As the air temperature in Pembrokeshire starts to climb, livestock producers are being advised to adopt strategies to keep their animals cool in the heat of summer.

When the humidity index reaches 68 or higher, cattle struggle to cool themselves by panting or sweating and develop heat stress.

Tell-tail signs include lethargy and inactivity and cattle will often stand with their heads bowed.

This is a serious condition which caught out livestock farmers last summer when Pembrokeshire experienced record high temperatures.

Early intervention is the key to survival and to preventing problems with animal welfare and production this summer.

Drinking water provision should match cattle requirements on the hottest day and additional water supply is needed when demand is higher, says beef expert Dr Norman Weatherup.

Water needs vary according to air temperature and physiological state, such as if the animal is lactating, although diet is influential too.

Animals on a ration high in silage or grass with relatively low dry matter will have their water needs met in part by that feed but farmers can encounter problems when these animals switch to a diet which contains a high percentage of dry feed.

“They may potentially overlook increasing water provision to reflect the change in diet and you have situations where cattle are queuing up for water as drinkers are inadequate under the new feed regime,’’ says Dr Weatherup.

Shading outdoor metal water troughs from the sun will allow the water to have a cooling effect on the cattle.

Rumen fermentation is an underlying reason why cattle are prone to heat stress.

Normal digestive processes create heat and this reaches a maximum several hours after feed is consumed.

Dr Weatherup suggests moving feeding time in indoor systems to late afternoon or evening to allow fermentation during the cooler night temperatures.

This will also increase lung capacity for the cattle during the hotter periods of the day.

If cattle are fed several times a day, an option is to provide the largest proportion of the ration in the evening.

In grazing systems, large fields subdivided into paddocks can mean that blocks of land have no trees or hedges for shade.

Shade is particularly critical for older and younger cattle and for those that are dark haired and fleshy as they are most prone to heat stress.

During periods of extremely strong sunshine the paddock rotation may have to be altered as animals need access to shade, says Dr Weatherup.

In housed systems, cattle in poorly ventilated buildings are at risk of heat stress due to high humidity levels.

Beef animals at the finishing stage are most susceptible because they have the least amount of lung capacity relative to bodyweight.

Jamie Robertson, a specialist in livestock building design, says opening doors during hot weather is an obvious solution but consideration should also be given to removing the roof ridge to allow moisture to escape.

“Removal of the ridge will let more moisture out than the volume of rain that will ever enter,’’ says Mr Robertson, who emphasised that roof work is dangerous and requires competence.

The area of outlet required can be calculated using the AHDB Buildings Guide – go to and search for 'Better cattle housing design' (ignore the first four sponsored results).

Opening sidewalls is more difficult as the building needs to work in the autumn and winter months too but look for the same area of inlet in each sidewall as is calculated for the area of outlet in the ridge.

“Turning space board cladding into proper Yorkshire board on the prevailing wind side of a building will give almost 50 per cent more inlet area, gain control of rainwater ingress and reduce the cost of straw used,’’ Mr Robertson advises.