A study on cassava residue preservation for dairy cattle feeding

Cassava (Manihot esculenta, crantz) is an important food crop for many tropical zones in the world such as Africa, Asia and Latin America. In Vietnam it is an annual plant with the purpose of obtaining its tuber as food and ranked as the third, food crop after the rice and maize. In recent years when rice production has been more than enough for the domestic food demand of the people, cassava has become a raw material as starch for the processing industry. In the country, there have appeared many agricultural zones where cassava is planted for starch production. The residue from the cassava starch production is by-product which may contain 8% of starch, 15-20% of crude fibre and thus could be theoretically used as ruminant feed.

A STUDY ON CASSAVA RESIDUE PRESERVATION FOR DAIRY CATTLE

FEEDING

Bui Quang Tuan

Hanoi Agricultural University

Abstract

Cassava residue samples were taken to determine chemical composition, HCN and aflatoxin contents In a laboratory experiment cassava residue was ensiled with either 0.5% salt or 0.5% salt plus 3% molasses (on a fresh matter basis) Fermentation characteristics of the silages were determined at 4 weeks of ensiling Results showed that cassava residue was very poor in CP and minerals Sun-drying was difficult because fresh cassava residue contained very high moisture levels (>80%) HCN content was very high in fresh cassava residue (162.4 mg/kg), but it decreased rapidly with storing time (8.84 mg/kg after 10 days of storage) Aflatoxin content of sun-drying cassava residue was low (33.5µg/kg) Cassava residue ensiled with 0.5% salt had a white color and cassava residue ensiled with 0.5% salt plus 3% molasses had a light yellow color with a pleasant smell The pH value of the silages was 3.9, the lactic acid content was relatively high (0.89 and 1.14%, respectively) Utilization

of ensiled cassava residue with 0.5 % salt instead of cassava meal in dairy cow’s ration as an energy source guaranteed high milk production (17.2 kg milk/head/day), decreased feed cost/kg milk (1,549 vs 1,805 VND/kg milk)

Introduction

Cassava (Manihot esculenta, crantz) is an important food crop for many tropical zones

in the world such as Africa, Asia and Latin America In Vietnam it is an annual plant with the purpose of obtaining its tuber as food and ranked as the third, food crop after the rice and maize In recent years when rice production has been more than enough for the domestic food demand of the people, cassava has become a raw material as starch for the processing industry In the country, there have appeared many agricultural zones where cassava is planted for starch production The residue from the cassava starch production is by-product which may contain 8% of starch, 15-20% of crude fibre and thus could be theoretically used as ruminant feed However, without immediate treatment the high water content in this product could promote mould growth At the same time, there exists cyanogen as a toxin retained in this by-product Many dairy farms have used this by-product as animal feed but there have been several cases of intoxication which have caused considerable economic losses for the farmers Therefore, there is a practical need for research into processing and preserving cassava residue

to become a safe feed for ruminants

Materials and Methods

Survey on sources of cassava residue

The potential sources of cassava residue was determined by a field survey on traditional cassava starch production operations in Duong Lieu, Cat Que, and Lien Hiep communes (Ha Tay province) Data were collected from production reports of the communes

Ensiling cassava residue

Under laboratory conditions cassava residue was ensiled in plastic vessels or chambers for fermentation and under farm conditions in sealed nylon sacks with 2 ensilage formulae as follows:

Formula 1: Cassava residue with 0.5% salt (on fresh basis);

Formula 2: Cassava residue with 0.5% salt plus 3% molasses (on fresh basis)

After 4 weeks of fermentation reprsentative samples were taken for assessment of color, smell, pH, organic acids, aflatoxin and HCN contents Determination of pH followed the method of Hartley and Jones (1978) with 5g of sample added into 100 ml of distilled water in

a beaker which was then shaked for a while and kept during 15 minutes before measuring with

a pH meter

Feeding trial

A feeding trial with dairy cows was carried out at dairy households in Dong Thap commune (Dan Phuong, Ha Tay) from January to April 2005 In the dairy cow diet ensiled cassava residue was considered as an energy source to replace cassava meal for the diet recommended by Guyomarch company Dairy cows were raised in 4 households with 2 cows each The nutrient requirements of the experimental cows were calculated following NRC recommendations (1989) The trial lasted for 2.5 months (excluding 15 days of the adaptation period)

Table 1 The experimental design of the feeding trial

Milk yield before exp (kg/head/day) 20.7 ± 0.3 21.0 ± 0.4

Cassava residue ensiled with 0.5% salt (kg/kg milk) 0 1

Chemical analysis

Chemical composition of cassava residue was determined in laboratory of the Faculty of Animal Science and Veterinary Medicine, Hanoi Agricultural University following AOAC (1995)

HCN and organic acid contents in the cassava residue were analysed in laboratory of the National Institute of Animal Husbandry;

Analysis of aflatoxin was carried out in laboratory of the Department of Animal Hygiene

of the National Institute of Veterinary Research

Results and discussion

Potential sources of cassava residue in the study area

In the North of Vietnam prosessing cassava starch is done mainly in the villages by artisan methods Half of the households in the studied communes were involved in cassava starch production Results from the present study showed that the amount of dry cassava starch and cassava residue from prosessing 1000 kg fresh cassava tuber were 192.1 ± 1.13 and 185.3 ± 2.92 kg, respectively Le Viet Ly et al (2004) reported that the amounts were 200 and

180 kg, respectively Therefore, the amount of cassava residue in the area was high

Table 2 Cassava and arrowroot starch production in the study area

Agricultural product processing households 1,800 1,500 1,200 Cassava, arrowroot starch processing households 1,400 1,200 850 Quantity of cassava starch produced (tons/year) 60,000 45,000 35,000 Quantity of arrowroot starch produced (tons/year) 20,000 10,000 5,000 Quantity of cassava residue (tons/year) 57,600 40,500 33,600

Source: Duong Lieu, Cat Que, and Lien Hiep commune production reports, 2004

In the prosessing season it was estimated that only a very small part of the total fresh cassava residue produced was used to feed animals directly in the area, while the majority was dried under the sun for sale

Chemical composition of cassava tuber and cassava residue

Results of chemical analyses of cassava products and cassava residue are given in Table 3

Fresh cassava residue contained very high levels of water (>80%), so it was very difficult for sun-drying and mould easily developed during sun-drying, especially the cassava starch prosessing season is in Winter Therefore, it is necessary to find suitable methods to preserve cassava residue

As can be seen, cassava tuber, cassava meal and cassava residue were rich in energy but poor in protein These products were also poor in minerals Thus, attention should be payed to protein and mineral supplements to meet the requirements of animals to be fed

Crude fibre of cassava residue was relatively low and it was always fine ground (reduced rumination), whereas the diet of cattle should contain “structural fibre” to maintain normal numination and rumen pH

Table 3 Chemical composition of cassava products and cassava residue (% DM)

(%)

Crude protein Lipid

Crude fibre NDF

Crude

Fresh cassava tubers 40.45 3.70 0.90 3.51 5.79 3.60 0.11 0.11 Dry cassava chips 88.20 3.10 0.94 2.30 3.69 2.01 0.20 0.06 Cassava meal 88.12 3.55 0.51 2.72 5.56 2.85 0.15 0.15 Fresh cassava residue 14.35 2.02 0.55 10.52 18.60 1.88 0.27 0.06 Dry cassava residue 85.30 2.29 1.17 9.37 15.94 2.07 0.37 0.07

Table 4 Contents of toxins in cassava tubers and cassava residue

(mg/kg)

Aflatoxin B 1 (µg/kg)

Cassava residue inside stock 3th day of storage 5.2 110.40 Negative Cassava residue inside stock 7th day of storage 4.6 10.60 Negative Cassava residue inside stock 10th day of storage 4.4 8.84 Negative Cassava residue inside stock 60th day of storage 4.0 6.28 Negative Cassava residue in surface of stock 10th day of storage 4.7 - Negative Cassava residue in surface of stock 60th day of storage 4.5 - Negative

Cassava residue ensiled with 0.5% salt plus 3% molasses 3.9 5.20 Negative

The HCN content in fresh cassava tubers varied depending on cassava variety, growing conditions, age of plant and type of soil In a study in Central Vietnam it was found to be about 300mg/kg DM (Loc, 1996) Owing to grinding, washing and decanting during starch extraction, HCN is partly dissolved in the sewage and consequently the HCN content in cassava residue is considerably lower than that in fresh cassava tubers (Ninh Thi Len, 2001) The authour (2001) also reported that the HCN content in fresh cassava residue was only 185 mg/kg DM In our research the HCN content in fresh cassava residue was much higher (162.40 mg/kg) than that reported by Ninh Thi Len (2001) The HCN content in cassava

residue was high because it is mainly concentrateed in cassava peel (outer cover) which remains in the cassava residue after starch processing

A high content of starch in cassava residue facilitates fermentation and on the 7th day

of storage pH value dropped to 4.6, and on the 10th day to 4.4 This condition inhibited mould development, disintergrated HCN in cassava residue

Aflatoxin B1 was found only in dry cassava residue but in a harmless amount (33.5

µg/kg) Due to vaporization the HCN content in dry cassava residue was also harmless for feeding animals

The results in Table 4 indicated that aflatoxin was not a cause of death of cattle which were fed cassava residue There could be 2 causes of death of cattle fed cassava residue:

- Cattle were fed fresh cassava residue The critical amount for cattle is 2-4 mg

HCN/kg bodyweight (Makkar et al., 1991) Therefore, feeding 5-10 kg fresh cassava residue

is enough to kill a cattle Cassava residue silage is a very safe feed for cattle

- Using cassava residue as a main feed in the ration (due to lack of roughage in dry season) may lead to rumen acidosis Adding “structural fibre” like rice straw, maize stover would help increase saliva secretion which reduces the risk of rumen acidosis

Color and acidity of ensiled cassava residue

Cassava residue ensiled with 0.5% salt had a white color and cassava residue ensiled with 0.5% salt plus 3% molasses had a light yellow color and a pleasant smell The pH value

of cassava from the 2 treatments was 3.9, and the lactic acid content was relatively high (0.89 and 1.14%, respectively)

Table 5 Acidity of ensiled cassava residue

Lactic acid (%)

Acetic acid (%)

Butyric acid (%)

Cassava residue ensiled with 0.5% salt 3.9 0.89 0.23 0.01 Cassava residue ensiled with 0.5% salt plus 3% molasses 3.9 1.14 0.13 -

Responses of dairy cattle to feeding ensiled cassava residue

Table 6 shows results of the feeding trial using ensiled cassava residue to feed lactating cows Ensiled cassava residue had a pleasant smell so dairy cattle liked to eat much (they eat all the amount provided in the ration) Because feed intake was very high and the diet was adequately calculated, milk production of the experimental group was high There was no

significant difference between two groups (17.2 vs 17.5 kg/head/day) Feed convertion ratio of

two groups was 0.92 and 0.94 kg DM/kg milk, respectively Since the ensiled cassava residue was very cheap (about 70 VND/kg) the feed cost per kg milk was lower in the experimental

group than in the control group (1,549 vs 1,805 VND/kg milk) There were no significant

difference in quality of milk between the control group and the experimental group

Table 6 Performance of lactating cows fed cassava residue silage

Conclusions

- The quantity of cassava residue in the study area was large (estimated over 100,000 tons per year)

- The HCN content in fresh cassava residue was too high (162.4 mg/kg) to be directly fed to animals

- Cassava residue ensiled with 0.5 % salt with or without molasses had good quality and it is safe to feed animals (the HCN content reduced to 5.2 mg/kg)

- Use of cassava residue ensiled with 0.5 % salt to replace cassava meal in a dairy cow diet as an energy source could maintain a high milk production (17.2 kg milk/head/day) and decreased feed cost/kg milk (1,549 vs 1,805 VND/kg milk)

Acknowledgments

The authour would like to express sincere thanks to the Norwegian Council of Universities' Committee for Development Research and Education (NUFU) for the financial support to the present study

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