F. hepatica peut infester la plupart des espèces animales, mais elle n'a d'importance économique que chez les bovins et les ovins. Dans la forme aiguë, très fréquente chez les jeunes ovins, moins résistants à l'infestation que les bovins, la mortalité peut être très importante, surtout au début de l'hiver. La forme chronique affecte beaucoup l'état général des animaux. Le tissu hépatique est profondément lésé par la migration des larves, ce qui peut entraîner une forte anémie et parfois une hépatite nécrosante mortelle. Les canaux biliaires étant obstrués, les animaux présentent des troubles hépatiques et maigrissent ; dans la phase ultime de la maladie, des œdèmes apparaissent, en particulier sous la gorge (signe de la bouteille). Les infestations, même légères, sont responsables de pertes économiques importantes : baisse de production, saisie des foies à l'abattoir, perte de 20 à 30 % de la valeur de la toison pour les moutons.
Les traitements préventifs et curatifs doivent être effectués avant la mise à l'herbe, à intervalles réguliers pendant la saison de pâture, et surtout au début de l'hiver. La lutte contre la grande douve passe aussi par la destruction de l'hôte intermédiaire (molluscicides), le drainage des pâturages ou l'épandage de cyanamide calcique dans les zones humides.
Guillot
fatshedera
Arbuste d'ornement ou plante d'appartement (espèce Fatschedera x, famille des araliacées).
Le fatshedera est un hybride obtenu en France vers 1910 de Fatsia japonica et de Hedera helix, le lierre commun. Ses feuilles, persistantes, ont une forme intermédiaire entre celles des 2 espèces qui lui ont donné naissance. Le fatshedera se multiplie par bouturage au printemps et en été. À l'extérieur, il apprécie les situations abritées, bien qu'il supporte le froid (jusqu'à 8 °C).
Dorion
faucardeur
Appareil servant à couper les herbes aquatiques dans les rivières, les étangs et les canaux d'irrigation ou d'assainissement. SYN. : faucardeuse.
Le faucardeur comporte une lame à mouvement alternatif ou un disque rotatif muni de sections coupantes à sa périphérie. Il est porté par un tracteur ou monté sur une barque.
Aubineau
fauchage
Action de couper les tiges d'une plante cultivée en vue de sa récolte. SYN. : fauchaison, fauche.
Les termes de fauchage, fauche et fauchaison s'appliquent surtout aux fourrages. Pour les céréales, on préfère parler de coupe. Effectuées autrefois à la faucille, la faux ou la sape, la fauche et la coupe sont aujourd'hui réalisées par les barres de coupe équipant les machines de récolte.
Illustration page suivante.
Aubineau/RE
faucheuse
Machine agricole mobile servant à couper le fourrage.
Les faucheuses sont traînées, semi-portées à l'arrière ou portées latéralement (plus rarement, frontalement) sur les tracteurs. On trouve aussi des faucheuses frontales sur les grosses automotrices utilisées dans les chantiers de récolte des fourrages destinés à la déshydratation et sur les petites motofaucheuses de montagne. L'ensemble des organes de coupe est appelé barre de coupe.
La faucheuse à barre de coupe à lame unique animée d'un mouvement alternatif rectiligne (dite faucheuse alternative) existait en traction animale. Ce principe de coupe, adapté au tracteur, a été longtemps le seul utilisé, malgré la vitesse de travail relativement lente (5 à 8 km/h).
Les faucheuses à assiettes rotatives (dites faucheuses rotatives) ont supplanté les faucheuses alternatives en raison de leur vitesse de travail supérieure (12 à 15 km/h) sans bourrage.
Les faucheuses alternatives ou rotatives sont le plus souvent complétées de dispositifs conditionneurs.
Aubineau
faucille
Outil à main constitué d'une lame métallique unie ou dentée, en forme de croissant plus ou moins incurvé et engagée dans un manche en bois très court.
Apparue dans l'Antiquité égyptienne sous une forme rudimentaire, la faucille a servi, jusqu'au milieu du XIXe siècle, à la coupe des fourrages et surtout des céréales. On ne l'utilise plus aujourd'hui que dans les jardins pour couper certaines plantes ou débroussailler un terrain avant de le bêcher.
Aubineau
faune
1. Ensemble des animaux vivant dans un milieu donné (sol, eau, forêt) ou sur un territoire donné (parcelle, région, pays). 2. Ouvrage faisant l'inventaire et la description des animaux d'un milieu ou d'une région.
Mazoyer
faux
Outil formé d'une lame d'acier recourbée fixée à un long manche que l'on manie à deux mains pour couper l'herbe, les fourrages, les céréales, etc.
La faux est apparue en France au XVIIIe siècle, bien plus tardivement que la faucille. Pour couper les céréales, elle est munie d'une armature en bois sur laquelle s'accumulent les épis coupés d'un coup de lame.
La faux à lame courte sert à faucher les broussailles. Les lames sont affûtées à la meule ou martelées sur une petite enclume ; l'affûtage est complété au champ à l'aide d'une pierre à aiguiser.
Aubineau
faverolles
Race de poules créée à la fin du XIXe siècle, et qui était alors championne pour la vitesse de croissance, utilisée aujourd'hui en croisement pour la production de poulets label.
Le plumage du coq est argenté sur la partie supérieure du corps et noir sur la partie inférieure et la queue ; la poule a le dos et le dessus des ailes saumoné clair, la poitrine et le ventre étant blanc crémeux. Les plumes situées sous les yeux et sous le bec forment des favoris et une cravate.
Coquerelle
fèces
Résidus de la digestion des animaux, éliminés par l'anus sous forme plus ou moins liquide.
Les fèces contiennent des aliments non digérés, des produits de sécrétions digestives, des cellules mortes de l'intestin, etc.
Bougler/Gallouin
fécondation
1. Biologie. Fusion des gamètes (cellules reproductrices) mâle et femelle, ce qui produit l'œuf, ou zygote (première cellule du nouvel individu).
2. Botanique. Au sens strict, fusion des gamètes mâle et femelle ; au sens large, ensemble des phénomènes qui, chez les plantes à fleurs, se déroulent entre la pollinisation et la fécondation proprement dite.
Chez les végétaux.
Une fois parvenu sur les stigmates du pistil, le grain de pollen germe ; il produit un tube pollinique qui descend dans le style pour arriver au contact d'un ovule, à l'intérieur de l'ovaire. Dans le tube pollinique en croissance, le noyau reproducteur du pollen se scinde en 2, chez les espèces pour lesquelles cette division n'a pas déjà eu lieu lors de la maturation du grain de pollen. Parvenu à l'ovule, le tube pollinique pénètre, par un pore appelé micropyle, jusqu'au sac embryonnaire. Là, un des noyaux mâles (gamète mâle, n chromosomes) va fusionner avec l'oosphère (gamète femelle, n chromosomes) pour produire l'œuf principal, ou zygote (2n chromosomes), à l'origine de la future plantule. Le second noyau mâle va fusionner avec les 2 noyaux polaires de la cellule centrale du sac embryonnaire, pour produire l'œuf accessoire ou œuf albumen (3n chromosomes) qui sera à l'origine du futur albumen (tissu nourricier de la graine servant à la nutrition de la future plantule).
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