Water is one of those things that we’re never really satisfied with. There is either too much, too little or it doesn’t come at the right time. Or it’s too expensive, tastes funny, is too hot — the list goes on and on. Still, we tend to take for granted that, when we open the tap, it will be there. Water is essential to life, yet we rarely discuss it in relation to nutrition.
Much like humans, our bovine friends are mostly comprised of water. On average, water makes up 65 percent of a mature cow’s weight. To put that into perspective, 845 lbs. of a 1,300-lb. cow is water (equivalent to 105.6 gallons). Water has many functions in the body, including temperature regulation, growth, reproduction, lactation, metabolism, digestion, execration, lubrication of joints, nervous system cushioning, sound transportation and eyesight. When you consider how important water is to life, you wonder: why don’t we talk about it more?
My theory for putting less of an emphasis on water is because we make assumptions about it. We assume that cattle are getting enough, whether from grazing or the tank in the pasture. Cattle can get a portion of their water requirement from lush pastures; however, it’s important to remember that forage dry matter changes over the grazing season. As dry matter in the diet increases, so does the water requirement. Other factors that change the water requirement include the level of salt in the diet, lactation, gestation, ambient temperature, temperature of available water and humidity.
So just how much water does your herd need?
A quick and dirty estimate is 1 to 2 gallons per 100 lbs. of body weight. Our 1,300-lb. cow will need roughly 19.5 gallons of water daily. Predicting the exact water requirement is not as simple. You must consider temperature, moisture and salt level of the diet, as well as weight, lactation, stage of production and more. As I mentioned above, the temperature of the water supplied makes a difference, too. As the water in a tank increases from 70 to 95 degrees Fahrenheit, cattle will need to drink approximately 2.5 times more to regulate their body temperature. Air temperature also increases water requirement around 1 additional gallon for every 10 degrees above 40 degrees Fahrenheit. The table below is a good reference for water requirements at various temperatures and stages of production.
A key component of meeting the water requirements of your herd is not only providing enough water, but also enough space for cattle to drink. Like bunk space, cattle should have 15 linear inches of space, on average, at the water source. The location of the water source also has an influence on how much space should be available. In grazing situations where the water source is relatively close to where cattle are grazing, enough space should be available for at least 10 percent of the herd to drink at one time. For example, if you have 100 head in a pasture, 150 linear inches of tank space is needed. For grazing situations where cattle must travel longer distances to get to water, space for 30 percent of the herd to drink at one time is needed. That same 100-head herd now needs 450 linear inches.
I’m sure you might be wondering why I’m using linear inches when tanks are generally round. Think back — perhaps way back, for some of us — to high school geometry, as we’re going to calculate circumference. In inches, 3.14 x diameter equals the circumference of a round tank. A 20-ft. diameter tank has a 753.6-inch circumference (20 ft. x 12 inches per ft. = 240-inch diameter x 3.14 = 753.6 inches). In this example, it’s large enough for the 100-head herd.
The final step is to know the capacity of your tank. You can go back to geometry and calculate the volume of a round tank: capacity in gallons = [3.14 x radius2 (in inches) x depth (inches)]/231. However, if you don’t care much for math, Tractor Supply Co. has a good article on measuring livestock tank capacity on their website, including tables for round and oval tanks with estimated volumes.
When it comes to water, we can’t skimp. Adequate access and ample supply of water is important as we enter the hottest part of the year, especially with calves at the sides of many cows. When cattle aren’t getting enough to drink, intake (both forage and supplement) drops. When intake drops, performance suffers, and the downward spiral only grows from there. Providing cattle with good quality water is the first step to ensuring good nutrition.