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).

• bTW0: 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).
• 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 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*X_B/X_A)*100, where X_A and X_B 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.

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.

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).

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).

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

• 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 apparent digestibility of the protein.
  
  
• There was no effect of stage of gestation on digestibility coefficients.

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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