Ensuring sufficient water supplies this grazing season

When we think of livestock nutrition, we often talk about grass supply and allocation, or input of concentrates. But for all livestock – particularly dairy cows whose milk is roughly 85% water – ensuring clean, fresh water is available at all times freely is paramount to production and overall animal health.

Two major factors will dictate if the current water system in place is fit for purpose or if modifications are required: trough size and flow rate of pipes.

Peak demand for water occurs at peak grazing time, which for dairy herds, is after each milking. Teagasc suggests that up to 50% of the daily water intake of a cow occurs in the three hours after each milking.

It is recommended that 10% of the herd are able to drink at the one time, with each cow requiring 450mm of trough space. Typically, rectangular troughs have a greater perimeter-to-water-capacity ratio compared to round or elliptical troughs. A recommendation by Teagasc is for a trough capacity of 9 litres/2 gallons per cow, equating to a 900-litre or 300-gallon trough for a 150-cow herd.

Cows should never be more than 250m from a trough to encourage drinking, with troughs placed in the centre of paddocks for this reason and to encourage even graze outs; locating troughs closer to a paddock boundary can cause lounging around this area with further corners of the paddock left poorly grazed.

Troughs should be situated on an elevated, dry site, and due to the high traffic around them, it is preferential to have a hardcore/gravel base around troughs.

Not only will this prevent the area around troughs becoming poached and waterlogged, but will also prevent troughs becoming unlevel due to sinking in to the top soil.

Generally, removal of top soil under the hardcore base is not required.

For other livestock types, a good rule of thumb is that for every 100kg of liveweight, an animal will drink approximately 15l water/day.

For lactating ewes with lambs, this will equate to a water intake of 9-10l.

For drystock, a reduced rate of 7l per livestock unit (LU) can be used to calculate trough requirements. Take this example:

25 cows @ 1.0 LU +

25 calves @ 0.4LU x 7 litres/lu

= 245 litres/53.89 gallons.

Pipe diameter

A far more common issue with water supply on farms is inadequate pipe diameter resulting in poor flow capacity. As dairy herd sizes have increased, so too have milking platforms and the distance water must be piped.

The further the distance that water has to travel through a pipe, the greater the loss of pressure due to friction between the water and the internal pipe surface.

For example, at a flow rate of 3m3 per hour (50l/min or 11gal/min) with a 32mm (1¼in) pipe the pressure is reduced by 4.83PSI for every 100 metres of pipe.

To determine flow rate in a trough, lift the ball cock, empty a fixed amount (eg, 50l) and time how long it takes the trough to refill. A simple calculation will show the l/minute flow rate. Where flow rate is inadequate, a larger diameter pipe can be installed. For herds with less than 150 cows, pipe diameter should be a minimum 25mm (1in), and for herds of 150-300 cows this should rise to 32mm minimum (1 ¼ in). A 40mm (1½in) pipe should be installed for herds greater than 300 cows.

Pipes carrying water with a high iron concentration can also have a build-up of iron cause a reduced flow rate, especially where the PSI is lower than ideal. Where pipes are checked and found to have iron build ups, the likelihood is that they will have to be replaced.

Pressure can also be lost in pipes where the source (public scheme or private well) is lower than the destination, with each foot of a rise in the pipe leading to a drop in pressure of 0.433PSI.

A 20ft rise will therefore lead to a drop in pressure of 8.66 PSI. Normally, pumps at private wells are set at 20/40, where the pump kicks in at 20PSI and kicks out at 40PSI, but where there is an issue with pressure loss due to elevation, then the pressure can be readjusted to 30/50.

In short: