Effect of Taro (Colocasia esculenta) silage on digestibility of basal diets of palm syrup, rice bran and water spinach for growing pigs

Cheat Sophal

Faculty of Animal Science and Veterinary Medicine, Royal University of Agriculture (RUA),
PO Box 2696, Phnom Penh, Cambodia
sophalcheat@yahoo.com

Abstract

Three cross-breed pigs with average weight 12 kg were allocated at random to 3 diets within a 3*3 Latin square with periods of 10 days (5 days for adaptation and 5 days for collection of data). The treatments were levels of taro silage (5%, 10% and 15% in diet DM) replacing water spinach, the other components of the diet being rice bran and palm syrup.

The taro silage was consumed completely but the planned levels of water spinach were not all consumed, especially on the diets with 5 and 10% taro silage. As a result the crude protein level in the consumed diet was highest on the 15% taro silage diet. There were no differences among diets in apparent digestibility of DM and OM but there was  an indication (P = 0.16) that crude protein digestibility increased with increasing proportions of taro silage in the diet. Daily N retention and N retention as a proportion of N intake and N digested increased as the level of N from taro silage was increased. The high value for N retained as proportion of N digested (73%) indicates that the protein in taro foliage has a high biological value.

Key words: dry matter, feces, feed intake, forage, Latin square, N balance, N retention, organic matter, urine
 

Introduction

From the point of view of agriculturalists, livestock play a pivotal role for initiating the improvement of the economy of the country. Pigs are livestock that are involved in animal production which can improve the family food supply and family income. In commercial pig production as well as household scale, they can use the locally available feed resources such as paddy rice by-products, water spinach, palm syrup and molasses.

Rice byproducts are the most commonly used feeds for pigs in rural areas in Cambodia.  The byproducts from rice milling are  rice bran and broken rice both of which are used to feed animals. Rice bran is regarded as an energy source which can be used to supply the energy requirements for animals especially pigs (McDonald et al 2002). Rice bran consumption has shown to be successful in reducing cholesterol level in pigs (Roy and Lundy  2005). Its oil contains a range of fatty acids:  47% mono-unsaturated, 33% poly-unsaturated, and 20% saturated fatty acids. The most common fatty acids in the rice bran oil are oleic (about 43%) and linoleic (39%) (Anon-1 no date). Other studies have shown the high content in rice bran of both tocopherols and tocotrienol, which are precursors of E and act as antioxidants in the body (Roy and Lundy 2005).

Water spinach (Ipomoea aquatica) is a water plant. It can be planted or grown naturally  for utilization by both animals and humans. It does not appear to contain anti-nutritional compounds and has been used successfully for growing pigs as the only source of supplementary protein in a diet based on broken rice (Ly 2002). Prak Kea et al (2003) reported a linear increase in growth rates in pigs fed water spinach, palm oil and broken rice when up to 6% fish meal replaced equivalent amounts of water spinach, which they attributed to an improved amino acid balance, especially in terms of the sulphur-rich amino acids. According to Le Thi Men et al (1999) and Le Thi Men et al (2000), the leaves and stems of water spinach contain more than 20 % crude protein in dry matter basis. Chhay Ty and Preston (2006) reported that water spinach was more palatable and had higher digestibility than cassava leaves.

Palm syrup derived from the sugar palm tree (Borassus flabellifer) has been used as the sole energy source for growing and finishing pigs (Khieu Borin and Preston 1995). Farmers can collect the juice from the flowers and make the palm syrup by themselves from the palm trees surrounding their village. Feeding systems using the products and/or by-products of sugar cane, the African oil palm, cassava and the sugar palm have been developed for all classes of livestock and are slowly finding acceptance in many tropical countries (Sarria et al 1990; Preston 1995; Ocampo 1994; Khieu Borin and Preston 1995; Perez 1997).

Sources of protein are usually the limiting factors in pig diets in tropical countries. Traditional sources of protein such as soybean andand fish meal are becoming more expensive and there is therefore ncreasing interest in the use of vegetative sources of protein.

Taro (Colocasia esculenta) is known as a food crop which provides high yield of roots (or corms) and foliage. Its leaves are rich in protein and easy to ensile (Peng Buntha et al 2008). It can be grown under flooded or upland conditions. In Cambodia, taro is known in Khmer as 'Trao' and is planted as food supply for both human and animals. Chhay Ty et al (2007) reported that most taro varieties contain an irritating or acrid agent and cannot be eaten fresh. To this point, the leaves can be chopped and ensiled to considerably reduce undesirable substances in taro, which thus becomes more palatable (Chittavong Malavanh et al 2008). In one experiment with growing pigs, taro leaf silage provided 38% of the dietary DM and 75% of the dietary protein. The apparent digestibility of DM and OM tended to be higher for the diets with dried versus ensiled taro leaves (Chhay Ty et al 2007).  In research with cassava leaves as protein sources for pigs it was found that there were advantages from offering a combination of cassava leaves and water spinach compared with cassava leaves alone (Chhay Ty and Preston 2005).

The objective of this experiment therefore was to determine the potential benefits from offering combinations of water spinach with ensiled taro foliage leaves in diets for growing pigs based on palm syrup and rice bran.

Materials and methods

Location and duration

The experiment was carried out in the Kampong Cham National School of Agriculture, Kampong Cham province, Cambodia, about 124 Km to the North-East of Phnom Penh capital city of Cambodia, from 11^th August to 10^th September, 2008.

Experimental design and treatments

The treatments  in a 3*3 Latin square design with three local cross-breed pigs were levels of taro silage at 5, 10 and 15% replacing water spinach levels which were 45, 40 and 35% of diet DM  (Table 1). Each period was 10 days, of which 5 days for adaptation and 5 days for the collection of data. Pig 2 died after the second period. It was replaced  by a new pig in period 3.

The feeds used in the experiment were: rice bran, sugar palm syrup, water spinach and silage made from taro leaves and stems (Photos 1 to 4)

Feeds and feeding

Rice bran, sugar palm and water spinach were purchased from the market around the experimental area in Kampong Cham. The taro silage was made from the leaves and stems of taro (Colocasia esculenta). These were harvested from ponds in Kandal province, chopped into small pieces and wilted for 24 hours before being ensiled without additives. The palm syrup was diluted in water (1:1 fresh basis) to give a solution with 38% sugars. The sugar palm and rice bran were each fed at 25% of recorded DM intake; the levels of water spinach and taro silage were those planned for the experimental treatments. The total offer level was about 3 kg DM per 100 live weight. The rice bran, palm syrup and taro silage were mixed together and given as the first feed in the morning (about 07.00am). The water spinach was fed after the mixed feeds were consumed.

Data collection

Feeds offered and residues (only water spinach) were recorded daily and representative samples taken for analysis. Each morning, prior to feeding, the feces and urine from the experimental animals were collected separately (nylon net for the feces and plastic bucket for urine). In the plastic urine buckets, 20 ml of a solution of 10% concentrated sulphuric acid (H₂SO₄) were added daily to preserve the nitrogen in the urine.

Chemical analysis

The moisture content in the water spinach was determined by the micro-radiation method (Undersander et al 1993). Crude protein (CP) and ash were analyzed according to AOAC (1990). The sugar content (considered as DM) of the sugar palm was determined as the “Brix” value corresponding to total sugars by using a hand-held refractometer (Atago N1, no date Japan).

Statistical analysis

During and after the experiment, data were collected and analyzed by using analysis of variance (ANOVA) according to the general linear model (GLM) of the Minitab software (version 13). The sources of variation in the model were; levels of taro silage, periods, animals and error.
 

Results

Feed composition and intake

The crude protein content of the rice bran was very low, perhaps through being contaminated with a low protein meal such as from cassava roots (Table 2).

The mixed ingredients (Taro silage, rice bran and palm syrup) were consumed completely. By contrast, there were residues of water spinach  on all treatments, but especially on the treatments (TS5 and TS10) where the offer level of water spinach was highest. As a result the crude protein level in the consumed diet was highest on the TS15 treatment (Table 3).   The total DM intake as a function of live weight increased as the level of taro silage was increased (Figure 3). The difference between daily DM intake and intake as a function of live weight was caused by the substitution of a new pig on treatment TS15 in period 3. Intakes of OM mirrored the intakes of DM (Table 4 and Figures 4 and 5).

Apparent digestibility coefficients

Thee were no differences among diets in apparent digestibility of DM, OM and crude protein (Table 5).

N balance

Intakes of N from the different ingredients ((Table 6; Figures 6 and 7) showed that most of the N (70-80%) came from the water spinach. Total N intake reflected the contribution of N from the Taro silage and was highest on the TS15 diet. Components of the N balance (Figure 8)showed that losses in urine and faeces were lowest in the TS15 diet, despite the N intake being highest on this diet. Because of the differences in N intake the components of the N balance were corrected by covariance for total N intake (Figure 11).  After correction for N intake  there were major differences in N retention, in N retention as a percentage of N intake (Figure 9) and in N retention as percentage of N digested with the best results obtained on the TS15 diet.

Discussion

Replacing water spinach with silage of taro leaves and stems brought about major increases in daily N retention and in N retained as percentage of N digested. This implies that the biological value of the protein in ensiled taro leaves and stems is higher than that in water spinach. Rodríguez et al (2008a) fed fresh leaves of New Cocoyam (Xanthosoma  sagittifolium) as replacement for soybean meal to pigs fed sugar cane juice as the basal diet. N retained as percentage of N digested was higher (71%) for the New Cocoyam leaves than for the soybean meal (56%). Similar high values for N retained as percentage of N digested were observed by Rodríguez et al (2008b), when ensiled leaves of New Cocoyam were the only protein source for pigs fed a sugar cane juice diet, and by Du Thanh Hang and Preston (2008) when ensiled Taro leaves were fed in a basal diet of cassava root meal and rice bran. 

Conclusions

• Replacing water spinach with silage of taro leaves and stems brought about major increases in daily N retention and in N retained as percentage of N digested in a low-protein basal diet fed to growing pigs

Acknowledgement

The author would like to express their gratitude to the MEKARN project funded by the SIDA-SAREC Agency and the Kampong Cham National School of Agriculture (KCNSA) for conducting this experiment.

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