Feed intake, digestibility and N retention in Mong Cai pigs fed ensiled cassava (Manihot esculenta Cranz) root and protein-rich foliages

Vanhnasin Phoneyaphon and T R Preston¹

Department of Animal Science, Faculty of Agriculture and Forest Resource
Souphanouvong University, Luang Prabang Province, Lao PDR
Vanhnasin83@gmail.com
¹ Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV),
Carrera 25 No 6-62 Cali, Colombia

Abstract

The aim of the study was to determine the effect of three sources of protein (soybean meal, taro foliage (Colocasia esculenta (L.) Schott) silage and cassava foliage silage) on feed intake, digestibility and N retention in Mong Cai pigs fed ensiled cassava root as source of energy. Four male Mong Cai pigs with average live weight of 12 kg were allotted at random to 4 diets within a 4*4 Latin square design.

Feed intake, apparent digestibility coefficients of DM and crude protein, and N retention, were higher when the protein supplement was soybean meal compared with ensiled taro foliage, which in turn was better than ensiled cassava foliage or a mixture of ensiled taro and ensiled cassava foliage.

Key words: Colocasia esculenta, leaves, petioles, taro

Introduction

Lon Mong Cai (Mong Cai pig) is an indigenous breed that originated from Quang Ninh province, in northern Vietnam. The breed is very well adapted to the harsh conditions in the region and is known for its early puberty, good litter size and maternal ability. The Mong Cai have been shown to perform better than Large White sows when the diet was based on forages (Nguyen Van Lai 1998; Hoang Nghia Duyet et al 2006).

Taro is well-adapted to the Vietnamese climate and can grow almost everywhere with minimal maintenance, under either dry-land or wet-land conditions (Toan and Preston 2010). The leaves are rich in vitamins, minerals and are a good source of thiamin, riboflavin, iron, phosphorus and zinc, vitamin B6, vitamin C, niacin, potassium, copper and manganese.

The foliage of Taro appears to have more potential than cassava as a protein source for pigs (Preston 2006). It was reported that Taro leaves are rich in protein (21-26% of DM) while the petioles are rich in soluble carbohydrates (Hang and Preston 2009; Rodríguez and Preston 2009; Hang and Kien 2012). However, the plant contains oxalic acid present as calcium salts which form small crystals in all parts of this plant, and when consumed cause irritation in the mouth and throat epithelium (Miller 1929). Normally, the Taro leaves are cooked with rice or rice bran and cassava roots, in order to reduce the concentration of calcium oxalate before feeding them to pigs. Recent research in Vietnam and Cambodia showed that the oxalate problem could be avoided by ensiling the leaves with molasses or combining them with the petioles (Hang and Preston 2010; Chhay Ty et al 2007; Giang et al 2011).

Cassava (Manihot esculenta, Crantz) is extensively cultivated throughout the tropics and subtropical regions due to its ability to grow in diverse soil conditions and with minimal management (Wanapat 2003; Wanapat et al 2006). The root is composed almost entirely of easily digestible carbohydrate. However, it contains cyanogenic glucosides which are changed to hydrocyanic acid (HCN) by the action of the laminarase enzyme when roots are crushed or sliced (Wanapat et al 1999). This feature of the cassava root can be a constraint to its utilization for human consumption and for livestock feeding. Sun drying the sliced root or ensiling it after grinding have been shown to reduce the levels of cyanide to tolerable levels and that ensiling was a less costly procedure than sun-drying (Loc et al 1997).

The cassava root has minimal levels of protein (<3% in DM), thus using it as the basal diet requires major supplementation with this nutrient source. However, cassava root also has minimal levels of fiber. Considered together, these two features of cassava roots (low protein and low fiber) offer the opportunity to use locally available protein-rich foliage that otherwise have limited potential for use in conventional pig diets because of their content of fiber (Preston 2006).

Incorporation of the leaves of the cassava plant in cassava root diets has been studied by Phuc et al (1995, 1996). DM and N digestibility and N retention were better when the leaves were ensiled rather than sun-dried, but these criteria were reduced linearly as the cassava leaves replaced soybean meal as the source of protein.

The purpose of the present study was to compare foliage from Taro and from cassava, preserved by ensiling, as replacement for soybean meal in a cassava root basal diet fed to growing Mong Cai pigs.

Material and methods

Location and duration

The experiment was conducted in the Technology and Research Center, Nong Lam University, Vietnam from May to July, 2015.

Treatments, experimental design and feeds

Four female of Mong Cai Pigs (initial weight 12 kg) were used to compare four treatments arranged in a 4*4 Latin Square with 10 days per period: 5 days for adaptation and 5 days for collection of feed refusals, feces and urine (Table 1).

The treatments were:

• SBM: ensiled cassava root plus soybean meal (SBM)
• TS: ensiled cassava root plus Taro silage (TS)
• CFS: ensiled cassava root plus cassava foliage silage (CFS)
• TSCFS: ensiled cassava root plus a 50:50 mixture of Taro silage (TS) and cassava foliage silage (CFS)

Animals and housing

Four male Mong Cai pigs with average live weight of 12 kg were housed individually in metabolism pens made from local materials and designed to separate feces and urine. They were bought from a pig farm in Nong Lam Province, Vietnam. They were vaccinated against swine fever and were treated against round worms with Ivermectin (1 ml/20kg LW), before starting the experiment. The pigs had free access to water through nipple drinkers.

Photo 1. Housing made from local materials	Photo 2. Mong Cai pigs in individual pens

Feeds and feeding

Cassava roots were bought in the market, chopped and ground by machine into small pieces (1 mm length) and ensiled in sealed 30 liter plastic bags for 14 days before being fed to the pigs. Cassava foliage (leaves and petioles) (bitter variety) and Taro leaves and petioles were collected from plots in the Research and Technology Transfer Center in Nong Lam University. They were chopped into small pieces (1-2cm length) and packed tightly into 30 liter plastic bags which were sealed and stored for 14 days before feeding. Soybean meal was collected from a Feed Factory in Ho Chi Minh City.

The ingredients in each diet were mixed together according to the proportions shown in Table 2 taking account of the values for DM and crude protein in the diet ingredients (Table 3). The diets were offered twice daily at 6:30am and 4:30pm, the amount being based on an offer level of 40g DM/kg live weight, but with daily adjustments to avoid refusals. Water was supplied ad libitum.

Measurements and data collection

Live weight was recorded in the morning before feeding at the beginning and at the end of each period. Feed refusals, feces and urine were collected daily during the 5 days of the collection period, and stored in the refrigerator at (4°C). To prevent loss of N from the urine, 20ml of dilute sulphuric acid (10% concentrated sulphuric acid + 90% distilled water) were added daily to each urine collection bucket. At the end of each period, samples were mixed together and ground (feeds and feces) with a coffee grinder.

Chemical analysis

AOAC (1990) methods were followed for DM and N analyses of sub-samples of feeds offered and refused and of feces; and for N in urine.

Statistical analysis

The data were analyzed by the General Linear Model option in the ANOVA program of the Minitab (2000) software. Sources of variation in the model were: pigs, treatments, periods and error.

Results and discussion

DM intake, digestibility and N retention

DM intake was highest for the diet supplemented with soybean meal and lowest for diets supplemented with ensiled cassava foliage alone. Ensiled Taro foliage supported higher intakes than ensiled cassava foliage with intermediate values for the mixed silages of Taro and cassava foliages (Table 4; Figure 1).

Figure 1. Effect of soybean meal, Taro foliage silage, cassava foliage silage and mixtures of the two silages on DM intake of Mong Cai pigs fed ensiled cassava root as the basal diet

Apparent digestibility coefficients and N retention

The apparent digestibility coefficients of DM and crude protein were highest for cassava root supplemented with soybean meal and lowest when ensiled cassava foliage was the only protein supplement; ensiled Taro foliage was better than ensiled cassava foliage with intermediate values for the mixed silages of Taro and cassava foliage (Table 5; Figures 2 and 3). Values for N retention followed the same pattern (Figures 4 and 5).

Figure 2. Effect of soybean meal, Taro foliage silage, cassava foliage silage and mixtures of the two silages on DM digestibility by Mong Cai pigs fed ensiled cassava root as the basal die		Figure 3. Effect of soybean meal, Taro foliage silage, cassava foliage silage and mixtures of the two silages on crude protein digestibility by Mong Cai pigs fed ensiled cassava root as the basal diet
Figure 4. Effect of soybean meal, Taro foliage silage, cassava foliage silage and mixtures of the two silages on N retention by Mong Cai pigs fed ensiled cassava root as the basal diet		Figure 5. Effect of soybean meal, Taro foliage silage, cassava foliage silage and mixtures of the two silages on N retention as percent of digested N by Mong Cai pigs fed ensiled cassava root as the basal diet

The results of this experiment indicate that silage made from the leaves and petioles of Taro is superior to ensiled cassava foliage (leaves and petioles) and only slightly inferior to soybean meal to provide all the protein needed to balance the energy in a basal diet of ensiled cassava root. These findings are in agreement with other reports that have demonstrated a positive role for ensiled Taro foliage as a protein source to supplement rice byproducts in diets for growth (Chay Ty et al 2007; Hang and Preston 2010; Manivanh and Preston 2011) and reproduction in pigs (Malavanh et al 2008) and growth in ducks (Giang and Preston 2011).

Conclusions

• In a basal diet of ensiled cassava root, feed intake, apparent digestibility coefficients of DM and crude protein, and N retention, were higher when the protein supplement was soybean meal compared with ensiled Taro foliage, which in turn was better than ensiled cassava foliage or a mixture of ensiled Taro and ensiled cassava foliage.

Acknowledgements

This research was done by the senior author as part of the requirements for the MSc degree in Animal Production "Improving Livelihood and Food Security of the people in Lower Mekong Basin through Climate Change Mitigation" in Cantho University, Vietnam. The authors would like to express sincere gratitude to the MEKARN II program, financed by Sida (Swedish International Development Agency) for supporting this research. We are also grateful to Le Thuy Binh Phuong and staff and of the Research and Technology Transfer Center, Nong Lam University, for providing infrastructure support.

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Received 7 July 2016; Accepted 13 September 2016; Published 1 October 2016

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