Cattle can be injured or poisoned by certain pastures while grazing. This is primarily because some plants in the grazing fields usually contain toxins which are potentially unsafe for the livestock. The toxic elements in the pastures are often a defense mechanism used by the plants against predation by the cattle and have a peculiar bitter taste and unpleasant smell. As such, they are not preferentially grazed. Ingestion of unpalatable pastures typically intensifies under certain conditions, mainly when other silage is not possible to obtain. Some toxins act at a rapid speed, so that by the time the warning signs are manifested, the likelihood of saving the cattle is minimal. It is, therefore, necessary to learn to identify the toxic pastures in advance and prevent poisoning from taking place. In this respect, the essay will discuss the types of poisoning that occur when cattle graze on poisonous plants as well as the effects the poisoning has on the domestic animals. A good comprehension of toxic pastures, their dangers, and management tactics will help in decreasing the risk of cattle poisoning.
First, it is important to understand how toxicity takes place. There are several plant and animal factors that lead to the poisonous principles in pastures and influence the plants' ability to poison respectively. To begin with, there are many factors that influence the plants’ toxicity such as the difference in their toxin content from the first stages of development to maturity (Robinson & Alex, 2016). For certain pastures, their capability to poison augments at the advanced phases of growth, while for others such risk is smaller. In addition, a plant's state when being consumed is also an important factor. This is because there are cases when wilting or even damage to pasture produces toxins which were absent when the plant was still fresh (Robinson & Alex, 2016). Furthermore, there are instances where a plant may contain poison in its fresh state but not in its dry condition as it happens with buttercups. In addition, there are pastures that contain toxins in some of its body parts while other parts of the same plant do not have the poison. This is the case with the rhubarb whose leaf stalk is palatable and not poisonous while its leaves are toxic (Robinson & Alex, 2016). Animals also have several features that influence the degree of poisoning with different species of animals being vulnerable to various plants and toxins. The age of cattle is, for instance, important wherein young animals are in most cases more susceptible to poisoning than the older ones (Robinson & Alex, 2016). Besides, cattle may turn out to be resistant to some toxins through its initial exposure to little amounts of poison. In other cases, where a greater amount of toxin is ingested, the cattle may become resistant due to their metabolism adjusting to get more tolerant to the poison (Robinson & Alex, 2016). In addition to this, if the animals are hungry or rather have some dietary deficiencies, they are more probable to eat poisonous pastures compared to those that are well fed (Luginbuhl, 2015).
There are also certain external conditions that determine the palatability and poisoning capacity of plants. To begin with, climate, seasons and growth stages of plants can influence the toxicity and palatability of some plants (Oregon State University, 2017). Certain pastures, especially those that amass nitrates, have the potential to increase their poisonousness on cool, cloudy daybreaks and sunsets or after rainfall. Other plants turn out to be more edible after a frost, while at the same time remain poisonous (Panter et al., 2011). Some toxic pastures have certain plant parts that undergo certain growth phases at which they are most poisonous, for instance, the tall larkspur that turns out to be most toxic and most edible while it locks and cliques flowers (Smallfarms.oregonstate.edu, 2017). It is therefore essential to understand the conditions in which pastures are most unsafe in order to avoid allowing cattle to graze toxic pastures to lessen the chances of them being harmed. Poisonous plants can also turn out to be more edible after the application of herbicide (Stalcup, 2017). It is therefore vital to take extra care when managing unwanted plants to ensure that cattle are not affected adversely. Pastures, for instance, should be grazed for a period of three weeks after the application of herbicides up until the poisonous plants are dried and lose their edibility, especially in cases where toxic species of plants grow in abundance (Oregon State University, 2017). It is also important to note that an incorrect usage of broad-spectrum herbicides can unintentionally affect the desirable pastures. As such, precautions must be taken during herbicide application to prevent over spraying and drift (Oregon State University, 2017). When controlling unwanted plants, desirable competitive pastures should be seeded immediately following the removal of toxic plants to avoid the reinfestation of the segment with other poisonous species.
Having observed the various factors that influence plants’ toxicity, the current section of the paper will focus on the types of plant poisoning and their effect on cattle. First are pastures that cause nitrate poisoning. Examples include the oats, sorghum, mangels, celery, turnip, sugar beets and rutabaga among others. Such plants accumulate nitrates from the soil in excess amounts and store them in their tissues (Oregon State University, 2017). The accumulation of nitrates is usually influenced by environmental factors which change the metabolism of minerals in plants. During dry seasons and in the event of low light intensity and uneven rainfall distribution, for instance, nitrate toxicity is more expected to happen if the pasture grows in soils that contain a high quantity of nitrogen (Thomas, 2017). Plants that have a nitrate percentage of more than 1.5 are hazardous to cattle. Besides, the consumption of nitrates in quantities as minimal as 0.05 percent of the weight of an animal is considered lethal (Hart, McGinty & Carpenter, 2014). Nitrate toxicity of cattle essentially represents nitrite poisoning, which occurs in the gastrointestinal tract of cattle when nitrate is converted to nitrite (Robinson & Alex, 2016). The nitrite is distributed into the capillaries where it forms methemoglobin after reacting with hemoglobin. Methemoglobin, a brown compound is not able to release oxygen (Thomas, 2017). In cases where acute nitrate poisoning takes place, the livestock are normally found lifeless. Such incidences are not associated with a previous history of ill health. The demise occurs at a rapid rate because sixty to eighty percent of hemoglobin in the cattle's body is comprised of methemoglobin (Robinson & Alex, 2016). Less acute nitrate toxicity, on the other hand, can be identified by various symptoms. The warning signs include weakness, unstable gait, collapse, shallow and swift breathing, quick pulse, coma and eventually death. Chronic toxicity may cause poor production of milk, poor growth and abortions (Robinson & Alex, 2016). In addition to this, nitrate poisoning causes the animals' body parts that are unpigmented like the tongue, eyes, and lips to have a discoloration of blue-brown. Furthermore, the cattle's blood may turn to a chocolate-brown color (Hart, et al., 2014).
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Second are plants that cause glycoside poisoning. Glycosides are products generated from plants that contain sugar glucose. This group of pastures can be split into three main divisions, namely those that cause cyanogenic glycoside toxicity, saponin glycoside poisoning and mustard oil glucoside poisoning (Robinson & Alex, 2016). In this regard, plants that produce cyanogenic glycoside poisoning include wild cherries, sudangrass, sorghum and marsh-arrow grass among others. The quantity of cyanogenic glycosides in pastures depends on several factors. Some species of plants contain the highest levels of cyanogenic glycosides at early growth phases while the lowest levels occur when they mature (Robinson & Alex, 2016). Besides, such factors as the soil quality, environmental conditions, and shade, which slow down the development and growth of plants, increase the content of cyanogenic glycosides in pastures. In addition, high nitrogen, low phosphorus, and reduced soil moisture stimulate the production of cyanogenic glycoside in plants. Furthermore, physical damage of plants like frost and wilting may induce a quick increase of cyanogenic glycosides in plants (Robinson & Alex, 2016). Cyanogenic glycosides are not toxic on their own but are instead hydrolyzed in the presence of some enzymes to form hydrocyanic acid, which is extremely poisonous. The hydrocyanic acid interferes with the exchange of oxygen to the cattle's body tissues from the lungs. As a result, tissues in various organs like the brain experience oxygen starvation and are permanently damaged. As such, cattle experience muscle tremors, seizures and rapid respiration (Robinson & Alex, 2016). It is, however, worth mentioning that these symptoms are not always observed, because the animals die within minutes. The other division of glycoside poisoning is saponin glycoside toxicity which is caused by pastures such as the purple cockle, bouncingbet, cow cockle, and pokeweed. When cattle graze on these plants, saponin glycosides get absorbed into their bloodstream causing the red blood cells to break down and consequently damage the central nervous system. As a result, the cattle experience diarrhea, vomiting and colic and in due course die from seizures and paralysis (Robinson & Alex, 2016). The last division includes plants that cause mustard oil glucoside toxicity. These pastures belong to the Mustard family, and when cattle graze on them, the plants bring about severe gastroenteritis. As a result, the animals suffer purging and severe colic (Robinson & Alex, 2016).
Third are pastures that cause ergot poisoning. They include such pastures as brome grasses, quack grass, bent grasses, orchard grass, blue grasses, poverty oat grass and reed canary among others (Robinson & Alex, 2016). Ergot, a type of fungus infests grasses and when consumed in sufficient amounts, is toxic because of mycotoxin production. The presence of ergot is identified through the observation of masses, which are hard and dark-colored or purplish, and can be found in flowering grass heads. The masses are called ergot bodies and are normally two to five times bigger than the grass seeds (Robinson & Alex, 2016). When cattle graze on pastures that contain the ergot bodies, ergotoxine, which is an active toxin, triggers the animal's nervous centers causing the small blood vessels that supply blood to the body to contract. The effect of ergot toxicity on cattle generally depends on the quantity of the fungus ingested. If only a small amount has been consumed, the cattle involved may get well without suffering any severe symptoms (Robinson & Alex, 2016). Nevertheless, in cases when a large quantity of ergot has been taken in, the animals involved may suffer abortion if pregnant, dry gangrene and even death in extreme cases. The most common warning signs of ergot poisoning include dullness, subnormal temperature, loss of appetite and abdominal pain (Robinson & Alex, 2016). In severe cases, there are two distinct kinds of symptoms that are likely to develop. One is the nervous form which is manifested in depression and tediousness in cattle. The animals may also suffer delirium, convulsions, trembling and contractions of legs. Besides, the animals may experience loss of appetite, gastrointestinal catarrh and progressively develop a deteriorating condition (Robinson & Alex, 2016). This kind of symptoms develops very rapidly, and the animals may experience death in convulsions or spasms. The other kind of symptoms is the general or gangrenous form wherein the cattle experience a stoppage of blood that is brought about by the small blood vessels contracting and eventually causes necrosis of extremities including the tail, ear tips or the feet. The parts of the animals that get affected are usually cold and dry, forming a slight furrow that splits the dead tissue from the living one. Typically, the cattle experience insignificant blood loss or none at all, and there is usually no pus. If the cattle recover, they may get crippled for the rest of the lifetime. On the other hand, the animals may develop gangrene or be invaded by bacterial entities causing death (Robinson & Alex, 2016).
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Fourth are pastures that cause sensitivity to sunlight and liver disease. These plants are grouped together because photosensitivity is usually a secondary indication of liver disease brought about by toxic plants. They include plants like onion, clover, false lupine, puncture vine, cowcockle, buckwheat, blue-green algae and cocklebur among others (Smallfarms.oregonstate.edu, 2017). When consumed, these pastures cause cattle to become sensitive to strong sunshine. As a result, the animals suffer from sun burning, inflammation of the sensitive body parts, gangrene, and ulcers. The cattle may also become blind. It is worth pointing to the fact that sensitivity to sunlight can either be primary or hepatogenic. In cases of primary photosensitization, toxins photosensitize the animals' skin directly through ingestion or skin contact. The toxins are then accumulated and distributed to the skin through blood where they are stimulated by sunrays. As a result, the unpigmented skin being initially white in color is affected. Buckwheat is an example of a plant that causes primary sensitivity to sunlight (Robinson & Alex, 2016). In hepatogenic photosensitization, plants do not directly cause sensitivity to sunlight but rather contain toxins that cause damage to the liver. Consequently, phylloerythrin, chlorophyll's breakdown product, is prevented from being eliminated from the bile fluid. As such, phylloerythrin is distributed throughout the skin's capillaries where its activation takes place and eventually causes symptoms that are similar to the ones produced by primary photosensitization (Robinson & Alex, 2016). It is, therefore, necessary to treat the liver in the event of hepatogenic photosensitization. Blue-green alga is an example of a plant that brings about hepatogenic sensitivity to sunlight.
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Fifth are plants that cause cyanide toxicity. They include pastures like arrowgrass, wild carrot, larkspur, yellow star thistle, poison hemlock and hemp dogbane among others. This variety of plants has glycosides that normally transform into hydrogen cyanide or rather prussic acid through hydrolisation in case their cells get damaged (Smallfarms.oregonstate.edu, 2017). The hydrogen cyanide reacts with methemoglobin and the compound formed interferes with oxidative phosphorylation (Yildiz, Dokuzeylul & Gonul, 2017). Chronic cyanide poisoning causes a loss of nerve functioning over time while acute cyanide toxicity brings about death of cattle. If treatment is provided timely, the poison can be neutralized, but in many instances, the animals die because of the quick action of the cyanide toxin (Yildiz, et al., 2017).
Sixth are plants that cause irritation. They include such pastures as the leafy spurge, buttercup, western juniper, burdock, fleabane and wooly among others. These plants contain compounds that have the ability to irritate the cattle's skin, digestive tract or mouth when eaten, making the cattle exposed to infections and toxins (Oregon State University, 2017). Generally, these pastures are not edible and are naturally avoided. Plants like the burdock are a common source of irritation. When eaten, the burs of this plant form some kind of a ball in the stomach which is indigestible. Consequently, the wall of the digestive tract is injured, making it susceptible to secondary infections and poisoning (Robinson & Alex, 2016). Besides, pastures like buttercups and spurges are also a source of irritation. The sap from such plants often irritates the skin of cattle. In the event the livestock gets in contact with the juices from these pastures, their skin will swell and form blisters, which are painful. If this occurs in the area around the animal's mouth, their ability and even desire to eat will be significantly reduced (Robinson & Alex, 2016).
Seventh are pastures that have the ability to cause physical injury to cattle. They include such plants as the stinging nestle, sand bur, cheat, velvet grasses, longspine, puncture vine, wild rye, medusahead and foxtail barley among others. These pastures possess characteristics that cause physical injury to cattle in the course of grass grazing making them vulnerable to infections and toxins (Oregon State University, 2017). Some are palatable but can injure the cattle's eyes, ears, nose, mouth and some other body parts. The damage may be internal or external. When injury takes place, the cattle are also exposed to infections and poisons which may turn out to be even more detrimental. The awns or barbs of wild rye, for instance, are usually harmful for the throats or mouths of cattle. This is because they contain spines that are small and pointing backward, which make the awns stick in the throat or mouth. They are very hard to dislodge, causing mechanical injury in the throat or mouth (Robinson & Alex, 2016). Besides, the sand burs' fruits contain spines which are somewhat stiff and therefore injure an animal's muzzle when grazing. In addition, the burs may also cause painful wounds when they get into the cattle's mouth (Robinson & Alex, 2016).
The discussion above has highlighted several kinds of poisoning by pasture affecting cattle. It would, therefore, be necessary to also mention some of the strategies that can be employed to lessen or eradicate the toxicity. Grazing management is one of the most fundamental approaches of keeping healthy plants away from toxic ones. This tactic involves avoiding overgrazing, which in turn helps in maintaining a large quantity of appropriate fodder pastures that have the ability to favorably fight against the unwanted plants and lessen the risk of cattle being compelled to consuming toxic pastures due to a lack of other silage options (Behnken & Durgan, 2017). Grazing management also entails a reduction of grazing pressure in the event of drought because dry periods increase the consumption of toxic pastures if other fodder is available in reduced amounts (Oregon State University, 2017). Another strategy is developing and executing an all-inclusive weed control method that integrates chemical, biological, cultural and physical weed management. The use of herbicides and mowing are two important weed control programs (Oregon State University, 2017). Correct application of herbicides helps eliminate particularly detrimental weed populations (Panter et al., 2011). Mowing, on the other hand, assists in the reduction of probable development of seed as well as persistent spot and dispersal.