Grazing-Related Animal Health Concerns

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This module outlines some potential animal health concerns that need to be considered when grazing including pasture bloat, grass tetany, poisonous plants and water quality. Generally, prevention is a more economical and practical approach to these animal health concerns on pasture than treatment of symptoms.

Pasture Bloat

Key points:

  • Including bloat-causing legumes in a pasture stand increases production but does pose risks.
  • Bloat-causing potential of a forage is related to the rate of digestion, with rapidly digested material (fines) carrying the most risk. Consumption of the entire plant results in both stem (coarse) and leaf (fine) material present in the rumen, slowing digestion.
  • More mature plants have less fine material to consume and bloat risk is reduced.
  • Legumes that are rapidly growing and in the vegetative to early bloom stages have the most risk.
  • Mixed stands with some bloat-safe legumes and/or grasses reduce risk of bloat.
  • Moving cattle to new pasture in the afternoon has a lower bloat risk than moving in the morning.
  • Avoid moving cattle to new pasture when they are hungry.
  • Uniform and regular intake of legumes reduces bloat risk.
  • Talk to your veterinarian about the use of surfactants (e.g., Alfasure) or ionophores (e.g., Rumensin) to help prevent bloat.
What is bloat and what does it look like?

Bloat is the swelling of the rumen with gases produced by microbes during fermentation that cannot escape through eructation (belching). Fermentation always occurs during digestion, but the rate of fermentation varies between forages. Rapid fermentation combined with an abundance of small particles in the rumen causes froth or foam to be produced, preventing the animal from releasing gas. In severe cases the gas builds up putting pressure on the lungs until the animal goes into respiratory failure, leading to death.

Bloated animals will have distension on the upper left side where the rumen is located, will frequently urinate and defecate, alternate between laying down and standing and kick at their flank. In severe cases the animal will have laboured breathing, a protruding tongue and an extended neck. Death can occur two to four hours after the onset of bloat.

What forages are highest risk for bloat?

Grasses are usually considered bloat safe, but many common legumes pose bloat risk when used for grazing. For example, the initial rate of ruminal digestion of alfalfa is five to ten times greater than that of most grasses. Examples of the bloat potential of different forages are presented in the table below.

As noted in the figure below, incidence of bloat rises as the rate of digestion increases and particle size in the rumen decreases. The risk of bloat increases when the plant is immature (pre-bud to bud stage) when grazed and when plants are moist from the morning dew or rain, as the initial rate of digestion is higher from moist plants.

Frost on a bloat-causing legume stand increases the risk of bloat for up to five days as it ruptures the plant cell walls, increasing the initial rate of digestion.

What are tannins and how do they impact bloat risk?

Tannins are a type of chemical compound produced by some forage plants. They prevent bloat by binding to protein as it is released from plant tissue in the rumen. This prevents the rapid fermentation of protein in the rumen, and instead, it is digested more slowly in the lower gastrointestinal tract. Some legume species, such as sainfoin, are considered bloat-safe due to the levels of condensed tannins in the forage.

How do I minimize bloat risk?
  • Never turn hungry livestock into a pasture containing a high proportion of bloat-causing plants.
  • Fill animals with dry hay or grass pasture before beginning to graze high bloat-potential pastures.
  • Avoid turning animals onto fresh, high bloat-potential pasture that is moist with dew, rain, or irrigation water. Both rate of intake and initial rate of digestion are higher from moist plants, causing more rapid initial digestion.
  • Never allow animals grazing high bloat-potential pasture to get so hungry that they consume too much in one feeding. Always have sufficient feed available.
  • Move animals mid-day or later to help minimize moisture and increase plant carbohydrate concentration.
  • Avoid dramatic changes in forage quality when rotating from paddock to paddock by leaving adequate residue.
  • Observe livestock closely the first several days and remove any “chronic-bloating” animals.
  • Avoid grazing legumes before they begin to bloom. Monitor animals more closely for bloat when many plants are at an earlier growth stage.
  • Manage grazing to encourage livestock to consume low- or non-bloating plants and plant parts (such as an alfalfa/grass forage blend) rather than just succulent top growth. For example, use daily strip grazing or use high stock density in multiple paddock systems rather than continuous grazing.
  • Once grazing begins, don’t remove animals from pasture or make frequent, major changes in the type of pasture being grazed unless animals have greatly distended rumens. Mild bloat is common on high bloat-potential pastures. Frequent diet changes prevent rumen microbes and animals from adapting to pastures with higher bloat potential.
  • Be extra observant for cattle bloat when high bloat plants show a rapid flush of growth such as during cloudy, wet periods in the spring and after a plant stress event such as hail or drought.
  • Delay grazing high bloat-potential plants for three to five days after freeze damage.
  • Graze high bloat-potential plants with animals that have smaller rumen capacities, like yearlings and calves, rather than mature cows.
  • Talk to your veterinarian about the advisability of using surfactants or ionophores.

Excerpt adapted from the Beef Cattle Research Council’s Blog Post “Fear of Bloat Costs More Money Than Actual Cases of Bloat Do.”

Grass Tetany

Key Points:

  • Caused by a magnesium deficiency.
  • Occurs when grazing lush, rapidly growing grass pasture. Including a legume in the pasture mix reduces risk.
  • Characterised by nervousness, lack of coordination and muscle twitching.
  • Rapid treatment is necessary to avoid death.
  • High potassium levels and nitrogen fertilization of the pasture may increase risk.
  • A mineral mix with magnesium oxide can help prevent this condition.
  • Mature, lactating cows are at highest risk.
What is grass tetany and what does it look like?

Hypomagnesemic tetany, also known as grass tetany or grass staggers, is a complex metabolic disorder caused by a magnesium deficiency or a decrease in magnesium absorption.

Symptoms of this disorder include nervousness, muscle twitching, decreased milk production, decreased weight gain and a depressed appetite. In acute cases, this may develop to hyper-excitability, aggression, muscle spasms and trembling, frequent urination and defecation, lack of coordination, stiffness, staggering, and convulsions that eventually lead to death. Often the first sign of grass tetany is a dead cow that has marked up the ground around her head and legs due to struggling or paddling.

Animals with a high magnesium requirement are at the highest risk, such as cows in early lactation. Older cows are more susceptible to grass tetany as magnesium absorption decreases with age.

How do I prevent grass tetany?

Grass tetany is typically observed in lush grass pastures (boot stage or earlier) that have received high levels of nitrogen and potassium fertilizer or manure application, especially in the early spring. As levels of other nutrients like potassium increase in forage, the availability of magnesium decreases. Low soil phosphorus levels reduce the plant’s ability to take up magnesium from the soil. Cold, wet weather increases this risk as it reduces availability of soil phosphorus.

Risk of grass tetany can be reduced by:

  • Using a mineral that includes magnesium at a rate of one to three percent.
  • High magnesium levels can reduce the palatability of the mineral, so ensure that animals are consuming adequate amounts.
  • Magnesium is not stored by the animal, so it needs to be consumed on a regular basis.
  • Adding legumes, which have higher magnesium concentrations than grasses, to the pasture mix and avoiding heavy fertilization in the spring also reduces the risk of grass tetany.

Poisonous Plants

key points:

  • Few plants cause immediate death, but many have ill effects when consumed in large quantities and/or repeatedly.
  • Prevention of ingestion is key. Some effects may be untreatable.
  • Maintain pastures with an adequate quantity of desirable forage.
  • Fence off areas with populations of poisonous plants.
  • Livestock tend to avoid poisonous species but will consume them when few other options are available, or they are hungry:
  • Some poisonous species are the first to grow in the spring and may be the only thing to graze if cattle are turned into pasture too early.
  • Overgrazed pastures can force cattle to consume poisonous plants when the desirable plants are already grazed.
  • When drought impacts growth and regrowth of desirable plants, poisonous plants may be consumed.
  • Hungry animals are less selective. When cattle are moved to a new pasture when they are hungry, they will graze the first thing that they find. Yearlings or young calves may also be less selective grazers.
  • A lack of salt and/or minerals may lead to cattle consuming poisonous plants to fulfill a craving.
  • Trailing animals to a new pasture can expose them to poisonous plants in road ditches.
  • Monitor pastures over time as overgrazing can reduce desirable plant populations and allow the invasion of poisonous plants.
Which poisonous plants cause death in cattle?

Arrow grasses, water hemlock, tall larkspur and death camas are the most prevalent species in Canada that can result in death when consumed by cattle. This is not a complete listing of lethal poisonous plants, merely the most commonly found. Many other plants have ill effects on cattle when consumed in large quantities and/or over a long period of time.

Arrow grasses

Seaside arrow grass and marsh or small arrow grass are herbaceous, perennial, grass-like plants that grow between 15 and 76 cm (6 to 30 inches) tall.  These grasses are most often found in marshes and sloughs where there are damp, alkaline soils or the water is brackish. Arrow grasses are found throughout Western Canada but are not present in large numbers.

Arrow grasses begin growing early in the spring and regrow rapidly after being cut in comparison to other grasses. This can heighten the risk of poisoning as the arrow grasses can be more abundant than desirable forage species at these times. Arrow grasses are palatable to livestock because of their high salt content. The plants are more toxic when they have been stunted by frost or drought and in regrowth after cutting. Hay containing arrow grass loses toxicity over time. Symptoms include slobbering, excitement, rapid breathing, staggering, muscle spasms and convulsions with death occurring from asphyxia.

Water hemlock

Water hemlock is considered the most poisonous plant in North America. It can grow to a height of 7 feet and has smooth, branching stems that are swollen at the base. The stems are purple-striped or mottled and hollow except for where they meet the roots. The leaves have serrated edges with veins proceeding to the edge of the leaf. Water hemlock is found in wet places around marshes, sloughs and streams. It can be found in a stand or as a lone plant and often persists in the same place year after year. It can be confused with water parsnip, which is more common and can be used for forage. Water hemlock’s fleshy root is where it stores food reserves for the plant and is a distinguishing feature. A pungent oil in the roots changes from yellow to red within a few minutes of exposure to the air. The bundle of roots resembles those of dahlias with hollow internodes and diaphragms of pith tissue across the cavities. One root bulb has enough toxin to kill a cow. While water hemlock is not a highly palatable plant, when cattle are hungry, they may pull the plant out and consume the roots.

While the roots have the highest levels of toxin, lower concentrations are also found in the foliage. The foliage decreases in toxicity during the growing season and when drying but it is still not advisable to feed hay containing water hemlock. The roots are never safe to feed. Symptoms develop within 15 minutes of consumption and include slobbering, violent convulsions, muscle tremors, painful abdominal spasms and diarrhea with death occurring from asphyxia. Usually, symptoms are not observed, and cattle are found dead close to the source of the poisoning since death is so rapid.

Water hemlock is also extremely toxic to humans and as little as two drops of the oil from the root on an open cut can kill a human.

Tall larkspur

Tall larkspur is perennial forb that grows between 1 and 2 metres tall with deeply cleft leaves and purple flowers. It is most common in areas of the boreal forest, especially in higher elevations in the foothills of Alberta and British Columbia.

Early spring poses the most risk as the toxicity of the plant declines with maturity until late pod stage when Tall Larkspur is relatively safe to graze. However, late summer storms can increase the plant’s metabolism and increase the toxic alkaloid concentration. Dried, mature plants are low in toxicity, but the seeds are toxic although rarely consumed.

Tall larkspur is difficult to control with herbicide, so the most effective control measure is to cut it early in the season. Sheep are less susceptible to the toxin and can be used to graze tall larkspur ahead of cattle.

Symptoms include weakness, muscle twitching and convulsions as the toxin affects the nervous system. Animals will fall down repeatedly. Recovery or death is rapid, usually within hours.

Death camas

Death camas is a small, slender perennial herb with creamy yellow flowers that grows from an onion like bulb to a height of 20-50 cm. It is most common in Saskatchewan and Alberta and is found around wetlands and areas that flood in the spring.

Since this plant begins growing early in the spring the risk is highest early in the year. All parts of the plant are poisonous whether in pasture or in hay. To decrease risk, delay spring turn out until there is adequate growth of other desirable forage species. Symptoms include rapid, severe congestion and bleeding in the lungs with death occurring from cardiac arrest. Cattle may remain in a coma for several hours before dying.

Are there other poisonous plants?

Other plants with varying levels of toxicity to cattle are found across Alberta. More information on each of the above species and other poisonous species is available in the Stock Poisoning Plants of Western Canada and Common Weeds Poisonous to Grazing Livestock.

When are animals most likely to graze poisonous plants?

Under normal circumstances, cattle tend to avoid poisonous plants. However, when cattle are hungry, they are less particular about the forage they consume and are more likely to eat undesirable plants. For example, overgrazing pastures forces cattle to graze plants they would normally avoid, such as water hemlock in low areas. This is common during a drought when feed is scarce. When moving cattle that are hungry, they are more likely to graze forage in the ditches and graze the first plants that they find in the new pasture, regardless of whether it is a desirable plant. Early spring turnout can pose a higher risk as some poisonous plants, such as death camas and arrow grasses, begin growing early in the season before many of the desirable forage species and may make up a larger portion of the available forage at that time.

How can poisoning be avoided?
  • Identify whether your pastures contain poisonous plant species and which ones are present.
  • Always ensuring there are ample desirable plants to graze greatly reduces the risk of consumption of poisonous plants.
  • Avoid moving cattle to new pastures when they are hungry
  • Avoiding overgrazing pastures and re-grazing before sufficient regrowth has occurred. 
  • Fencing, mowing, herbicide application, or tillage may be control options to consider, but effectiveness will vary depending on the type of poisonous plant present.

Many producers graze and/or hay different fields and areas of pastures during a drought due to feed shortages. Familiarize yourself with these fields and the forage species present in order to mitigate the risk of consumption of poisonous plants. For example, sloughs and wetlands that are typically fenced off may be used as an emergency feed source and are prime habitat for poisonous species such as water hemlock and arrow grasses.

Water Quality

Key Points:

  • Water quality can affect consumption and animal health.
  • Factors affecting water quality:
  • Blue-green algae: occurs in stagnant, warm water (i.e., dugouts, sloughs) that have high nutrient run-off from manure and/or fertilizer
  • Bacteria, viruses and parasites: a large variety of these organisms can cause health issues. Common in water sources that collect runoff directly from a manure source (i.e., winter feeding grounds, feedlot).
  • Sulphates: high concentrations occur in surface water sources that are fed from saline areas and/or groundwater. Sulphur intakes above 0.4% of dry matter intake may be toxic.
  • Total Dissolved Solids (TDS) or salinity: Refers to mineral quantities in water. Water with TDS of greater than 5,000 mg/L should not be used for lactating or pregnant cows. Greater than 7,000 mg/L is unsuitable for cattle.
  • Nitrates: can be found in groundwater contaminated by manure or nitrogen fertilizer. Uncommon in surface water. Rare to be an issue on its own but can be problematic when combined with feed containing nitrates.
  • Water quality can vary substantially throughout the grazing season and also from year to year and should be monitored regularly to determine if specific water quality problems exist.
  • Laboratory testing is the gold standard for water testing, but handheld conductivity meters can be useful for screening for water quality problems as long as they are calibrated, maintained, and operated correctly.

The Rural Water Quality Information Tool can help you interpret your test results.

Why is water quality important?
Source: Beef Cattle Research Council

Animals that have access to high quality water drink more and eat more resulting in an increase in weight gain and/or milk production.  In addition, it leads to lower incidence of disease and other health problems.

Livestock can tolerate poorer quality water than humans, but specific compounds at high enough concentrations can cause ill effects. While most factors affecting water quality are not lethal to cattle, they can affect lactation, weight gain and reproduction.

What is blue-green algae and what impact does it have on cattle?

Blue-green algae has a shimmering blue-green colour that looks like spilled paint floating on the water. Heavy blooms appear thicker and have a consistency similar to pea soup.

Two types of toxins are produced by blue-green algae. One is a nerve toxin that can cause sudden death and the second is a liver toxin that can cause death within hours or days. Symptoms of acute poisoning are tremors, staggering, convulsions, abdominal pain, diarrhea, difficult breathing and death. Chronic symptoms are liver damage, jaundice and photosensitization.

Blue-green algal blooms are common problems in dugouts and ponds. Warm water conditions, steady gentle wind, the presence of high levels of nutrients (i.e., phosphorus from manure runoff) and stagnant water are ideal conditions for blue-green algae growth.

Limiting nutrient loads in the water and aerating the water body are the best ways to prevent algal blooms. Also, placing the water intake at least a metre below the water surface and pumping the water to a trough for livestock to drink from will help to avoid the ingestion of concentrated toxins.

Water with a blue-green algal bloom can be treated with registered chemicals containing copper, please consult with a livestock agrologist, specialist, or your veterinarian for the correct treatment for your situation. The most common chemical used is copper sulphate. If there is a natural blue-green algal bloom die off, or if chemical treatment is used, direct cattle to an alternative water source for about two weeks to avoid the rapid release of toxins that occur when the algae die.

What impact do bacteria, viruses and parasites have on water quality?

Dugouts and reservoirs that receive run-off from a manure source, or that livestock have direct access to, often have high counts of bacteria, viruses and parasites. There are a wide variety of these organisms that can cause production losses including decreased weight gain and miscarriages. Young animals are most susceptible as they have a lower resistance to many of these contaminants compared to mature animals.

To lower the risk of water contamination by these pathogens, prevent the inflow of water from manure sources and limit the animals from having direct access to the water source.  Many disease-causing organisms are killed by the sun’s ultraviolet rays so clear water generally has lower numbers of pathogens compared to murky water.

What impact do sulphates have on water quality?

Sulphur intakes above 0.4 percent of dietary dry matter intake may be toxic to beef cattle. In the rumen, the sulphate is converted to sulphide which can kill rumen bacteria that produce thiamine or be directly toxic to the brain, resulting in sulphate/sulphur induced polioencephalomalacia (PEM). Signs of sulphur induced PEM include blindness, lack of coordination, an inability to rise, seizures, muscle twitching, and death. If sulphur induced PEM is suspected contact a veterinarian for immediate assistance. Treatment may be possible if administered early.

Lower concentrations of sulphates can also affect trace mineral metabolism, resulting in deficiencies of copper, zinc, iron and manganese leading to depressed growth rates, infertility and depressed immune response. High concentrations of sulphates can be found in surface sources that are fed from saline areas and groundwater fed dugouts. Canadian Water Quality Guidelines recommend a maximum sulphate concentration of 1,000 mg/L. Reducing sulphates is costly and it may be advisable to find an alternative water source instead.

What impact do total dissolved solids have on water quality?

Total dissolved solids (TDS) refers to mineral quantities in the water including common salts such as sodium chloride, calcium, magnesium, sulphates and bicarbonates. Water with a TDS higher than 5,000 mg/L should not be used for lactating or pregnant cows and levels higher than 7,000mg/L are unsuitable for all classes of cattle.

The main symptom of drinking water with high TDS is diarrhea. If the TDS is high enough, cattle will avoid drinking until they are dehydrated, and then they will consume a large volume which can cause illness or even death.

Treatment of high TDS water is expensive, and it may be advisable to find an alternative water source.

What impact do nitrates have on water quality?

Nitrate toxicity from water is rare but may be cause for concern when combined with forages or feed with high nitrate levels. A combination of nitrates from these two sources can result in death as quickly as three to five hours after consumption. Chronic nitrate toxicity can occur even if clinical signs are not observed, resulting in depressed weight gain and appetite, a greater susceptibility to infection, and increased rates of miscarriage. Chronic nitrate toxicity from water is more common than acute poisoning.

Nitrates are occasionally found in groundwater that has been contaminated by manure or fertilizer. High concentrations are rarely found in dugouts unless there is direct runoff from a manure or chemical fertilizer source.

What impact do alkalinity and pH have on water quality?

Water pH ranging from 6.0 to 8.5 is considered acceptable for most livestock. Water with a pH less than 5.5 may reduce feed intake and performance. Excessive alkalinity can cause physiological and digestive upset including diarrhea.

How do taste and odour impact water consumption?

Cattle are sensitive to certain tastes and odours. For example, excessive manure contamination will alter the water’s taste and odour resulting in decreased water consumption. Keeping source waterways grassed, preventing direct livestock access, and aerating dugouts are examples of management practices that minimize unwanted tastes and odours in water sources.

What impact does water temperature have on water consumption?

Water temperature may affect water intake by livestock. Research has shown that cool water helps livestock maintain a proper body temperature and can increase water intake, in turn increasing weight gains.

Deep dugouts and groundwater are naturally cool. Use of a water pump which draws this cool water out only when desired by livestock is beneficial. Shallow sloughs and dugouts as well as small water troughs may heat up to a point where livestock water intake is affected.

How to test water

The best way to get an accurate idea of your water quality is to have it tested in a laboratory. There are several laboratories across Canada and the United States that will test water samples. Each laboratory may have different requirements for sample size and type, so it is best to contact them directly to get the correct specifications. The Saskatchewan Ministry of Agriculture has a list of water testing laboratories on their website, and the Rural Water Quality Information Tool can help you interpret your test results.

Handheld conductivity meters may be used as a screening tool for water quality but are not as reliable as laboratory tests.

Water testing should be conducted annually if circumstances are normal, but if environmental conditions change, or if you notice animal drinking behaviour or water property (e.g., smell, taste, clarity, etc.) changes, an immediate re-test is a good idea.

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