17 December 2007

4 minute read

What happens if a lactating cow doesn’t drink enough water? If the question is a joke, the answer could be, “you will get evaporated milk or dried milk powder.” If it’s a serious question, the answer will be “you will not get optimal milk production and health can be adversely affected.”

The amount of water a cow drinks depends on her size and milk yield, quantity of dry matter consumed, temperature and relative humidity of the environment, quality and availability of the water, amount of moisture in her feed and the sodium, salt and protein content of the diet. If your cows have inadequate water intake, you may see signs showing up such as firm, constipated manure; low urine output; infrequent drinking; high packed-cell volume or hematocrit in blood; dehydration from toxins; and/or fever.

Pounds of water intake (1 gallon of water weighs 8.32 pounds) can be predicted using the following equation (Murphy et al., 1983), used for the 2001 NRC recommendations:
35.25 + 1.58 x dry matter intake (lb/day) + 0.90 x milk yield (lb/day) + 0.11 x sodium intake (grams/day) + 2.65 x weekly mean temperature (degrees F divided by 1.8 minus 17.778)

This equation predicts that water consumption will change 1.58 lb for every 1 lb of milk produced, 0.11 lb for each gram of sodium consumed, and 1.47 lb for each degree F change in the weekly mean temperature. The following table shows the estimated daily water intake for a 1,500 lb lactating cow (assumes sodium intake at 0.18% of dry matter).

Estimated daily water consumption for a 1,500 lb lactating cow.

(Looper, New Mexico State & Waldner, Okla State)

How do you measure actual water consumption? The best way is to install an in-line water meter at each water source. Measure the water intake for at least 5 to 10 consecutive days. Be sure to determine daily feed intake for those same days and determine the moisture content of the feed so the water intake from the feed source is discounted when estimating water intake.

What are some possible causes of cows not drinking enough water? One of the main reasons can be because it is too crowded around the waterers, or the waterers are not delivering the water fast enough. Penn State researchers (Adams and Sharpe) reported water intake may be limited by:

1. a lack of supply or drinking devices or restricted flow from corroded valves, pipes clogged from iron-bacteria slime or scale;
2. low chemical quality such as very acidic, very alkaline, hydrogen sulfide (rotten egg odor), metallic taste from iron, manganese, sulfates; high total dissolved solids content;
3. pollution -- from high total bacteria counts (most common); coliform from fecal or non-fecal sources;
4. bad taste;
5. algae (especially blue-green type);
6. sites of contamination -- water source, pressure tank, reservoir, drinking device (feed or manure).

If you find that milk production has dropped dramatically, it is time to take action and evaluate the water supply.

1. Flow Rate. Cows should never have to wait for water to be available. There must be enough tanks, troughs, or fountains to enable most cows to drink relatively soon after milking or eating. Use valves that permit 15 gal/min of flow at 20 lb pressure. For stall barns, the types and valves of drinking cups for dairy cows need to be relatively trouble-free.
2. Watering Space. According to Michigan State University researchers, a minimum of one watering space or 2 ft of tank perimeter for every 15 to 20 cows is recommended. Provide 2 ft of linear trough space per cow in return alleys or breezeways from the milking parlor. Cows will line up side by side and drink, just like they do at the feed bunk, and they like to have sufficient space to back away from the trough after drinking. Cows drink 50 to 60% of their total daily water intake immediately after milking. Head clearance around water troughs should be at least 2 ft on every side. Water troughs should be an optimal height of 24 to 32” (2 to 3” less for Jerseys). Water depth should be a minimum of 3” to allow the animal to submerge its muzzle 1 to 2”. However, water depth should be no more than 6 to 12” in order to prevent stagnant water, for ease of cleaning, and for rapid filling so cows never have to wait to consume water. Waterers should be within 50 ft of the feed bunk or at every crossover in the freestall barn. Make sure there is no dead end alley where the water source is located, as can be the case in some remodeled freestall barns. For grazing operations, water should be located at the milking parlor exit and in each paddock so that animals are always within 600 ft of clean, fresh water sources.