Water on Pastures: Does it Pay or Cost?

Water is the most important nutrient and the least costly nutrient for the lactating dairy cow. Dairy cows need 4-5 lbs. of water to make 1 lb. of milk. Dairy producers should attempt to get water into each paddock. This investment in labor and cost may pay for itself quicker than almost any other management practice on the farm. 

I have attended pasture walks where the entire discussion was about water. The best systems, whether pressurized or gravity, have been invented on the farm, so attend those pasture walks to get ideas. Here are some basic needs your watering system should address: Cattle needs, laying out pipe, tub size, payback period. Granted, my calculation here for payback period is just based on not losing milk.

1. Dairy cattle needs

Penn State and other sources have excellent numbers for what water needs are. Holstein heifer yearlings need 7-10 gallon/day, Jersey milking cows 15-18 gallons/day, Holstein milking cows 25-27 gallons/day. Cows need 4-5 lbs. water per 1 lb. milk produced. Holstein cows milking 50 lbs. need 225 lbs. of water or 27 gallons/day. During the hot summer, cows may consume up to 50 gallons per day.

Some of this water will come from the barn during milking time and some will come from the feed. Wet, fresh spring pasture can provide a large amount of water. A cow that consumes 140 lbs. of fresh pasture at 80% moisture, is consuming 28 lbs pasture dry matter and 112 lbs. water, or 14 gallons of water.

2. Determine tub and pipe size with flow rates

By knowing your herds’ needs (50 cows x 27 gallons = 1350 gallons) and using the pipe size guide, you can figure out your pipe size and tub size. Compare your situation to the flow rate chart to pick your pipe size. A good rule of thumb is use 3/4” pipe for less than 1000 ft. Use 1” for the first 1000 ft. and 3/4” for runs longer than 1000 ft. Then in-crease the first pipe from the barn by 1/4-inch for each additional 1000 ft.

Ben Bartlett from Michigan State says that a single tub in a continuous pasture system should hold 1/4 of the herd needs and have a flow rate that will fill the tub in 1 hour or less. Water tubs in an intensive grazing system can be 20 - 100 gallons in size so long as the flow rate to the tub can deliver the total herd needs in 4-8 hours.

Height of rise to the tubs is an important factor for some paddocks. Remember for every 2.3 feet in fall you can gain 1 psi. However, 1 psi is needed to push water up 2.3 ft. To move water up 30 ft, one may need 60 psi already to pump the water. You can use land elevation to your advantage when going down hill.

The following example will be for relatively flat pastures.
50 cows milking 50 lbs. milk will require:

• Milk production lb. x 4.5 = Lb. water/head/day (lb. water / 8.3 lb. water per gal.)
• Gallons per head x # cows = Herd needs in gallons.

Example: 50 cows milking 50 lb. need 1350 gallons per day total and the waters are 1000 feet from the barn. Mostly flat ground.

A. Continuous grazing or a single water source
Rule: 1/4 of the herd in gallons is the tub size and it should fill in less than 1 hour.
1350 / 4 = Min. of 340 gallon tub and/ 60 minutes = 5.6 gallons /minute flow rate.

B. Intensive grazing with waters in each paddock
Rule: Use a 20-100 gallon tub size and deliver the flow rate to meet the herd needs in 4-8 hours.
Ideal: 1350 / 4 hours = 340 gallons / 60 minutes = 5.6 gallons /minute flow rate.
Min.: 1350 / 8 hours = 169 gallons / 60 minutes = 2.8 gallons /minute flow rate.

3. Water pipe sizing

Our 50-cow herd would need:

• One tub system, a minimum of 1-inch hose to get 6 gal./minute. 1 1/4 inch would easily give us 12 gal/min. for good flow.
• Water in every paddock, 1 inch for the ideal 5.6 gallons and 3/4 inch for to minimum 2.8 gallons to work.

Both of these systems will work fine as long as the water can enter the tank easily and quickly. Hot weather time may need more water to be safe.

4. Does it cost or pay?

Cows may produce 3-5 lbs more milk with access to water in the paddock than cows that have to walk long distances to get water. Or they could lose this production while they are in the pasture without water.

• 3lb. of milk for a fifty cow dairy herd = 150 lb. per day loss.
  
• 150 lb. X $15.00/cwt. = $22.50 loss per day in milk production.

So our payback period to save $22.50 loss is 13 days.

- By J. Craig Williams, extension educator, Penn State Extension. Email: jcw17@psu.edu. Phone: 570-724-9120