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Effect of replacing soybean meal with a mixture of Taro (Colocasia esculenta (L.)Schott) leaf silage and water spinach on apparent digestibility in Mong Cai gilts at two stages of gestation

Chittavong Malavanh, T R Preston* and B Ogle**

Faculty of Agriculture, National University of Laos (NUOL), Vientiane city,Lao PDR
malavanc@yahoo.com
*
UTA, TOSOLY, AA #48, Socorro, Santander, Colombia
**
Swedish University of Agricultural Sciences, Department of Animal Nutrition and Management, PO Box 7024, 750 07, Uppsala, Sweden

 

Abstract

The treatments in an experiment with purebred Mong Cai gilts were: TW0: 100% of supplementary protein supplied by soybean meal (no green foliage supplied); TW50: 50% of supplementary protein supplied by soybean meal and 50% by mixture of ensiled taro leaves and water spinach (equal parts of each foliage on DM basis) and TW100: 100% of supplementary protein supplied by a mixture of taro leaf silage and water spinach (equal parts of each foliage on DM basis). The basal diet was a 50:50 mixture (DM basis) of ensiled cassava roots and broken rice.

Coefficients of apparent total tract digestibility (CATTD), measured by the acid-insoluble ash method, of dry matter, crude protein, organic matter and crude fibre decreased as the proportion of the mixture of taro leaf silage and water spinach that replaced soybean meal increased (P<0.001). There were no differences between the CATTD obtained in late (85 days after service) compared with early (25 days after service) gestation (P>0.05).

It is concluded that 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. The limiting factor to the utilization of the taro leaf silage and water spinach appears to be the lower digestibility of the protein. There was no effect of stage of gestation on digestibility coefficients.

Key words: Digestibility, Mong Cai gilts, soybean meal, Taro leaf, water spinach


Introduction

Taro (Colocasia esculenta (L.)Schott) originated in India and South East Asia and is presently cultivated in many tropical and subtropical countries, primarily as a food for its edible corm, and secondarily as a leaf vegetable (http://www.fao.org/docrep/003/w3647e/W3647E05.htm). The leaves of taro can be made into silage for feeding to pigs (Chittavong Malavanh et al 2008a). Preston (2006) has suggested that the leaves from shrubs such as cassava and mulberry, and from vegetables such as sweet potato and cocoyam, together with water plants such as duckweed (Lemna spp) and water spinach (Ipomeoa aquatica), can be used successfully in diets for pigs, replacing at least half the protein usually supplied as soybean and fish meal. Recent research has shown that the roots and leaves of Giant taro (Alocasia macrorrhiza) can be fed successfully to pigs, provided they are cooked or ensiled (Pham Sy Tiep et al 2006). The leaves of New cocoyam (Xanthosoma sagittifolium) were successfully fed in the fresh state to pigs in experiments reported by Rodriguez et al (2006 a,b).

Water spinach is a water plant that grows well in the water or in soil. It is cultivated mainly as human food, but is also used as feed for pigs and cattle in Southeast Asia (AFRIS 2005). 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). The crude protein content in the leaves and stems can be as high as 32 and 18 % in dry basis, respectively (Luyen 2003). Recent research has shown that fresh water spinach was more palatable than cassava leaves for growing pigs, as reflected in higher total dry matter (DM) intake, and the high proportion of the diet (47%) provided by the leaves (Chhay Ty and Preston 2005).

It is important to measure the digestibility of the nutrients in leaves intended for use as pig feed, as the digestibility of crude protein especially may be impaired by the linkages between the protein and cell wall constituents (Jørgensen et al 1996; Kass et al 1980). There is also evidence that the apparent digestibility of fibrous feeds is higher in mature sows as opposed to growing pigs (Varel and Pond 1985).

The aim of this study was 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.
 

Materials and Methods

Location and climate

The experiment was carried out in the farm of the Faculty of Agriculture, National University of Laos, located in Xaythani District, Vientiane City, Laos. The mean daily temperature in the area at the time of the experiment was 27 oC (range 22-32 oC).

Treatments and design

The experiment was done according to a RCBD Nested design, with five replications of three treatments. There were 2 stages of gestation (early, 25 days after service and late, 85 days after service).

The three dietary treatments were the same as in Chittavong Malavanh et al (2008).

The fifteen Mong Cai gilts were housed individually and were those used by Chittavong Malavanh et al (2008b). In early gestation (25 days after service) the average live weight was 46 kg and in late gestation (85 days after service) it was 68 kg.

Feeds and management

Details of feeds and feeding were the same as in Chittavong Malavanh et al (2008b).

Data collection

Feed and faeces samples were taken over 5 consecutive days in the early and late stages of gestation. On each occasion, samples of faeces were collected daily from the floor of the pens 3 to 4 h after the first feed in the morning and stored at -18°C. At the end of the 5 days the samples were bulked according to individual animals. Feed samples were taken over the same time period.

Chemical analyses

Feed and faeces samples were analysed for acid-insoluble ash (AIA) according to the method of Van Keulen and Young (1977), for DM by micro-wave radiation (Undersander et al (1993) and N, CF, HCN and ash according to AOAC (1990).

The calculation of the coefficient of apparent total tract DM digestibility was:

DM digestibility (%) = (1- A/B)*100, where A and B are the acid insoluble ash concentrations in feed and faeces, respectively.

The digestibility of other nutrients (X) was calculated as follows:

Digestibility (X in %) = (1- A/B*XB/XA)*100, where XA and XB are the concentrations of X in feed and faeces, respectively.

Statistical analysis

The data were analyzed using the General Linear Model procedure of ANOVA in the MINITAB software (version 13.12) (2000). Sources of variation were stage of gestation, blocks, treatments (diets), interaction stage*diets, interaction stage*blocks and error.
 

Results

Ingredient and chemical composition of the diets

The taro leaf silage contained 19.2 % crude protein in DM, with similar protein content in the water spinach (18.8 % CP in DM). The chemical composition of the diets and ration formulation are shown in Tables 1, 2 and 3.


Table 1.  Composition  of the vitamin-mineral  premix supplied

Item

 per kg

Vitamin-mineral premix

 

Vitamin A, million IU

10.0

Vitamin D3, million IU

2.50

Vitamin E, IU

5000

Vitamin K3,g

1.60

Vitamin B1, g

1.20

Vitanin B2, g

3.20

Vitamin B6, g

1.20

Niacin, g

5.00

Pantothenic acid,g

4.00

Folic acid, g

5.00

Biotin, g

0.12

Vitanmin C, g

30.0

Additives and preservatives, g

12.0

Other, kg

1.00

Mineral premix

 

Manganese, g

5.40

Iron, g

14.2

Copper, g

1.00

Zinc, g

2.90

Sodium, g

3.90

Iodine

19.0

Potassium, mg

0.90

Cobalt, mg

1.10

Other, g

1.00



Table 2.  Chemical composition of ingredients, % dry basis

Ingredient

DM

CP

CF

Ash

Oxalic acid, %

HCN, mg/kg DM

Water spinach

8.19

18.8

16

15.1

 

 

Taro leaf silage

20.2

19

13.2

11.6

0.30

 

Soybean meal

87.8

41.8

8.02

7.4

 

 

Cassava root silage

43.7

1.12

4.12

3.5

 

325

Broken rice

86.9

5.74

2.78

0.81

 

 

Salt

95.1

 

 

 

 

 

Premix

98.2

 

 

 

 

 



Table 3.  Formulation of diets, % of DM

 

Ingredient

TW0

TW50

TW100

Broken rice

37.0

33.9

18.5

Cassava root silage

49.5

44.6

48.0

Taro leaf silage

0.00

7.00

16.0

Water spinach

0.00

7.00

16.0

Soybean meal

12.0

6.00

0.00

Premix

1.00

1.00

1.00

Salt

0.50

0.50

0.50

Total

100

100

100

% Crude protein

10.0

10.0

10.0


The protein was supplied almost entirely by soybean meal and the mixture of taro leaf silage and water spinach. The proportions of the diet crude protein derived from individual ingredients during the first and last stage of gestation are shown in Figure 1.


* WS= water spinach; TLS= taro leaf silage; SBM= soybean meal; BR= Broken rice and
CRS= cassava root silage


Figure 1.  Proportion of diet crude protein derived from individual ingredients* in gestation.


Coefficients of apparent total tract digestibility (CATTD) in Mong Cai gilts fed a mixture of taro leaf silage and water spinach

Apparent digestibility coefficients of DM, CP, OM and CF declined as the proportion of the mixture of taro leaf silage and water spinach that replaced soybean meal increased (P<0.05) (Table 4; Figure 2).


Table 4. Apparent digestibility coefficients in Mong Cai gilts in gestation fed diets with different
proportions of a mixture of taro leaf silage and water spinach  replacing soybean meal

Apparent digestibility, g/kg 

TW0

TW50

TW100

SEM

P-value

 

 

 

 

 

DM

900c

832b

809a

2.06

0.001

OM

917c

864b

837a

2.40

0.001

CP

816c

655b

595a

4.85

0.001

CF

623c

586b

554a

5.40

0.001

a, b Mean values within rows with different superscript letters are different at P<0.05




Figure 2. 
Apparent dry matter digestibility in early and late gestation in Mong Cai gilts
fed diets in which a mixture of taro leaf silage and water spinach replaced soybean meal


There were no differences between the CATTD obtained in late compared with early gestation (P>0.05) (Tables 5 and 6).


Table 5. Effect of stage of gestation on the apparent digestibility coefficients in Mong Cai gilts fed
diets containing a mixture of taro leaf silage and water spinach

Apparent digestibility, g/kg 

Early gestation

Late gestation

SEM

P-value

Dry matter

845

848

1.68

0.235

Organic matter

873

871

1.96

0.480

Crude protein

691

687

3.96

0.471

Crude fibre

588

588

4.41

0.992



Table 6.  Nutrient digestibility at two stages of gestation in Mong Cai gilts fed diets* in which a mixture of taro leaf silage replaced soybean meal

Digestibility, g/kg 

Early (day 25) gestation

Late (day 85) gestation

SEM

P-value

TW0

TW50

TW100

TW0

TW50

TW100

Dry matter

898

831

807

901

832

811

2.91

0.845

Organic matter

917

867

836

916

860

837

3.39

0.451

Crude protein

814

660

598

818

649

592

6.85

0.572

Crude fibre

628

585

551

619

588

556

7.63

0.589


Discussion

The extent of the decline in apparent digestibility of DM (from 900 to 809 g/kg) and crude protein (from 816 to 595 g/kg) as the foliages completely replaced soybean meal was similar to the findings of Rodriguez et al (2006) for pigs fed sugar cane juice and fresh leaves of new cocoyam replacing soybean meal (939 to 834 g/kg for DM apparent digestibility and 821 to 614 g/kg for crude protein digestibility). In the present study there was a linear negative relationship between apparent crude protein digestibility and crude fibre in the diet (Figure 3).



Figure 3
.  Relationship between apparent digestibility of crude protein and
crude fibre content in the diets of Mong Cai gilts during early and late gestation


This trend was to be expected, as the role of dietary fibre in reducing protein digestibility is well understood (Jørgensen et al 1996; Kass et al 1980). 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. Varel and Pond (1985) provided evidence that the apparent digestibility of fibrous feeds is higher in mature sows as opposed to growing pigs. However, it would appear that in our study 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 between these two stages.
 

Conclusions


Acknowledgements

We are very grateful to the Swedish International Development Cooperation Agency, Department for Research Cooperation (Sida-SAREC) through the regional MEKARN Project, for the financial support of this study.

We would also like to thank the Faculty of Agriculture, National University of Laos for allowing and helping us to carry out this experiment. The authors thank Mr Bounlerth Syvilai for analytical assistance in the laboratory of the Faculty of Agriculture.
 

References

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