Effet de la saison de collecte sur la valeur nutritive, la production de méthane et de tannins condensés d’arbustes fourragers locaux.

Abstract

The main objectives of this thesis were to study, in a first part, the effect of season collection or harvest on the nutritional value, tannin content and methane production of three forage shrubs, Atriplex canesens, Astragalus and Calobota sahrae taken from an arid area of Algeria during three different seasons, through several aspects: chemical characterization, evaluating their potential nutritive value by measuring their fermentation and digestibility in vitro. In a second part, a reduction test of ruminal methanogenesis in vitro by the use of three medicinal plants selected according to their therapeutic characteristics in traditional medicine (Nigella sativa, Rosmarinus officinalis.L and Zingiber officinale), first , on ruminal fermentation parameters, gas production, methane and digestibility, and on the other hand, the impact of their use in the quantitative and qualitative production of volatile fatty acids. Chemical analysis revealed that the collection season has a significant effect on all the chemical components of the three shrubs investigated herein, except on condensed tannins. Atriplex canescens, has a very high crude protein content during winter that can reach 200 (g / kg DM). Regarding its content of cell wall constituents, they are very high in winter and spring, compared to values obtained for the summer. The same variations in chemical composition were recorded with Astragalus gombo, unlike Calobota sahrae which has very high values in summer compared to winter and spring. This is probably due to climate conditions in M'sila region, characterized by high temperatures and low rainfall. From the chemical point of view, the temporal variations show that the season effect on the different results obtained is significant. This is an effect of climate change associated with it. Indeed, we recorded a net variability for crude protein content and cell wall constituents. Despite the outstanding features of adaptation of spontaneous flora Sahara to harsh climatic conditions of their desert environment, it is clear that their survival, proliferation and their chemical compositions are highly dependent on climatic variations. This study has practical implications for the development of agro-forestry technologies. The three plants studied show good potential as fodder shrubs for ecosystem rehabilitation projects in degraded arid and semi-arid rangelands. Medicinal plants are a natural source of chemical molecules that can positively alter rumen fermentation. In general, a high methane reduction was noted with Monensin and Nigella sativa and no effect was observed with the other treatments. This study again confirms that the Monensin significantly inhibits the production of CH4 in the rumen. In terms of Nigella sativa, it is widely known that this plant is very rich in lipids and sterols, which could be the cause of the reduction. Information in the literature with respect to antimethanogenic effects of certain plant species and plant secondary metabolites and on secondary metabolites in these species can be described as a major interest for the interpretation of such results and discuss future research to identify the chemical components responsible for antimethanogenic activity.