Effect of fresh mulberry leaves and sweet potato vines on growth performance of pigs fed a basal diet of broken rice

Chiv Phiny, T R Preston* and Khieu Borin

Center for Livestock and Agriculture Development (CelAgrid), P.O box 2423, Phnom Penh, Cambodia
chphiny@celagrid.org
* TOSOLY, A48 Socorro, Colombia

Abstract

Twelve crossbred pigs (range of 15 to 20 kg weight) were fed a basal diet of broken rice (restricted to 2% of LW as DM) supplemented with fresh mulberry leaves, fresh sweet potato vines or a mixture of the two foliages.

It appeared that a period of some  30 days was required for adaptation to the diets. during which time there were no differences among treatments. From 30 to 90  days and for the overall period of 0-90 days, intake of DM and crude protein, and live weight gain was highest for pigs fed the diet supplemented only with sweet potato vines with lowest values for pigs fed only mulberry leaves as the supplement. There was a tendency for feed conversion to follow a similar pattern.  DM intake and growth rate were positively correlated (R² = 0.83).

It is concluded that the benefits of the sweet potato vines are their superior palatability compared with mulberry leaves, which resulted in higher intakes of DM and crude protein and better pig performance .

Key words: Adaptation, DM intake, feed conversion, palatability

Introduction

Mulberry trees have been domesticated for many centuries for feeding silkworms (Tingzing et al 1988). The leaves have been shown to be valuable sources for ruminant animals (Benavides 1999; Sánchez 1999; Yao et al 2000; Nguyen Xuan Ba et al 2005; Pathoummalangsy Khamparn and Preston 2008) but information on their nutritive value for pigs is more variable.  Ly et al (2001) reported that apparent digestibility of DM and crude protein was higher in pigs fed leaves of mulberry than those fed  leaves of Trichanthera gigantea when these foliages provided 30% of the DM of a diet based on wheat bran, cassava root byproduct and dried fish. A more comprehensive trial with different levels of mulberry leaf meal replacing up to 100% of the dried fish (50% leaf meal in the diet) showed no differences in apparent crude protein digestibility nor in N retention for increasing levels of mulberry leaf in the diet (Chiv Phiny et al 2003).  In a related experiment, there were no differences in apparent digestibility of DM  or of crude protein when fresh mulberry leaves were compared with sun-dried leaves in a basal diet of broken rice and wheat bran (Chiv Phiny et al 2003).  Kaensombath Lampheuy and Sivilay Bounlerth  (2008) compared fresh and ensiled mulberry leaves as the protein supplement for pigs fed broken rice. Apparent digestibility of DM and crude protein was higher for the ensiled leaves.

Two studies have been made with combinations of mulberry leaves and other forages for growing pigs. Partial replacement of water spinach by fresh mulberry leaves appeared to support better growth and feed conversion than water spinach alone as the only source of supplementary protein in diets based on rice bran and cassava root meal or sugar palm syrup and broken rice (Chiv Phiny et al 2008a,b). By contrast, there were no advantages in apparent DM and crude protein digestibility or in N retention from feeding a combination of mulberry leaves and sweet potato vines compared with either forage given as the sole supplement (Chhay Ty et al 2007). The present study aimed to provide further information on the effects of combinations of mulberry leaves with sweet potato vines on growth and feed conversion of pigs, using a basal diet of broken rice.
 

Materials and methods

Location and climate

The experiment was carried out from 06 April to 07 July 2008 in the Center for Livestock and Agriculture Development (CelAgrid), located in Preh Theat village, Rolous Commune, Kandal steung district, Kandal province about 25km from Phnom Penh City, Cambodia.

Experimental design and treatments

Twelve crossbred pigs (range of 15 to 20 kg initial weight) were allocated to three treatments with 4 replications in a completely randomized block design.  Housing was in individual pens with a concrete floor, brick walls and provided with feeders and drinking nipples. The experimental layout is in Table 1. The experimental treatments were the following supplements incorporated in a basal diet of broken rice:

·         SPV: Fresh sweet potato vines

·         ML: Fresh mulberry leaves

·         SPVML: A mixture (50:50 DM basis) of fresh sweet potato vines plus fresh mulberry leaves 

Feeds and feeding

Sweet potato vines and mulberry leaves were harvested daily from plots in CelAgrid.. Mulberry leaves were from re-growths after harvesting at 2 month intervals; sweet potato vines were harvested 45 days after planting and then at 25 day intervals. Broken rice was purchased from a  local rice mill. The sweet potato vines and mulberry leaves were fed immediately after harvesting. Broken rice was restricted to 2% of live weight (DM basis). The foliages were offered ad libitum. Feeds offered and refuseds were weighed daily and samples taken once per week for analysis. The pigs were fed 3 times daily at 8:00, 11:00 and 16:00h  The composition of the diets is shown in Table 2.  

Animals and housing

The pens were 1.2 m wide, 1.6 m in length and 1 m in height (Photo 1). In each pen there was one drinking nipple and two feed troughs, in order to separate the ingredients of the diets; vegetative protein sources in one trough and energy sources in the other. The pens were in an open shed covered by a roof made from wood, bamboo and thatch (Photo 2). The pigs were vaccinated against common infectious diseases, and de-wormed and then adapted to the diets and the pens for 15 days before starting the experiment.

Data collection

The animals were weighed in the morning before feeding, at the beginning of the trial and every 10 days thereafter. Feed offered and refusals were collected and weighed every day, and samples kept frozen at -20⁰C in plastic bags until analysis. At the end of each 10 day period, samples of feed refused and offered were mixed thoroughly by hand and homogenized in a coffee grinder prior to analysis.

Chemical analysis 

Samples were analyzed for DM (Undersander et al 1993) and N (AOAC 1990).  

Statistical analysis 

The data for feed intake, feed conversion and growth rate were compared using the general linear model (GLM) option in the Minitab ANOVA software release 13.31 (2000). The sources of variation were: treatments and error.
 

Results

The pigs were in good health during the trial. There were no symptoms of discomfort from the consumption of the diets.

Feed composition and intake

Mulberry leaf had slightly higher levels of crude protein and crude fiber than the sweet potato vine (Table 3).

Intakes of DM and crude protein were higher for the pigs fed the diets with sweet potato vines (Table 4; Figures 1 and 2).

Figure 1.  Relative intakes of DM from dietary ingredients by pigs fed a basal diet of broken rice with supplements of fresh mulberry leaves, sweet potato vines or a combination of both	Figure 2.  Intakes of DM during successive 30 day intervals by pigs fed a basal diet of broken rice with supplements of fresh mulberry leaves, sweet potato vines or a combination of both

Relative differences in DM intakes among treatments increased during successive 30 day intervals (Table 5; Figure 2).

Growth and feed conversion

Overall live weight gain for the 90 day trial was highest for pigs fed the diet supplemented only with sweet potato vines with lowest values for pigs fed only mulberry leaves as the supplement (Table 6; Figure 3).

Figure 3.  Growth curves of pigs fed a basal diet of broken rice with supplements of fresh mulberry leaves, sweet potato vines or a combination of both	Figure 4.  Relationship between DM intake and live weight gain in pigs fed a basal diet of broken rice with supplements of fresh mulberry leaves, sweet potato vines or a combination of both

Discussion

The improvement in growth rate resulting from supplementation with sweet potato vines can be explained entirely by the rate of DM intake (Figure 4). These results were in marked contrast with those reported earlier by Chhay Ty et al (2007), when there were no differences between mulberry leaves and sweet potato vines in DM and CP intake, apparent DM and CP digestibility, and N retention. The basal diets were different: broken rice in the present experiment compared with sugar palm syrup and rice bran used by Chhay Ty et al (2007); however, this does not explain the different responses to the sweet potato vines in the two experiments.  It appears from the growth curves (Figure 5) that there were no differences among treatments during the first  30 days of the experiment but after this point there was increasing divergence in the growth rates. The same pattern was seen in the relative DM intakes (Figure 2). This implies that it took some time for the pigs to adapt to the forage supplements, but once they were adapted the advantages of the sweet potato vine supplement were clearly apparent. This need for adaptation would also explain why in the earlier metabolism trial there were no treatment differences, as the experimental periods of 14 days would not have been sufficient for the necessary adaptation to the forages.  

Conclusions

• Intakes of DM and crude protein were higher, and growth rates and feed conversion were improved, when pigs fed a basal diet of broken rice were supplemented with fresh sweet potato vines compared with mulberry leaves or mulberry leaves mixed with sweet potato vines.

• There was a close linear relationship (R² = 0.83) between DM intake and live weight gain

• The improvements in performance when fresh sweet potato vines replaced fresh mulberry leaves were only manifested after a period of adaptation to the forages  of some  30 days.

Acknowledgments

The authors wish to thanks the MEKARN project, financed by Sida/SAREC for supporting this research. Thanks are given to the staff of CelAgrid for assistance during the entire experiment, especially Mr Muth Sovan, Chea Sokhon and Seun Bros for taking care of the feeding and management of the pigs. Thanks to Mr Pek Samnang for helping to analyze the experimental samples in the laboratory.

References

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Received 13 January 2010; Accepted 18 February 2010; Published 1 March 2010

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