Oxalate concentration in taro leaves and petioles and effect of added calcium on nitrogen and calcium retention in pigs given diets containing 50% ensiled taro leaves and petioles

Du Thanh Hang and Le Van Binh

Faculty of Animal Husbandry and Veterinary Medicine,
Hue University of Agriculture and Forestry, Hue City, Vietnam
hangduthanh@yahoo.com.vn

Abstract

The objectives of the present study were to obtain more information on oxalate levels in local taro varieties and to determine if there was a need to provide higher levels of calcium in a diet containing 50% of the DM as taro leaf and petiole silage. In experiment 1, leaf and petiole samples of the three taro varieties (Mon Tim [Alocasia odora C. Koch], Chia Voi (Alocasia odora C. Koch) and Mon Nuoc [Colocasia esculenta L. Shott] [Green stem]). widely cultivated by farmers in Quang Tho village in Thua Thien Hue province were analyzed for oxalate and crude protein. Total oxalate varied little between leaves and petioles but was higher in Alocasia odora variety than in Colocacia esculenta).

In experiment 2, five castrated male pigs with initial body weight of 58 ± 0.3 kg and age of four months were randomly allotted to diets containing five levels of supplementary calcium carbonate (0, .3, 0.6, 0.9 and 1.2% in diet DM) according to a 5*5 Latin square design. The basal diet was a 50: 50 (DM basis) combination of rice bran/maize and ensiled taro leaves and petioles. Calcium retention was increased with a curvilinear trend as supplementation with calcium carbonate was increased with the optimum level coinciding with an overall calcium concentration in diet DM of 0.86%.   N retention was also increased with calcium carbonate supplementation with the optimum calcium level at between 0.79 and 0.85% in DM.

Keywords: Alocacia odora, Colocacia esculenta, insoluble oxalate, soluble oxalate

Introduction

Taro (Colocasia esculenta) is a tropical crop widely cultivated in Central Viet Nam usually in small plots near the farm house.  Assuming that harvests were made at 30 day intervals throughout the year then annual yields of Taro foliage (leaves plus petioles) would be of the order of 250 tonnes of fresh biomass (Du Thanh Hang and Nguyen Trung Kien 2012). Similar estimates were made by Ngo Huu Toan and Preston (2008). The ability of taro to grow in waterlogged conditions allows for the utilization of soils with poor drainage capacity, which are unsuitable for other crops.  According to Du Thanh Hang and Preston (2010), the total oxalate in petioles ranged from 2404 to 4416 mg/100 g dry matter (DM) while the levels in the leaves ranged from 2021 to 6342 mg/100 g DM.  Levels of soluble oxalate in the petioles ranged from 142 to 2794 mg/100 g DM while the levels in the leaves ranged from 83 to 1475 mg/100 g DM. Insoluble oxalate levels were higher than for soluble oxalate and ranged from 961 to 6259 mg/100 g DM in the leaves and in the petioles from 811 to 3613 mg/100 g DM. Oscarsson and Savage (2006) found that the total oxalate content was higher in young leaves (589±36 mg/100 g fresh basis) than in older leaves (433±15 mg/100 fresh basis) and that soluble oxalate was 74% of the total oxalate in the leaves. In the study of Mårtensson and Savage (2008), taro leaves were reported to contain 524±21.3 mg/100 g fresh weight of total oxalates (presumably as calcium salts) and 241±21 mg/100 g fresh weight in the soluble form. Such high oxalate levels may increase the risk of kidney stone formation in susceptible individuals and decrease calcium availability through soluble oxalate binding to dietary calcium in the digestive tract (Simpson et al 2009).  

The objectives of the present study were to obtain more information on oxalate levels in local taro varieties and to determine if there was a need to provide higher levels of calcium in a diet containing 50% of the DM as  taro leaf and petiole silage.

Material and methods

 Experiment 1. Oxalate and crude protein concentration in taro leaves and petioles and effect of ensiling

 Leaf and petiole samples of the three taro varieties (Mon Tim [Alocasia odora C. Koch], Chia Voi (Alocasia odora C. Koch) and Mon Nuoc [Colocasia esculenta L. Shott] [Green stem]). widely cultivated by farmers in Quang Tho village in Thua Thien Hue province were analyzed for oxalate and crude protein. They were grown in low-lying land and were collected in mid-April 2011. Three kg of each variety was sampled at a mature stage. They were harvested on the same day from the gardens of three farmers. After drying at 65 °C for 48 h they were analyzed for crude protein by AOAC (2002) and total and insoluble oxalate by the procedure developed by Savage et al (2000).

Chopped pieces of Mon Nuoc variety were spread out on a plastic sheet under a roof and allowed to wilt for 18 hours.  Five kg of wilted tissue were then mixed with 3% sugar cane molasses and 1 kg of the mixture placed into polyethylene bags (100 mm x 200 mm) and pressed to exclude as much air as possible. The bags were then sealed. After 14 days, samples were taken for DM analysis; other samples were dried at 65^°C for 18 hours for analysis of crude protein (AOAC 2002) and oxalate (Savage et al 2000).  

Experiment 2. Effect of calcium supplementation on calcium and nitrogen retention in growing pigs fed diets containing 50% ensiled taro leaves and petioles

Animals and housing

Five crossbred castrated male pigs with initial body weight of 58 ± 0.3 kg and age of four months were randomly allotted to diets containing five levels of supplementary calcium (Table 1) according to a 5*5 Latin square design.  The pigs were housed individually in metabolism cages that allowed the separate collection of urine and feces. The experimental periods were of 10 days: five days for adaptation period to allow the pigs to become familiarized with the new diet and a five day period for collection of feces and urine. The diets were based on rice bran and maize as energy sources taroleaf and petiole silage providing 50% of the diet DM. The taro silage was made by the method described in experiment 1, with 3% molasses as additive, and was stored for 14 days before feeding.

Diets and feeding

The supplementary calcium was provided as calcium carbonate at levels of 0, 0.3, 0.6, 0.9 and 1.2 (% in DM) (Table 1). The ensiled taro was fed four times per day at 7h30, 11h30, 15h30 and 18h. After 60 minutes the uneaten feed was collected and weighed.  Rice wine by-product was incorporated with the rice bran and maize and fed after the ensiled taro at 8h30, 12h30 and 19h30. Samples of feeds offered and refused were taken for analysis.

Measurements

Urine and feces of each pig were collected separately and weighed twice daily and stored at - 20 ºC. 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 feces from each animal were collected for five days and at the end of the period feces were mixed, dried (at 60-65 ºC), ground and representative samples taken for analysis.

Chemical analyses

Samples of feed and refusals were dried at 60⁰C for 24h and ground through a 1 mm sieve prior to chemical analysis. DM, calcium, phosphorus, N and ash of feeds offered and refused and feces, and Ca and N in urine, were determined according to AOAC (2002).  according to the standard methods of AOAC (2002). The total and soluble oxalate contents of 0.5 g of finely ground samples of taro silage were determined in triplicate using the method outlined by Savage et al (2000).

Statistical analysis

The experimental data were analyzed using the General Linear model of the ANOVA program in the Minitab (2000) software.  Sources of variation were treatments and error. Linear and polynomial regression equations were fitted to N and calcium retention data using the statistical functions in the Microsoft Excel software.

Results and discussion

Experiment 1. Oxalate and crude protein concentration in fresh and ensiled taro leaves and petioles
 

Total oxalate varied little between leaves and petioles but was higher in the Mon Tim (Alocasia odora) variety than in the Mon Nuoc (Colocacia esculenta) and Chia Voi varieties (Table 2). The proportions of insoluble to total oxalate was higher in leaves than in stems of Colocacia esculenta with little difference in the case of Alocacia odora.

Experiment 2. Effect of addition of calcium carbonate on calcium and nitrogen retention in growing pigs

Intakes of DM and crude protein were similar on all diets (Table 3).

Calcium retention was increased with a curvilinear trend as supplementation with calcium carbonate was increased with the optimum level coinciding with an overall calcium concentration in diet DM of 0.86% (Table 4; Figure 1). This is considerably higher than the normal requirement for growing pigs which according to NRC (2000) is in the range of 0.5 to 0.7% in DM depending on the availability of calcium in the source of the supplement. The calcium in calcium carbonate is considered to be 100% available (NRC 2000). N retention was also increased with calcium supplementation with the optimum calcium level being the same as for calcium retention at between 0.79 and 0.85% in DM (Table 5 and Figure 2).

Conclusions

Calcium retention was increased with a curvilinear trend as supplementation with calcium carbonate was increased with the optimum level coinciding with an overall calcium concentration in diet DM of 0.86%itrogen and calcium retention.

Acknowledgements

Support for this research from the MEKARM program, financed by SARECSida, is gratefully acknowledged.

References

AOAC 2002 Official methods of analysis of AOAC International (17th Ed.). Gathersberg, MD, USA: AOAC International.

Du Thanh Hang and Nguyen Trung Kien 2012  Taro (Alocasia odora (C) Koch, Xanthosoma nigra (vell) Stellfeld and Colocasia esculenta (L) schott) in Central Vietnam: biomass yield, digestibility and nutritive value. Livestock Research for Rural Development. Volume 24, Article 12.

Du Thanh Hang and  and Preston T R 2010  Effect of processing Taro leaves on oxalate concentrations and using the ensiled leaves as a protein source in pig diets in central Vietnam. Livestock Research for Rural Development. Volume 22, Article #68.http://www.lrrd.org/lrrd22/4/hang22068.htm 

Minitab 2000 In Minitab reference manual release 13.31 for Windows. Minitab Inc., Minnesota State College, USA.

Ngo Huu Toan and Preston T R  2008  Taro as a local feed resource for pigs in small scale household condition. Proceedings MEKARN Regional Conference 2007: Matching Livestock Systems with Available Resources (Editors: Reg Preston and Brian Ogle), Halong Bay, Vietnam, 25-28 November 2007 http://www.mekarn.org/prohan/toan_hue.htm

NRC 2000 Nutrient Requirements of Swine: Eleventh Revised Edition. Subcommittee on Swine Nutrition, Committee on Animal Nutrition, National Research Council

Oscarsson K V and Savage G P  2006 Composition and availability of soluble and insoluble oxalates in raw and cooked taro (Colocasia esculenta var. Schott) leaves. Food Chemistry. Volume 101, Issue 2, 2007, Pages 559-562

Savage G P, Vanhanen L, Mason S M and Ross A B 2000 Effect of cooking on the soluble and insoluble content of some New Zealand foods. Journal of Food Composition and Analysis, 13(3), 201e206

Simpson T S, Savage G P, Sherlock R and Vanhanen L  2009 The soluble and insoluble content of some New Zealand foods. Journal of Agricultural and Food Science, 57, 10804-10808.

Received 17 March 2013; Accepted 21 March 2013; Published 2 April 2013

Go to top