Drought Affects Water Quality

Teri Walsh, Nutrition Technical Support Specialist

Many parts of the US are experiencing unprecedented drought. Closer to home, many regions of the Midwest and New England are abnormally dry to extreme drought. During periods of drought, concern turns immediately to forage supplies, and rightfully so, cattle need to eat. Water is one of those things that is taken for granted, however, it’s essential and quality can fall off during drought as well.

During drought, there several things to consider when it comes to water quality. We’ll discuss four:

1. 1. Blue-green algae
   2. Nitrates
   3. Total dissolved solids
   4. Managing stock tanks/automatic waterers

Blue-green Algae

Following hot, dry, still days, you’ll see ponds, stock dams and a few water tanks with a layer of scum or be completely green in color. This scum/green color is blue-green algae, photosynthetic bacteria also known as cyanobacteria. As the water temperature rises, the cyanobacteria will bloom, causing the noticeable changes. Drought conditions increase the likelihood of a bloom. This year couples low water levels with high temperatures making ideal conditions for cyanobacteria.

Cyanobacterial blooms are harmful to livestock. As the cyanobacteria grow, they store toxins, which are released in the water when they die. There are 2 types of toxins that are associated with blooms, neurotoxin and hepatotoxin. Neurotoxin poisoning is fast acting (15-20 min) and ultimately ends in death. Hepatotoxin (liver) poisoning is much slower acting (a few hours to a day) and is survivable, but the animals will be chronic poor doers. Unfortunately, dead animals are often the first sign that there is a problem with cyanobacteria.

However, the toxins are only half of the problem. This scummy, green water tastes and smells bad, which could cause livestock to avoid water altogether. If this is the only water source, livestock are then facing dehydration. When water intake drops off, so does dry matter intake and it’s a downhill slide with all production.

There are several practices to prevent cyanobacteria; aeration, aquatic dyes, copper sulfate, straw mats and barley straw to name a few.

Nitrates

Nitrates are utilized by rumen bacteria to produce ammonia. Nitrate/nitrite toxicity happens when higher than normal amounts of nitrates are consumed. This causes a buildup of nitrites in the rumen, which are absorbed into the bloodstream. Nitrites convert hemoglobin to methemoglobin, rendering it unable to transport oxygen.

Signs of nitrate toxicity include: chocolate colored blood, bluish or chocolate colored mucus membranes, difficulty breathing, noisy breathing, salivation, tremors and staggering. Unfortunately, the first sign of a problem can be a dead animal as symptoms can appear 30 minutes to 4 hours after ingestion. If you suspect nitrate poisoning, it’s important to call your veterinarian immediately and tell them what you suspect. Nitrate poisoning is treatable, but only if your veterinarian is prepared. A quick way to check a suspect animal is to give it a small cut and check the blood color.

All water sources have the potential to contain nitrates. Nitrate sources include run off from heavily fertilized (manure, commercial fertilizer, human waste) fields and pastures as well as decomposing organic matter. Surface water sources such as stock dams, ponds, ditches, and poorly sealed, shallow wells are more likely to have higher nitrate levels, due to run off. Evaporation of stock dams, ponds, etc. without replenishing the water level will concentrate the level of nitrates.

Nitrate levels in water and forage can have an accumulative effect in the rumen. Testing water sources, and forages, is the only way to know what the total nitrate level is. Nitrate levels can be reported as either nitrate-nitrogen (NO₃-N) or nitrate (NO₃). Your county extension service can assist you with proper testing techniques as well as interpreting the results.

NO₃-N in water

• • 0-100 ppm Safe
  • 101-300 ppm Use with caution, consider level in feed
  • >301 ppm Potentially toxic

NO₃ in water

• • 0-440 ppm Safe
  • 441-1300 ppm Use with caution, consider level in feed
  • >1301 ppm Potentially toxic

Total Dissolved Solids

Drought conditions can lead to evaporation of stock ponds and other natural water sources. This can lead to declining water quality due to the concentration of total dissolved solids in the remaining water. Total dissolved solids (TDS) is a measure of the total concentration of dissolved substances in water. It is often used to denote the level of water salinity. The higher the TDS value, the lower the water quality.

Higher salt concentrations in water can lead to lower consumption. However, concentrations that lead to no consumption can also cause over consumption when cattle get too thirsty. Cattle have varying tolerances to salt levels in water depending on age, breed, season, and stage of production.

In general, cattle will avoid high saline water sources, but will drink it if no other sources are available. Clinical signs of salt poisoning are weakness, dehydration, tremors, aimless wandering, ataxia, seizures, partial paralysis, and death. Cattle can die within 24 hours after the appearance of sever clinical signs.

Testing the water source is the only way to know what the TDS concentration is. The results are reported as either parts per million (ppm) or milligrams per liter (mg/L) (ppm is equal to mg/L). Your county extension service can assist you with proper testing techniques as well as interpreting the results.

TDS (ppm or mg/L)

• • <3,000 – Usually satisfactory for most livestock.
  • 3,000-5,000 – May not cause adverse effects for adult livestock.
  • 5,000-7,000 – Should not be consumed by pregnant or lactating cows/heifers. Usually a laxative and may result in reduced water intake.
  • 7,000-10,000 – Do not use for pregnant or lactating cattle.
  • >10,000 – May cause brain damage or death.

Managing Stock Tanks/Automatic Waters

Stock tanks and automatic waters offer producers more control over water quality and quantity but can still pose a few challenges during drought.

First, ensuring enough water for the cattle utilizing the tank. On average, you can estimate 1 to 2 gallons of water per 100 pounds of body weight. A 1,300-pound cow will need roughly 19.5 gallons of water daily. This requirement increases with increases temperature (1 gallon for every 10 degrees above 40^o F) and as the water heats up with the day, from 70 to 95^o F, cattle will need to drink 2.5 times more to help regulate body temperature. The table below is a quick reference.

Estimated daily water intake for beef cattle based on temperature and production
	Growing Cattle			Finishing Cattle			Pregnant Cows		Lactating Cows	Mature Bulls
Temp.	400 lbs.	600 lbs.	800 lbs.	600 lbs.	800 lbs.	1,000 lbs.	900 lbs.	1,100 lbs.	900 lbs.	1,400 lbs.	1,600 lbs.
40	4.0	5.3	6.3	6.0	7.3	8.7	6.7	6.0	11.4	8.0	8.7
50	4.3	5.8	6.8	6.5	7.9	9.4	7.2	6.5	12.6	8.6	9.4
60	5.0	6.6	7.9	7.4	9.1	10.8	8.3	7.4	14.5	9.9	10.8
70	5.8	7.8	9.2	8.7	10.7	12.6	9.7	8.7	16.9	11.7	12.6
80	6.7	8.9	10.6	10.0	12.3	14.5			17.9	13.4	14.5
90	9.5	12.7	15.0	14.3	17.4	20.3			16.2	19.0	20.6
Adapted from Nutrient Requirements for Beef Cattle, Seventh Revised Edition, Updated 2000

Evaporation from a tank, without an automatic filler, can lead to concentration of nitrates and total dissolved solids. There are a few ways to help minimize evaporation in tanks, regardless of size.

• • Place in a shaded area.
  • Add a permanent shade overhead.
  • Utilize a floating shade cover such as ball floats or a floating mat. This will also help keep the water temperature cooler.

Keeping the tank free of algae is another challenge. Warm summer temperatures, abundant sunlight and nutrients come together to create ideal conditions for algae growth. Algae growth may lead to less desirable drinking water taste, and there is a possibility for blue-green algae to develop as well. Additionally, viruses, parasites and other bacteria may also thrive in tanks that are not properly cleaned.

Finally managing tank fill helps conserve water. Inspect tanks before the first fill. Check for cracks and holes that will leak water and make sure they are clean and free of debris. When utilizing an automatic filler, ensure that the tank is properly leveled so the float stops before water starts to overflow. Check the float throughout the grazing season to ensure it maintains proper filling and function. When filling a large stock tank, do not leave the tank unattended. Use that as an opportunity to time how long it takes to fill. On subsequent fills, you will know when to come back to turn the water off to prevent overfilling.

Drought has a number of effects on water quantity and quality. By monitoring natural sources of water, producers can ensure cattle always have clean, fresh water, to maintain forage intake, and animal performance.