Editor's note: The following article originally appeared in the July/August 2014 issue of Bovine Veterinarian magazine.

 With much of California under severe to extreme drought, we are witnessing impacts on beef cattle producers well beyond simple shortages of water and forage. We expect a difficult year for California ranchers, and similar problems could emerge in other drought-affected areas, creating a need for additional vigilance among veterinarians and producers to assure cattle health and productivity.

Drought can increase the risks of animal poisonings and nutritional imbalances. In addition, should drought‐breaking rains occur, the grazing conditions for cattle may dramatically change and pose additional health risks. The conditions most commonly associated with the end of severe drought conditions include bloat, plant poisonings and clostridial diseases. The following are some drought‐related threats to cattle health and productivity.

Water quality

Drought‐related risks to cattleWater is the most critical factor in the diet and is involved directly or indirectly with essentially all physiologic processes. During a drought it is especially important to frequently monitor water quality, especially as quantity becomes more limited, and have plans for alternate water sources.

Water consumption varies with age, weight, breed, species, ambient temperature, humidity, lactation status, diet and level of production. Dry cows need 8 to 10 gallons of water daily, whereas cattle in the last three months of pregnancy might drink up to 15 gallons per day. Lactating cows require a water intake of approximately five times the volume of milk produced.

Total dissolved solids (TDS): TDS are all of the organic and inorganic substances in water that can pass through a 2-micron filter. Elevated TDS adversely affects the palatability of water and, therefore, water consumption. In general, TDS concentrations below 1,000 parts per million (ppm) should ensure the safety from almost all of the inorganic constituents present, whereas individual components should be identified and quantified to more fully characterize potential problems if TDS values are greater than 1,000 ppm.

Sulfate: High sulfur (S) concentrations reduce feed and water intake in animals, resulting in reduction of growth and performance. The most common form of S in water is sulfate. Outbreaks of polioencephalomalacia have occurred when water has been a significant source of S. During droughts, sulfate becomes more concentrated in water, and water intake increases during periods of high ambient temperatures. Elevated sulfate concentration (as low as 500 ppm) is reported to decrease copper absorption, thus potentially exacerbating marginal or low copper intakes. (See Table 1)

Nitrate/nitrite: Contamination of water with nitrate or nitrite can occur from a variety of sources, mostly fertilizer and manure run‐off, and drought conditions can increase water concentrations. Nitrate/nitrite can cause sudden death of ruminants, and the risk of intoxication needs to take into consideration intake from both plants and water. Frequent monitoring of water nitrate/nitrite concentrations is recommended, and tests are quick and inexpensive. Water nitrate concentrations less than 400 mg/L and nitrite concentrations less than 100 mg/L should not cause poisoning in livestock. Water nitrate concentrations greater than 750 mg/L can be hazardous to non‐adapted ruminants.

Toxic algae: Hot, dry conditions, stagnant water and high levels of nutrients can encourage proliferation of blue‐green algae (cyanobacteria) in water. Blue‐green algal blooms can reduce water quality and intake, and be potentially toxic. Windy conditions can concentrate algal blooms along water edges, increasing the risk of ingesting algae. If algal blooms are noticed, testing of water for toxins is recommended as not all algal blooms produce toxins. Cyanobacteria can produce toxins that can affect the liver and nervous system. Depending on the specific toxin and amount ingested, animals may die suddenly, or suffer from weakness, staggering or photosensitization. It is important to limit access to water that has visible algal blooms until it tests negative.

Feed quality and nutritional deficiencies

Drought conditions frequently result in the need to feed poor-quality forages, which can cause or exacerbate deficiencies of important minerals, vitamins, energy and protein. Even in non‐drought years, deficiencies of selenium and copper are common in beef cattle.

Copper: Soils in many regions are low in copper, resulting in low copper concentrations in forages. Forages for cattle are deficient if copper concentrations are less than 7 ppm on a dry-weight basis; total rations are deficient when copper concentrations are less than 10 ppm on a dry-weight basis. One of the earliest manifestations of copper deficiency is loss of hair color in dark‐haired breeds of cattle and rough hair coats. Other manifestations of copper deficiency include ill thrift, reduced production, diarrhea, decreased resistance to infectious agents and parasites, poor vaccine response, loss of bone strength in calves, weakness and wobbling in neonates, reproductive failure and sudden death of adult animals. Severe copper deficiencies can be diagnosed in live animals from serum testing, whereas liver testing is used to diagnose deficiencies in animals that die.

Selenium: Selenium is essential to help protect cells from day‐to‐day damage and is a critical component of the body’s antioxidant enzymes. Soil and forage selenium concentrations are either marginally adequate or deficient in many areas. Selenium deficiency is one of the more frequently diagnosed mineral deficiencies, and combined copper and selenium deficiencies are common, particularly in non-supplemented beef cattle. Selenium deficiency causes white muscle disease of skeletal and heart muscles, resulting in stiff gaits, slow movement, heart damage and weak neonates. Ill‐thrift and reduced production occur and, similar to copper-deficient animals, there is less resistance to infectious agents and parasites. Selenium status of live animals can be tested from whole-blood samples while liver samples are used to diagnose selenium deficiency in dead animals.

Vitamin E: Vitamin E is an antioxidant that helps to protect cell membranes. Its actions are complementary to those of selenium. Thus, an adequate intake of one can help, but not completely prevent, the adverse effects of a deficiency of the other. A concomitant deficiency of both can have significant adverse effects. Vitamin E deficiency occurs most commonly when animals are fed inferior-quality hay or straw, which is more likely during periods of drought. Clinical signs of vitamin E deficiency are similar to those listed for selenium. The vitamin E status of animals can be assessed by testing serum or liver samples. Vitamin E in serum is susceptible to degradation, and veterinarians can help ensure proper collection and storage of samples.

Vitamin A: Primary vitamin A deficiency occurs in beef cattle on dry pasture during periods of drought. Due to relatively good storage in the liver, cattle can subsist on naturally deficient diets for five to 18 months before clinical signs of deficiency appear. Clinical signs in cattle include night blindness, dry eye, retarded growth rate, reproductive failures and increased mortality. Beef calves coming off dry summer pastures at 6 to 8 months of age are commonly marginally deficient. A maternal deficiency of vitamin A can result in herd outbreaks of congenital vitamin A deficiency in calves. Maternal deficiency of vitamin A can cause abortions, stillbirths or calves born alive but blind and weak and death within one to three days. Cows should be given an injection of vitamin A (and D) about 30 days prior to calving, and calves should be given a vitamin A injection at birth. Vitamin A status can be assessed through the testing of serum and liver samples. Like vitamin E, sample quality is critical for proper determination of status based upon serum testing.

Mechanically irritating plants: Spiny plants such as prickly pear cactus (Optunia spp.) or those with bur such as burdock (Arctium minus) and cocklebur (Xanthium spp.) can injure the lining of cattle’s mouths and digestive tracts. Some common grasses such as foxtail barley (Hordeum jubatum) and bristle grass (Setaria spp.) have seeds with sharp awns that can become embedded in the tongue and gums of animals ingesting them. Initially excessive salivation occurs, but embedded awns or spines eventually lead to large ulcers. Some sharp grass awns can also penetrate an animal’s skin, migrate through the tissues, and cause abscesses and draining wounds far from the point of entry.

Increased incidence of plant poisonings

Drought conditions increase the risk of plant poisonings in situations where available feed/forage is inadequate to maintain cattle. Cattle will seek out and consume plants that they would not otherwise find palatable.

Plant‐associated nitrate poisoning: Nitrate poisoning is one of the most common plant-associated intoxications, and drought can result in a high accumulation of nitrates within plant tissues. Normally, plants absorb nitrates from the soil, converting the nitrate into plant proteins. Application of nitrate fertilizers along with stunting of plant growth as a result of drought can cause potentially toxic concentrations of nitrates. Many common weeds, forage crops and cereal grain plants have the potential for nitrate accumulation, with highest concentrations typically in the stems. Properly prepared silage reduces nitrate concentrations significantly, while there is little reduction of nitrate in dried hay.

The potential for nitrate poisoning is increased when water sources also contain elevated concentrations. The threat of nitrate poisoning is greatest in ruminant animals since the environment of the rumen results in the reduction of nitrate to toxic nitrite. Nitrite interferes with normal oxygen delivery to tissues. The first sign of nitrate poisoning is often the sudden and unexplained deaths of one or more animals. Other clinical signs include drowsiness, weakness, muscle tremors, increased heart and respiratory rates, staggering or recumbency. Signs can develop within several hours of ingesting a toxic amount of nitrate. Consider submitting forage samples to a diagnostic laboratory prior to feeding when the potential for nitrate accumulation is high. Serum samples can be tested for nitrate levels from live animals showing clinical signs. A variety of samples including postmortem blood samples and ocular fluid can be used to diagnosis nitrate poisoning in dead animals.

Oaks/acorns:  Acorns and oak leaves might be attractive to livestock during periods of scarce forage. All parts of oak trees contain tannins and phenols and are potentially toxic. Young oak buds emerging in the spring contain the highest concentrations of tannins. Poisoning is most typically associated with consumption of large amounts of buds, leaves or acorns over a several-day period.

Signs of poisoning vary with the amount of plant ingested. Initially, animals stop eating, become depressed and develop intestinal stasis. Excessive thirst and frequent urination might be noted. Initially feces are hard and dark, but black, tarry diarrhea occurs later. Teeth grinding and hunched back are often indicative of abdominal pain. Severe liver and kidney damage occurs. Animals might live for five to seven days after the onset of clinical signs. A condition called “acorn calf syndrome” can occur in calves born to cows that consume large quantities of acorns during the third to seventh month of pregnancy. Clinical signs include joint laxity, shortened legs, deformed hooves and either a domed skull or long, narrow head.


During periods of drought, veterinarians can help clients monitor the quality of feed and water available for their animals. Consideration should be given to monitoring water-quality parameters that might indicate the potential for problems. Pastures and hay should be scrutinized for the presence of weeds or mechanically irritating grasses. Animals on over‐grazed pastures should be provided with supplemental feed and adequate vitamins and minerals. For additional information, contact your state’s diagnostic laboratory system for assistance.

Click here to read more from our July/August issue.