Fermented sweetpotato vines for more efficient pig raising in Vietnam

Dai Peters* - International Potato Center (CIP-Hanoi)

Nguyen Thi Tinh - National Institute of Animal Husbandry, Vietnam (NIAH)

Tran Than Thuy - Vietnam Agricultural Science Institute (VASI)

Pham Ngoc Thach - Hanoi Agriculture University (HAU)

* - corresponding author.

In the Red River Delta area near Hanoi, two on-farm trials were carried out to see if using fermented sweetpotato vines could reduce women's labor and feed processing costs, and improve pig growth efficiency. First, twelve different mixtures of sweetpotato vines, corn and cassava meals, rice bran, sun-dried chicken manure and salt were fermented, and the results were analysed for nutritional value. Nutritional analyses conducted 14, 30, 60, and 90 days after fermentation showed no significant differences over time. However, vines fermented with chicken manure had significantly higher crude protein, dry matter and ash contents than the other fermentation treatments (p<0.001). None of the preparations were found to contain aflatoxin or Salmonella. E. coli, although present in the original samples, disappeared after 14–21 days of fermentation.

The subsequent three-month on-farm feeding trial compared fresh sweetpotato vines, vines fermented with cassava meal, and vines fermented with sun-dried chicken manure and cassava meal in terms of pig growth and economic efficiency. Pigs fed the preparation containing chicken manure achieved statistically higher growth rates than those fed fresh vines (P< 0.05); neither of these feeds was significantly different from the vines fermented with cassava meal in terms of feed efficiency (P=0.013). The chicken manure preparation was also considerably cheaper (cost per kg of weight gain) than the other two preparations.

Table of Contents

Introduction

Materials and methods

Results and discussion

Conclusions

References

Introduction

In recent years, as incomes in Asia have risen, meat has become a much more important part of the diet, particularly in urban centers (Pezo et al., 2000). In Hanoi, Vietnam, meat production increased from 31,000 t. in 1997 to 33,000 t. in 1999, but this production meets only 50 per cent of the total demand of the city: the rest must come from neighboring provinces and rural areas (Tinh, 2000). Meat demand is expected to increase to 87,000 t. by 2005 and to 119,600 t. by 2010, with 80 per cent of the production coming from peri-urban farmers (Anh, 2000). Meat production in Vietnam is often constrained by shortages of feed, both local and imported. The profitability of current pig-raising practices is low, and better feed, and hence enhanced growth efficiency, are necessary for pig farmers to increase profits. Low profitability presents a serious constraint to pig farmers because pigs often provide the only source of cash income.

Sweetpotato is a valuable pig feed: the roots provide energy and the leaves protein, and both can be used fresh, dried or fermented into silage (Woolfe, 1992). It is a common feed for pigs, and other livestock, in many countries in Asia, including China, India, a few eastern islands of Indonesia (Bali and Irian Jaya), Korea, Philippines, Papua New Guinea, Taiwan, Uganda and Vietnam. In China, for example, which produces 85 per cent of the world production of sweetpotato, a large part of the crop goes to feed animals, mainly pigs (Scott, 1991; Yi Wang, CIP-Beijing, personal communication). In Vietnam, feeding sweetpotatoes to pigs is common in the north and central parts of the country.

The main constraints to using sweetpotato vines as pig feed are labor and storage. Regardless of how they are fed to the animals, the vines must first be chopped into small pieces, a daunting and time-consuming task mainly undertaken by women. If the vines are fed fresh, the women must allocate time each day for this task, even during the busy field season. Silage offers a potential alternative to overcome this constraint: sweetpotato vine silage has been a common livestock feed during winter (Sutoh et al., 1973) whenever seasonal lack of feed for livestock may limit productivity (Brown and Chavalimu, 1985). Use of vine silage overcomes both main constraints: the women are able to process the vines during the off-season when labor is more abundant, and store the silage for use when feed is limited. Moreover, there is also the economic advantage of ensiling/storing vines: to process and store the sweetpotato vines during the harvest season when vines are cheap and feed them to pigs during off-season when vines are expensive.

Ensiling may also increase nutritional value and feed efficiency if it involves a fermentation process that converts nitrogen into protein. This paper describes a fermentation trial to compare the nutritional value (particularly crude protein content) of 12 fermented mixtures of sweetpotato vines with various combinations of additives. Moreover, because high crude protein content does not necessarily guarantee better quality feed (Gerpacio et al., 1967), a subsequent on-farm pig-feeding trial was conducted to test the hypothesis that sweetpotato vines fermented with chicken manure results in better pig growth and economic efficiency.

Materials and methods

Sweetpotato Vine Fermentation Trial

The fermentation trial consisted of 12 treatments (Table 1) based on sweetpotato vines with combinations of corn meal, cassava meal, rice bran, and sun-dried chicken manure, all locally available and affordable material. The weights were based on dried ingredients except for pre-wilted sweetpotato vines which still contained 60-70 per cent moisture. To facilitate farmers preparing these combinations, the weights were calculated from the ingredients as they were fed to pigs, not on a dry matter basis. All materials were prepared (weighed, chopped, pre-wilted, mixed and put into labelled double-aerobic plastic bags) on-farm in a village in Ha Tay Province in the Red River Delta, by the farmers. Each treatment consisted of three replications for each scheduled analysis, at 14, 30, 60 and 90 days after fermentation started; hence a total of 12 samples for each treatment, or 144 samples in total were obtained. The samples remained on farm until the scheduled date for analysis when they were transported to the laboratory of the National Institute of Animal Veterinarian or National Institute of Animal Husbandry in Hanoi to be analyzed. Chemical analyses included pH and dry matter, crude protein, ether extract, crude fibre and ash contents. These analyses were derived from Vietnamese standards (TCVN), with dry matter content based on 4326-86 and from IS0-standard 6496, total ash based on TCVN-4327-86 and ISO-standard 5984, crude fibre based on TCVN-4329-86 and ISO-standard 5498, crude protein based on TCVN-4328-86 and ISO-standard 5983 (Kjeldahl method), ether extract based on TCVN-4327-86 and ISO-standard 5986, and pH determined by electrode method.

Table 1

Ingredient compositions of the twelve fermentation treatments.

¹ All treatments also contained 0.5 per cent salt

Microbiological tests for aflatoxin, Salmonella and E. coli were performed on vines fermented with various types of chicken manure, to ensure feed safety. When fermentation uses any type of chicken manure, it is essential to check feed safety. Costs of the nutrients were calculated to determine the economic efficiency. Aflatoxin analysis utilised thin layer chromatography while E. coli and Salmonella were determined from enterobacteria diagnosis.

Pig-feeding Trial

The on-farm feeding trial was conducted in the same village. Five households were selected, each with six pigs (a total of 30 pigs). All trial pigs were F1 pigs, a crossbreed between the local Mong Cai sow and the introduced Largewhite boar. Efforts were made to ensure that there were no significant difference in the weights of the piglets in each treatment of the feeding trial in order not to bias the results (P = 0.657). The sex ratio was also evenly distributed, with five female and five male pigs in each treatment. The piglets went through an adjustment period of five days before the trial began. During this period, the piglets were fed increasing amounts of fermented feed each day to help them adjust to the new diet.

In each household, two pigs were assigned to each of three treatments (i.e., two replications per treatment per household):

Treatment 5 and Treatment 6 of the fermentation trial were selected for the feed trial due to the abundance of cassava roots in this area.

The base feed was common to all three treatments and it consisted of rice bran, corn meal, cassava meal, fish meal and soy bean. The first three ingredients are commonly used by all farmers as pig feed. Fish meal and soy bean are less common in the rural area, but more commonly used by peri-urban farmers who raise pigs for the urban centers. The percentage of each ingredient was formulated based on the weight of the pigs: the bigger the pig, the lower percentage of protein and higher percentage of starch (Table 2). The recommended daily ration of this base feed also varied with pig weight: the bigger the pigs, the more ration (i.e., kg of feed) per day (Table 3).

Table 2

Ingredient compositions, nutritive value and prices of the base feed formulated for each pig weight category (per cent unless otherwise stated).

Rice bran

¹ Estimate based on National Institute of Animal Husbandry (1995, pp. 108, 114, 120, 124, 128, 134).

² Exchange rate: US$1 = 14,000 VND. The exchange rate is fairly stable and has remained approximately 14,000 for the two-year period, 1999-2000.

Table 3

Daily feeding schedule in the performance trial for each treatment based on pig weight categories.

¹ See text for description.

The trial lasted three months between 29 January and 30 April 2000 (93 days). The pigs were weighed four times: on the first day, after one month, after two months, and on the last day. The amount and the price of feed were recorded to calculate the costs of total feed and per kg weight gain.

ANOVA one way classification by Minitab 12.21 was performed to analyze the variance and determine the P value while Tukey was used to test the mean differences among categories.

Results and discussion

Sweetpotato Vine Fermentation Trial

After 30 days fermentation, the pH of all the treatments with chicken manure met the basic requirement of the acidity level (pH 3.7) for livestock (Ruiz et al., 1981) (Table 4). The pH of the treatments with chicken manure were significantly higher than the ones without, and had already attained the required level after only 14 days of fermentation. In terms of pH, therefore, the treatments with chicken manure may be regarded as more effective than fresh vines or fermented vines without chicken manure.

Table 4

Treatment effects on pH profiles in the vine fermentation trial.

¹ See text for treatment descriptions.

² Letters to the left of and to the right of the means indicate significant differences (P < 0.05) across rows and columns respectively.

Dry matter (DM), crude protein (CP), ether extract (EE), crude fiber (CF), and ash showed no significant difference over time (at 14, 30, 60, and 90 days of fermentation). However, these parameters did differ significantly across treatments, especially between treatments with and without chicken manure (Table 5): DM, CP and ash contents of the treatments with chicken manure were all significantly higher than those of the treatments without.

Table 5

Nutrient compositions of the fermented sweet potato vine treatments at 90 days (per cent off dry matter basis).

¹ See text and Table 1 for treatment descriptions.

Letters to the right of the means indicate significant differences due to treatment (P < 0.05) across columns.

Microbiological tests on vines fermented with various types chicken manure showed no aflatoxin or Salmonella in freshly dried chicken manure. E. coli was found when freshly dried, but was no longer detectable after 21 days of fermentation. The chicken manure used in this trial was purchased from a chicken farm near the trial village and the low price of the manure resulted in the low cost of crude protein and ash content in the fermented mix. In practice, farmers may collect and use manure from their own chickens. Therefore other types of chicken manure were also subjected to microbiological tests in this study. Sun dried manure from Kabir dual-purpose broilers and Tam Hoang layers, which are commonly raised by farmers, showed no aflatoxin or Salmonella: E.coli was a little more persistent in the fermented mixture, but was no longer detectable after 21 days of fermentation.

Pig-feeding Trial

In the feeding trial, the daily weight gain of the pigs over 93 days showed no significant difference between the fresh vine and non-chicken-manure fermentation (Table 6). Growth of pigs on the chicken manure treatment, however, was significantly greater than that of pigs fed fresh vines. Even though differences in the daily weight gains of pigs on the two fermented treatments were not significant, because of the large SD that resulted from the highly uneven weight of the pigs, the difference (554 versus 488 g) was quite substantial.

Table 6

Treatment effects on performance traits of pigs fed fermented sweetpotato vines under on-farm conditions.

See text for treatment descriptions.

Letters to the right of the means indicate significant differences due to treatment (P < 0.05) across columns (Tukey test by Minitab 12.21).

The chicken manure treatment achieved the highest feed and dry matter conversion rates (i.e., lowest feed or DM input per kg of weight gain), and consequently the lowest feed cost per unit of weight gain (Table 6). No statistics were performed for feed costs because the two pigs in each treatment in each household were fed together and the feed costs for each individual pig could not be determined. The farm gate prices of live pigs in the Red River Delta area have been fluctuating between 9000 and 10,000 VND/kg, so farmers would suffer a loss by feeding fresh vine and would make only a small profit by feeding the non-chicken-manure treatment. The chicken manure treatment, however, would provide farmers with a substantial profit, as well as the highest weight gain.

Conclusions

Fermentation is a simple process that requires little investment or equipment. Chicken manure is readily available and cheap because only small quantities are required. The only equipment needed is a set of scales for weighing the ingredients, and bags for storing the ferment. Thus, this fermentation method can easily be adopted, or even adapted, by farmers to improve pig growth and increase profit. During an extension meeting held soon after the trial, 40 women showed great interest and enthusiastically copied the fermentation formula and the daily feeding formulation without any prompting from the extension staff.

During the extension meeting, the women voiced their concern about the formulation of the daily diet for pigs. Not all crops included in the formulation are available year round, even though all are used as pig feed at different times of the year; and farmers cannot afford to buy fish meal or soy beans every day, however small the amount required. As a result, farmers may not be able to follow the complete feed formulation. However, the trial shows that, holding the base feed stable, vines fermented with chicken manure should yield higher daily weight gain with lower cost per unit of weight gain than feeding fresh vines or vines fermented with cassava meal. In other words, replacing fresh vines with chicken manure-fermented vines will lead to improved growth, the extent of which depends on the base feed.

These results may be disseminated widely to pig farmers in north and central Vietnam where sweetpotato vines are an important component of pig feed. Policy should be formulated to encourage the Departments of Agricultural and Rural Development at the district and commune levels to disseminate the information and demonstrate the processing and feeding method to farmers. Instead of encouraging the use of commercial protein supplement that is mainly imported, the policy should create favorable conditions for farmers to experiment with using locally available materials to increase the necessary protein for pig feed.

References

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