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#DrTrippsTips, Cow Studies, Water 5 min read

How much water should a cow drink every day?

Written by Dr. Scott Tripp

When we talk about how much water a cow should drink every day, we need to talk about how much a lactating cow drinks versus a dry cow. Since milk is high in water, the water requirements of a lactating cow are closely related to milk production. There are many factors, but a dry cow should drink 9 to 12 gallons a day. A lactating cow should drink 30 to 40 gallons day.

How much water does a lactating cow drink?

The amount of water a lactating cow can drink is often dependent on how often they are drinking. Typically, we expect them to drink 10 to 20 liters of water per visit to the trough. However, besides frequency, there are many factors that alter the amount of water a cow can drink:

  • Milk production - Generally cows need 4 to 4.5 liters of water per kilogram of milk they produce.
  • The cow size.
  • Quantity of Dry Matter Consumed - The water intake accounts for 90% of their daily requirement.
  • Moisture content of the dry matter consumed.
  • Temperature and relative humidity.
  • Temperature of the water.
  • Salinity of the water and the amount of salt consumed – the totally dissolved solids should be less than 1000 ppm.

The Equation

To figure out how much water a cow should drink, there is actually an accepted equation from the 2001 National Ruminate Committee. First, you’ll need to understand that one pound of water is 16 fluid ounces or 453.6 milliliters.

Here is the equation:

Water intake, pounds/day

=

35.25 + 1.58 x dry matter intake (pounds per head per day)

 

+

.90 x milk yield (pounds per head per day)

 

+

.11 x sodium intake (grams per day)

 

+

2.65 x weekly mean minimum temperature (degrees F/1.8-17.778)

 

Okay… what does that mean?

In plain English it states:

  • For each pound change in dry matter intake, the cow will consume more or less 1.58 lbs. of water.
  • For each pound of milk produced, water will go up .9 of a pound. (For those that don’t weight lift milk, the conversion is 1 ¾ cups (1.85 cups) of milk per pound.)
  • For each gram of sodium consumed, water will go up .11 pounds.
  • For each degree of Fahrenheit, water goes up 1.47 pounds.

How much water does a dry cow drink?

The major factors affecting dry cow intake is:

  • the concentration of dry matter in the diet,
  • dry matter intake,
  • and the amount of protein in the diet.

So, if we take a large Holstein dry cow at a temperature between 50 F to 80 F consuming 28 pounds of dry matter at 12 % moisture and 12 % crude protein… she would consume 96 pounds of water (11.6 gallons).

If the temperature is in the heat stress range, it could be 1.2 to 2 times higher.

If it’s hot outside, should cows have cold water?

This is an interesting additional thought… as humans, we all like something cold when we are hot.

The trouble is that cows are not humans… In fact it is important to understand that cows are really fermentation vats—think of a 55 gallon drum making beer.

Temperature becomes critical because of the rumen and its population of bacteria and protozoans. There are studies with rumen bolus that show that water can alter the fermentation process for a long time. This alters end products by changing the population growth and types of bacteria.

This post is part 2 of a 2 part article on water.
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