Digestive utilization of tropical foliages of cassava, sweet potatoes, wild cocoyam and erythrina in Creole growing pigs

Total tract digestive utilization of cassava (Manihot esculenta) leaves and leaves + stems, sweet potatoes (Ipomoea batatas) leaves and leaves + stems, cocoyam (Xanthosoma sagittifolium) leaves, and erythrina (Erythrina glauca) leaves was studied in three simultaneous Latin square designs with a total of nine castrated Creole growing pigs. Each dried foliage was included at 200 g/kg in a basal maize-soybean meal diet (MSBM) and the difference method was used to calculate the nutritional value of each of the six foliages. These leaves were characterized by a high fibre content and the presence of some anti-nutritional factors (such as tannins, 0.8–3.1%). Each of the foliage diets was measured on three animals (nine for the MSBM diet). Rate of passage variables of diets were also determined using a pulse dose of ytterbium. Mean retention time in the gastrointestinal tract was shorter (P<0.01) for diets including tropical foliages (30.4 h vs. 42.1 h for the MSBM diet) and shorter for the two cassava diets than for the other diets (26.8 h vs. 32.2 h on average; P<0.05). The total tract apparent digestibility coefficient (CTTAD) of dietary energy was reduced (P<0.01) by the inclusion of tropical foliages (−0.098 on average). Similar results were observed for dietary crude protein (CP) (−0.143 on average; P<0.05), except for the cocoyam diet that did not differ from the MSBM diet. For cassava and sweet potatoes, the addition of the stems to the leaves did not affect CTTAD of CP and energy. According to the difference method, the CTTAD was −0.328, 0.112, 0.212 and 0.647 for CP and 0.266, 0.310, 0.434 and 0.466 for energy and the corresponding digestible energy contents were 5.21, 6.22, 7.47 and 8.37 MJ/kg DM for erythrina, cassava, sweet potatoes and cocoyam leaves, respectively. The inclusion of the stem to the leaves fractions did not affect digestibility of energy and nutrients (P>0.05) for cassava and sweet potatoes. It is concluded that the high fibre content in addition to the presence of tannins are the main limiting factors of these tropical foliages in pig nutrition with a subsequent low energy value.