Résumé:
This study was conducted in order to evaluate the possibility of valorization of agro-industrial by-products and their integration as alternative feeds for ruminants. In this context, three residues from food industry: tomato peels, orange pulp, and apple pomace were tested alone and mixed with fibrous forage: milk thistle (Sylibum marianum L. Gaertn.), crown daizy (Chrysanthemum corpnarium L.), and Hay. The physico-chemicals aspects were evaluated by the determination of chemical composition and the measurement of buffering capacity and pH. The metabolic aspects were evaluated by the in vitro degradation kinetics of substrates and the apparent degradability. A test for microbial protein enrichment of by-products was evaluated using two types of culture media and three successive fermentations, and various levels of nitrogen. Chemical composition results show that by-products contain relatively low fiber content (7.48-26.02%), high total sugars (31.25-77.76%) but low protein (2.26-5.75%), with the exception of tomato residues, which are diferent from the other substrates by moderately high
protein content (12.1%). The study of in vitro fermentability of substrates alone by rumen microflora shows that byproducts are easily metabolized. In comparison to fibrous plants, they produce significantly (P<0.05) more gas (203.4- 239.5 ml / g DM) with higher rates (0.108-0.144 b/h), and halftimes gas production (3.8 9-6.41 hrs), and shorter lag times (0.19- 0.48 h). The mixture (50 %: 50 %) with fibrous forage improved degradability of the latter (19.5%) while reduced the total volume gas (29.6%), gas production rate (28.6%) , and improved half-time of gas production (28.77%) and final ruminal pH (0.10 units) of by-products. Protein balance shows that a greater protein gain is recorded when oranges by-products were incubated alone (74.8%) or mixed with milk thistle (41.9%). In contrast, a protein loss is reported for tomato residues (3.4%) and for their mixture with milk thistle (10.2%). Microbial protein synthesis was higher when the culture medium is composed of an organic nitrogen source (simplified media) (27.6%) only when mineral nitrogen is used (Menke media) (14.5%). The amount (ml) of ruminal fluid also affected protein gain, which is higher (34%) when a low amount of inoculum is incubated (5 ml). Repeated fermentation strongly affected (P <0.0001) microbial protein synthesis which decreased gradually from the first (55.6%) to the third incubation (-6.4%). In conclusion, with the exception of mixtures of hay with a residues and mixture of oranges by-product: crown daizy all binary mixtures (50:50) with Sylibum marianum and Chrysanthemum coronarium could used as alternative feeds that can meet needs of ruminal flora while being compatible with its activity. In addition, oranges by-products are a promising substrate for the production of protein-enriched feeds.
