Aquatic plants and macroalgae as potential feed ingredients in ruminant diets

The aim of this research was to investigate the nutritive value of three aquatic plants, the seagrass (Ruppia maritima) and two green macroalgae (Chaetomorpha linum and Ulva lactuca). Biomass from three aquatic plants collected from the lagoon Ghar el melh of Bizerte (northeast of Tunisia) was washed and dried, and tested alone (compared to barley grain and barley grass) or included at different levels in isonitrogenous concentrate mixtures. Four rumen cannulated Barbarine rams were used as donors of rumen fluid for in vitro incubations and as hosts for in situ nylon bags rumen incubations. Gas production, fermentation rate, gas produced after 24 h of incubation and apparent OM digestibility were greater for barley grain and grass than for the three aquatic plants (P < 0.05). The estimated extent of degradation in the rumen was greatest for grain, whereas the values were similar for biomass from the three aquatic plants and for barley grass. The in situ degradability of the three aquatic plants was similar to barley grass, but less than that of barley grain. Effective degradability of R. maritima and barley grass was significantly less than that of the macroalgae. When the aquatic plants biomass was included in concentrate mixtures, the three aquatic plant species induced a significant (P < 0.05) linear depressing effect of level of inclusion on in vitro fermentation kinetics. However, no effects were observed when concentrate mixtures were incubated in nylon bags (P > 0.05). Inclusion of biomass of the three aquatic plant species studied as ingredients should not exceed 200 g kg(-1) in concentrate feeds, because the rate and extent of degradation of the mixture may be reduced with greater addition.