How do we know when a dairy cow is affected by summer heat?
A cow’s breathing rate is normal at 40 to 60 breaths per minute.
Sixty breaths per minute correlates to a core body temperature of 39°C and at this point you need to take action. There may be moderate panting and the presence of a small amount of drool or saliva.
At 70-plus breaths per minute, cows are struggling to survive. The cow is panting hard and there is a lot of saliva or drool present.
Above 80 breaths per minute, heat stress is severe, and cows may die. The cow’s neck is extended, her tongue is protruding and there is excessive drooling and panting.
A temperature and humidity index is a way to standardise different combinations of temperature and humidity and how that might contribute to the heat load of dairy cattle.
At Ellinbank Research Farm in Victoria, cows were monitored for heat stress.
On a day where the air temperature was above 36°C, the cows’ temperature was recorded at above 41°C, and with extended necks and panting hard.
“Mature cows are generally more susceptible to heat stress,” said Josie Garner, Dairy Australia’s development and regional adaptation lead.
This susceptibility is also influenced by temperament, diet, previous exposure to hot weather, genetics, breeding and physical activity level (the topography and layout of the farm and how far cows have to walk in hot weather).
Ms Garner said the easiest method to help cool cows is to set up a sprinkler system at the dairy yard.
“Use it for an hour before the cows arrive in the dairy yard, and continue to use it while the cows are standing in the yard.”
She also recommends mustering and milking cows in smaller groups to minimise the amount of time they are waiting in the dairy yard. Mustering cows during the heat of the day will increase their core temperature and therefore increase risk of heat stress.
“The next infrastructure investment is installing industrial fans in the dairy for cow and human comfort,” Ms Garner said.
Install water troughs in all paddocks, laneways and one near the dairy exit laneway — cows will drink 20 litres/hour or up to 250 litres/day of water.
“If only one infrastructure upgrade this year, install a water trough near the dairy exit laneway. Cows will always stop for a drink,” Ms Garner said.
A shade structure for your dairy yard is really effective where heat stress is an issue.
Rate paddocks from hottest to coolest, based on shade cover, water trough size and flow rate, and proximity to the dairy.
“Identify the coolest paddocks on the farm, that can be used as sacrifice paddocks during hot weather days,” Ms Garner said.
“Have the coolest paddocks ready with adequate water and shade and feed-out area, before milking begins so the cows can return to this paddock as soon as possible.”
Significant tree planting should be part of annual plans.
“Modelling has shown that when shade is provided, there are 53 per cent fewer moderate and 86 per cent fewer severe heat stress events.”
Dairy Australia’s investment in the ‘Feeding Cool Cows Project’ has also identified that diets that include high quality forage fibre and adequate protein has been shown to reduce increases in body temperature and support cows to maintain milk production in warm conditions.
High quality forages such as chicory and hays with low neutral detergent fibre (NDF) concentration have been used in research trial diets to prove the efficacy of feeding them to lower cow body temperature and maintain milk yields.