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Peas --- intestines --- Swine --- animal nutrition --- Digestive absorption --- Matiere azotee endogene --- Alimentation animale

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Today, the livestock sector has to address multiple concerns. Being criticized for its environmental impact and competition for land use, a better efficiency at transforming vegetal proteins into animal proteins while limiting food-feed competition is now one of its main challenges. Several strategies have been identified to improve nitrogen use efficiency (NUE) and reduce environment damage of livestock production; the use of plant secondary compounds such as tannins is one of them. These natural molecules can bind with proteins and protect them against degradation by micro-organisms. Their action can thus help improve nitrogen efficiency and reduce nitrogen losses.Our meta-analysis conducted on 58 experiments showed that tannins are generally ineffective at improving zootechnical performances but a shift in N excretion was observed, urinary N being reduced in favor of faecal N. However, hydrolysable tannins and the effect of tannins addition before ensiling have been little studied to date, unlike condensed tannins. This thesis thus aimed at testing the following hypotheses : i) hydrolysable tannin extracts can reduce proteolysis both in grass-based silage and rumen, ii) hydrolysable tannin extract added before ensiling can improve nitrogen use efficiency in lactating dairy cows.The first experimental results showed that hydrolysable tannin extracts were effective at reducing ammonia-nitrogen content of silages suggesting a reduction of proteolysis. NH3-N proportion was reduced by 12 to 18% with oak tannin and up to 16% with chestnut tannin. Tannins also decreased ruminal nitrogen degradability of grass silage during enzymatic in vitro trial and in an artificial rumen. Proteolysis reduction thanks to oak tannin extract linearly increased with tannin dose in silage. The best dose range for oak and chestnut tannin extracts in silage seems to be around 30 g/kg of dry matter (DM) of forage. From 50g/kg DM, tannins showed a detrimental effect on in vitro organic matter digestibility. The second part of the work revealed that oak tannins extract (added at 26g/kg DM in grass before ensiling) had no effect on nitrogen use efficiency of lactating dairy cows. However, a shift from urine to faecal nitrogen was observed in this trial in presence of oak tannins. This strategy can thus be adopted to decrease the environmental impact of ruminant protein feeding. This experiment also documented the use of the "nitrogen isotopic discrimination" proxy to compare nitrogen use efficiency of two contrasting diets. The results indicated that the proxy would specifically sign the N partitioning at the metabolic level rather than the overall NUE, the latter also being impacted by digestive processes.The greatest interest of tannins would thus lie in their positive impact on environment preservation. The addition of tannin before ensiling seemed pointless in our conditions as compared to direct feeding given that the benefit from protecting proteins in silo did not persist in the rumen. The influence of pH on stability of hydrolysable tannin-protein complexes seems contradictory to literature data on condensed tannins. The specificity of tannin-protein complexes to both tannin and protein structures is a great challenge in the understanding of tannin impacts and the development of tannin applications in ruminant feeding.

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Dairy cattle --- Animal Nutrition Sciences. --- Cattle. --- Vaches laitières --- Diet. --- Alimentation.

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Selon la littérature, les tanins dans la ration des ruminants augmentent l’efficience
azotée. Ils diminuent la digestion des protéines dans le rumen, ce qui a pour conséquence
d’augmenter la proportion digestible dans l’intestin grêle. Cette réaction est due au fait que les
tanins complexent les protéines lorsqu’elles sont en solution dans un milieu à pH neutre
comme le rumen. Les tanins inhibent aussi le métabolisme d’une partie de la flore du rumen et
certaines enzymes utiles à la digestion des protéines dans celui-ci.
Une expérience a été réalisée sur six vaches laitières de race Holstein. L’objectif de
cette expérimentation est d’analyser l’impact de tanin de chêne hydrosoluble ajouté à
l’ensilage d’herbe, à une concentration de 1% de la matière sèche totale de la ration, sur
l’efficience azotée. L’expérience a été décomposée en trois périodes : une préadaptation de
dix jours et deux périodes de trois semaines. Les six vaches séparées en deux lots homogènes
ont reçu, à tour de rôle, la ration avec et sans tanin, à la manière d’un carré latin.
Durant la dernière semaine de chaque période, est réalisée la semaine de
prélèvement où tous les inputs (aliments) et les outputs (lait, urine, fèces) sont pesés et
analysés. Les données collectées ont permis de réaliser un bilan protéique complet et
d’analyser comment agissent les tanins.
Les résultats n’ont pas montré de différences significatives sur la production laitière
ni sur la composition du lait. Seul le ratio perte d’azote urinaire sur perte d’azote fécal et la
qualité de l’ensilage semblent être modifiés. Le tanin ajouté à l’ensilage réduirait les pertes
d’azote urinaire mais augmenterait les pertes d’azote fécal. Cette expérience n’a pas montré
de modification de l’efficience azotée.
La faible concentration ou l’emploi de tanins hydrolysables seuls (plus efficaces
cumulés aux tanins condensés) sont probablement les raisons de ces résultats. Les tanins,
ajoutés au moment de l’andainage, ont réagi avec l’ensilage mais peu avec la flore du rumen.

Tanin --- Vache laitière --- Efficience azotée --- Emission de méthane --- Ensilage d'herbe --- Sciences du vivant > Agriculture & agronomie