Nutritive value of tropical forage plants fed to pigs in the Western provinces of the Democratic Republic of the Congo
Introduction
In the tropics, pig production is only tolerated if pigs do not compete with humans for food (Leterme et al., 2006), especially in developing countries where monogastrics are in direct competition with humans for the resources required to produce concentrate feed. Because of the high and volatile prices of the latter (Braun, 2007, FAO, 2012), smallholders often replace the cereals and oilseed by-products in pig feeds with large amounts of cheap and unconventional fibre-rich ingredients such as crop residues, agro-industrial by-products, and grass and legume forage collected in the forest or in fallow fields near pigsties (Kumaresan et al., 2009, Phengsavanh et al., 2010). A recent survey realised in the Kinshasa and the Bas-Congo Provinces of the Democratic Republic of the Congo (DRC) confirmed that less than 2% of the farmers use commercial feeds and the most abundant cereal resource, namely corn, is used as an ingredient in pig feed on less than 10% of the farms. Although the growth performances of forage-fed pigs is often lower than that of concentrate-fed and is negatively correlated with the inclusion rate of the forages (Phengsavanh and Lindberg, 2013, Régnier et al., 2013), farmers in Western DRC do not feed crop grains to their pigs because they consider it a waste of crops even in mixed farming systems producing both pigs and crops.
The use of forage resources as pig feeds does have several drawbacks including low digestibility of forage owing to their high content in fibre, the presence of anti-nutritive compounds and the lack of suitable conservation methods. However, compared to cereals, they have distinct advantages justifying their use by farmers: low cost, non-competitiveness with human food, high levels of protein, minerals and vitamins (reviewed by Martens et al., 2012). As feed is the most critical expense in pig rearing activity, it can be profitable to substitute a significant part of a concentrate-based diet with some forage ingredients (Kaensombath et al., 2013). Unfortunately, the lack of information on the nutritive value of most of the forage resources used in tropical areas in general and in Western DRC specifically can lead to unbalanced diets, low pigs growth and reproduction performances, low incomes for the farmers and less locally produced animal protein available on the market. The aim of this work is to assess using an in vitro model of the pigs gastro-intestinal tract, the nutritive value of the forage species the most commonly used by smallholder farmers in Western DRC in order to provide information that could guide them in the choice of forage resources for improved pig performances.
Section snippets
Plant material
Samples of 20 forage species used as pig feed by farmers in the Kinshasa and Bas-Congo Provinces of the DRC and identified as the most commonly used during a survey of 319 pig smallholders were gathered from the smallholders’ farms (Table 1). For each species, 4 independent samples were collected on different farms. All forage samples were harvested during the vegetative growth phase before flowering and, depending on the species, whole plants or only leaves were sampled according to the
Chemical composition
Crude protein contents of the forage species ranged from 88 to 324 g/kg DM and NDF content ranged from 279 to 688 g/kg DM (Table 1). The lowest CP values (88–147 g kg−1 DM) and the highest NDF contents (554–688 g/kg DM) were found in grasses (M. maximus, P. purpureum, S. officinarum, U. ruziziensis, T. andersonii) and Eichhornia crassipes. In contrast, the dicotyledons such as Amaranthus hybridus, Ipomoea batatas, M. pruriens, V. unguiculata, Psophocarpus scandens, Leucaena leucocephala, Manihot
Discussion
Feeding is the most important component in the efficiency of pig production systems, yet a recent survey (Kambashi et al., submitted for publication) showed that in the Kinshasa and Bas-Congo provinces of the DRC, smallholders feed their pigs with by-products and locally available forage plants. The efficiency of such a system depends on the nutrients that are provided by forage and the capacity with which these nutrients are assimilated and converted into meat.
The in vitro approach used in
Acknowledgements
The authors gratefully acknowledge Wallonie-Bruxelles International (Brussels, Belgium) and the Walloon government (Namur, Belgium) for their support of the CAVTK project.
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