273 species of harmful and poisonous plants are known. They are found on pastures, in hay, silage, haylage, and straw. Poisonous plants are most common where acidic soils are present, in damp and swampy meadows and pastures, forest areas, among shrubs, in abandoned parks and gardens. Animals in pastures usually leave poisonous plants intact. However, where few edible and many poisonous plants grow, animals can eat (more often hungry) both. In the spring, poisoning by plants from the family of buttercups, umbrella, orchid and autumnal plants is observed, and in summer, during drought, euphorbia, swallow, kutrovy, etc.
The toxicity of plants is caused by the content of certain substances in them.
Alkoloids are nitrogen-containing organic compounds of predominantly vegetable origin, composed of hydrocarbon, hydrogen, nitrogen and oxygen atoms. The content of alkaloids in different parts of the plant may be different, but in general it reaches 0.2 - 2% of all toxic substances. Due to the strong physiological effect of alkaloids (for example, on the function of the nervous system), they are the most dangerous for animals.
Glycosides are nitrogen-free organic compounds of complex structure. Their molecules are composed of a carbohydrate and a non-carbohydrate part, the so-called aglycone (genin). According to the chemical composition of aglycones, glycosides can be of the following types: phenyl glycosides (upon hydrolysis, they form disinfectants, for example hydroquinone, and other compounds from bearberry leaves, in particular from arbutin); thioglycosides (contain sulfur, mustard essential oil is formed from mustard sinigrin); nitrile or cyano glycosides (hydrocyanic acid is formed from lianmarin contained in flaxseed oil).
Plants may also contain flavone glycosides, or flavones, yellow plant pigments, which eliminate increased permeability and fragility of capillaries, have a hypotensive effect, protect ascorbic acid from oxidation, anthraglycosides (characterized by a laxative effect - hay, sabur, rhubarb); saponins (form highly foaming colloidal solutions with water like soap, are cell poisons, cause blood hemolysis), etc.
There are also glycosides-alkaloids - combinations of glycosides and alkaloids (for example, solanine in potatoes, etc.). Albumin, a protein substance (for example, ricin in the seeds of slander), essential oils (the main part is terpenes and their oxygen-containing derivatives), organic acids and their anhydrides (oxalic acid, euforbic acid anhydride), substances such as lactones ( dicumarin, santonin, etc.).
Donkeys, mules, horses, pigs, birds are most sensitive to poisonous plants, sheep, goats, and rabbits are the least sensitive. Poisoning can occur in acute (occur suddenly and have pronounced symptoms), subacute and chronic (develop gradually with more prolonged use of feed containing toxic substances) forms.
The central nervous system, gastrointestinal tract, cardiovascular system, etc. are affected. For cases of poisoning, the following symptoms are characteristic: suddenness of the disease after changing pasture or forage; mass disease of animals with the same clinical signs and pathological changes; new cases of the disease do not appear when suspicious food is withdrawn.
According to their physiological effect on the body of animals and the clinical picture they cause, poisonous plants include plants that mainly affect the central nervous system, respiratory organs, heart, gastrointestinal tract, kidneys, liver, causing symptoms: salt metabolism disorders, as well as anoxemic phenomena.
The content of toxic substances in plants during the entire growing season, as a rule, changes. Some plants are more toxic during flowering, others before and after flowering. In some, both ground parts and roots and rhizomes are dangerous, while in others, poisonous substances can accumulate only in seeds or vegetative parts of plants. Most of them contain alkaloids. When the plants are dried, the toxic properties are preserved. Some of them (hellebore, etc.) remain poisonous even during ensiling. The content of volatile toxic substances is significantly reduced when dried.
For the prevention of poisoning in the pasture and with stall keeping, appropriate measures are carried out both in summer and in winter.
Poisonous plants in pastures and meadows are destroyed by liming, plastering, plowing, reclamation, etc. Corresponding crop rotations with grass sowing are introduced. Mow and destroy plants that remain uneaten after grazing.
Explore the pasture area before pasturing the animals. When places with a large number of poisonous plants are found, shepherds are warned about the danger of grazing animals. In such cases, it is advisable to enclose these areas.
Livestock should not be driven