There is a lot of science around managing cows, production and pastures during hot weather, and there are effective changes Australia’s dairy farmers can implement to help their business.
Veterinarian Lauren Foster and GippsDairy extension officer Jess Blackstock led a discussion at a recent Dairy Australia field day, held at the Macalister Demonstration Farm, in Gippsland.
The field day discussion and points raised about managing herds in hot weather are relevant to dairy farmers across Australia.
Jess said Brown Swiss and Jersey cows had a low susceptibility to heat, compared to Holstein and Friesian cattle, which had a high susceptibility.
Smaller cows, with their surface area, are potentially better at tolerating and dissipating heat.
Holsteins are larger animals and higher production cows, and require more feed, which Lauren said exponentially increased the temperature of the cow, the blood flow to its udders, and the likelihood of heat stress.
“So big cows with big udders and high production are going to experience more side effects of heat stress,” Lauren said.
Heat stress in the udder can also mean increased mastitis.
“Their immune system is not functioning as well because their whole body is under stress, so cows are more susceptible to infection,” Lauren said.
Even at 25°C, cows begin to feel uncomfortable and must start to actively burn energy to keep cool, which also lowers the energy they can put into producing milk.
Milk from even mildly heat stressed cows has been shown to have altered components, including a decline in proteins and fat content.
There is a research project under way at Ellinbank, where the cows’ environment is deliberately being manipulated to measure the effects of heat stress on the animals.
As an initial observation for farmers, the panting score of cows’ breath is a clear indicator of heat stress.
Jess said as the cow’s core body temperature started to rise and reached a critical point of 39°C, the cows’ panting will be 60 breaths per minute.
As cows start to struggle, their panting rises to 70-plus breaths per minute and the cow is noticeably panting hard.
The likelihood of death increases exponentially as panting increases to 90-100 breaths per minute. The cow’s tongue will protrude, there is excessive drooling, and her neck is extended.
“Moderate heat stress in your cows can produce a 25 per cent reduction in milk yield,” Lauren said.
“In severe heat stress, that can be up to about 40 per cent.
“The 40 per cent drop in milk yield is also noticeable on the first hot day of summer, if there are no factors to mitigate heat stress.”
Sources of heat gain and heat stress include direct radiation from the sun and sky, reflected off the ground (for example, bare earth and laneways), reflected from built infrastructure, and conducted through warm surfaces (feed pads and the walls of the dairy shed) into the cow’s body.
Cows reduce their heat load by panting, sweating and evaporation – hence the need for ready access to water and shade – and by shedding heat to the ground when they are standing on cool pasture at night.
Cows also get hotter when their internal metabolic processes are working, particularly with feed intake.
“High quality digestible forages that are low in fibre are ideal on heat stress days,” Lauren said.
“Fibre takes the longest to digest and produces more heat per kg of dry matter than any other nutrient.
“But I think the timing of feeding is the quickest change you can make to reducing the impact of heat on cows.”
When the heat load reaches a critical point, changes start to occur in metabolism, hormonal regulation and feed intake, and affects milk production, milk quality, fertility and health.
“We’ve seen cow heat stress become more of an issue, including in dairy regions where it hasn’t been an issue before,” Lauren said.
What the cow needs is opportunities to avoid increasing its heat load and to shed heat. Each cow needs a minimum of four square metres of shade each day.
“You can make some management changes quickly to keep your cows comfortable, and then longer-term think about nutritional strategies and looking at breeding decisions.”
Ensuring good nutrition to ensure production is easier to achieve by providing cows with access to quality feed during the night, when temperatures are cooler.
“Night time is when cows are going to want to try and compensate for the daytime heat,” Lauren said.
“Provide cows with the highest quality pasture to graze overnight, when they are cooler.
“In terms of diet, there are many ways you can manipulate to compensate for hot weather, but I think the timing for feeding is probably the quickest change that you can make,” she said.
Initial changes included retaining and planting tree breaks, moving the cattle into paddocks with good shade and using a shaded feed pad.
Fans, solid roofs and shade sails can also be installed in the dairy yard.
Lauren recommended early milking so the complete milking herd can be grazing in the paddock by 9am, before the heat of the day kicks in.
“Send cows out to graze in the first part of the morning, then they’ve time to fill their bellies on quality feed,” she said.
“Then bring them into the shade, or where they can stand close to sprinklers.
“Installing sprinkler systems in the dairy yard is a really positive change.”
While the sprinklers or centre pivot in the paddock can be left on, providing spray drift to cool cows – subject to water allocation – Lauren said a sprinkler in the yards should be turned on for a while to cool down surfaces, then turned off for a while.
The water drops can cause their own issues for cow comfort.
If the sprinkler in the dairy yard produces too fine a mist, that can increase humidity, also increasing cow distress, and have increased implications for infection contamination and mastitis in the udder.
“Cows tend to stand next to where the water is falling, where the air temperature is cooler, rather than under the water droplets,” Lauren said.
She also recommended the cows have ready access to clean drinking water.
“A water trough at the entrance and exit to the dairy and water troughs in all paddocks also helps cow comfort,” Lauren said.
“Up to 40 per cent of the cows’ water intake is at the exit trough at the dairy, so it’s worth having a trough there and ensure ready access, with an automatic refill mechanism.
“Longer term, tree breaks to provide shade along laneways and in paddocks and your infrastructure in sheds and shade sails are things you can think about installing if you’ve not already got a lot of natural shade.”
Lauren said there had been an increase in the past decade in sheds being built for shade on dairy farms.
“We’ve seen them being built more in the hotter for longer regions, but they also use them in winter time as a shelter set up against cold and wet weather,” she said.
“We’re heading towards more built infrastructure for shade and shelter for cows.”
Lauren also recommends delaying the afternoon milking for as long as possible, until the air temperature is cooler and more comfortable for cows.
Hose down the dairy and yard before the cows arrive to reduce the temperature of the air and built infrastructure.
“Then it’s not too hot for the cows to walk into the dairy and they’ve got that cooler temperature to walk back to the paddock,” Lauren said.
“Make sure they have access to good quality feed at night time. That’s when they are going to utilise it best.
“They’re also going to enjoy standing on grass overnight because grass is cooler than concrete.”
Shade and environmental protection should also be extended to calves.
Dairy Australia has produced a range of resources detailing strategies for managing heat stress in dairy cows.
These resources including analysing the efficacy of built infrastructure including fans, shade sails, sprinklers, sheds and farm planning to incorporate vegetation for shelter and shade.
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