Effect of a tannin-rich foliage (Mimosa pigra) on feed intake, digestibility, N retention and methane production in goats fed a basal diet of Muntingia calabura

Sitone Kongvongxay, T R Preston*, R A Leng** and Duong Nguyen Khang***

Livestock Research Centre, NAFRI, Laos
sitonek@yahoo.com
* Finca Ecologica, TOLOGY, UTA (Colombia)
AA#48, Socorro, Santander, Colombia
** University of New England, Armidale NSW
*** Nong Lam University, Ho Chi Minh City, Vietnam

Abstract

Four male weaned crossbred goats (Bachthao x local female) with an initial weight of 11.61 ± 0.3 kg were used in a 4 x 4 Latin Square design to compare  replacement of Muntingia calabura foliage with Mimosa pigra at four levels: 0, 25, 50 and 75% (DM basis).

Increasing the replacement of N in Muntingia by that in Mimosa led to increases in DM intake, apparent digestibility of crude protein and N retention. Methane production was reduced by replacing Muntingia N with Mimosa N with the greatest effect (42% reduction) with 72% of the diet N from Mimosa.

Key words: Back Thao, greenhouse gases, metabolism, methane:carbon dioxide ratio

Introduction

Muntingia (common name Jamaica cherry) (Muntingia calabura) belongs to the family Elaeocarpacae. According to Nguyen Xuan Ba and Le Duc Ngoan (2003) it can grow everywhere (sandy land, humid areas, and high land area) and is well adapted to the dry season. Traditionally, it is used as a shade tree around the homestead, and along the roadsides. It is a tall tree with a large canopy of leaves but it is not normally used as feed for animals. Very little is known about the nutritive value of foliage from Muntingia for ruminant species. Pok Samkol (2003) reported that the foliage was palatable to goats; and that DM intake was higher when the foliage was offered hanging in the feed trough (33.5 g/kg LW) compared with giving the leaves alone (26.9 g/kg LW). Tran Trung Tuan (2009) hypothesized that the nutritive value for goats of Muntingia leaves and stems would be improved when supplemented with a rapidly rumen degradable forage (water spinach) and/or a source of leaves with known capacity to act as a source of bypass protein. However, contrary to expectations, N retention was high on all the diets and was not improved by either the Jackfruit or the water spinach.

Giant Mimosa (Mimosa pigra) has been described as one of the worst invasive weeds of the Mekong River basin (Photo 1).  However, Nguyen Thi Thu Hong et al (2008) found that with suitable management (Photo 2) it produced a foliage of high nutritive value which when offered as the sole feed to goats supported growth rates in a grazing situation of 94 g/day and 61 g/day in confinement.

Photo 1. Mimosa pigra as an invasive weed in the Mekong delta (MWBP/RSCP 2006)	Photo 2. Mimosa pigra managed as a forage for goats (Nguyen Thi Thu Hong et al 2008)

Ruminant animals major contributors of greenhouse gases (Steinfeld 2006) which are considered to be the main causes of global warming (IPPC 2007). There is therefore a major incentive to find ways in which emissions of these gases can be reduced. Methane which is produced by enteric fermentation is the major GHG produced by ruminants. Recently, a number of authors have studied the effects of naturally occurring compounds in plants which might act to modify the rumen fermentation and specifically to reduce methane production.  Puchala et al (2005) fed Angora goats a forage legume (Lespedeza cuneata) with a moderately high  content of condensed tannins (17.9 g/kg DM) compared with a mixture of grasses (Digitaria ischaemum and Festuca arundinacea) with negligible tannin content (0.5 g/kg DM). Methane production was 10.7 g/kg digestible DM on the high tannin legume forage compared with 21.5 on the low tannin grass.  Mimosa has been shown to contain from 4 to 8 %  of condensed tannins in the DM of the leaves, the level increasing with stage of growth (Nguyen Thi Thu Hong et al 2008). 

The purpose of the present study was to determine if supplementation with foliage of Mimosa would improve the nutritive value for goats of Muntingia calabura and at the same time lead to a reduction in methane production.

Materials and Methods

Location

The experiment was conducted at the experimental farm of the Faculty of Animal Science, An Giang University, Vietnam, from August to October 2010.

Treatments and experimental design

Four male weaned crossbred goats (Bachthao x local female) with an initial weight of 11.6 ± 0.3 kg and aged from 3 to 4 months were used to evaluate four experimental diets consisting of different ratios of Muntingian and Mimosa. The experimental design was a 4*4 Latin-square (Table 1), with periods of 10 days.  The experimental diets were:

• MP0: Foliage of Muntingia calabura offered  ad libitum
• MP25: A mixture of Muntingia foliage 75 % + 25%  as Mimosa pigra foliage  (DM basis)
• MP50: Muntingia 50% + 50% Mimosa (DM basis)
• MP75: Muntingia 25 % + 75% Mimosa (DM basis)

Animals and housing

The goats were confined in metabolism cages made from bamboo, adapted for the separate collection of feed residues, feces and urine. They were gradually introduced to the cages and diets over 7 days before beginning the experiment.

Feeds and feeding system

The foliages of Muntingia and Mimosa were collected daily from natural stands in the University campus. The branches were hung separately in bunches above the feed trough. The amounts offered were based on a feeding level of 40 g DM/kg live weight at the start of each period. The goats were fed with 50% of their daily ration at 08:00h and 50% at 14:00h.The feed offered for each goat, and residues from the previous day,  were weighed every morning. Fresh water was always available.   The ratio of leaves plus petioles and stems was determined on samples (1 kg of foliage) taken 2 times per day.

Live weight was recorded in the morning before feeding at the beginning and end of each period. Feeds offered and refusals  were collected daily during the 5 days of the collection period. Urine was collected in buckets with 20 ml of a solution of sulphuric acid (10% concentrated sulphuric acid + 90% distilled water). Feces were collected daily and stored at -18ºC and, at the end of each period, sub-samples were mixed together and ground with a coffee grinder prior to analysis for DM and N. Ratio of methane and carbon dioxide in eructed gas was measured (Photo 3) at the end of the 2nd and 4th  period, 2h after feeding in the morning, using a portable "Gasmet 4030"  meter (Gasmet Technologies Oy, Pulttitie 8A, FI-00880 Helsinki, Finland).

Chemical analyses

The sub-samples of the foliages offered to and refused by the goats, and of feces,  were analyzed for DM content by micro-wave radiation (Undersander et al 1993) and for N and ash following standard procedures as outlined by AOAC (1990).  Urine was analysed for N by AOAC (1990) procedures.  A sample of rumen fluid was taken by stomach tube on the last day of each period 2h after feeding in the morning. The pH was measured immediately with a glass electrode and digital pH meter. A drop of concentrated sulphuric acid was then added to preserve the samples prior to analysis for ammonia by steam distillation (Nguyen Van Lai and Ly 1997).

Photo 3. Goats were confined in a closed space for the measurement of the eructed gases with the Gasmet 4030 equipment

Statistical analysis

The data were analyzed with the GLM option of the analysis of variance software of Minitab Version 13.31 (Minitab 2000). Sources of variation in the model were animals, periods, foliages and error.

Results and Discussion

Feed composition

Mimosa pigra had a higher content of protein and OM content in leaves and stem, and a slightly higher leaf: stem ratio, than Muntingia (Table 2).

Feed intake and apparent digestibility

Most indices of nutritive value were improved when mimosa foliage replaced Muntingia in the diet of the goats (Tables 3 and 4).

There was a positive linear relationship between the proportion of N derived from mimosa and DM intake (Figure 1), but not between CP content of the DM and DM intake (Figure 2),

Figure 1.  Effect of proportion of forage protein from Mimosa on DM intake in goats fed mixtures of Mimosa with Muntingia	Figure 2.  Effect of proportion of crude protein in diet DM on DM intake in goats fed mixtures of Mimosa with Muntingia

Increasing the rate of replacement of muntingia N by mimosa N had no effect on apparent digestibility of DM (Figure 3) but resulted in a positive curvilinear increase in apparent digestibility of crude protein (Figure 4). There was a tendency (P=0.07) for apparent OM digestibility to increase with increasing proportion of Mimosa N in the diet (Figure 5).

Figure 3. Relationship between apparent digestibility of DM and the proportion of forage N derived from Mimosa	Figure 4. Relationship between apparent digestibility of crude protein and the proportion of forage N derived from Mimosa

Figure 5. Relationship between apparent digestibility of organic matter and the proportion of forage N derived from Mimosa

Nitrogen balance

Nitrogen intake increased as Mimosa replaced Muntingia (Table 4). This was due partly to a higher per cent of crude protein in Mimosa than in Muntingia (Table 2) and also to the increase in DM intake as Mimosa replaced Muntingia. There were no differences in daily excretion rates of N in feces and urine (Table 4)  thus N retention increased markedly as the proportion of N from Mimosa increased. (Figures 6 and 8). However, when the N balance was expressed on a per cent basis (Figure 7), it was apparent that the N in Mimosa was used more efficiently for tissue synthesis than the N in Muntingia.

Figure 6. N balance according to the planned replacement of Muntingia by Mimosa	Figure 7.  Per cent of the diet N excreted and retained according to the planned replacement of Muntingia by Mimosa

Figure 8. Relationship between proportion of forage protein from Mimosa on N retention as per cent of N digested	Figure 9. Relationship between proportion of crude protein in diet DM and N retention

A higher biological value for the protein in Mimosa is also inferred from the better relationship between N retention and proportion of diet N from Mimosa (R² =0.77; Figure 8) compared with N retention and proportion of crude protein in the diet DM (R² =0.33; Figure 9). Increases in N retention as per cent of N intake (Figure 10) and per cent of N digested (Figure 11), as the proportion of diet N from Mimosa was increased,  provide more evidence for the high biological value of the Mimosa protein.

Figure 10. Relationship between proportion of forage protein from Mimosa and N retention as per cent of N intake	Figure 11. Relationship between proportion of forage protein from Mimosa and N retention as per cent of N digested

Rumen ammonia and ratios of methane to carbon dioxide in the eructed breath of the goats

The mean values of ruminal pH appeared (P=0.078) to be slightly lower on the diets containing Mimosa as were the values for rumen ammonia (P=0.14) (Table 5). The ratio of methane to carbon dioxide in the eructed breath of the goats was lowered by Mimosa at all levels (Figure 12) with the greatest reduction (50%) on the 50:50 ratio of the foliages (Figure 13). The per cent reduction in methane production was calculated on the basis that CO₂ production reflects energy utilization by the animal thus the ratio of methane to carbon dioxide in eructed gas is a measure of relative production of methane as a function of the intake of metabolizable energy (Madsen et al 2010; Leng and Preston 2010).

Figure 12. Relationship between ratio methane/carbon dioxide and proportion of forage N from mimosa	Figure 13. Reduction in methane production by increasing the proportion of foliage from mimosa

The improvements in most indices of nutritive value as Mimosa pigra replaced Muntingia calabura confirm the findings of Nguyen Thi Thu Hong et al (2008) that Mimosa has a high nutritive value for goats, almost certainly related to the Mimosa protein having good rumen escape properties due to its content of condensed tannins.  The indications that methane: carbon dioxide ratios were reduced with Mimosa may also be a result of the tannin content as a positive role of tannin-rich plants in reducing enteric methane production has been reported for other leguminous plants rich in tannins (Puchala et al 2005; Hess et al 2006). 

Conclusions

• Increasing the rate of replacement of N in Muntingia calabura by that in Mimosa pigra, in the diet of growing goats, led to increases in DM intake, apparent digestibility of crude protein  and N retention.

  
  

• Methane production was reduced by replacing Muntingia N with Mimosa N with the greatest effect (42% reduction) with 72% of the diet N from mimosa.

Acknowledgments

The authors would like to express their gratitude to the MEKARN program, supported by Sida, and to the Norwegian Programme for Development, Research and Higher Education (NUFU), for their financial support. The research forms part of the requirement by the senior author for the MSc degree from Cantho University. The administration and teaching staff of An Giang University are gratefully acknowledged for providing resources and advice for conducting the research.

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Received 7 January 2011; Accepted 1 February 2011; Published 6 March 2011

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