Résumé:
The current work focuses on the valorization of non conventional vegetal resources in ruminant feeding so far ever undertaken in Algeria. Its main objective is to investigate on new unconventional marine food substrates in ruminant diets through several aspects:
characterization of nutrients and secondary metabolites of a green seaweed Ulva lactuca and a brown seaweed Halopteris scoparia, assessing their nutritional potential by measuring in vitro ruminal fermentability by the microbiota of cow, determining the fermentation profile of the green seaweed individually or simultaneously incorporated in different proportions to a reference fodder. The characterization of the associated microbial profile fermented in vitro by real time PCR and study of the specific activity of carboxymethylcellulase (CMCase)
enzyme were also performed.
According to their chemical composition, seaweeds are rich in minerals and then could be used as a food supplement to compensate the lack of minerals in certain physiological conditions and improve the growth of the ruminal microbiota. Similarly, they are characterized by an important content of crude protein and can therefore be recommended as a protein additive in diets with poor nitrogen content.
The evaluation of the in vitro ruminal fermentability of singular substrates by ruminal microbial flora showed that the brown seaweed is not fermentable. However, Ulva lactuca were weakly degraded compared to vetch oats (P <0.0001). The use of Ulva lactuca in combination with vetch oats is marked by a synergistic effect due to the protein and mineral contents of the green seaweed. However, the incorporation of the green seaweed affects the in vitro digestibility and microbial fermentation in terms of volatile fatty acids and ammonia concentration.
Molecular analysis of the relative abundance of different rumen microbial populations after 24hours of fermentation against 0h (control), reveals significant changes in the microbial profile of the rumen. It appears a significant imbalance among cellulolytic groups, including the three major cellulolytic bacteria (Fibrobacter succinogenes, Ruminococcus flavefaciens, Ruminococcus albus) and total anaerobic fungi. The species F.succinogenes predominates and
represents 69 to 84% of the analyzed bacteria. Furthermore, significant quantitative changes in target populations appear with the increase in the proportion of the seaweed up to the threshold of 40%. This is due to the optimization of growth conditions allowing the adherent cellulolytic population to grow and increase. This is corroborated by the increase in cellulase activity (CMCase).
Overall, it appears that the green seaweed Ulva lactuca has an appreciable nutritional potential that allows it to be recommended as a protein and mineral supplement. Similarly, its association with a coarse substrate (vetch-oats) improves the fermentability through a better proliferation of cellulolytic flora.
