High humidity in feedpad pens can result in a potentially dangerous heat load situation, especially if there is little to no wind, according to Virbac Australia’s veterinarian Paula Gonzalez-Rivas.
“High ambient temperature and relative humidity can affect animal physiology and production from conception and fertility rates to immunity, health, meat quality and milk production, leading to significant economic impact for producers,” Dr Gonzalez-Rivas said.
“In extreme cases, it can even lead to high livestock mortality.”
What’s often surprising is that it’s not only extremely high daytime temperatures that trigger heat stress. High humidity and warmer nights can have added impact.
“Hot nights and high humidity can be dangerous for livestock, as it’s harder to thermoregulate and dissipate heat accumulated during the day to reduce their core temperature,” Dr Gonzalez-Rivas said.
“That places them under continuous stress, increasing respiration, heart rate and water intake, and affecting multiple physiological processes.
“In fact, recent research has revealed air temperatures rising just 1.5℃ above average can decrease conception rates by as much as five per cent.
“Even before birth, calves suffer the negative consequences of heat stress if cows are heat-stressed during late pregnancy.
“Heat stress increases the production of free radicals and reduces the activity of antioxidant enzymes, leading to oxidative stress.
“In dairy cows, oxidative stress negatively impacts fertility, milk production and health.
“Cattle under oxidative stress have an increased incidence of mastitis, higher somatic cells count, poor responses to vaccination, decreased fertility, increased embryo mortality, abortion, premature calving, retained foetal membranes and uterine infections.
“Furthermore, oxidative stress also affects sperm concentration and viability in males.”
Dr Gonzalez-Rivas said producers should review their preparedness plans for heat stress.
This should include an inspection of the livestock environment and infrastructure, good shade and water sources, with the addition of fans and sprinklers in intensive production environments.
“Abundant water is essential,” Dr Gonzalez-Rivas said.
“It's worth remembering that animals under heat stress lose much more water through respiration and perspiration, often requiring to drink up to five times more than usual.”
Having a good summer nutrition program that includes trace mineral supplementation is also key.
Dr Gonzalez-Rivas recommended using a trace mineral supplement like Multimin injection to improve health, fertility and performance.
“Multimin contains important trace minerals like manganese, zinc, selenium and copper, to help boost antioxidants, reproductive performance and immune function of sheep and cattle.”
She said Multimin had been demonstrated to help reduce the incidence of metritis and stillbirth and improve the immune function of dairy cows undergoing the transition period under heat stress conditions.
Victorian dairy farmer Renee Murfett is a big believer that it pays to be preventive rather than reactive when it comes to heat stress in cattle.
“Summer can be harsh on our cows, so we make sure they’ve always got access to shade and water,” Renee said.
“We have a sprinkler system set up in our yard for hot days, which not only cools the cows but also stops their frustration with flies.
“The first signs of heat stress we notice are heavy breathing and stock not wanting to move away from the shade. In more severe cases, they go down with exhaustion.
“We can lose anywhere from 500 to 1000 litres of milk a day during a heatwave so Multimin is definitely something we are open to trialling in our cows during a heat stress event.”