Chemical and biological evaluation of the nutritive value of Algerian green seaweed Ulva lactuca using in vitro gas production technique for ruminant animals

This study aimed to determine the nutritive value of seaweed Ulva lactuca collected from the Algerian coast by estimation of its chemical composition and fermentation characteristics, comparatively to vetch-oat hay (control), using in vitro gas production technique. Seaweed and control were incubated with rumen liquor taken from fistulated and non lactating cows. Gas production was recorded at: 2, 4, 6, 8, 12, 24, 48 and 72h. The in vitro rumen fermentation parameters were measured after 24h and 72h of fermentation. Proteins degradability was investigated by the enzymatic technique using a protease extracted from Streptomyces griseus. The results showed a wide variation between the chemical components of seaweed and conventional fodder used as control. The main constituents in Ulva lactuca were ashes (39.1% DM), fibers (22.8 % DM) and proteins (15.3% DM). The gas production profile of seaweed during 72h of incubation showed a slow and low gas production. Cumulative gas production obtained after 24h for seaweed (42 ml/g OM) was significantly lower than control (128.4 ml/g OM) (P<0.001). pH, ammonia, volatile fatty acids (VFAs), apparent digestibility of dry matter (DDM), organic matter digestibility (OMD) and metabolizable energy (ME) were significantly different between seaweed and vetch-oat hay (6.86, 290.1 mg/ml, 1.25 mmol/g DM, 38.3%, 29.2%, 3.81MJ/Kg DM respectively for seaweed). Protein degradability measurement indicates the weak hydrolysis of seaweed crude protein which is beneficial for ruminants. This study showed that the use of Ulva lactuca as non conventional feed in ruminant nutrition can be considered under certain conditions.