Taro (Colocacia esculenta) leaves as a protein source for growing pigs in Central Viet Nam

Du Thanh Hang and T R Preston*

Hue University of Agriculture and Forestry

Hue, Vietnam

hangduthanh@yahoo.com.vn

* UTA-TOSOLY, Colombia
 

Abstract

Taro (Colocasia esculenta) leaves  were cooked, ensiled with 4% molasses or fed fresh to F1 (Large White x Mong Cai) and Mong Cai growing pigs as supplements to a basal diet of cassava root meal and rice bran. After 7 days the pH in the ensiled leave/petioles had decreased from 7 to 4 and then remained stable for 56 days. Intake of cooked and ensiled taro leaves was significantly higher than of the fresh leaves, and was higher in F1 (Large White x Mong Cai) than in Mong Cai pigs. The taro leaves contributed 20% of the diet dry matter and 46% of the crude protein after cooking or ensiling. Apparent digestibility and nitrogen retention were higher in pigs fed cooked or ensiled taro leaves than in pigs fed fresh taro leaves. F1 (Large White x Mong Cai) pigs retained more nitrogen than Mong Cai pigs.

Key words: Cooking, digestibility, ensiling, Mong Cai, N retention, pigs

Introduction

Taro (Colocasia esculenta) is traditionally planted in the villages for two purposes: human consumption and feeding of pigs.  The farmers use the taro leaves for pigs by cooking them with rice or rice bran and cassava roots. Taro leaves are rich in vitamins and minerals. They are good sources of thiamin, riboflavin, iron, phosphorus and zinc, and are a very good source of vitamin B6, vitamin C, niacin, potassium and manganese. According to Rodriguez et al (2006),  fresh leaves of Xanthosoma sagittifolium (a member of the same family as Colocacia esculentalo)  had a chemical composition (g/kg DM) of: crude protein, 248; crude fibre, 142; NDF, 255; ADF, 198; Ca, 17.7; P 2.0; Mg, 2.2 and K, 32.3.  The amino acid (AA) composition of the leaves indicated a superior balance of the main essential AA (Methonine + Cystine and Threonine) compared with soybean meal.

Pham Sy Tiep et al (2006) discussed the “itching” effect on the skin of humans and pigs caused by contact with fresh leaves of Alocasia macrorrhiza, considered to be due to the presence of crystals of calcium oxalate which can irritate the mouth and throat. These authors showed when the leaves were ensiled with rice bran or molasses, the content of calcium oxalate was reduced to very low levels, and that the silage could be included in the diet of growing pigs at the 10% level without affecting growth rate. In Colombia, Rodriguez et al. (2006) reported that the leaves of the New Cocoyam (Xanthosoma sagittifolium) could be fed fresh to young pigs at a level replacing 50% of the protein from soybean meal (approximately 45% of the diet DM) and that growth rates (500 g/day) were similar to those on the control diet without the leaves.  Chittavong Malvanh et al (2006) found that a mixture of taro (Coloccacia esculenta) leaf silage and water spinach could replace 100% of the soybean meal in pregnancy and lactation diets for Mong cai gilts without affecting sow reproduction.

The aims of the present study were to compare different ways of processing the foliage (leaves and petioles) of taro (Colocacia esculenta) when used as a major supplement in diets of unimproved (Mong Cai) and improved (Large White x Mong Cai) pigs.

Materials and methods

Experiment 1: Effect of ensiling taro leaves and taro stem with molasses on chemical composition

Fresh leaves of  taro were collected 3-6 months after planting and chopped into small pieces (2 - 3 cm) and spread out on the floor some hours for wilting. The wilted leaves were mixed with 4% molasses by weight and placed in sealed plastic bags with a capacity of 2-3 kg. Samples of silage were taken prior to, and after 7, 14, 21 and 56 days of ensiling. Analyses of pH, DM, CP, CF and ash  were made using the methods of AOAC (1990).

Experiment 2: Effect of processing of taro leaves on feed intake, apparent digestibility and N retention

There were three diets, according to processing method:

FTL: Basal diet + fresh Taro leaves (FTL) chopped and fed immediately

ad-libitum

ETL: Basal diet + ensiled taro leaves (ETL) fed ad-libitum

CTL: Basal diet + cooked taro leaves (CTL) fed ad-libitum

The basal diet was composed of cassava root meal and rice bran (1:1 ratio, DM basis) with an estimated crude protein content of 6.2% in DM.

Three Mong Cai (MC) and 3 F1 (Mong Cai x Large White) pigs of the same age (about 12 weeks) with average initial weight of about 20 kg were allocated to the three treatments in two Latin square arrangements (3*3) with periods of 14 days (Table 1).

 Animals and housing

Three Mong Cai and three F1 (Large White x Mong Cai) castrated male pigs with initial body weight of 23 kg and age of three months were housed individually in metabolism cages that allowed the separate collection of urine and faeces. The size of the metabolism cage was 1.5 x 0.55 m (length x width) and they were made of galvanized steel with plastic slatted floors. The experimental periods were of 10 days: five days for adaptation to allow the pigs to become familiarized with the new diet and a five day period for collection of faeces and urine.

Diets and feeding

The taro leaves (after removing petioles) were chopped into small pieces (1-2 cm) and:  ensiled with 4% "A" molasses and stored for 14 days before feeding (ETL); cooked in boiling water for 10 minutes (CTL); or fed immediately in the fresh state (FTL).

The diets consisted of cassava root meal and rice bran (mixed in a ratio 1:1) and the taro leaves processed in the different ways (Table 2). The pigs were given restricted amounts at a level of 80% of observed voluntary intake divided among each of three meals daily. After 40 minutes the uneaten feed was collected and weighed. Amounts offered and refused were weighed and samples taken for analysis. The taro leaves were then fed separately ad libitum.  After 40 minutes the uneaten feed was collected and weighed.

Measurements

Urine and faeces of each pig were collected separately twice daily, weighed and stored at - 20 ºC. Urine was collected in a bucket via a funnel below the cage. To prevent nitrogen losses by evaporation of ammonia, the pH was kept below pH 4 by collecting the urine in 50 ml of 25 % sulphuric acid. The urine and faeces from each animal were collected for five days and at the end of the period, the faeces were mixed, dried (at 60-65 ºC), ground and representative samples taken for analysis. Dry matter of feed offered and refused, dry matter and nitrogen in faeces and nitrogen in urine were determined according to AOAC (1990).

Statistical analysis
The data were analyzed using the GLM option of the ANOVA program in the Minitab software (Minitab 2000). Sources of variation in the models were:  

Experiment 1:

Treatments (processing), sources (leaves or stems), interaction (processing*stems) and error

Experiment 2:

Treatments (processing), breed (Mong Cai or crosses), interaction (processing*breed) and error
 

Results and discussion

Experiment 1: Effect of ensiling taro leaves  or taro stem  with molasses on chemical composition

There was a marked reduction of pH from around 7 to 4 after 7 days of ensiling and then a slight increase to 4.4 (leaves) or 4.1 (stems) after 56 days (Table 3). The pH of the ensiled stems was lower than that of the ensiled leaves although both had acceptable pH levels for a good quality silage (Figure 1). Mean crude protein content was high in leaves and very low in stems. The converse was the case for crude fibre levels.

 Experiment 2: Effect of processing of taro leaves on feed intake, apparent digestibility and N retention

Intake of taro leaves

The fresh leaves were consumed at only half the rate observed for the cooked and ensiled leaves (Table 4). The taro leaves contributed 13 to 21% of the diet DM and from 31 to 45% of the total crude protein, resulting in a crude protein level in the diets in the range of 10-12% crude protein in diet DM, with the lower values corresponding to results with the fresh leaves. There were no differences between breeds in intakes of taro leaves or in total DM, when these were expressed on the basis of metabolic live weight (to account for differences in live weight between the breeds) (Tables 5 and 6).

The taro leaves contributed from 13 to 21% of the diet DM and 31 to 35% of the total crude protein, resulting in a crude protein level in the diets in the range of 10.0-11.6% crude protein in diet DM (Table 4). The intakes of ensiled  and cooked taro leaves  were higher than of fresh taro leaves presumably because of the presence of crystals of calcium oxalate in fresh leaves which can irritate the mouth and throat (Tiep et al 2006). This factor can be reduced by cooking and ensiling (Tiep et al 2006; Jiang Gaosong et al 1996; Wang 1983). The DM intake of taro leaves by F1 pigs (MCxLW) was higher than by Mong Cai pigs (Table 6).

Digestibility and nitrogen retention in growing pigs fed taro leaves

Taro leaves are high in crude protein content (25% in DM) and there were no differences in CP content according to processing method (Table 2). Using a mixture of rice bran and cassava root meal in the basal diet, which had a low crude protein content (7%) and supplementing 20% taro leaves (in dry matter) as protein source, as expected, increased the crude protein in the diets to 11% (in DM). However, the actual feed intakes were less than the planned amounts, being 16.9, 16.8 and 17.1% compared with the planned 20% (Table 7).
 

It is not known if the inability of the pigs to consume the highest levels of taro leaves was because of low palatability of the taro leaves or a physical effect due to the fibre content or even the residual level of calcium oxalate. The fibre level increase of 1-1.5 % of DM for the diets is relatively low and would not be expected to be a constraint to intake.  It would seem that some other factor is constraining the intake of taro at levels in excess of 20% of the diet dry matter.

There were no significant effects of processing method on digestibility of dry matter and organic matter (Table 8). However there were highly significant effects of processing method on the digestibility of  crude protein and crude fibre. The digestibility of crude protein was higest in ETL and lowest in FTL (p= 0.02). Similarly crude fibre digestibility was also higest in ETL and lowest in FTL (p=0.03).

Daily nitrogen retention was 10.8 g/day on the CTL diet, 10.2 g/day on ETL and 8.4 g/day on FTL (P=0.004).  This result is similar to that reported by Bui Huy Nhu Phuc et al (1996) who worked on cassava leaves as replacement for soybean meal, but was lower than that reported by Du Thanh Hang (1998) when cassava leaves replaced fish meal. There were significant differences between processing method of taro leaves in the nitrogen retained as a percentage of nitrogen consumed and nitrogen digested. These findings show that ensiling and cooking are good methods for processing taro leaves for use as a protein source in pig diets. Also the biological value of the protein in taro leaves increased from 63 % to 73 or 77% after ensiling or cooking.

There were no significant differences between MC and F1 (MC x LW) in the digestibility of DM, OM, CF and CP, but nitrogen retention and  nitrogen retained as a percentage of nitrogen consumed and nitrogen digested were higher in F1 (MC x LW)  than in MC (Table 9).

Conclusions

-Pigs given restricted amounts (80% of observed voluntary intake) of a 1:1 mixture of cassava root meal and rice bran, and free access to fresh taro leaves, which had been cooked, ensiled,  or fed fresh consumed different amounts of total DM. The range was 15.5 to 26.4 g DM/kg W^0.75 and was higher when the leaves were cooked and ensiled than when they were fed fresh.

- The taro leaves were readily consumed, providing 20% of  the dietary DM and over 40% of the dietary protein.

- The Biological Value of taro leaves was increased from 65 to 77% by cooking and ensiling.

Improved (Large White- x Mong Cai) pigs retained more nitrogen than Mong Cai when fed taro leaves as the protein source.

References

Bui Huy Nhu Phuc 2006  Review of the nutritive value and effects of inclusion of forages in diets for pigs. Workshop-seminar "Forages for Pigs and Rabbits" MEKARN-CelAgrid, Phnom Penh, Cambodia, 22-24 August,  2006. Article #7 Retrieved March 16, 107, from http://www.mekarn.org/proprf/phuc.htm

Chittavong M, Preston T R and Ogle B 2006. Ensiling leaves of Taro (Colocasia esculenta) with sugar cane molasses. Workshop-seminar "Forages for Pigs and Rabbits" MEKARN-CelAgrid, Phnom Penh, Cambodia, 22-24 August 2006.  http://www.mekarn.org/proprf/mala.htm

Du Thanh Hang and Preston T R 2005 The effects of simple processing methods of cassava leaves on HCN content and intake by growing pigs. Livestock Research for Rural Development. Volume 17, Article No. 99. http://www.cipav.org.co/lrrd/lrrd17/9/hang17099.htm

Du Thanh Hang 1998 Digestibility and nitrogen retention in fattening pigs fed different levels of ensiled cassava leaves as a protein source and ensiled cassava root as energy source. Livestock Research for Rural Development. 10 (3): http://www.cipav.org.co/lrrd/lrrd10/3/hang1.htm

Jiang Gaosong, Ramsden L and Corke H 1996: Multipurpose uses of Taro (Colocasia esculenta). Review. In Proceedings of the International Symposium held in Nanning, Guangxi, China. November 11-15, 1996. pp.262-265.
 

Rodríguez L, Lopez D, Preston, TR, Peters K 2006 New Cocoyam (Xanthosoma sagittifolium) leaves as partial replacement for soya bean meal in sugar cane juice diets for growing pigs. Workshop on Forages for Pigs and Rabbits, Phnom Penh, 22-24 August 2006. http://www.mekarn.org/proprf/rodr2.htm

Tiep P S, Luc N V, Tuyen TQ, Hung N M and Tu T V 2006 Study on the use of Alocasia macrorrhiza (roots and leaves) in diets for crossbred growing pigs under mountainous village conditions in northern Vietnam. Workshop-seminar “Forages for Pigs and Rabbits” MEKARN-CelAgrid, Phnom Penh, Cambodia, 22-24 August, 2006.  http://www.mekarn.org/proprf/tiep.htm

Wang J K 1983 Taro, a review of Colocasia esculenta and its potential. University of Hawaii Press. pp. 300-312.

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