With this summer set to be one of the hottest on record, dairy farmers are being encouraged to put a strategy in place to optimise cow comfort and minimise milk lost as a result of heat stress.
Dairy cows have a high intake of feed, resulting in high metabolic activity, which in turn produces a lot of heat. Cows are homeothermic animals, which means their temperature needs to remain at 38.8degsC (+/- 0.5degsC) at all times.
Andrew Crutchley, from Westmorland Veterinary Group, says: “Cows can cope with a range of temperatures and remain thermoneutral between -15degsC and +25degsC. But they are happiest at 15degsC and start to show mild signs of heat stress at about 20degsC .
“Humidity has a significant influence on the temperature at which a cow becomes heat stressed.
“Typically humidity in the UK is around 70 per cent. At this level a cow would start to show the signs at about 24degsC, however many sheds can be up to 90 per cent humidity, and a cow would start to become heat stressed at 22-23degsC. They can handle dry heat up to 26degsC before they start to become hyperthermic.”
Milk yields are known to drop by between 10 and 20 per cent during periods of hot weather. But milk components are also at risk, the main driver being decreased feed intakes.
Mr Crutchley also says fertility can take a downward turn, and this is due to a number of factors.
“Many cows display less oestrus behaviour during hot weather and become more lethargic, conserving energy,” he adds.
“Secondly, increased core body temperature has a negative impact on egg quality, meaning even if she is spotted in heat, the egg may not be of sufficient quality to create a pregnancy.”
Tackling heat stress in the dairy herd
Water: High yielding dairy cows can increase water consumption by up to 20 per cent in hot weather, meaning they may require up to 120 litres per day. Ensure there is a 10cm availability of water trough space per animal in the shed, constantly supplied with clean water and flow rates must be high.
Fans: Air flow in the shed is important. Installing fans can have a huge effect on keeping cows cool.
Dairy farmer Andrew MacKellar, from Staffordshire, made the decision to install a single large fan in his cubicle shed. He says: “We didn’t realise the extent of our problems until we nearly lost two cows through heat stress.
“Since we have installed the fan, we have not had any problems, the temperature in the shed is lower, air flow is greatly improved and there is less of a fly burden. The fan has been on 24 hours a day for the last few months.”
Reduce stocking density: A cow producing 30kg of milk per day generates 50 per cent more heat than a dry cow. Minimising stocking density can help to decrease the heat in the shed.
Provide shade: Cows out at grass can be even more susceptible to heat stress, so it is important to provide adequate shade.
Technology: There are many devices which are able to warn of changes in behaviour, or physiological state before any serious consequences of heat stress are encountered.
Many modern heat detection devices, as well as measuring movement, are tuned into physiological indicators of health.
Dan Finchett, Allflex says: “When a cow is in a state of heat stress, there will be a decrease in lying time and less time spent feeding. Less movement will be recorded through the device, which also records breathing rate. Any recording above 60 breaths per minute, indicates symptoms of heat stress.”
Other devices available include the ability to record body temperature, rumination and time spent feeding.
Michael Halliwell, of World Wide Sires, says: “With the recent hot weather we are seeing an increase in health alerts 24 hours after oestrus behaviour is recorded.
"The common belief is that cows will show less oestrus behaviour in times of increased temperatures, this is the case for some cows but in reality a percentage of cows display normal oestrus behaviour and end up spent; resulting in an alert for excessive resting time and therefore a decrease in feed intakes.”