Use of Giant taro leaves (Alocasia macrorrhiza) for replacement of soybean meal in diets of Mong Cai sows in Central Vietnam

Hoang Nghia Duyet, Pham Thi Loan and Truong Thi Thuan

Hue University of Agriculture and Forestry

duyethue2005@yahoo.com

Abstract

Farmers in the sandy coastal area of Thua Thien Hue often grow taro in their gardens or fields and use the leaves and tubers for the pigs and roots for people. This study was carried out between September 2006 and May 2007 at 104 household farms to evaluate the benefit of growing taro and using the leaves for replacement of a conventional protein source (soybean meal) for Mong Cai (MC) sows. Results show that even on the very poor sandy soils in Vinh Phu commune farmers can get a net benefit of about five million VND per sao (500 m²), which is five times higher compared with rice production.

Eighteen Mong Cai sows from third parity were mated by AI with the same semen of a Yorkshire boar and allocated to three diets based on rice bran and cassava root meal: T0: 100% soybean meal as protein supplement, T50:  50% taro leaves and 50% from soybean; T100: 100% taro leaves. Rice bran was 20% of diet and cassava root meal 61, 49 and 38% and taro leaves 0, 22 and 42% of the DM for T0, T50 and T100, respectively. Taro leaves were chopped and boiled for 10 minutes before mixing with other ingredients. Feeding was 1.2 kg DM/day in pregnancy and ad lib in lactation

 Litter size at birth was 12.1, 12.7, 13.2 and at weaning 10.7, 11.1, 11.3 for T0, T50 and T100, with no differences among treatments. Piglet weight at weaning decreased with increasing level of taro leaves (7.15, 6.95, 6.48 kg) but did not differ for litter weight (76.2, 77.6 and 73.5 kg). Live weight loss of sows during lactation increased (7.31, 10.95 and 16.0%) and time to re-mating increased (7.2, 8.5 12.7 days) with increasing level of taro leaves. Economic benefit was increased linearly with substitution of soybean by taro leaves.

Keywords: Boiling, cassava root meal, lactation, piglets, reproduction, rice bran

Introduction

Taro has been grown for thousands of years in the tropics (Mai Thach Hoang and Nguyen Cong Vinh 1003). The starch grains of the corms are very small, which makes taro highly digestible. The level of crude protein is slightly higher than that in yam, cassava or sweet potato (FAO 1993). The chemical composition of Colocasia esculenta is as follows: Tubers, dry matter (DM) 26.2%, crude protein (CP) 8.7% and leaves DM 8.2%, CP 25%. When cooked taro tuber was used for feeding growing pigs, average gain was 590g/day and feed conversion ratio (FCR) 3.2 kg feed/kg gain (Anon 1985).

In the coastal area of Thua Thien Hue Province (Phu vang, Phong dien and Huong Thuy districts), farmers have been growing several species of taro, such as Bac Ha (Alocasia odora), Quang (Xanthosoma violeaceum) and Cham (Colocasia esculenta) in the sandy soil areas. On average households plant taro on about 500 m² for leaves and roots. Mean yield is about 10 tonnes of root and 20 - 30 tonnes of leaves per hectare per crop (Hoang Van Tha 1003). The chemical composition is as follows: DM 22% and CP 17 - 23% in DM (NIAH 1001). Taro leaves are commonly given to pigs, especially to MC sows.

Vietnam has about one million Mong Cai (MC) sows, concentrated in the North and Central part of the country (Hoang Nghia Duyet 1992). Traditionally farmers in Central Vietnam use large amounts of vegetables in the diet of MC sows, such as sweet potato leaves, taro leaves and water spinach, mixed with rice bran, cassava root meal, broken rice, and then cook the mixture before feeding. Taro leaves have high nutrient content (high CP and vitamin content, and well balanced amino acids), but have a high oxalic acid content. Farmers often select the cheapest materials such as rice bran, cassava root meal and sweet potato root meal for feeding pigs, including taro leaves and stems,  that they grow in their garden or in the field. A forage based diet is useful for MC sows, because then the sows do not become so fat during pregnancy, and the milk production is higher. Duncan et al (1960) reported that the effect of vitamin and mineral levels on the reproductive performance of the sows is more important than high protein levels. Mong Cai sows can obtain these nutrients from high levels of forage in the diet. Le Thi Men et al (1999) and Hoang Nghia Duyet et al (2003, 2004) showed that a suitable proportion of forage leaves in the diet of MC sows is 30 - 40 % (in DM) in the pregnancy period and 20 - 30% in the lactation period. However, very little research has been done on the use of taro leaves as replacement for conventional protein sources in diets for MC sows. In view of rapidly increasing price of soybean meal, it is important to find alternative protein sources for MC sows.

Hypotheses

• Conventional protein sources in the diets of MC sows can be replaced by taro leaves, without reducing reproductive performance.

• Higher benefit can be obtained using a higher ratio of taro leaves in the diet of the sows.

• The optimum ratio of taro leaves in the protein supplement in diets for MC sows is 50%.

Material and methods

Eighteen local third parity Mong Cai sows were randomly allocated to three treatments:

• T₀: 100 % of protein supplement from soybean meal

• T₅₀: 50 % of protein supplement from soybean meal and 50 % from taro leaves

• T₁₀₀: 100% of protein supplement from taro leaves

The experimental model is shown in Table 1.

Growing and processing of the taro leaves:

Taro leaves were purchased from farmers who grow the crop in their fields or gardens. The foliages were harvested by taking leaves and stems from the taro plants, chopping them finely (3 -5 mm in length) and mixing in the planned ratio according to the dietary treatment. The mixture was then boiled for 10 minutes to destroy the calcium oxalate, and allowed to cool before feeding. The diets were offered 2 times per day (at 10.00h and 17.00h) in pregnancy and 3 times per day (at 07.00, 12.00 and 17.00h) in lactation.

Animals:

In total 18 MC sows were selected from farms in Vinh Phu commune (Phu Vang district). All were in their third parity with a live weight of about 80 kg. They were allocated at random to the three diets. All were mated by AI with semen from the same Yorkshire boar. The sows were kept in individual concrete floored pens and were fed the experimental diets from three weeks after mating.

The amount of feed (DM basis) was the same in all treatments. During pregnancy, the sows were given  1.2 kg of feed (in DM) per day. In lactation the sows were fed with increasing amounts after farrowing and after 5 days were fed ad-libitum. The crude protein level was 13% in DM both in pregnancy and lactation. The ingredient and chemical composition of the feedstuffs and experimental diets are shown in Table 2, 3, 4 and 5.

Measurements:

For the Taro:

Growing time, time at start and finish of harvesting, yield of stems, leaves and roots and economic benefit of growing taros (income for one Sao = 500 m²)

For the Mong Cai sows:

Litter size at birth and at weaning (piglets/ litter), live weight of the piglets at birth and at weaning (kg/ piglet).

Litter weight of piglets at 21 days of age, FCR and price for producing1 kg of weaned piglets (kg feed / kg weaned piglet and price).

An economic comparison was made between the diets.

Results and discussion

Agronomy trial

Table 6 and Figures 1, 2 and 3 show that the main taro species grown in the sandy soil of Vinh Phu commune are Bac Ha (Alocasia odora), Mon Quang (Xanthosoma violeaceum) and Mon Cham (Alocasia esculenta). Although these species are very well adapted and produce very high yields of leaves and roots the average area for growing taros in Vinh Phu is still small.

Table 7 and Figures 4 and 5  show that although only one crop per year of taro is grown in the sandy soils of the commune, very high yields and benefit per unit area are possible: about 10 tonnes of leaves and stems, and 1 tonne of roots per sao. Total income ranged from 5.6 to 6.2 million VND / sao. If compared with rice, growing taro can result in 5 times higher benefit. When comparing communes, Table 7 also shows that the yield of stems and leaves was almost the same (P>0.05), but the yield of roots and total benefit was higher in Bac Ha and Quang, and lower in Cham (P<0.05).

Reproduction in Mong Cai sows

Table 8 and Figures 6, 7, 8 and 9 show that length of pregnancy, litter size at birth and at weaning, and percentage of piglets alive at weaning were very high and between treatment differences were non-significant. Sow live weight at farrowing and at weaning were significantly higher in treatment T₀ and were lowest in T₁₀₀ (P< 0.05), but total litter live weight at weaning was not significantly different between treatments (P>0.05). 

Table 9 and Figures 10 and 11 show the total live weight/litter of piglets at 21 days of age, which is an indication of the potential milk production of the sows. The percentage of live weight lost during the lactation period, the time to re-mating of the sows after weaning and the number of litters / sow / year were higher in treatments T0 and T50 than in T100 (P< 0.05), but the differences between T0 and T50 were non-significant (P>0.05).

Table 10 and Figures 12 and 13 show that the total feed to produce 1 kg live weight of weaned piglets was not significantly different between treatments (P>0.05), but feed cost was much higher in treatment T₀ and lowest in treatment T₁₀₀ (P<0.05), and so net benefit was highest in treatment T₁₀₀ and lowest in treatment T₀ (P<0.05).

Conclusions

·        Taro leaves can completely replace soybean meal in the protein supplement for MC sows without reducing reproductive performance, except for higher sow live weight loss in lactation and increased weaning to service interval.

·        Economic benefits were highest when taro leaves replaced all the soybean meal in the diet for pregnant and lactating MC sows.

Acknowledgements

The authors are grateful to the MEKARN project, financed by Sida – SAREC, and assistants Ms. Pham Thi Loan and Ms. Truong Thi Thuan for their technical help. Thanks are also due to the 18 farmers in Vinh Phu commune, Phu Vang Distric, Thua Thien Hue province, who shared their experiences and participated actively in this study.

References

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NIAH (National Institute of Animal Husbandry) 2001  Composition and nutritive value of feeds in Vietnam.

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