Heat stress is one of the most overlooked seasonal problems on the dairy farm, largely due to it coinciding with a natural drop in production over the summer months. This means a lot of farmers think of heat stress as something out of their control, when there are nutritional strategies that can be used to mitigate the effects of heat stress.
When temperatures climb above 21degC and humidity above 70%, both the cow and the grass can become stressed.
In terms of grasses, natural toxins and mould build up in the grass, the toxins contained in this grass can affect the cow’s central nervous system.
In terms of the cow, she becomes stressed when she can’t expel excess heat, which causes her to drool more and decreases the amount of saliva reaching her rumen. Combined with reduced feed intake, excess body heat can disrupt rumen pH and can trigger acidosis.
The effects of this lead to decreased production, lower disease immunity, poorer conception rates, and can increase instances of lameness.
Symptoms of heat stress are observable behaviours that cows exhibit as they try to bring down their body temperatures.
These behaviours include panting and drooling, increased water intake and time standing at the water trough, the herd grouping together to extract shade from each other, and a drop in appetite and feed intake. This results in a decrease in milk production, specifically milk solids.
While the pressure of production may have eased a little over the summer months, it’s crucial to keep up mineral supplementation for your herd. Cows still require energy, even if it’s not going into milk. They are still experiencing the pressure of walking, maintaining their immune function, and growing their calves.
Farmers may also be feeding more supplementary feeds in the drier months, which means the need for mineral supplementation increases.
Research shows it’s important to maintain good trace mineral levels during hotter months, especially selenium, copper, cobalt and zinc.
Selenium increases the cow’s ability to deal with oxidative damage, which has a direct impact on the reproductive system and all other health processes in the cow.
Chromium helps to support the cow through heat stress as it increases the amount of energy the cow can metabolise, which in turn increases appetite.
Cobalt is important in the conversion of energy, and zinc plays an integral part in immunity and metabolic responses.
Growing amounts of research are being undertaken around the efficacy of seaweed, with results showing it protects and increases the health of the liver by fortifying it and stripping toxins out of the cow before they can do damage.
Finally, live yeast has been proven to enhance rumen function by increasing nutrient digestibility and stabilising the rumen pH. The key to a health cow is a healthy rumen, and yeast supports the rumen in better feed conversion.
At a time when both the cow and the pasture it grazes are suffering from the heat, keeping up with mineral supplementation is a crucial part of the puzzle in heat stress mitigation.
This article first appeared in our sister publication, Dairy Farmer.