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Habilitation à diriger des recherches

Efficience alicamentaire des plantes à tanins pour une production animale agroécologique

Abstract : Nutraceutical efficiency of tropical tannin rich plants for agroecological livestock production In view of the global challenges associated with food security and climate change by 2050, agro-ecology is an innovative option which seeks to improve in a greener way, the efficiency of production and use of resources in livestock systems. Livestock production is one of the mainstays of the world's diet, sheep and goats dominating in the tropics in terms of numbers and purposely raised for their milk and meat. However, unfavorable climatic conditions, threatens the production of livestock owing to unavailability of food resources and to increase in diseases inception. The risk of the latter is increased by globalization and human behavior, as illustrated by the high prevalence of gastrointestinal pathogens in farmed small ruminants, which, in addition, have developed significant resistance to most synthetic products worldwide. In order to enhance animal productivity, in the face of new challenges of global agriculture, alternative feed resources, prevention of disease resistance and natural resources, should be given the needed attention. Agroecology relies on fundamentals, among which, the crop-livestock synergy, found in more or less integrated in mixed farming systems (MFS). These MFS are based on certain agro-ecological principles contributing to the greater autonomy of the farm, such as the reduction of inputs on the farm, the recycling of co-products of harvest, the valorization of unconventional resources for animal feed, and the choice of local breeds for livestock. In tropical and subtropical PBS, sheep and goats of tropical breeds have a unique adaptation to tropical climates and local food resources. In addition, the presence of biomass with nutritional properties allows both to feed and care for animals. It is in this context that the valorization of plant secondary metabolites is important, given their food and / or health values. Condensed tannins (CT), which are part of plant secondary metabolites, have bio-activities that do not only influence animal's use of plant resource, but also its health, and gas emissions into the environment. The effects include toxicity, nematicidal activity (anthelmintic), rumen nitrogen fermentation and urinary nitrogen losses, microbial ruminal fermentation orientation and CH4 emissions, and intestinal protein digestibility. These polyphenolic multi-active compounds are present in many feed resources utilized in animal production. The biological effects of CTs depend on their concentration, structure, and molecular weight. The knowledge, and therefore the characterization of CT is an important criterion for the choice of the plant resource to be utilized. The study of the bioactive potential of plant resources rich in CT, for animal production, must therefore focus on the qualitative and quantitative evaluation of the compounds in plant materials. The research project, presented in this HDR, was conducted as part of the INRA-URZ research unit scientific project (which I have been part of since 2007), with the support of 44 students trainees (from Bac + 2 ; to Master degree) and 1 PhD thesis. The study sought to ascertain the chemical structures, nutritional value and anthelmintic characteristics of CTs from tropical resources and the optimal utilization of plant resources, while reducing the environmental footprint (CH4 emissions). The chemical and bio-active (anthelmintic, fermentation, nutraceutical) characterizations of CTs was concurrently studied with the small ruminant farming systems, before moving towards a finalized section for application to the breeding system (pellet test). Studies on CT have been done, partly, in support of our biological experiments, in particular for the evaluation of the CT content in the tested plant species. However, current assay methods do not allow for the comparison of CT concentrations of samples that do not belong to the same plant species. Based on the analytical database that generated, the current study focuses on the development of a common standard and a calculation model (equation) to estimate the CT content of plants, and to allow the comparison of samples, independently of the internal standards of each plant species. In addition, the results obtained during the chemical characterization of the CTs highlighted the presence of specific galloyls and epi-afzelechins groups in some plant species. These functional groups, rarely found in such high proportions, could influence the biological effect of CTs. On the other hand, the database, derived from the wide phytochemical screening of plant resources containing CT, supplemented with data obtained by near-infrared spectroscopy (NIRS), was evaluated during a first calibration study, for the prediction of levels and the discrimination of CT of the 3 model resources Manihot esculenta, Leucaena leucocephala, and Cajanus cajan. A NIR database has thus been created and can now be used to evaluate these 3 model resources, in terms of CT (3 plant species, 3 botanical families, 481 PIR spectra and CT contents: 246 with Manihot esculenta, 64 with Leucaena leucocephala and 81 with Cajanus cajan). A quantitative method for the rapid prediction of CT contents using the NIRS method was developed for Manihot esculenta (cassava) and Cajanus cajan (pigeon pea). The coefficients of correlations of the calibration straight lines for the estimation of the CT contents and standard errors of cross-validation (SECV) were 0.64 and 3.16% for Manihot esculenta, and 0.87 and 2.95% for Cajanus cajan. Standard Errors of Prediction (SEP) were 3.89% and 1.58% respectively for Manihot esculenta and Cajanus cajan. On the other hand, the study of fifteen tropical plants with CT, carried out for their biological influence on animal productions, validated their nutritional, fermentative and anthelmintic effects. The CTs of all tested resources had significant depressive effects on CH4 emissions (eg 4.7%, 29.3% and 28.9% for Glyricidia sepium, Leucaena leucocephala and Manihot esculenta compared to the control, gCH4 / kg of digestible organic matter ingested ) and on the fecal excretion of gastrointestinal nematode eggs by the animals (from 33 to 80% reduction of parasite fecal egg count, for a ≥50% quantity of ingested DM). In addition, the fertility of female worms and the eggs of the gastrointestinal parasitic nematode H. contortus appeared to be weakened. The fermentation profiles and the effects on the parasitic stages being variable according to different CT, the structure-activity link was thus highlighted. Similarly, the differences in CT reactivity at the different parasite stages (from 0 to 60% efficiency on the larval development of L1 to L3 stages and from 0 to 99% efficiency on the exsheathment of the L3 infesting stage, at the concentration of 2.5 mg / ml CT extract, relative to the negative control) are explained, depending on the dose, but are also related to the chemical structure. For example, according to our results, prodelphinidin CTs would be more effective on parasite development, while prodelphinidin monomers would be more effective on L3 stage larval exsheathment. The analysis of the chemical and biological databases established, allow us, in part, to strengthen the structure-activity link thereafter. In addition, a more in-depth study of the structural differences in CTs should allow a better understanding of the differences in action and in the CT-protein interactions involved. For the use of the 3 forages with CT, namely, Manihot esculenta, Leucaena leucocephala and Cajanus cajan, selected for their dual nature (presence of CT and proteins) and their availability on the farm, drying and granulation of the forages promoted the nutraceutical effect on Manihot esculenta, Cajanus cajan and Leuacaena leucocephala. This process preserved dietary and anthelmintic effects. In addition, the mixture of the 3 resources showed a synergistic in vitro effect against the nematode H. contortus, and substantially increased by granulation (+ 3% inhibition of larval exsheathment of H. contortus). Moreover, quantities of plants with CT were determined (75 to 150 g of fresh product, i.e. 15 to 30 g of dry product, per kilo of live weight) making it possible to treat the animals against gastrointestinal parasitism (reduction of the parasite infestation of animals at 67% relative to the alfalfa control), while ensuring good growth (increase in post-infestation growth of 6.8, 31.1, 45.8 and 21.7 g / day respectively for Manihot esculenta, Cajanus cajan, Leucaena leucocephala, and the combination of the three forages). It is now a matter of refining the values by studying a dosing regimen. For the future, an exploration of the potentials of the NIR technology and chemometrics, should be considered by coupling databases from phytochemical and biological works on plant resources with CT, with those obtained from the NIR study. A high-throughput qualitative and quantitative analysis of CT rich plants could thus contribute to developing, more rapidly, the knowledge of the anthelmintic, nutritional and environmental values of tropical CT rich plants, for small ruminant breeding. It may also lead to a tool for predicting the bio-activity of the resources on the health, production and emissions from animals.
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Carine Marie-Magdeleine. Efficience alicamentaire des plantes à tanins pour une production animale agroécologique. Chimie. Université des Antilles (UA) - Site de Guadeloupe, FRA, 2019. ⟨tel-02958089⟩

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