Nutritional value of aquatic ferns (Azolla filiculoides Lam. and Salvinia molesta Mitchell) in pigs

Aquatic ferns (AFs) such as Azolla filiculoides and Salvinia molesta are grown on swine lagoons in the tropics and used to feed pigs. The present work aimed to determine their nutritional value. Azolla samples collected in Colombian pig farms contained from 184 to 317 g crude protein/kg DM, 469–620 g NDF and 98–145 g ash. Those of Salvinia contained from 112 to 169 g crude protein/kg DM, 518–629 g NDF and 161–232 g ash. The content in all macro- and micro-minerals were high and exceeded the pig's requirements expressed per kg diet. The proteins of the two species presented a similar amino acid profile and contained from 47 to 53 g lysine/kg protein, 11–17 g methionine, 53–55 g threonine and 14–15 g tryptophan. A digestibility study in 60 kg pigs was carried out with diets containing maize, soybean meal, minerals and 0, 125 or 250 g AF/kg diet. The weight and length of the digestive organs was also measured. The presence of AF decreased the faecal digestibility of crude protein, NDF and gross energy of the diet (P<0.001). The ileal protein digestibility decreased (P=0.03) with the increase in AF level in the diet. The digestible energy content per kg AF, calculated by difference between the basal diet and that of the diet containing 125 g AF/kg was 10.76 MJ/kg DM for Azolla and 6.58 MJ/kg DM for Salvinia. AF intake did not affect the gastrointestinal tract, with the exception of an increase in the length and weight of the colon of pigs fed 250 g AF/kg diet (P<0.01). In conclusion, Azolla and Salvinia are good sources of minerals and essential amino acids but their interest is limited in pig production by their low digestible energy and protein content.