Taro leaf silage and water spinach as replacement for soybean meal in diets of Mong Cai gilts during pregnancy and lactation

Malavanh Chittavong

Faculty of Agriculture, National University of Laos, Vientiane City, Lao PDR
malavanc@yahoo.com

Introduction

In Laos, commercial pig farms are found near population centres such as Vientiane. These agribusinesses are small cottage industries with few employees. In general, production costs tend to be high, since semi-intensive pig production is dependent on concentrate feed which, in many cases is imported from Thailand. Concentrate feeds are mixed with locally available feeds such as rice bran and brewers' grains to reduce production costs (Stur et al 2002). In view of the high production costs, because of the increasing prices of concentrate feeds, and especially protein concentrates such as soybean and fish meal, recent research in Vietnam, Cambodia, and Laos has been directed to the use of leaves from crops such as cassava (Hang and Preston 2005; Chhay and Preston 2005), sweet potato (Malavanh and Preston 2006) and mulberry (Cheiv et al 2003), and water plants such as water spinach (Men et al2000; Ly 2002) for feeding pigs and supplemented with local energy feed resources such as sugar cane juice, cassava root, palm oil and broken rice (Rodríguez et al 2006; Chhay and Preston 2006; Kea et al 2003). All these energy feed resources are very low in protein content in the dry matter and as a consequence of this all the amino acids in the diet have to be supplied in a protein supplement (Preston 1995).

Leaves from Taro (Colocasia esculenta (L.) Schott), Giant taro (Alocasia macrorrhiza), and New Cocoyam (Xanthosoma sagittifolium) are traditionally used in pig diets by small-scale farmers in many tropical countries. A preliminary report from Colombia (Rodríguez et al 2006) showed that weight gains in young pigs fed a sugar cane juice diet were the same when the supplementary protein was from a 50:50 mixture of fresh leaves of New Cocoyam and soy bean meal compared with soy bean meal as the only protein source. Also results from Tiep et al (2006) show that including 10% ensiled Alocasia macrorrhiza leaves (replacing fish meal and soybean meal) with 45% Alocasia macrorrhiza root meal in diets for crossbred (Yorkshire x Mong Cai) pigs had no negative effects on performance, and resulted in higher benefit for the farmers in mountainous areas in Northern Vietnam.

Water spinach (Ipomoea aquatica) is a water/marsh plant which grows well in the water or in the soil. It is traditionally consumed by people in South East Asia and appears to be devoid of non-nutritional elements. The fresh leaves and stem of water spinach have a crude protein content of 28 % of DM (AFRIS 2005). It has been shown that fresh, chopped water spinach can replace 30% of the DM of concentrate diets for gestating sows and 15% of the diet of lactating sows of both local (BaXuyen) and exotic breeds (Large White), resulting in somewhat improved reproductive performance and welfare (Men et al 2000)

Objectives

• To determine the optimum level of molasses additive for ensiling taro leaves

• To evaluate the effect of protein-rich leaves as replacement for soybean meal on the performance of Mong Cai gilts during gestation and lactation

• To determine the apparent digestibility coefficients in the early and late stages of gestation in Mong Cai gilts fed ensiled cassava roots and broken rice with protein derived from different ratios of soybean meal and a mixture of taro leaf silage and water spinach

General discussion

Feed resources for pig production in Laos

In Laos, where many farmers are growing paddy rice for sale, pig diets are usually based on rice bran as the main ingredient, fed together with a small amount of green feed. Green feed or vegetable matter is traditionally collected from forest margins and fallow fields and includes Colocasia esculenta, Alocasia macrorrhiza, Crassocephalum crepidioides, paper mulberry leaves and several other herbs, depending on local availability. Some farmers also feed the residues from making rice wine and spirits, maize, cassava root, and in some cases broken rice. In all situations the main feed ingredient is rice bran of varying quality. Many micro rice mills are not able to effectively separate rice husks from the bran, resulting in a lower-quality product with reduced protein and high fibre content. Rice bran tends to be available for most of the year, except for a short period in July to September before the new rice is harvested. The use of Stylosanthes guianensis CIAT 184 as a supplement to traditional feeds has great potential for resource-poor smallholder farmers in the uplands of Lao PDR. Legumes can be grown on farm, save labour and increase the productivity of pigs (Phengsavanh and Stur 2006; Keoboualapheth 2003). Recent research in Laos has focused on local protein feed resources from crop and fishery products for feeding pigs, such as sweet potato leaves and water spinach (Chittavong and Preston 2006), Stylosanthes guianensis, dry cassava leaves (Koutsavang 2005) and Golden Apple Snail (Pomacea spp) (Kaensombath 2005).

Nutritive value and anti-nutritional compounds of Taro

Taro (Colocasia esculenta (L.) Shott) is a member of the Araceae family, which originated in India and South East Asia, and is presently cultivated in many tropical and subtropical countries (AFRIS 2005; Lee 1999). It can be grown under flooded or upland conditions. Although it has high yielding potential, most taro varieties contain an irritating or acrid agent and can not be eaten fresh. Research has demonstrated that taro, despite its high moisture content can be ensiled. The resultant silage stores well and is acceptable to sheep and pigs and can be used as animal feed. An integrated taro production system that produces fresh taro for food, uses taro top silage for swine production, and uses excess corms for fuel production has been developed (Wang et al 1981). Taro leaves are rich in vitamins and minerals, and are a good source of thiamin, riboflavin, iron, phosphorus, and zinc, and a very good source of vitamin B6, vitamin C, niacin, potassium, copper, and manganese. Taro corms are very high in starch, and are a good source of dietary fiber, vitamin B6, and manganese. Oxalic acid may be present in the corm and especially in the leaf, and calcium reacts with the oxalate to form calcium oxalate which is very insoluble. The chemical and essential amino acid composition of taro is shown in Tables 1 and 2.

Table 2: Essential amino acid composition of Xanthosoma sagittifolium (g/kg protein), and requirements of growing pigs and lactating sows
	Xanthosoma sagittifolium a	Xanthosoma sagittifolium b			Requirements b, c
	Leaves	Leaves	Stems	Tubers	50 kg pigs	Lactating sows
Arginine		50.0	31.0	37.0	17.0	27.0
Histidine		19.0	15.0	10.0	15.0	21.0
Isoleucine		37.0	26.0	17.0	27.0	29.0
Leucine		75.0	49.0	33.0	46.0	55.0
Lysine	4.60	56.0	40.0	28.0	48.0	52.0
Methionine	2.71	18.0	11.0	7.00	13(28)d	13 (25)d
Phenylalanine		47.0	29.0	24.0	28 (45)d	27 (57)d
Threonine	4.95	42.0	29.0	28.0	33.0	33.0
Tryptophan		13.0	8.00	5.00	9.00	9.00
Valine		48.0	38.0	35.0	34.0	34.0
Source: aRodríguez et al 2006; bLeterme et al 2005 c Requirements: pigs of 50-80 kg, 15.5% crude protein in the diet d In brackets: requirements for methionine + cystine and phenylalanine + tyrosine.

Anti-nutritional factors in pig feed are widespread, and may lower feed intake, nutrient utilization, food conversion efficiency and hence animal performance as well as economy. At high levels of dietary intake toxicity ensues and sometimes even animals will die (Phuc 2006). FAO (1990) reported that the high content of calcium oxalate crystals (about 780 mg per 100 g in some species of cocoyam, Colocasia and Xanthosoma) has been implicated in the acridity or irritation caused by cocoyam. Oxalate also tends to precipitate calcium and makes it unavailable for use by the body. Oke (1967) has written an extensive review of the role of oxalate in nutrition, including the possibility of oxalaurea and kidney stones. The soluble oxalate content of the raw leaves of taro (Colocasia esculenta (var.) Schott) was 236 mg oxalate/100 g wet matter (WM) (Savage et al 2006). Soaking the raw leaves in water for 30 min was shown to marginally reduce the soluble oxalate, while soaking for 18 h resulted in a 26% reduction, although the insoluble oxalate (calcium oxalate) content of the leaves remained constant. Boiling the taro leaves resulted in a 36% loss of soluble oxalates, and is considered to be an effective way of reducing the soluble oxalate content (Savage et al 2006). This is in agreement with the present study (Paper I), in which the concentration of oxalic acid in fresh and ensiled leaves of taro was found to be 2.20 and 0.37 % of DM, respectively. The acridity of high oxalate cultivars of cocoyam can also be reduced by peeling, grating, soaking and fermenting during processing. Acridity can also be caused by proteolytic enzymes, as in snake venoms. Attempts have been made to isolate such enzymes from taro, Colocasia esculenta, and the principal component has been called "taroin" by Pena et al (1984).

Ensiling taro leaves

Principle of ensiling

In the humid tropics, sun-drying is difficult, often resulting in a low quality product with severe Aspergillus mould and related aflatoxin contamination (Gómez et al 1988). Ensiling is the preservation of forage (or crop residue or by-product) of high moisture content based on a lactic acid (ideally) fermentation under anaerobic conditions (Moran 2005; McDonald et al 2002). Ensiling can also render some previously unpalatable products useful to livestock by changing the chemical nature of the feed (Chedly and Lee 1998). The term fermentation is a process to describe the breakdown of carbohydrate materials under anaerobic conditions (Potter 1978). Ensilage is a simple and low cost option, which can preserve feeds that are seasonally abundant for later feeding during periods of feed shortage (Kaensombath 2005). Ensilage of forage can be carried out with simple technology so that forages such as tropical grasses, forage legumes, forage tree legumes, forage sorghum and pennisetums can be produced and ensiled successfully in this way. However, there is still much to be researched in how the quality of these silages, both in terms of fermentation and nutrition, can be improved through the use of intercropping or mixing at ensilage, and with the use of additives. There is also potential for the ensilage of many agro-industrial by-products with forages and legumes and this needs increased attention in the field of research into low-cost feeds for livestock (Titterton and Bareeba 1999).

Nutrient losses in silage

Ensiling material with less than 30% DM may create an environment that is totally anaerobic (suited to clostridial bacteria) rather than micro-aerophilic (suited to lactic acid bacteria). In addition, it may result in the loss of valuable nutrients because water and soluble nutrients accumulate at the bottom of the silo as silage effluent (Titterton and Bareeba 1999). The crops cut and ensiled the same day, nutrient losses are negligible and even over a 24 hour wilting period, losses of dry matter of not more than 1 or 2 percent (McDonald et al 2002). Over periods of wilting longer than 48 hours, considerable losses of nutrients can occur depending upon weather conditions. Dry matter losses can be as high as 6 percent after 5 days and 10 percent after eight days of wilting in the field. The main nutrients affected are the water soluble carbohydrates and protein, which are hydrolysed to amino acids (McDonald et al 2002).

Silage additives

Silage additives can be classified into two main types: fermentation stimulants, such as sugar-rich materials, inoculants and enzymes, which encourage the development of lactic acid bacteria, and fermentation inhibitors, such as acids and formalin, which partially inhibit microbial growth (McDonald et al 1995). The main function of a silage additive is to increase the nutritional value or improve fermentation (Ohio Sate University Extension 2001).

Molasses is the carbohydrate source used most frequently, and is of particular benefit when applied to crops low in soluble carbohydrates, such as tropical legumes and grasses. Good silages have been reported when molasses was applied at 3-5% (Bareeba 1977; Sarwatt 1995). However, if the treated silage has a very low DM content, most of the carbohydrate source may be lost in the effluent during the first few days of ensilage in pits or bunkers.

The advantages of ensiling

The advantages of ensiling are the following:

• For feeding to livestock at times of the year when the original material is not available

• Increasing feed resources and an insurance for high nutrient demands

• Reducing demands on homegrown forages

• Improvement of the palatability of the original material

• Reducing toxicity to safe levels

• Destroying harmful bacteria

Ensilage of taro leaves for feeding pigs

The leaf of taro contains around 25% crude protein in dry matter, in addition to calcium, phosphorus, iron, vitamin C, thiamine, riboflavin and niacin (AFRIS 2005), and also soluble oxalate (236 mg oxalate/100 g wet matter according to Savage et al 2006). The leaves can be chopped and ensiled with molasses to considerably reduce undesirable substances in Taro, which thus becomes more appetising for pigs. Prior to feeding to the Mong Cai gilts in the present study, the leaves were made into silage, with levels of sugar cane molasses of 0, 2, 4 and 6%, and the silage was evaluated at 0, 14, 21 and 28 days (Paper 1). A level of 4% molasses and an ensiling period of from 14 to 21 days appeared to be the most appropriate for ensiling the leaves, as determined by pH and ammonia concentration. In the present study (Paper I), ensiling taro leaves for 21 days with 4% molasses reduced oxalate concentration from 2.20 to 0.3% of DM. Recently Tiep et al (2006) reported that ensiling Alocasia macrorhiza leaves with 7% rice bran and 2% molasses reduced the oxalate content by 79% at 30 days, and maintained the pH at 4.05-4.12 until 60 days after ensiling, without reducing the nutritive value of the silage. Including 10% of Alocasia macrorhiza leaves and 45% of Alocasia macrorhiza root meal as replacement for fish meal and soybean meal in the diet of crossbred pigs (Yorkshire x Mong Cai) had no negative effects on performance, and resulted in higher benefits for the farmers (Tiep et al2006)

Water spinach (Ipomoea aquatica)

Water spinach (Ipomoea aquatica) is a water plant that has high biomass productivity. There are two common types of water spinach: one that grows on land and one that grows in water. The first is an aquatic plant or paddy vegetable in the Southern part of India and Southeast Asia, propagated by cuttings and growing in the wild or cultivated in fish ponds and water courses. The second is an upland vegetable, cultivated on dry or marshy land and propagated by cutting or seeds (Palada and Crossman 1999). The plants has hollow, water-filled stems and shiny green leaves, and big funnel-shaped flowers, 2-5 cm long, and purple or white in colour. Water spinach can reproduce sexually by producing one to four seeds in fruiting capsules or vegetatively by stem fragmentation (Dressler 1996). An important feature of water spinach is its capacity to yield high levels of biomass when fertilized with effluent from biodigesters charged with pig manure (Kean and Preston 2001). It is cultivated mainly as human food, but is also used as feed for pigs and cattle in Southeast Asia (AFRIS 2005; Gohl 1981).

Nutritive value of water spinach

The fresh leaves and stems of water spinach contain 20.0 to 31% CP in DM basis (Phuc 2000; Luyen 2003) that is well-balanced in essential amino acids, i.e. 1.3% lysine, 0.4% methionine and 1.1% threonine on a DM basis (Men et al 2002). Ash and crude fiber concentrations of around 12 and 13.6% of DM, respectively have been reported (Gohl 1981; Chittavong and Preston 2006), and water spinach has a lower fibre content than alfalfa leaves (Thacker 1990). Most tropical leaf vegetables are rich sources of nutrients, particularly minerals and vitamins (Oomen and Grubben 1978). The trace mineral content of fresh water spinach (mg/kg) was: Zn 5.03, Mn 22.2, Cu 1.37 and Fe 75.3 according to NIAH (1995).The chemical composition of water spinach is shown in Table 3.

Use of water spinach as a protein supplement for pigs

The feeding of water spinach for growing pigs has been studied in Cambodia (Chhay and Preston 2005; Kea et al 2003), Laos (Chittavong and Preston 2006) and Vietnam (Men et al 2000; Dung et al 2006). Recent research has shown that fresh water spinach was more palatable than cassava leaves for growing pigs, as reflected in higher total DM intake, and the proportion of the diet (47%) provided by the leaves (Chhay and Preston 2005). Kea et al (2003) found that the growth rate of pigs was improved when dried fish was fed at a level of 6% of a diet of broken rice and water spinach. It has been shown that water spinach can replace 30% of the DM of concentrate diets for gestating sows and 15% of the diet of lactating sows of both local and exotic breeds, resulting in somewhat improved reproductive performance (Men et al 2000). The results in Paper II support the findings of Men et al (2000).

Effect of tropical forages on the reproductive performance of pigs

The use of tropical energy-rich feeds low in protein, such as cassava, sugar cane juice and sugar palm syrup facilitates meeting requirements for essential amino acids with lower overall levels of protein in the diet, as compared with temperate country diets based on cereal grains, the protein of which contains many non-essential amino acids, thus requiring higher overall levels of protein to meet the needs of essential amino acids (Preston 1995). Preliminary research from Men et al (1997) showed that fresh duckweed and cassava root silage can replace half of the conventional protein sources (soybean meal and fish meal) and energy sources from cereal grain and improved the reproductive performance of sows. Duyet et al (2006) reported that a mixture of foliages (sweet potato leaves, water spinach and cassava leaves) can replace 50% of a conventional protein supplement for both Mong Cai and Yorkshire sows without affecting piglet performance or sow reproduction, and resulting in lower feed costs per kg of piglet weight gain. This is in agreement with Paper II, in which it is shown that a mixture of taro leaf silage and water spinach can replace 100% of the soybean meal in pregnancy and lactation diets for Mong Cai gilts without affecting sow reproduction, measured as numbers of live piglets born and weaned, and the interval from weaning to estrus. However, total litter weight at weaning decreased with a linear trend as the soybean was replaced by the forages.

Effect of fibrous forages on digestibility in pigs

Feeding diets with a high fiber content increases the time needed to consume the daily allowances (Morz et al 1986). The utilization of fiber in pigs depends on the level of fibre fed, source of fiber, stage of forage maturity, and level of other nutrients in the diet (Farrell and Johnston 1973). Ogle (2006) indicated that as well as dietary fibre, other mechanisms are involved in the reduction in nutrient digestibility on high forage diets, including level of feeding, processing of the forage, the age of the pig, increased rates of passage of digesta as a result of its increased bulk and water-holding capacity, and irritation of the gut wall mucosa by VFA produced in the hind-gut. Le Goff and Noblet (2001) reported that the digestibility of energy increased from 82.1 to 85.2%, of crude protein from 80.3 to 85.1% and of NDF from 56.3 to 64.4% in mature sows as opposed to growing pigs. However, it would appear that in our study (Paper III) the difference in age (from early to late stage of the first pregnancy) was not sufficiently large to have been a factor influencing digestibility, as there were no differences in digestibility coefficients found between these two stages.

The nutrient requirements of pigs

According to Preston (1995), the nutritional requirements for pigs reared in tropical regions are different from those in the temperature countries. High ambient temperatures can be beneficial in that little energy is needed to maintain body temperature. On the other hand, there is the negative effect of high ambient temperature with respect to the reduction that occurs in voluntary feed in take. The protein needs of pregnancy are for maintenance, deposition of reproductive tissue, especially conceptus tissue, and for maternal gain. Other factors may be pregnancy anabolism associated with the catabolism of body reserves in the previous or subsequent lactation or true growth if the sow has still to reach mature body weight (Close and Cole 2000). The requirements for nutrients, including amino acids, vitamins and minerals of sows in gestation and lactation are shown in Tables 4 and 5.
 

Conclusions

• Taro leaves can be preserved by ensiling with sugar cane molasses. A level of 4% molasses and an ensiling period of from 14 to 21 days appeared to be the most appropriate for ensiling taro leaves, as determined by pH and ammonia and oxalate concentration.

• A mixture of taro leaves silage and water spinach can replace 100% of soybean meal in pregnancy and lactation diets for Mong Cai gilts without affecting sow reproduction, measured as number of live piglets born and weaned, and the interval from weaning to estrus. However, litter weights at weaning decreased with a linear trend as the soybean was replaced by the forages.

• Digestibility of dry matter, crude protein, organic matter and crude fibre decreased with increased proportions of a mixture of taro leaf silage and water spinach replacing soybean meal in a basal diet of ensiled cassava root and broken rice, but there was no effect of stage of pregnancy.

• The limiting factor to the utilization of the taro leaf silage and water spinach appears to be the lower apparent digestibility of the protein.

Acknowledgements

The studies in this thesis were carried out at the farm of the Faculty of Agriculture, National University of Laos, Vientiane City, Lao PDR. The author gratefully acknowledges the Swedish International Development Co-operation Agency, Department for Research Cooperation (Sida-SAREC) for its financial and material support of this study.

I would like to thank the Faculty of Agriculture, National University of Laos, Vientiane City, Lao PDR, for allowing me study leave and helping me to carry out the studies.

I would like to express my sincere gratitude to Professor Dr Brian Ogle my main supervisor, the director of the MSc course, for his kind, support, professional guidance, and valuable advice in many different ways.

I wish also to express thanks to Dr Thomas Reg Preston, my associate supervisor, Director of the University of Tropical Agriculture (UTA) for his guidance, discussion, encouragement and much good advice.

I would like to thank Professor Dr Inger Ledin, Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, for her scientific guidance and warm heart during the MSc course.

I would also like to express my appreciation to all professors, doctors, and lecturers who gave the theoretical lectures and supervised the practical work in the MSc course.

My sincere thanks to Dr. Luu Trong Hieu, the regional consultant of the Sida-MEKARN project, Dr Ngo Van Man, the regional coordinator of the Sida-MEKARN project, Dr Bounthong Bouahom, the director of National Agriculture and Forestry Research Institute of Laos (NAFRI) and Dr Thongly Xayyachak, the Dean of the Faculty of Agriculture of the National University of Laos, for their help and encouragement.

I would like to thank the Feed Analysis Laboratory of the Department of Livestock and Fisheries of the Ministry of Agriculture and Forestry for analysis of samples.

Special thanks to all staff of Faculty of Faculty of Agriculture, National University of Laos, for their help, suggestions and comments.

Many thanks to my classmates in the MSc course for their contributions, suggestions and friendship.

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