level of rice bran (Table 4; Figure 3).

Figure 1. Effect of planned level of dietary rice bran on total daily DM intake	Figure 2 . Effect of planned level of dietary rice bran on percent of crude fibre in the overall diet

Fecal characteristics

Fecal DM content increased with offer level of rice bran, reflecting the lower feed DM intake (Table 5; Figure 4) and therefore the slower rate of passage of ingesta as the content of crude fiber in the diet was increased. It is well established that more water will be absorbed from the large intestine when feed intake is reduced and therefore ingesta stays  longer in the digestive tract.

Figure 3. DM intake decreases as proportion of rice bran in the diet increases	Figure 4. Relationship between DM content of feces and voluntary feed intake

Apparent digestibility coefficients

The apparent digestibility of OM, CP and CF decreased as rice bran replaced mixed silage of taro foliage - banana stem in the diet (Table 6; Figures 5-7).  This effect is probably a direct result of the increased fiber content of the diet as rice bran replaced the mixed Taro foliage-banana stem silage. This negative effect on digestibility of increased content of dietary fiber is well established (Jorgensen et al 1996; Ogle 2006; Lindberg 2014).

Figure 5: Trend in apparent digestibility of DM in pigs as rice bran replaced mixed taro foliage - banana stem silage	Figure 6: Trend in apparent digestibility of CP in pigs as rice bran replaced mixed taro foliage - banana stem silage
Figure 7: Trend in apparent digestibility of CF in pigs as rice bran replaced mixed taro foliage - banana stem silage	Figure 8: Trend in daily N retention in pigs as rice bran replaced mixed taro foliage - banana stem silage

N balance

N retention was negatively related to level of rice bran in the diet (Table 7; Figure 8).

Discussion

The ensiled combination of banana stem and taro foliage appears to be of superior value to the low quality rice bran  typically produced in small scale rice mills at village level in Cambodia. This finding contrasts with that of Duyet and Preston (2013) which showed a 7% improvement in overall feed conversion during pregnancy and lactation in Mong Cai sows when rice bran replaced 25% of the taro foliage-banana stem silage. The saving was 17% when the rice bran replaced 50% of the silage. The difference beween the two studies was probably in the quality of the rice bran which in Vietnam normally has 10 to 12% protein and less than 12% crude fiber (Du Thanh Hang 2014, personal communication) compared with 9.3% protein and 47.5% crude fiber in the bran used in the present trial (Table 3).

Both the rice bran and the ensiled mixture of banana stem and taro foliage, used in the present experiment,  provided insufficient protein (<10% in DM) for optimum growth of pigs. Future studies should be made with higher levels of crude protein, which can be achieved either by raising the proportion of Taro foliage in the silage, or including a protein-rich foliage such as sweet potato vines or water spinach.

Conclusions

• The ensiled mixture of taro (Colocasia esculenta) foliage and banana stem was more palatable than rice bran
  
  
• All measures of dietary nutritional value (DM intake, apparent digestibility of DM, CP and N retention) were decreased when rice bran replaced the ensiled mixture of taro and banana stem.

Acknowledgements

The authors would like to express their gratitude to the MEKARN project financed by Sida and to the Center for Livestock and Agriculture Development (CelAgrid), for providing resources for conducting this experiment.

References

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Received 17 January 2014; Accepted 27 March 2014; Published 5 April 2014

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