Domínguez et al., 1996. Livest. Res. Rural Dev., 8 (4)

Growing water plant in ponds fertilized with pig manure is one way of recycling the N given in the original feed. Either water hyacinth (Eichhornia crassipes (Mart, EC), duckweed (Lemna minor, L) or azolla (Azolla spp, A) grown on liquid pig slurry after an anaerobic treatment were sun dried, milled and included as an alternative source of N at 0, 100 or 200 g/kg in sugar cane molasses and soybean meal diets given to pigs. N and OM content (g/kg in dry basis respectively) of macrophytes were EC, 26.3 and 810; L, 45.6 and 643; A, 50,9 and 809. Nine 45 kg pigs prepared by an ileo-rectal anastomosis were distributed at random to diets in 3 digestion trials according to a 3 x 3 Latin square design. Ileal OM but not N digestibility of the basal diet was high as expected (OM, 811 - 842; N, 696 - 719 g/kg respectively). In vitro and in vivo ileal protein digestibility were lowest in water hyacinth and highest in azolla (EC, 412 and 162; L, 674 and 560; A, 701 and 646 g/kg respectively). Ileal OM digestibility was less influenced by azolla than by water hyacinth at 200 g/kg level of inclusion in the diet (EC, 739; L, 769; A, 778 g/kg) thus indicating that the efficiency of recycling the excreted N by the pig may largely depend on the type of macrophyte to be used for this purpose.